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A phosphatidylinositol-3-OH kinase family member regulating longevity and diapause in Caenorhabditis elegans
Abstract
A pheromone-induced neurosecretory pathway in Caenorhabditis elegans triggers developmental arrest and an increase in longevity at the dauer diapause stage. The gene age-1 is required for non-dauer development and normal senescence. age-1 encodes a homologue of mammalian phosphatidylinositol-3-OH kinase (PI(3)K) catalytic subunits. Lack of both maternal and zygotic age-1 activity causes dauer formation, whereas animals with maternal but not zygotic age-1 activity develop as non-dauers that live more than twice as long as normal. These data suggest that phosphatidylinositol signalling mediated by AGE-1 protein controls lifespan and the dauer diapause decision.
Supplementary resource (1)
Nucleotide Sequence
April 1996
... The gene for age-1 is PI3 kinase; the gene for another long-lived mutant, daf-2, has a conserved sequence similar to that of the human insulin-like growth factor (IGF) receptor. (4,5) Subsequently, these two proteins were shown to be key components of the insulin/IGF-1 signaling pathway (Ins/IGF-1 pathway) involved in energy metabolism. ...
... Furthermore, it was also revealed that DAF-16, which is homologous to the human FOXO family of genes, is a transcription factor that regulates gene expression 4 downstream of this pathway. (6) DAF-16 is involved in many signaling pathways, such as aging, development, stress response, immunity, and metabolism. ...
The molecular mechanism of aging, which has been a “black box” for many years, has been elucidated in recent years, and the nematode C. elegans, which is a model animal for aging research, has played a major role in its elucidation. From the analysis of C. elegans longevity-related mutant genes, many signal transduction systems, with the insulin/insulin-like growth factor signal transduction system at the core, have emerged. It has become clear that this signal transduction system is greatly affected by external nutrients and is involved in the downstream regulation of oxidative stress, which is considered to be one of the main causes of aging.
... Despite the many ILP ligands, DAF-2 is the only known insulin receptor in C. elegans. In contrast, humans have several tyrosine kinase receptors that bind to insulin, including the insulin, IGF-1, and IGF-2 receptors (Kimura et al., 1997;Morris et al., 1996) After ligand binding, the DAF-2 receptor auto-phosphorylates and recruits the catalytic subunit of PI3K/AGE-1 ( Fig. 1) (Morris et al., 1996). AGE-1 catalyzes the conversion of phosphatidylinositol 4,5-bisphosphate (PIP 2 ) into phosphatidylinositol 3,4, 5-trisphosphate (PIP 3 ) (Weinkove et al., 2006). ...
... Despite the many ILP ligands, DAF-2 is the only known insulin receptor in C. elegans. In contrast, humans have several tyrosine kinase receptors that bind to insulin, including the insulin, IGF-1, and IGF-2 receptors (Kimura et al., 1997;Morris et al., 1996) After ligand binding, the DAF-2 receptor auto-phosphorylates and recruits the catalytic subunit of PI3K/AGE-1 ( Fig. 1) (Morris et al., 1996). AGE-1 catalyzes the conversion of phosphatidylinositol 4,5-bisphosphate (PIP 2 ) into phosphatidylinositol 3,4, 5-trisphosphate (PIP 3 ) (Weinkove et al., 2006). ...
While aging was traditionally viewed as a stochastic process of damage accumulation, it is now clear that aging is strongly influenced by genetics. The identification and characterization of long-lived genetic mutants in model organisms has provided insights into the genetic pathways and molecular mechanisms involved in extending longevity. Long-lived genetic mutants exhibit activation of multiple stress response pathways leading to enhanced resistance to exogenous stressors. As a result, lifespan exhibits a significant, positive correlation with resistance to stress. Disruption of stress response pathways inhibits lifespan extension in multiple long-lived mutants representing different pathways of lifespan extension and can also reduce the lifespan of wild-type animals. Combined, this suggests that activation of stress response pathways is a key mechanism by which long-lived mutants achieve their extended longevity and that many of these pathways are also required for normal lifespan. These results highlight an important role for stress response pathways in determining the lifespan of an organism.
... These aging-associated genes were the C. elegans orthologues of mammalian genes that encode components of the insulin and insulin-like growth factor signaling (IIS) pathway (Campisi et al. 2019). age-1 turned out to be a phosphatidylinositol-3 kinase (Morris et al. 1996), daf-2 encodes an insulinlike receptor and daf-16 encodes a FOXO-like transcription factor that acts downstream of the insulin signaling pathway in mammals (Kenyon 2010(Kenyon , 2011. This evidence was supported by findings in yeast (Fabrizio et al. 2001) and flies (Clancy et al. 2001;) that inhibition of components of the IIS pathway extended lifespan (Campisi et al. 2019). ...
... In C. elegans, the IIS and TOR signaling pathways converge at the level of transcription factors (DAF-16/FOXO and SKN-1/Nrf), target genes (the lipase lipl-4 and the insulin-like peptide ins-7), as well as potential effector mechanisms (autophagy and lipid metabolism). Under favorable environmental conditions, IIS activation confers normal development and adult lifespan, while under metabolic stress downregulation of IIS regulates metabolic dormancy, and favors longevity in a variety of species (Klass 1983;Friedman & Johnson 1988a, b;Johnson 1990;Kenyon et al. 1993;Gottlieb & Ruvkun 1994;Morris et al. 1996;Kimura et al. 1997;Apfeld & Kenyon 1998;Ogg & Ruvkun 1998;Katic & Kahn 2005;Bartke 2008;Narasimhan et al. 2009;Lant & Storey 2010;Padilla & Ladage 2012;Nolan et al. 2015;Penkov et al. 2015;Storey 2015;López-Otín et al. 2016;Mathew et al. 2017). Likewise, one unifying theme for diapause in diverse species appears to be insulin signaling Williams et al. 2006;Sim & Denlinger 2008). ...
... The screens for genes that modified dauer formation had been done previously Riddle et al., 1981), identifying daf-2 and age-1 mutants (in previous publications denominated daf-23) as dauer constitutive which means that even in favorable growth conditions, a percentage of those populations would still go into the dauer stage; with mutations in daf-16 suppressing this dauer constitutive phenotype (Vowels and Thomas, 1992). This interplay between AGE-1 and DAF-2, with DAF-16 opposing their functions in lifespan and dauer formation, would culminate in a series of publications identifying these genes as the components of the insulin/IGF-1 signaling (IIS) pathway in the nematode (Morris et al., 1996;Morris et al., 1996;Kimura et al., 1997;Lin et al., 1997;Ogg et al., 1997;Tissenbaum and Ruvkun, 1998), a pathway conserved throughout evolution and that regulates lifespan across different organisms (Tissenbaum and Ruvkun, 1998;Tatar et al., 2001;Barbieri et al., 2003;Blüher et al., 2003;Holzenberger et al., 2003;Hwangbo et al., 2004), including humans (Hwangbo et al., 2004;Suh et al., 2008;Willcox et al., 2008). ...
... The screens for genes that modified dauer formation had been done previously Riddle et al., 1981), identifying daf-2 and age-1 mutants (in previous publications denominated daf-23) as dauer constitutive which means that even in favorable growth conditions, a percentage of those populations would still go into the dauer stage; with mutations in daf-16 suppressing this dauer constitutive phenotype (Vowels and Thomas, 1992). This interplay between AGE-1 and DAF-2, with DAF-16 opposing their functions in lifespan and dauer formation, would culminate in a series of publications identifying these genes as the components of the insulin/IGF-1 signaling (IIS) pathway in the nematode (Morris et al., 1996;Morris et al., 1996;Kimura et al., 1997;Lin et al., 1997;Ogg et al., 1997;Tissenbaum and Ruvkun, 1998), a pathway conserved throughout evolution and that regulates lifespan across different organisms (Tissenbaum and Ruvkun, 1998;Tatar et al., 2001;Barbieri et al., 2003;Blüher et al., 2003;Holzenberger et al., 2003;Hwangbo et al., 2004), including humans (Hwangbo et al., 2004;Suh et al., 2008;Willcox et al., 2008). ...
Since its introduction as a genetic model organism, Caenorhabditis elegans has yielded insights into the causes of aging. In addition, it has provided a molecular understanding of mechanisms of neurodegeneration, one of the devastating effects of aging. However, C. elegans has been less popular as an animal model to investigate DNA repair and genomic instability, which is a major hallmark of aging and also a cause of many rare neurological disorders. This article provides an overview of DNA repair pathways in C. elegans and the impact of DNA repair on aging hallmarks, such as mitochondrial dysfunction, telomere maintenance, and autophagy. In addition, we discuss how the combination of biological characteristics, new technical tools, and the potential of following precise phenotypic assays through a natural life-course make C. elegans an ideal model organism to study how DNA repair impact neurodegeneration in models of common age-related neurodegenerative diseases.
... Environmental cues indicating harsh environmental conditions are perceived by sensory neurons, which initiate a cascade of neuroendocrine events involving both inter-and intra-cellular signalling events. The signalling pathways involved in the neuroendocrine signalling include the TGF-β and insulin/IGF pathways (Georgi et al., 1990;Estevez et al., 1993;Gottlieb & Ruvkun, 1994;Morris et al., 1996;Ren et al., 1996;Kimura et al., 1997). Mutations in the genes in these signalling pathways result in either the 'dauer formation defective' (Daf-d) phenotype of mutants that do not enter the dauer stage even under harsh conditions, or the 'dauer formation constitutive' (Daf-c) phenotype of animals that constitutively form dauers (Georgi et al., 1990;Estevez et al., 1993;Gottlieb & Ruvkun, 1994;Morris et al., 1996;Ren et al., 1996;Kimura et al., 1997). ...
... The signalling pathways involved in the neuroendocrine signalling include the TGF-β and insulin/IGF pathways (Georgi et al., 1990;Estevez et al., 1993;Gottlieb & Ruvkun, 1994;Morris et al., 1996;Ren et al., 1996;Kimura et al., 1997). Mutations in the genes in these signalling pathways result in either the 'dauer formation defective' (Daf-d) phenotype of mutants that do not enter the dauer stage even under harsh conditions, or the 'dauer formation constitutive' (Daf-c) phenotype of animals that constitutively form dauers (Georgi et al., 1990;Estevez et al., 1993;Gottlieb & Ruvkun, 1994;Morris et al., 1996;Ren et al., 1996;Kimura et al., 1997). Under favourable conditions, ligands for the TGF-β and insulin/IGF pathways are expressed in sensory neurons that suppress dauer formation, thus promoting reproductive development ( Fig. 10.2). ...
... In mammals, IIS is involved in the regulation of lifespan, reproductive development, and metabolism [4,5]. Research in Caenorhabditis elegans has revealed that the IIS pathway regulates lifespan, reproduction, and metabolism, suggesting that this pathway has a conserved function [6,7]. In addition, IIS signalling plays a role in dauer development in C. elegans [8]. ...
Background
The insulin/insulin-like signalling (IIS) pathway is common in mammals and invertebrates, and the IIS pathway is unknown in Fasciola gigantica. In the present study, the IIS pathway was reconstructed in F. gigantica. We defined the components involved in the IIS pathway and investigated the transcription profiles of these genes for all developmental stages of F. gigantica. In addition, the presence of these components in excretory and secretory products (ESPs) was predicted via signal peptide annotation.
Results
The core components of the IIS pathway were detected in F. gigantica. Among these proteins, one ligand (FgILP) and one insulin-like molecule binding protein (FgIGFBP) were analysed. Interestingly, three receptors (FgIR-1/FgIR-2/FgIR-3) were detected, and a novel receptor, FgIR-3, was screened, suggesting novel functions. Fg14-3-3ζ, Fgirs, and Fgpp2a exhibited increased transcription in 42-day-old juveniles and 70-day-old juveniles, while Fgilp, Fgigfb, Fgsgk-1, Fgakt-1, Fgir-3, Fgpten, and Fgaap-1 exhibited increased transcription in metacercariae. FgILP, FgIGFBP, FgIR-2, FgIR-3, and two transcription factors (FgHSF-1 and FgSKN-1) were predicted to be present in FgESPs, indicating their exogenous roles.
Conclusions
This study helps to elucidate the signal transduction pathway of IIS in F. gigantica, which will aid in understanding the interaction between flukes and hosts, as well as in understanding fluke developmental regulation, and will also lay a foundation for further characterisation of the IIS pathways of trematodes.
... Here we found that Dd-cpl-1 was located in the digestive system and silencing Dd-cpl-1 expression by RNAi in J3s resulted in developmental arrest in this stage. Thus, it is possible to speculate that Dd-CPL-1 may directly affect D. destructor development and growth by acting as a digestive enzyme to supply nutrition, or may play roles in the mTOR or in the IIS pathway through comparison of the phenotype (developmental arrest at third larval stage) after disruption of Dd-cpl-1, CeTOR, Ce-daf-2 and Ce-age-1 45,50,51 . Additionally, a developmental arrest phenotype in J3s was also observed after RNAi of Dd-cpl-1 at stage of J2. ...
Ditylenchus destructor is a migratory plant-parasitic nematode that severely harms many agriculturally important crops. The control of this pest is difficult, thus efficient strategies for its management in agricultural production are urgently required. Cathepsin L-like cysteine protease (CPL) is one important protease that has been shown to participate in various physiological and pathological processes. Here we decided to characterize the CPL gene (Dd-cpl-1) from D. destructor. Analysis of Dd-cpl-1 gene showed that Dd-cpl-1 gene contains a signal peptide, an I29 inhibitor domain with ERFNIN and GNFD motifs, and a peptidase C1 domain with four conserved active residues, showing evolutionary conservation with other nematode CPLs. RT-qPCR revealed that Dd-cpl-1 gene displayed high expression in third-stage juveniles (J3s) and female adults. In situ hybridization analysis demonstrated that Dd-cpl-1 was expressed in the digestive system and reproductive organs. Silencing Dd-cpl-1 in 1-cell stage eggs of D. destructor by RNAi resulted in a severely delay in development or even in abortive morphogenesis during embryogenesis. The RNAi-mediated silencing of Dd-cpl-1 in J2s and J3s resulted in a developmental arrest phenotype in J3 stage. In addition, silencing Dd-cpl-1 gene expression in female adults led to a 57.43% decrease in egg production. Finally, Dd-cpl-1 RNAi-treated nematodes showed a significant reduction in host colonization and infection. Overall, our results indicate that Dd-CPL-1 plays multiple roles in D. destructor ontogenesis and could serve as a new potential target for controlling D. destructor.
... concluded that IGF-1R heterozygous mice had a 26% longer lifespan than wild-type mice. Studies on Caenorhabditis elegans, a nematode that goes through four larval stages before reaching reproductive adulthood, observed genetic changes regulating aging under adverse external conditions, and extracted genes that encode for nematode IGF1 receptors [12] and subunits of phosphatidylinositol 3-kinase [13]. The phosphatidylinositol 3-kinase pathway has in humans been linked to various diseases such as diabetes mellitus and carcinoma and is thought to take part in regulating cell survival time. ...
Introduction: The process of aging is a progressive, patterned, and accumulative set of time-related changes resulting from a mix of genetic, epigenetic, and environmental factors, that are constantly evolving, and that lead the human body to be more prone to defects and susceptible to disease, and at last to death. On the molecular level, the accumulation of free radical reactions that constantly go on in every cell and tissue is thought to be the main culprit behind the process of aging [1]. These reactions amassed over time, hamper immune responses to external factors, cause homeostatic imbalance and lead to chronic pro-inflammatory status in body cells. This process has been dubbed “inflammaging” [2]. Physical activity, along with a balanced diet and a healthy lifestyle as a whole, has long been thought to be crucial in retaining health and good quality of life. Aim of the study: A review of current knowledge about the process of aging, a summary of underlying pathologies, and current preventive protocols, with a focus on physical activity as a preventative measure in combating illness and age-related pathologies.Methods and materials: A review of chosen literature in the PubMed database, MDPI database, and GoogleScholar was conducted using the following keywords: “aging pathophysiology”, “physical exercise in the aging process”, “aging process underlying conditions”, “molecular biology of aging”, “cell lifespan”, “cell longevity”.Results and conclusions: Physical activity helps decelerate the process of aging, both physical and cognitive, through various pathways in the human body.
... The canonical C. elegans IIS pathway begins with insulin-like ligands, which bind and activate or inhibit DAF-2. Receptor activation recruits phosphoinositide-3 kinase, AGE-1/PI3K, which initiates a signaling cascade that includes PIP 3 , and the serine/ threonine kinases PDK-1, AKT-1, and AKT-2 (Dorman et al., 1995;Morris et al., 1996;Paradis and Ruvkun, 1998;Paradis et al., 1999). Then, transcription factors are inhibited, including DAF-16/FOXO and SKN-1/Nrf2, preventing activation of downstream target genes that promote longevity. ...
The Transforming Growth Factor-β (TGF-β) superfamily of signaling molecules plays critical roles in development, differentiation, homeostasis, and disease. Due to the conservation of these ligands and their signaling pathways, genetic studies in invertebrate systems including the nematode Caenorhabditis elegans have been instrumental in identifying signaling mechanisms. C. elegans is also a premier organism for research in longevity and healthy aging. Here we summarize current knowledge on the roles of TGF-β signaling in aging and immunity.
... The lower number of pachytene stage nuclei in daf-2 may not be simply due to increased apoptosis as daf-16;daf-2 also showed similar elevated numbers ( Figure S2G). We also discovered that components of the canonical IIS signaling pathway are involved, as cdk-12 KD in age-1(hx546) (mammalian PI3K ortholog) (Morris et al., 1996;Paradis and Ruvkun, 1998) and pdk-1(sa680) (mammalian PDK ortholog) (Paradis et al., 1999) also arrested germ line at the pachytene stage of meiosis ( Figure S2H, I), similar to daf-2 on cdk-12 RNAi. ...
Germ line integrity is critical for progeny fitness. Organisms deploy the DNA damage response (DDR) signaling to protect the germ line from genotoxic stress, facilitating the cell-cycle arrest of germ cells and DNA repair or their apoptosis. Cell-autonomous regulation of germ line quality in response to DNA damage is well-studied; however, how quality is enforced cell non-autonomously on sensing somatic D NA damage is less known. Using Caenorhabditis elegans, we show that DDR disruption, only in the uterus, when insulin-IGF-1 signaling (IIS) is low, arrests oogenesis in the pachytene stage of meiosis I, in a FOXO/DAF-16 transcription factor (TF)-dependent manner. Without FOXO/DAF-16, germ cells of the IIS mutant escape the arrest to produce poor-quality oocytes, showing that the TF imposes strict quality control during low IIS. Activated FOXO/DAF-16 senses DDR perturbations during low IIS to lower ERK/MPK-1 signaling below a threshold to promote germ line arrest. Altogether, we elucidate a new surveillance role of activated FOXO/DAF-16 that ensures optimal germ cell quality and progeny fitness in response to somatic DNA damage.
... We found that a large number of differentially expressed genes were downstream targets of the highly conserved IIS pathway, one of the main signaling pathways that regulate metabolism across species (data S4 and S5) (59). In C. elegans, stimuli, such as food, lead to the release and subsequent binding of agonistic insulinlike peptides to the DAF-2/insulin/IGF-1 receptor (IIR), which in turn leads to a cascade of phosphorylation events ultimately resulting in the inhibitory phosphorylation and subsequent exclusion of the DAF-16/FoxO transcription factor from the nucleus (Fig. 2D) (51,(60)(61)(62)(63)(64). This signaling cascade leads to an overall down-regulation of 1532 DAF-16/FoxO-dependent ("class 1") and overall upregulation of 1671 DAF-16/FoxO-independent ("class 2") genes ( Fig. 2D) (65). ...
Exposure to adverse nutritional and metabolic environments during critical periods of development can exert long-lasting effects on health outcomes of an individual and its descendants. Although such metabolic programming has been observed in multiple species and in response to distinct nutritional stressors, conclusive insights into signaling pathways and mechanisms responsible for initiating, mediating, and manifesting changes to metabolism and behavior across generations remain scarce. By using a starvation paradigm in Caenorhabditis elegans, we show that starvation-induced changes in dauer formation-16/forkhead box transcription factor class O (DAF-16/FoxO) activity, the main downstream target of insulin/insulin-like growth factor 1 (IGF-1) receptor signaling, are responsible for metabolic programming phenotypes. Tissue-specific depletion of DAF-16/FoxO during distinct developmental time points demonstrates that DAF-16/FoxO acts in somatic tissues, but not directly in the germline, to both initiate and manifest metabolic programming. In conclusion, our study deciphers multifaceted and critical roles of highly conserved insulin/IGF-1 receptor signaling in determining health outcomes and behavior across generations.
... In vitro, the treatment of cell lines by PI3K inhibitors leads to an arrest of proliferation [47]. A direct cytotoxic effect was also reported with a pan-PIK3 inhibitor or a dual inhibitor PI3Kγ-PI3Kα. ...
Simple Summary
Breast cancer remains the fourth-leading cause of death worldwide, and therapeutic improvement is warranted. The phosphatidylinositol 3-kinase (PI3K) pathway is one of the major pathways in oncogenesis, and PI3K alterations are common in all breast cancer subtypes. Despite modest clinical activity and a high toxicity rate, pan-PI3K inhibitors paved the way for selective PI3K inhibitor development. In this overview, we cover the past, the present, and potential paths, as well as the therapeutic challenges to come for this therapeutic class.
Abstract
The phosphatidylinositol 3-kinase (PI3K) pathway is one of the most altered pathways in human cancers, and it plays a central role in cellular growth, survival, metabolism, and cellular mobility, making it a particularly interesting therapeutic target. Recently, pan-inhibitors and then selective p110α subunit inhibitors of PI3K were developed. Breast cancer is the most frequent cancer in women and, despite therapeutic progress in recent years, advanced breast cancers remain incurable and early breast cancers are at risk of relapse. Breast cancer is divided in three molecular subtypes, each with its own molecular biology. However, PI3K mutations are found in all breast cancer subtypes in three main “hotspots”. In this review, we report the results of the most recent and main ongoing studies evaluating pan-PI3K inhibitors and selective PI3K inhibitors in each breast cancer subtype. In addition, we discuss the future of their development, the various potential mechanisms of resistance to these inhibitors and the ways to circumvent them.
... The allegedly solid building of the ETAs endured the first cracks following the discovery that aging is subject to regulation by genes, transcription factors and classical signaling pathways (e.g. Klass 1983;Friedman & Johnson 1988a, b;Kenyon et al. 1993;Lithgow et al. 1995;Morris et al. 1996;Murakami & Johnson 1996;Lin et al. 1997;Guarente & Kenyon 2000;Kenyon 2010). This conflicted with the putative nonselected nature of aging, as the ETAs see it. ...
... With remarkable complexity in expression pattern 33 Indeed, several processes regulated by IIS activity exhibit prominent tissue-specificity. A decreased IIS activity leads to increased adult lifespan 3,5,24,25 , and promotes an alternative 'dauer' developmental state that confers resistance to starvation and dehydration [2][3][4][5] . Both processes depend on increased DAF-16 activity in the intestine. ...
C. elegans insulin/insulin-like growth factor 1 signaling (IIS) affects diverse physiological processes through the DAF-16/FOXO transcription factor. Despite its presence in all somatic cells, DAF-16's physiological effects, such as modulation of dauer formation, synapse maturation, axon regeneration, and adult longevity, exhibit prevalent tissue-specificity as well as tissue crosstalk. This implies that tissue-specific DAF-16 transcriptional programs contribute to the functional diversity of IIS. To further examine this possibility, we sought to identify tissue-specific and direct transcriptional targets of DAF-16 in muscle cells. Following FACS-sorting to enrich mature muscle cells from young adult animals, we compared the muscle transcriptomes under high and low IIS signaling conditions, with and without DAF-16. We further analyzed and compared the DAF-16 docking sites in muscle and intestine cells from published datasets. These analyses revealed 14 potential muscle-specific DAF-16 transcriptional targets, among which we validated two that are strongly and specifically activated by DAF-16 in muscles: a secreted protein C54F6.5 and a calcium-binding protein CEX-1/Calexcitin. Both genes exhibit DAF-16-independent non-muscle expression, explaining their low rank or absence from the current DAF-16 target lists generated by multiple independent whole-animal microarray or mRNA-sequencing analyses. These results support the notion of tissue-specific DAF-16 transcriptional programs and highlight the importance of verifying FOXO targets in a cell-type-specific manner.
... Studies have shown that PIP signaling pathways play an important role in cellular processes, such as membrane trafficking, cell signal transduction, and reproductive systems [42,43]. Previous studies have found that the phosphorylated PIP form in C. elegans has multiple functions, which play important roles in diapause [44] and thermotactic behavior [45]. However, there are no relevant studies of the effect of PIP on T. canis, thus further research is needed. ...
Toxocariasis, mainly caused by Toxocara canis, and to a lesser extent, Toxocara cati, is a neglected parasitic zoonosis. The mechanisms that underlie the changes in lipid metabolism of T. canis infection in Beagle dogs’ lungs remain unclear. Lipidomics is a rapidly emerging approach that enables the global profiling of lipid composition by mass spectrometry. In this study, we performed a non-targeted lipidomic analysis of the lungs of Beagle dogs infected with the roundworm T. canis using liquid chromatography–tandem mass spectrometry (LC-MS/MS). A total of 1197 lipid species were identified, of which 63, 88, and 157 lipid species were significantly altered at 24 h post-infection (hpi), 96 hpi, and 36 days post-infection (dpi), respectively. This global lipidomic profiling identified infection-specific lipid signatures for lung toxocariasis, and represented a comprehensive comparison between the lipid composition of dogs’ lungs in the presence and absence of T. canis infection. The potential roles of the identified lipid species in the pathogenesis of T. canis are discussed, which has important implications for better understanding the interaction mechanism between T. canis and the host lung.
... Upon binding of insulin-like ligand, the DAF-2 receptor auto-phosphorylates, which results in the recruitment and activation of the catalytic subunit of PI3K/AGE-1. This initiates an intracellular signaling cascade of protein kinases: AAP-1, the p55-like regulatory subunit of PI3K, is activated which enables the conversion of PIP2 to PIP3 by AGE-1, the catalytic subunit of PI3K (Morris et al., 1996;Wolkow et al., 2000). PDK-1 transduces the phosphorylation signal from PIP3 to SGK-1, AKT-1 and AKT-2 (Hertweck et al., 2004;Paradis et al., 1999;Paradis & Ruvkun, 1998) which in turn inactivates the FoxO transcription factor DAF-16 (Lin et al., 1997;Ogg et al., 1997). ...
... This mutant's life extension was the longest reported in any organism at that time and required a second gene, daf-16 -the homologue of human FOXO. Morris and colleagues, from Gary Ruvkun's team, later demonstrated that the C. elegans gene, age-1, encoded a phosphatidylinositol 3-kinase (PI3K) (16). Subsequently, Kimura and colleagues, also from Ruvkun's team, demonstrated that daf-2 encoded the nematode homolog of the human insulin and IGF-1 receptors that activate downstream PI3K pathways (17). ...
... As the unique negative regulator of PI3K/Akt/Foxo cascade pathway, the function of PTEN in lifespan regulation has attracted much attention in recent years. In the nematode Caenorhabditis elegans, both decreased activity of PI3K (AGE-1) and increased expression of PTEN (DAF-18) result in extended longevity (Dorman et al., 1995;Morris et al., 1996;Masse et al., 2005). In mice, PTEN tg mice carrying additional genomic copies of PTEN are protected from cancer and exhibited a significant extension of life span (Ortega-Molina et al., 2012). ...
Phosphatase and tensin homolog deleted on chromosome ten (PTEN) has been found to regulate longevity through the PI3K/Akt/FoxO pathway and maintenance of genome integrity in worms, flies, and mammals. However, limited information is available on the roles of PTEN in longevity of aquatic animals. Here we extended this paradigm using two closely related Argopecten scallops, Argopecten purpuratus , and Argopecten irradians , with significantly distinct life spans, which are commercially important bivalve species for fishery and aquaculture in China, United States, Peru, and Chile. The ORFs of the ApPTEN and AiPTEN were 1,476 and 1,473 bp, which encoded 491 and 490 amino acids, respectively. There were 48 synonymous and 16 non-synonymous SNPs and one InDel of three nucleotides between ApPTEN and AiPTEN , resulting in variations in 15 amino acids and lack of S453 in AiPTEN. Differences in conformation and posttranslational modification were predicted between ApPTEN and AiPTEN, which may indicate different activities of ApPTEN and AiPTEN. When the animals were subjected to nutrition restriction, the expression of both ApPTEN and AiPTEN was upregulated, with AiPTEN responded faster and more robust than ApPTEN . Ionizing radiation induced significantly elevated expression of ApPTNE but not AiPTEN in the adductor muscle, and the mortality rate of A. purpuratus was significantly lower than that of A. irradians , indicating that ApPTNE may play a protective role by maintaining the genome integrity. RNAi of ApPTNE significantly downregulated the expression of its downstream regulated genes known to favor longevity, such as FoxO , Mn-SOD , and CAT . These results indicated that PTEN may contribute to the longevity of A. purpuratus through regulation of nutrient availability and genomic stability, probably via PI3K/Akt/FoxO pathway. Our study may provide new evidence for understanding of the conservative functions of PTEN in regulation of lifespan in animals and human, and it may also benefit the selection of scallops strains with long lifespan and thus larger size.
... Early studies to identify the Daf genes revealed that organismal longevity was determined via canonical ILS signaling. DAF-2 (insulin/IGF1 receptor) activates AGE-1 (PI3K) to generate phosphatidylinositol-3,4,5-triphosphate (PIP 3 ) (Morris et al., 1996;Kimura et al., 1997), which is opposed by DAF-18 (PTEN, Phosphatase And Tensin Homolog) (Ogg and Ruvkun 1998). Accumulation of PIP 3 activates PDK-1 (PDPK1, 3phosphoinositide-dependent protein kinase-1), which activates AKT-1/2 (AKT Serine/Threonine Kinase, protein kinase B) via phosphorylation (Paradis et al., 1999). ...
Discoveries made in the nematode Caenorhabditis elegans revealed that aging is under genetic control. Since these transformative initial studies, C. elegans has become a premier model system for aging research. Critically, the genes, pathways, and processes that have fundamental roles in organismal aging are deeply conserved throughout evolution. This conservation has led to a wealth of knowledge regarding both the processes that influence aging and the identification of molecular and cellular hallmarks that play a causative role in the physiological decline of organisms. One key feature of age-associated decline is the failure of mechanisms that maintain proper function of the proteome (proteostasis). Here we highlight components of the proteostatic network that act to maintain the proteome and how this network integrates into major longevity signaling pathways. We focus in depth on the heat shock transcription factor 1 (HSF1), the central regulator of gene expression for proteins that maintain the cytosolic and nuclear proteomes, and a key effector of longevity signals.
... An increase in resistance and longevity occurs when partial loss-of-function of the phosphatidylinositol-3-OH kinase (PI(3)K)-encoding gene age-1, which relieves the suppression of DAF-16 [41,42]. Previously study has shown that long-lived age-1 mutant nematodes exhibited a significantly higher resistance to infection by Enterococcus faecalis, Staphylococcus aureus, and Pseudomonas aeruginosa than wild-type worms [43]. ...
Background
Cryptococcosis is a life-threatening infection is primarily caused by two sibling species Cryptococcus neoformans and Cryptococcus gattii. Several virulence-related factors of these cryptococci have been widely investigated in Caenorhabditis elegans, representing a facile in vivo model of host–pathogen interaction. While recent studies elucidated cryptococcal virulence factors, intrinsic host factors that affect susceptibility to infections by cryptococci remain unclear and poorly investigated.
Results
Here, we showed that defects in C. elegans insulin/insulin-like growth factor-1 (IGF-1) signaling (IIS) pathway influenced animal lifespan and mechanisms of host resistance in cryptococcal infections, which required the activation of aging regulator DAF-16/Forkhead box O transcription factor. Moreover, accumulation of lipofuscin, DAF-16 nuclear localization, and expression of superoxide dismutase (SOD-3) were elevated in C. elegans due to host defenses during cryptococcal infections.
Conclusion
The present study demonstrated the relationship between longevity and immunity, which may provide a possibility for novel therapeutic intervention to improve host resistance against cryptococcal infections.
... The cytochrome P450s are found in almost all living organisms including the nematodes and are chiefly engaged in detoxification of exogenous drugs and pesticide molecules (Laing et al. 2015). Other pathways, such as ErbB signaling (Yarden and Sliwkowski 2001), mTOR signaling (Aramburu et al. 2014), Wnt signaling (Silva-García et al. 2014), Jak-STAT signaling (Tanguy et al. 2017), FoxO signaling (Hesp et al. 2015), MAPK signaling (Kim et al. 2004), phosphatidylinositol signaling (Morris et al. 1996) and Hedgehog signaling (Hsia et al. 2015;Lin et al. 2016a, b) primarily act in stress responses and also participate in embryonic development and dauer induction of C. elegans. Phagosomal and lysosomal activity targets the xenobiotics and toxins to degrade by vesicular trafficking (De Voer et al. 2008). ...
Root-knot nematodes (Meloidogyne spp.) are notorious plant-parasitic nematodes that affect agricultural crops. These obligate soil-dwelling parasites typically maneuver the host plant physiology by forming specialized feeding cells resulting in heavy yield losses. Scant management tools are available to effectively combat this pest. In an exploratory attempt of identifying new fungal biocontrol agent(s) for M. incognita from India, a Paecilomyces tenuis isolate from rhizosphere soil was found to incur > 90% mortality of the infective second-stage juveniles (J2s) at 24 h post-exposure to the fungal filtrate with about 87% parasitization. The fungal filtrate also significantly reduced the egg hatching and host-root penetration of M. incognita under in vitro and in vivo conditions revealing its effectiveness in curbing nematode pathogenicity with positive effects on plant growth. Chromatographic analyses revealed the presence of Huperzine A (433.56 mg L⁻¹) in the P. tenuis isolate. Besides, the isolate possessed acetylcholinesterase inhibition attribute with an IC50 of 2.85 ± 0.12 mg mL⁻¹ of the fungal filtrate. Further, GC-MS analysis revealed the production of other nematicidal compounds by the fungus including acetic acid. To conceptualize the mode of nematicidal action, RNA-Seq was done post-treatment of the M. incognita J2s and model worm Caenorhabditis elegans with fungal filtrate and pure Huperzine A. The transcriptomic profile unraveled the molecular intricacies underlying the nematicidal action affecting several biological pathways and developmental checkpoints of the nematode. Thus, the P. tenuis isolate offers significant potential to be used as a biocontrol agent against M. incognita along with its commercial use for Huperzine A production.
... It must be noted that some of the key discoveries in the area of aging research included the identification of insulin/IGF-1 signaling pathway components, which, when inhibited or mutated, extended lifespan in C. elegans [18][19][20] and D. melanogaster [21,22] and those discoveries paved the way for further exploration of the involvement of this pathway in aging mammals. IGF-1 regulated processes in aging and interventions that target IGF-1 signaling in various model organisms are summarized in Figure 1. ...
Cellular, small invertebrate and vertebrate models are a driving force in biogerontology studies. Using various models, such as yeasts, appropriate tissue culture cells, Drosophila, the nematode Caenorhabditis elegans and the mouse, has tremendously increased our knowledge around the relationship between diet, nutrient-response signaling pathways and lifespan regulation. In recent years, combinatorial drug treatments combined with mutagenesis, high-throughput screens, as well as multi-omics approaches, have provided unprecedented insights in cellular metabolism, development, differentiation, and aging. Scientists are, therefore, moving towards characterizing the fine architecture and cross-talks of growth and stress pathways towards identifying possible interventions that could lead to healthy aging and the amelioration of age-related diseases in humans. In this short review, we briefly examine recently uncovered knowledge around nutrient-response pathways, such as the Insulin Growth Factor (IGF) and the mechanistic Target of Rapamycin signaling pathways, as well as specific GWAS and some EWAS studies on lifespan and age-related disease that have enhanced our current understanding within the aging and biogerontology fields. We discuss what is learned from the rich and diverse generated data, as well as challenges and next frontiers in these scientific disciplines.
... The transcription factor DAF-16/ FoxO, which is inhibited by insulin/insulin-like growth factor (IGF) and AGE-1/PI3K signaling Ogg et al. 1997), is a critical regulator of L1 arrest (Baugh and Sternberg 2006). AGE-1/ PI3K signaling transduces signals from activated DAF-2/IGF receptor (IGFR) and is opposed by DAF-18/PTEN in that the conversion of PIP2 into PIP3 by AGE-1 is reversed by DAF-18 via its lipid-phosphatase activity (Morris et al. 1996;Ogg and Ruvkun 1998;Mihaylova et al. 1999). As a result, null mutants of daf-16 and daf-18 are starvation-sensitive and L1 arrest-defective (Baugh and Sternberg 2006;Fukuyama et al. 2006;Cui et al. 2013;Kaplan et al. 2015;Zheng et al. 2018aZheng et al. , 2018bFry et al. 2021). ...
Mutations in the well-known tumor suppressor PTEN are observed in many cancers. PTEN is a dual-specificity phosphatase that harbors lipid and protein-phosphatase activities. The Caenorhabditis elegans PTEN ortholog is daf-18, which has pleiotropic effects on dauer formation, aging, starvation resistance, and development. Function of three daf-18 point-mutants, G174E, D137A and C169S, had previously been investigated using high-copy transgenes in a daf-18 null background. These alleles were generated based on their mammalian counterparts and were treated as though they specifically disrupt lipid or protein-phosphatase activity, or both, respectively. Here, we investigated these alleles using genome editing of endogenous daf-18. We assayed three traits relevant to L1 starvation resistance, and we show that each point mutant is essentially as starvation-sensitive as a daf-18 null mutant. Furthermore, we show that G174E and D137A do not complement each other, suggesting overlapping effects on lipid and protein-phosphatase activity. We also show that each allele has strong effects on nucleocytoplasmic localization of DAF-16/FoxO and dauer formation, both of which are regulated by PI3K signaling, similar to a daf-18 null allele. In addition, each allele also disrupts M-cell quiescence during L1 starvation, though D137A has a weaker effect than the other alleles, including the null. Our results confirm that daf-18/PTEN is important for promoting starvation resistance and developmental arrest and that it is a potent regulator of PI3K signaling, and they highlight challenges of using genetic analysis to link specific DAF-18/PTEN enzymatic activities to particular phenotypes.
... AGE-1 is homologous to mammalian phosphatidylinositol-3-OH kinase (PI(3)K) catalytic subunits and is one of the most upstream elements of IIS pathway. Thus, the lack of the gene age-1 extends the C. elegans lifespan more than twice as long as normal (Morris et al., 1996). Moreover, DAF-16, a homolog of human forkhead box O (FOXO) transcription factor, is widely expressed in C. elegans. ...
Candida albicans can cause infections ranging from superficial skin infections to life-threateningsystemic infections in immunocompromised hosts. Although several C. albicans virulence factorsare widely discussed in great detail, intrinsic host determinants that are critical for C. albicanspathogenesis remain less interested and poorly understood. In view of this, a model of Caenorhabditiselegans was used to study host longevity and immunity in response to C. albicans pathogenesis.The influence of C. albicans in pathological and survival aspects was evaluated using C. elegans.C. albicans hyphal formation in different C. elegans genetic backgrounds was evaluated. Moreover,several C. elegans fluorescent proteins as gene expression markers upon C. albicans infectionswere evaluated. C. albicans is pathogenic to C. elegans and reduces the lifespan of C. elegans inassociation with repression of the insulin/IGF-1-like signaling (IIS) pathway. Moreover, repressionof DAF-16/forkhead transcription factor increases aggressiveness of C. albicans by enhancing hyphalformation. In addition, infection of C. albicans increases lipofuscin accumulation, promotes DAF-16nuclear translocation, increases superoxide dismutase (SOD-3) expression, which coordinately linksbetween aging and innate immunity. Thus, we demonstrate here the strategy to utilize C. elegans asa model host to elucidate host genetic determinants that provide insights into the pathogenesis ofC. albicans infections.
... We now know that within a species, aging is malleable; by altering the function of single genes, we can increase lifespan dramatically (Friedman and Johnson, 1988;Kenyon et al., 1993;Morris et al., 1996;Pan and Finkel, 2017). Moreover, many of the discovered pathways appear to have evolutionarily conserved effects on aging. ...
Aging research is unparalleled in the breadth of disciplines it encompasses, from evolutionary studies examining the forces that shape aging to molecular studies uncovering the underlying mechanisms of age-related functional decline. Despite a common focus to advance our understanding of aging, these disciplines have proceeded along distinct paths with little cross-talk. We propose that the concept of resilience can bridge this gap. Resilience describes the ability of a system to respond to perturbations by returning to its original state. Although resilience has been applied in a few individual disciplines in aging research such as frailty and cognitive decline, it has not been explored as a unifying conceptual framework able to connect distinct research fields. We argue that because a resilience-based framework can cross broad physiological levels and time scales, it can provide the missing links that connect these diverse disciplines. The resulting framework will facilitate predictive modeling and validation and influence targets and directions in research on the biology of aging.
... Researchers noticed that daf-2 (homologous gene of the human insulin/IGF-1 receptor) and age-1 (homologous gene to the human phosphatidylinositol-3-OH kinase, PI3K) mutants not only possess the characteristics of longevity and dauer formation but also exhibit high resistance to oxidative stress through upregulation of the activities of SOD, CAT and GST [125][126][127][128][129]. In the IIS pathway, DAF-2 is activated by binding an insulin-like ligand, phosphorylates DAF-2, and recruits and activates its downstream target AGE-1 to catalyze the formation of PIP3 from PIP2, whereas DAF-18 (homologous with the human tumor suppressor PTEN) antagonizes the process. Subsequently, PIP3 activates 3-phosphoinositide-dependent protein kinase 1 and in turn results in phosphorylation and activation of serine/threonine kinases AKT-1, AKT-2 and SGK-1 [130][131][132]. Consequently, the principle downstream target DAF-16 (homologous with the human forkhead transcription factor) is phosphorylated and inactivated, failing in nuclear translocation and the transcriptional regulation of plentiful effectors involved in stress resistance, lifespan, fat storage and so on [133]. ...
Natural products are small molecules naturally produced by multiple sources such as plants, animals, fungi, bacteria and archaea. They exert both beneficial and detrimental effects by modulating biological targets and pathways involved in oxidative stress and antioxidant response. Natural products’ oxidative or antioxidative properties are usually investigated in preclinical experimental models, including virtual computing simulations, cell and tissue cultures, rodent and nonhuman primate animal models, and human studies. Due to the renewal of the concept of experimental animals, especially the popularization of alternative 3R methods for reduction, replacement and refinement, many assessment experiments have been carried out in new alternative models. The model organism Caenorhabditis elegans has been used for medical research since Sydney Brenner revealed its genetics in 1974 and has been introduced into pharmacology and toxicology in the past two decades. The data from C. elegans have been satisfactorily correlated with traditional experimental models. In this review, we summarize the advantages of C. elegans in assessing oxidative and antioxidative properties of natural products and introduce methods to construct an oxidative damage model in C. elegans. The biomarkers and signaling pathways involved in the oxidative stress of C. elegans are summarized, as well as the oxidation and antioxidation in target organs of the muscle, nervous, digestive and reproductive systems. This review provides an overview of the oxidative and antioxidative properties of natural products based on the model organism C. elegans.
... The nematode Caenorhabditis elegans is among the foremost models in ageing research, with a short lifespan of only a few weeks, but displaying similar ageing phenotypes and causes as humans (Mack et al, 2018). It was first shown in C. elegans that longevity is regulated by evolutionarily conserved signalling with the identification of the insulin/IGF-1 signalling (IIS) pathway (Johnson, 1990;Kenyon et al, 1993;Morris et al, 1996;Ogg et al, 1997;Kenyon, 2011). Mutations in critical IIS genes, such as FOXO3A, were later found to be associated with human longevity (Willcox et al, 2008). ...
Ageing is a complex process with common and distinct features across tissues. Unveiling the underlying processes driving ageing in individual tissues is indispensable to decipher the mechanisms of organismal longevity. Caenorhabditis elegans is a well-established model organism that has spearheaded ageing research with the discovery of numerous genetic pathways controlling its lifespan. However, it remains challenging to dissect the ageing of worm tissues due to the limited description of tissue pathology and access to tissue-specific molecular changes during ageing. In this study, we isolated cells from five major tissues in young and old worms and profiled the age-induced transcriptomic changes within these tissues. We observed a striking diversity of ageing across tissues and identified different sets of longevity regulators therein. In addition, we found novel tissue-specific factors, including irx-1 and myrf-2, which control the integrity of the intestinal barrier and sarcomere structure during ageing respectively. This study demonstrates the complexity of ageing across worm tissues and highlights the power of tissue-specific transcriptomic profiling during ageing, which can serve as a resource to the field.
... In this study, we performed the first genome-wide DNA methyla- as well as its downstream kinases mTOR and S6K has an essential role in aging and longevity in multiple organisms (Bjedov et al., 2010;Harrison et al., 2009;Kenyon, 2005;Morris et al., 1996;Piper et al., 2008;Selman et al., 2009). Phospholipids are the main lipid components of most cellular membranes and are associated with several age- CG(AT) sites, that is., "solo-WCGW" motifs, in PMDs as a universal indicator of methylation loss due to aging and mitotic cell division in mammalian cells. ...
Hutchinson-Gilford Progeria Syndrome (HGPS) is an extremely rare genetic disorder caused by mutations in the LMNA gene and characterized by premature and accelerated aging beginning in childhood. In this study, we performed the first genome-wide methylation analysis on blood DNA of 15 patients with progeroid laminopathies using Infinium Methylation EPIC arrays including 8 patients with classical HGPS. We could observe DNA methylation alterations at 61 CpG sites as well as 32 significant regions following a 5 Kb tiling analysis. Differentially methylated probes were enriched for phosphatidylinositol biosynthetic process, phospholipid biosynthetic process, sarcoplasm, sarcoplasmic reticulum, phosphatase regulator activity, glycerolipid biosynthetic process, glycerophospholipid biosynthetic process, and phosphatidylinositol metabolic process. Differential methylation analysis at the level of promoters and CpG islands revealed no significant methylation changes in blood DNA of progeroid laminopathy patients. Nevertheless, we could observe significant methylation differences in classic HGPS when specifically looking at probes overlapping solo-WCGW partially methylated domains. Comparing aberrantly methylated sites in progeroid laminopathies, classic Werner syndrome, and Down syndrome revealed a common significantly hypermethylated region in close vicinity to the transcription start site of a long non-coding RNA located anti-sense to the Catenin Beta Interacting Protein 1 gene (CTNNBIP1). By characterizing epigenetically altered sites, we identify possible pathways/mechanisms that might have a role in the accelerated aging of progeroid laminopathies.
... Similarly, mice raised on a calorically restricted diet have extended maximal lifespans and exhibit a delay in the evolution of agingassociated physiologic and pathologic changes (Arking 1998;Lee et al. 1999). Although the correlation between stress resistance and lifespan has been used to identify several genes that affect longevity, it remains poorly understood at a molecular level (Kenyon et al. 1993;Orr and Sohal 1994;Kennedy et al. 1995;Morris et al. 1996;Murakami and Johnson 1996;Ewbank et al. 1997;Kimura et al. 1997;Lin et al. 1997Lin et al. , 1998. ...
For a number of organisms, the ability to withstand periods of nutrient deprivation correlates directly with lifespan. However, the underlying molecular mechanisms are poorly understood. We show that deletion of the N-myristoylprotein, Sip2p, reduces resistance to nutrient deprivation and shortens lifespan in Saccharomyces cerevisiae . This reduced lifespan is due to accelerated aging, as defined by loss of silencing from telomeres and mating loci, nucleolar fragmentation, and accumulation of extrachromosomal rDNA. Genetic studies indicate that sip2Δ produces its effect on aging by increasing the activity of Snf1p, a serine/threonine kinase involved in regulating global cellular responses to glucose starvation. Biochemical analyses reveal that as yeast age, hexokinase activity increases as does cellular ATP and NAD ⁺ content. The change in glucose metabolism represents a new correlate of aging in yeast and occurs to a greater degree, and at earlier generational ages in sip2Δ cells. Sip2p and Snf1p provide new molecular links between the regulation of cellular energy utilization and aging.
... Another 12 INSs have an antagonistic effect on DAF-2, promoting dauer [59]. Through DAF-2, the phosphoinositide-3-kinase (PI3K) AGEing alteration 1 (AGE-1) is activated, and this phosphorylation of phosphatidylinositol 4,5-biphosphate (PIP 2 ) into phosphatidylinositol 3,4,5-triphosphate (PIP 3 ) in turn activates downstream kinases PDK-1, AKT-1 and AKT-2 [60][61][62]. AGE-1 is antagonized by DAF-18/PTEN [34]. AKT-1/2 phosphorylate the FoxO transcription factor DAF-16, thereby sequestering it in the cytoplasm (ref. ...
Nematodes are presumably the most abundant Metazoa on Earth, and can even be found in some of the most hostile environments of our planet. Various types of hypobiosis evolved to adapt their life cycles to such harsh environmental conditions. The five most distal major clades of the phylum Nematoda (Clades 8–12), formerly referred to as the Secernentea, contain many economically relevant parasitic nematodes. In this group, a special type of hypobiosis, dauer, has evolved. The dauer signalling pathway, which culminates in the biosynthesis of dafachronic acid (DA), is intensively studied in the free-living nematode Caenorhabditis elegans , and it has been hypothesized that the dauer stage may have been a prerequisite for the evolution of a wide range of parasitic lifestyles among other nematode species. Biosynthesis of DA is not specific for hypobiosis, but if it results in exit of the hypobiotic state, it is one of the main criteria to define certain behaviour as dauer. Within Clades 9 and 10, the involvement of DA has been validated experimentally, and dauer is therefore generally accepted to occur in those clades. However, for other clades, such as Clade 12, this has hardly been explored. In this review, we provide clarity on the nomenclature associated with hypobiosis and dauer across different nematological subfields. We discuss evidence for dauer-like stages in Clades 8 to 12 and support this with a meta-analysis of available genomic data. Furthermore, we discuss indications for a simplified dauer signalling pathway in parasitic nematodes. Finally, we zoom in on the host cues that induce exit from the hypobiotic stage and introduce two hypotheses on how these signals might feed into the dauer signalling pathway for plant-parasitic nematodes. With this work, we contribute to the deeper understanding of the molecular mechanisms underlying hypobiosis in parasitic nematodes. Based on this, novel strategies for the control of parasitic nematodes can be developed.
... Specifically, when active, the orthologs of PI3K and AKT oppose dauer formation, whereas the ortholog of PTEN promotes dauer formation. The single PI3K in C. elegans is encoded by age-1, also called daf-23 (Morris et al., 1996). age-1 was first identified based on the long-lived phenotype conferred by mutants (Klass, 1983). ...
Diapause is a state of developmental arrest adopted in response to or in anticipation of environmental conditions that are unfavorable for growth. In many cases, diapause is facultative, such that animals may undergo either a diapause or a non-diapause developmental trajectory, depending on environmental cues. Diapause is characterized by enhanced stress resistance, reduced metabolism, and increased longevity. The ability to postpone reproduction until suitable conditions are found is important to the survival of many animals, and both vertebrate and invertebrate species can undergo diapause. The decision to enter diapause occurs at the level of the whole animal, and thus hormonal signaling pathways are common regulators of the diapause decision. Unlike other types of developmental arrest, diapause is programmed, such that the diapause developmental trajectory includes a pre-diapause preparatory phase, diapause itself, recovery from diapause, and post-diapause development. Therefore, developmental pathways are profoundly affected by diapause. Here, I review two conserved hormonal pathways, insulin/IGF signaling (IIS) and nuclear hormone receptor signaling (NHR), and their role in regulating diapause across three animal phyla. Specifically, the species reviewed are Austrofundulus limnaeus and Nothobranchius furzeri annual killifishes, Caenorhabditis elegans nematodes, and insect species including Drosophila melanogaster, Culex pipiens, and Bombyx mori. In addition, the developmental changes that occur as a result of diapause are discussed, with a focus on how IIS and NHR pathways interact with core developmental pathways in C. elegans larvae that undergo diapause.
... The PI3K AGE-1 acts downstream of insulin receptor DAF-2 to modulate learning DAF-2 signalling activates AGE-1 , the worm homologue of PI3K in mammals (Morris et al. 1996). AGE-1 is involved in several forms of learning in C. elegans. ...
Learning is an essential biological process for survival since it facilitates behavioural plasticity in response to environmental changes. This process is mediated by a wide variety of genes, mostly expressed in the nervous system. Many studies have extensively explored the molecular and cellular mechanisms underlying learning and memory. This review will focus on the advances gained through the study of the nematode Caenorhabditis elegans. C. elegans provides an excellent system to study learning because of its genetic tractability, in addition to its invariant, compact nervous system (~300 neurons) that is well‐characterised at the structural level. Importantly, despite its compact nature, the nematode nervous system possesses a high level of conservation with mammalian systems. These features allow the study of genes within specific sensory‐, inter‐ and motor neurons, facilitating the interrogation of signalling pathways that mediate learning via defined neural circuits. This review will detail how learning and memory can be studied in C. elegans through behavioural paradigms that target distinct sensory modalities. We will also summarise recent studies describing mechanisms through which key molecular and cellular pathways are proposed to affect associative and non‐associative forms of learning.
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The moderate restriction of dietary energy intake (dietary restriction: DR) extends the lifespan and health span of various laboratory animals, suggesting that it delays the aging process inherent in many animal species. Attenuated growth hormone and insulin-like growth factor-1 (IGF-1) signaling caused by mutations also increases the lifespan of mice, even those allowed to feed freely. In nematodes, the Daf16, mammalian Forkhead box O (FoxO) transcription factor, was shown to be required for lifespan extension in response to reduced IGF-1 signaling. Because DR also decreases the plasma concentration of IGF-1 in mammals, the IGF-1–FoxO axis may play a central role in the lifespan extension effect of DR and, thus, retardation of aging. Studies using knockout mice under DR conditions revealed the importance of FoxO1 and nuclear factor erythroid-derived 2-like 2 (Nrf2) in tumor suppression, and FoxO3 in lifespan extension. Human genomic studies also identified a strong association between a FOXO3 single nucleotide polymorphism and longevity. The aging mechanism is the most important risk factor for disease and frailty in aging humans. Therefore, further research on the application of DR to humans, the development of compounds and drugs that mimic the effects of DR, and mechanisms underlying FOXO3 polymorphisms for longevity is highly relevant to extending the human health span.
Mulberrin, a naturally occurring flavone found in mulberry and Romulus Mori, exhibits diverse biological functions. Here, we showed that mulberrin extended both the lifespan and healthspan in C. elegans. Moreover, mulberrin increased the worms' resistance to toxicants and activated the expression of detoxification genes. The longevity-promoting effect of mulberrin was attenuated in nuclear hormone receptor (NHR) homologous nhr-8 and daf-12 mutants, indicating that the lifespan extending effects of mulberrin in C. elegans may depend on nuclear hormone receptors NHR-8/DAF-12. Further analyses revealed the potential associations between the longevity effects of mulberrin and the insulin/insulin-like growth factor signaling (IIS) and adenosine 5'-monophosphate-activated protein kinase (AMPK) pathways. Together, our findings suggest that mulberrin may prolong lifespan and healthspan by activating detoxification functions mediated by nuclear receptors.
Moderate restriction of dietary energy intake, referred to here as dietary restriction (DR), delays aging and extends lifespan in experimental animals compared with a diet of ad libitum feeding (AL) control animals. Basic knowledge of the mechanisms underlying the effects of DR could be applicable to extending the healthspan in humans. This review highlights the importance of forkhead box O (FoxO) transcription factors downstream of the growth hormone‐insulin‐like growth factor 1 signaling in the effects of DR. Our lifespan studies in mice with heterozygous Foxo1 or Foxo3 gene knockout indicated differential roles of FoxO1 and FoxO3 in the tumor‐inhibiting and life‐extending effects of DR. Subsequent studies suggested a critical role of FoxO3 in metabolic and mitochondrial bioenergetic adaptation to DR. Our studies also verified hypothalamic neuropeptide Y (Npy) as a vital neuropeptide showing pleiotropic and sexually dimorphic effects for extending the healthspan in the context of nutritional availability. Npy was necessary for DR to exert its effects in male and female mice; meanwhile, under AL conditions, the loss of Npy prevented obesity and insulin resistance only in female mice. Overnutrition disrupts FoxO‐ and Npy‐associated metabolic and mitochondrial bioenergetic adaptive processes, causing the acceleration of aging and related diseases.
Embryogenesis is highly dependent on maternally loaded materials, particularly those used for energy production. Different environmental conditions and genetic backgrounds shape embryogenesis. The robustness of embryogenesis in response to extrinsic and intrinsic changes remains incompletely understood. By analyzing the levels of two major nutrients, glycogen and neutral lipids, we discovered stage‐dependent usage of these two nutrients along with mitochondrial morphology changes during Caenorhabditis elegans embryogenesis. ATGL, the rate‐limiting lipase in cellular lipolysis, is expressed and required in the hypodermis to regulate mitochondrial function and support embryogenesis. The embryonic lethality of atgl‐1 mutants can be suppressed by reducing sinh‐1/age‐1 ‐ akt signaling, likely through modulating glucose metabolism to maintain sustainable glucose consumption. The embryonic lethality of atgl‐1(xd314) is also affected by parental nutrition. Parental glucose and oleic acid supplements promote glycogen storage in atgl‐1(xd314) embryos to compensate for the impaired lipolysis. The rescue by parental vitamin B12 supplement is likely through enhancing mitochondrial function in atgl‐1 mutants. These findings reveal that metabolic plasticity contributes to the robustness of C. elegans embryogenesis.
Numerous conserved signaling pathways play critical roles in aging, including insulin, TGF-β, Wnt, and autophagy pathways. Some of these pathways also play prominent roles in the formation and maintenance of the extracellular matrix. The nematode Caenorhabditis elegans has been an enduringly productive system for the identification of conserved mechanisms of biological aging. Recent studies in C. elegans highlight the regulatory circuits between conserved signaling pathways and the extracellular matrix, revealing a bidirectional relationship between these factors and providing a platform to address how regulation of and by the extracellular matrix can impact lifespan and organismal health during aging. These discoveries provide new opportunities for clinical advances and novel therapeutic strategies.
Studies of neuronal connectivity in model organisms, i.e., of their connectomes, have been instrumental in dissecting the structure-function relationship of nervous systems. However, the limited sample size of these studies has impeded analyses into how variation of connectivity across populations may influence circuit architecture and behavior. Moreover, little is known about how experiences induce changes in circuit architecture. Here, we show that an asymmetric salt-sensing circuit in the nematode Caenorhabditis elegans exhibits variation that predicts the animals' salt preferences and undergoes restructuring during salt associative learning. Naive worms memorize and prefer the salt concentration they experience in the presence of food through a left-biased neural network architecture. However, animals conditioned at elevated salt concentrations change this left-biased network to a right-biased network. This change in circuit architecture occurs through the addition of new synapses in response to asymmetric, paracrine insulin signaling. Therefore, experience-dependent changes in an animal's neural connectome are induced by insulin signaling and are fundamental to learning and behavior.
Current advances in geroscience are due in part to the discovery of biomarkers with high predictive ability in short-lived laboratory animals such as flies and mice. These model species, however, do not always adequately reflect human physiology and disease, highlighting the need for a more comprehensive and relevant model of human aging. Domestic dogs offer a solution to this obstacle, as they share many aspects not only of the physiological and pathological trajectories of their human counterpart, but also of their environment. Furthermore, they age at a considerably faster rate. Studying aging in the companion dog provides an opportunity to better understand the biological and environmental determinants of healthy lifespan in our pets, and to translate those findings to human aging. Biobanking, the systematic collection, processing, storage, and distribution of biological material and associated data has contributed to basic, clinical, and translational research by streamlining the management of high-quality biospecimens for biomarker discovery and validation. In this review, we discuss how veterinary biobanks can support research on aging, particularly when integrated into large-scale longitudinal studies. As an example of this concept, we introduce the Dog Aging Project Biobank.
Twenty-nine years following the breakthrough discovery that a single-gene mutation of daf-2 doubles Caenorhabditis elegans lifespan, it remains unclear where this insulin/IGF-1 receptor gene is expressed and where it acts to regulate ageing. Using knock-in fluorescent reporters, we determined that daf-2 and its downstream transcription factor daf-16 are expressed ubiquitously. Using tissue-specific targeted protein degradation, we determined that intracellular DAF-2-to-DAF-16 signaling in the intestine plays a major role in lifespan regulation, while that in the hypodermis, neurons, and germline plays a minor role. Notably, intestine-specific loss of DAF-2 activates DAF-16 in and outside the intestine, causes almost no adverse effects on development and reproduction, and extends lifespan by 94% in a way that partly requires non-intestinal DAF-16. Consistent with intestine supplying nutrients to the entire body, evidence from this and other studies suggests that altered metabolism, particularly down-regulation of protein and RNA synthesis, mediates longevity by reduction of insulin/IGF-1 signaling.
Brown algae produce varieties of potent metabolites in order to adapt to extreme environment. Among these metabolites, polyphenols comprised of phlorotannins serve as powerful multifaceted bioactive with vast pharmacological potentials against non-communicable diseases like cancer and diabetes. In this study, a new phlorotannin was extracted from Padina tetrastromatica and characterized by Fourier Transform-Infrared, Nuclear Magnetic Resonance & Electronspray Ionization-Mass Spectroscopy. The phlorotannin exhibited potent DPPH and nitric oxide radical-scavenging activity in in-vitro, which were better than the standard antioxidants and other phlorotannins, previously reported. Further, the novel phlorotannin explicitly inhibited advanced glycation end-products formation in both in-vitro and in-vivo studies using hyperglycaemic C. elegans as an animal model and confirmed by live-cell fluorescence imaging. In addition, a significant modulation in expression of stress-responsive genes daf-2 and daf-16 were observed in phlorotannin treated hyperglycemic C. elegans. Moreover, the cytotoxic potential of phlorotannin (2,4,6-trioxa-1,3,5(1,3) tribenzenacyclohexaphane-15,35,55-triol) was explored for the first time in human cervical cancer cells (HeLa) and interesting observation was made that the cancer cell death was induced by activation of autophagy and pro-apoptotic protein markers i.e., LC3I/II, p21 and p53 that were confirmed by western-blot technique. Therefore, phlorotannin can be postulated as a potential bioactive for oxidative stress-mediated diseases, including diabetes and cancer.
Advances in biomedical research have provided unprecedented opportunities to understand the complexities of human disease and translate these findings from the laboratory bench to the patient's bedside. Many of these biomedical advances are due to discoveries made using invertebrate model organisms. This chapter discusses how two invertebrate model organisms, the nematode Caenorhabditis elegans (hereafter: C. elegans) and the fruit fly Drosophila melanogaster (hereafter: Drosophila), are used in translational research. We enumerate the contributions of these two model organisms to understanding the cellular and molecular mechanisms of human disease and discuss current research approaches using C. elegans and Drosophila to study human disease.
The impact of dietary restriction (DR) on disease and aging has received increasing attention in recent years. There is substantial evidence that DR displays many benefits, including reduced inflammation, lowered cardiovascular risk and improved metabolic fitness. In addition, many growing evidence indicates that DR and aging interact through partially overlapping mechanisms in the activation of some conserved nutrient-signaling pathways, mainly the insulin/insulin-like growth factor (IIS) and the mammalian target of Rapamycin (mTOR). Although the involvement of the mTOR pathway and IIS signaling in regulating life span and aging has been studied extensively, the underpinning mechanisms remain elusive. On the other hand, recent discoveries indicate that the aging process can be improve or delay through specific pharmacological approaches. Therefore, this chapter reviews the literature concerning: (i) the emerging insights linking mTOR and IIS signals to various processes related to aging and disease; (ii) recent discoveries on how DR attenuates aging through AMPK and SIRT1 pathways; (iii) discuss the regulatory mechanisms that may delay or improve the aging process from pharmacological discoveries. We also focus on illustrating some potential anti-aging drugs, such as metformin, rapamycin or resveratrol, and verify their actual effects in vivo. In conclusion, systems approaches and polypharmacology to develop anti-aging drugs may be the most effective way to target nutrient-sensing network in improving late-life health.
Germline integrity is critical for progeny fitness. Organisms deploy the DNA damage response (DDR) signalling to protect germline from genotoxic stress, facilitating cell-cycle arrest of germ cells and DNA repair or their apoptosis. Cell-autonomous regulation of germline quality is well-studied; however, how quality is enforced cell non-autonomously on sensing somatic DNA damage is less known. Using Caenorhabditis elegans, we show that DDR disruption, only in the uterus, when insulin-IGF-1 signalling (IIS) is low, arrests germline development and induces sterility in a FOXO/DAF-16 transcription factor (TF)-dependent manner. Without FOXO/DAF-16, germ cells of the IIS mutant escape arrest to produce poor quality oocytes, showing that the TF imposes strict quality control during low IIS. In response to low IIS in neurons, FOXO/DAF-16 works cell autonomously as well as non-autonomously to facilitate the arrest. Activated FOXO/DAF-16 promotes transcription of checkpoint and DDR genes, protecting germline integrity. However, on reducing DDR during low IIS, the TF decreases ERK/MPK-1 signaling below a threshold, and transcriptionally downregulates genes involved in spermatogenesis-to-oogenesis switch as well as cdk-1/Cyclin B to promote germline arrest. Altogether, our study reveals how cell non-autonomous function of FOXO/DAF-16 promotes germline quality and progeny fitness in response to somatic DNA damage.
The surface engagement of high affinity immunoglobulin E receptor (Fc epsilon RI) of rat basophilic leukemia 2H3 (RBL-2H3) cells induced histamine secretion and leukotriene release following activation of the tyrosine kinase Lyn together with phosphatidylinositol 3-kinase (PI3-kinase). Wortmannin inhibited the activity of partially purified PI3-kinase from calf thymus, as well as the PI3-kinase activity in anti-PI3-kinase p85 immunoprecipitates from RBL-2H3 cells, at a concentration as low as 1.0 nM and with IC50 values of 3.0 nM, but did not inhibit PI4-kinase activity. The inhibition of PI3-kinase by wortmannin was irreversible. Wortmannin inhibited both Fc epsilon RI-mediated histamine secretion and leukotriene release up to 80% with IC50 values of 2.0 and 3.0 nM, respectively. Wortmannin inhibited PI3-kinase activity in intact cells up to 80% with an IC50 value of 2.0 nM, which is almost equal to those for PI3-kinase in vitro and for histamine secretion and leukotriene release. With anti-wortmannin antibody, we have shown that wortmannin binds to the 110-kDa protein, but not to PI3-kinase 85-kDa regulatory subunit both in vitro and in whole cells. Furthermore, there was a positive correlation between the potencies of wortmannin derivatives as inhibitors of PI3-kinase and as inhibitors of histamine secretion. Wortmannin had no effect on the activation of the tyrosine kinase Lyn. These results suggest that PI3-kinase is involved in the signal transduction pathway responsible for histamine secretion following stimulation of Fc epsilon RI and that wortmannin blocks these responses through direct interaction with the catalytic subunit of this enzyme.
The long-term goal of this project is the elucidation of the complete sequence of the Caenorhabditis elegans genome. During the first year methods have been developed and a strategy implemented that is amenable to large-scale sequencing. The three cosmids sequenced in this initial phase are surprisingly rich in genes, many of which have mammalian homologues.
Dauer larva formation in Caenorhabditis elegans is controlled by chemosensory cells that respond to environmental cues. Genetic interactions among mutations in 23 genes that affect dauer larva formation were investigated. Mutations in seven genes that cause constitutive dauer formation, and mutations in 16 genes that either block dauer formation or result in the formation of abnormal dauers, were analyzed. Double mutants between dauer-constitutive and dauer-defective mutations were constructed and characterized for their capacity to form dauer larvae. Many of the genes could be interpreted to lie in a simple linear epistasis pathway. Three genes, daf-16, daf-18 and daf-20, may affect downstream steps in a branched part of the pathway. Three other genes, daf-2, daf-3 and daf-5, displayed partial or complex epistasis interactions that were difficult to interpret as part of a simple linear pathway. Dauer-defective mutations in nine genes cause structurally defective chemosensory cilia, thereby blocking chemosensation. Mutations in all nine of these genes appear to fall at a single step in the epistasis pathway. Dauer-constitutive mutations in one gene, daf-11, were strongly suppressed for dauer formation by mutations in the nine cilium-structure genes. Mutations in the other six dauer-constitutive genes caused dauer formation despite the absence of functional chemosensory endings. These results suggest that daf-11 is directly involved in chemosensory transduction essential for dauer formation, while the other Daf-c genes play roles downstream of the chemosensory step.
Phosphatidylinositol 3-kinase (PI-3 kinase) is implicated in the regulation of diverse cellular processes, including insulin-stimulated
glucose transport. PI-3 kinase is composed of a 110-kDa catalytic subunit and an 85-kDa regulatory subunit. Here, we describe
p55PIK, a new regulatory subunit that was isolated by screening expression libraries with tyrosine-phosphorylated insulin
receptor substrate 1 (IRS-1). p55PIK is composed of a unique 30-residue NH2 terminus followed by a proline-rich motif and
two Src homology 2 (SH2) domains with significant sequence identify to those in p85. p55PIK mRNA is expressed early during
development, remains abundant in adult mouse brain and testis tissue, and is detectable in adult adipocytes and heart and
kidney tissues. p55PIK forms a stable complex with p110, and it associates with IRS-1 during insulin stimulation. Moreover,
the activated insulin receptor phosphorylates p55PIK in Sf9 cells, and insulin stimulates p55PIK phosphorylation in CHOIR/p55PIK
cells. The unique features of p55PIK suggest that it is important in receptor signaling.
The nematode Caenorhabditis elegans responds to conditions of overcrowding and limited food by arresting development as a dauer larva. Genetic analysis of mutations that alter dauer larva formation (daf mutations) is presented along with an updated genetic pathway for dauer vs. nondauer development. Mutations in the daf-2 and daf-23 genes double adult life span, whereas mutations in four other dauer-constitutive genes positioned in a separate branch of this pathway (daf-1, daf-4, daf-7 and daf-8) do not. The increased life spans are suppressed completely by a daf-16 mutation and partially in a daf-2; daf-18 double mutant. A genetic pathway for determination of adult life span is presented based on the same strains and growth conditions used to characterize Daf phenotypes. Both dauer larva formation and adult life span are affected in daf-2; daf-12 double mutants in an allele-specific manner. Mutations in daf-12 do not extend adult life span, but certain combinations of daf-2 and daf-12 mutant alleles nearly quadruple it. This synergistic effect, which does not equivalently extend the fertile period, is the largest genetic extension of life span yet observed in a metazoan.
Insulin activates the insulin receptor tyrosine kinase to phosphorylate signaling molecules such as insulin receptor substrate-1 (IRS-1). Phosphorylated IRS-1 binds to SH2 domains in the p85 regulatory subunit of phosphatidyl inositol (PI) 3-kinase, thereby stimulating the catalytic activity of PI 3-kinase. For most growth factor receptor tyrosine kinases (including receptors for epidermal growth factor and platelet-derived growth factor), the p85 regulatory subunit of PI 3-kinase binds directly to phosphorylated YXXM motifs contained in the cytoplasmic domain of the receptor itself. Previous studies in cell-free systems have shown that the phosphorylated YHTM sequence (amino acid residues 1322-1325) in the COOH terminus of the insulin receptor has the ability to bind to the p85 subunit of PI 3-kinase, thereby activating the enzyme. In this investigation, we demonstrate the occurrence of the same direct binding interaction in intact cells. Subsequent to insulin-stimulated phosphorylation of the insulin receptor, a complex is formed that contains the insulin receptor and PI 3-kinase. This complex can be immunoprecipitated by antibodies directed against either the insulin receptor or the p85 subunit of PI 3-kinase. The delta 43 mutant insulin receptor that lacks 43 amino acids at the COOH terminus does not bind p85. In addition, the delta 43 truncation impairs the ability of the receptor to mediate the activation of PI 3-kinase. Thus, by binding directly to p85, the phosphorylated YHTM motif in the COOH terminus of the insulin receptor contributes partially to mediating the effect of insulin to activate PI 3-kinase.
The effects of wortmannin (WT), an inhibitor of phosphatidylinositol (PI) 3-kinase, on differentiation of PC12 cells were analyzed. WT inhibited PI 3-kinase activity of PC12 cells at a concentration of 10(-7) M in vivo and in vitro. Transient inhibition of PI 3-kinase activity at the time of nerve growth factor stimulation had no effect on activation of the ras protein or neurite formation by the cells. However, continuous inhibition of PI 3-kinase blocked differentiation at the step just before neurite formation. When WT was applied to cells growing neurites, elongation of the neurites was stopped at that step. These results suggest that PI 3-kinase may be involved in neurite elongation.
Wortmannin, a fungal metabolite, inhibited 32P labeling of phosphatidylinositol trisphosphate, a product of phosphatidylinositol 3-kinase (PI 3-kinase), selectively in formyl peptide-stimulated 32P-loaded guinea pig neutrophils. The inhibition was of the same concentration dependence (with the half-maximal inhibition around 50 nM) as was observed for the simultaneous inhibition of formyl peptide-induced superoxide anion production. Wortmannin inhibited all three of the PI 3-kinase activities found in the cytosol fraction of guinea pig neutrophils, with a similar dose dependence (the half-maximal effects at 5 nM). Wortmannin was also effective on an immunologically purified preparation of the enzyme. The inhibition was of a noncompetitive type with regard to ATP and was observed consistently when PI, PI monophosphate, or PI bisphosphate was used as substrate. PI 4-kinase activity was not affected. It is concluded, therefore, that wortmannin abolished the formyl peptide-induced stimulation of neutrophils as a result of the inhibition of PI 3-kinase. An essential role of PI 3-kinase in receptor-mediated signaling in neutrophils thus evidenced with the use of wortmannin will be expanded to other cellular signaling systems.
Phosphatidylinositol (PI) 3-kinase has an 85 kDa subunit (p85 alpha) which mediates its association with activated protein tyrosine kinase receptors through SH2 domains, and an 110 kDa subunit (p110) which has intrinsic catalytic activity. Here p85 alpha and a related protein p85 beta are shown to form stable complexes with recombinant p110 in vivo and in vitro. Using a panel of glutathione S-transferase (GST) fusion proteins of the inter-SH2 region of p85, 104 amino acids were found to bind directly the p110 protein, while deletion mutants within this region further defined the binding site to a sequence of 35 amino acids. Transient expression of the mutant p85 alpha protein in mouse L cells showed it was unable to bind PI 3-kinase activity in vivo. Mapping of the complementary site of interaction on the p110 protein defined 88 amino acids in the N-terminal region of p110 which mediate the binding of this subunit to either the p85 alpha or the p85 beta proteins. The inter-SH2 region of p85 is predicted to be an independently folded module of a coiled-coil of two long anti-parallel alpha-helices. The predicted structure of p85 suggests a basis for the intersubunit interaction and the relevance of this interaction with respect to the regulation of the PI 3-kinase complex is discussed.
Dauer formation in Caenorhabditis elegans is induced by chemosensation of high levels of a constitutively secreted pheromone. Seven genes defined by mutations that confer a dauer-formation constitutive phenotype (Daf-c) can be congruently divided into two groups by any of three criteria. Group 1 genes (daf-11 and daf-21) are (1) strongly synergistic with group 2 genes for their Daf-c phenotype, (2) incompletely suppressed by dauer-formation defective (Daf-d) mutations in the genes daf-3 and daf-5 and (3) strongly suppressed by Daf-d mutations in nine genes that affect the structure of chemosensory endings. Group 2 genes (daf-1, daf-4, daf-7, daf-8 and daf-14) are (1) strongly synergistic with group 1 genes for their Daf-c phenotype, (2) fully suppressed by Daf-d mutations in daf-3 and daf-5 and (3) not suppressed by Daf-d mutations in the nine genes that affect chemosensory ending structure. Mutations in each group of genes also cause distinct additional behavioral defects. We propose that these two groups of Daf-c genes act in parallel pathways that process sensory information. The two pathways are partially redundant with each other and normally act in concert to control dauer formation.
We identified a serine/threonine protein kinase that is associated with and phosphorylates phosphoinositide 3-kinase (PtdIns
3-kinase). The serine kinase phosphorylates both the 85- and 110-kDa subunits of PtdIns 3-kinase and purifies with it from
rat liver and immunoprecipitates with antibodies raised to the 85-kDa subunit. Tryptic phosphopeptide maps indicate that p85
from polyomavirus middle T-transformed cells is phosphorylated in vivo at three sites phosphorylated in vitro by the associated
serine kinase. The 85-kDa subunit of PtdIns 3-kinase is phosphorylated in vitro on serine at a stoichiometry of approximately
1 mol of phosphate per mol of p85. This phosphorylation results in a three- to sevenfold decrease in PtdIns 3-kinase activity.
Dephosphorylation with protein phosphatase 2A reverses the inhibition. This suggests that the association of protein phosphatase
2A with middle T antigen may function to activate PtdIns 3-kinase.
age-1(hx546) is a recessive mutant allele in Caenorhabditis elegans that results in an increase in mean life span averaging 40% and in maximal life span averaging 60% at 20 degrees; at 25 degrees age-1(hx546) averages a 65% increase in mean life span (25.3 days vs. 15.0 days) and a 110% increase in maximum life span (46.2 days vs. 22.0 days for wild-type hermaphrodites). Mutant males also show extended life spans. age-1(hx546) is associated with a 75% decrease in hermaphrodite self-fertility as compared to the age-1+ allele at 20 degrees. Using two novel strategies for following the segregation of age-1, we present evidence that longer life results from a mutation in a single gene that increases the probability of survival at all chronological ages. The long-life and reduced-fertility phenotypes cosegregate and are tightly linked to fer-15, a locus on linkage group II. age-1(hx546) does not affect the timing of larval molts, the length of embryogenesis, food uptake, movement, or behavior in any way tested. Although age-1(hx546) lowers hermaphrodite self-fertility, it does not markedly affect the length of the reproductive period with all the increase in life expectancy due to an increase in the length of postreproductive life. In so far as we are aware, this mutant in age-1 is the only instance of a well-characterized genetic locus in which the mutant form results in lengthened fife. It is likely that the action of age-1 in lengthening life results not from eliminating a programmed aging function but rather from reduced hermaphrodite self-fertility or from some other unknown metabolic or physiologic alteration.
We have reported previously that Ras interacts with the catalytic subunit of phosphoinositide 3-kinase (PI 3-kinase) in a GTP-dependent manner. The affinity of the interaction of Ras-GTP with p85alpha/p110alpha is shown here to be approximately 150 nM. The site of interaction on the p110alpha and beta isoforms of PI 3-kinase lies between amino acid residues 133 and 314. A point mutation in this region, K227E, blocks the GTP-dependent interaction of PI 3-kinase p110alpha with Ras in vitro and the ability of Ras to activate PI 3-kinase in intact cells. In addition, this mutation elevates the basal activity of PI 3-kinase in intact cells, suggesting a direct influence of the Ras binding site on the catalytic activity of PI 3-kinase. Using an in vitro reconstitution assay, it is shown that the interaction of Ras-GTP, but not Ras-GDP, with PI 3-kinase leads to an increase in its enzymatic activity. This stimulation is synergistic with the effect of tyrosine phosphopeptide binding to p85, particularly at suboptimal peptide concentrations. These data show that PI 3-kinase is regulated by a number of mechanisms, and that Ras contributes to the activation of this lipid kinase synergistically with tyrosine kinases.
Recessive mutations in two genes, daf-2 and age-1, extend the lifespan of Caenorhabditis elegans significantly. The daf-2 gene also regulates formation of an alternative developmental state called the dauer. Here we asked whether these two genes function in the same or different lifespan pathways. We found that the longevity of both age-1 and daf-2 mutants requires the activities of the same two genes, daf-16 and daf-18. In addition, the daf-2(e1370); age-1(hx546) double mutant did not live significantly longer than the daf-2 single mutant. We also found that, like daf-2 mutations, the age-1(hx546) mutation affects certain aspects of dauer formation. These findings suggest that age-1 and daf-2 mutations do act in the same lifespan pathway and extend lifespan by triggering similar if not identical processes.
Featuring extensive references, updated for this paperback edition, Longevity, Senescence, and the Genome constitutes a landmark contribution to biomedicine and the evolutionary biology of aging. To enhance gerontology's focus on human age-related dysfunctions, Caleb E. Finch provides a comparative review of all the phyla of organisms, broadening gerontology to intersect with behavioral, developmental, evolutionary, and molecular biology. By comparing species that have different developmental and life spans, Finch proposes an original typology of senescence from rapid to gradual to negligible, and he provides the first multiphyletic calculations of mortality rate constants.
The free-living nematode Caenorhabditis elegans is used as a genetically manipulable experimental system for the study of aging. Utilizing a temperature-sensitive sterile strain with a normal life span, a method is described for the isolation of mutant strains with significantly increased life spans. Eight mutant strains were isolated each having increased life spans. Two mutant strains were spontaneous dauer formers, accounting for their increased longevity. Another was chemotaxis-defective, causing reduced food intake which could account for its increased life span. Five mutants suffered from varying degrees of paralysis affecting their rate of pharyngeal pumping and food ingestion. The high correlation of the decreased rate of food ingestion of these mutants with their increased longevity is interpreted as indicating that the increased longevity is most likely due to reduced caloric intake. These results appear to indicate that specific life span genes are extremely rare or, alternatively, life span is controlled in a polygenic fashion.
The dauer larva of Caenorhabditis elegans is a developmentally arrested stage induced by starvation or overcrowding. Mutant genes controlling the ability to form dauer larvae interact in a way which allows them to be ordered in a pathway. Mutant phenotypes suggest that the pathway corresponds to neural processing of environmental stimuli.
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Phosphoinositide-3 kinase activity is implicated in diverse cellular responses triggered by mammalian cell surface receptors and in the regulation of protein sorting in yeast. Receptors with intrinsic and associated tyrosine kinase activity recruit heterodimeric phosphoinositide-3 kinases that consist of p110 catalytic subunits and p85 adaptor molecules containing Src homology 2 (SH2) domains. A phosphoinositide-3 kinase isotype, p110 gamma, was cloned and characterized. The p110 gamma enzyme was activated in vitro by both the alpha and beta gamma subunits of heterotrimeric guanosine triphosphate (GTP)-binding proteins (G proteins) and did not interact with p85. A potential pleckstrin homology domain is located near its amino terminus. The p110 gamma isotype may link signaling through G protein-coupled receptors to the generation of phosphoinositide second messengers phosphorylated in the D-3 position.
A serine/threonine kinase, named protein kinase B (PKB) for its sequence homology to both protein kinase A and C, has previously been isolated. PKB, which is identical to the kinase Rac, was later found to be the cellular homologue of the transforming v-Akt. Here we show that PKB is activated by stimuli such as insulin, platelet-derived growth factor (PDGF), epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF). Activation of PKB was inhibited by the phosphatidylinositol-3-OH kinase (PI(3)K) inhibitor wortmannin and by coexpression of a dominant-negative mutant of PI(3)K. PDGF receptor mutants that lack detectable associated PI(3)K activity also fail to induce PKB activation, PKB kinase activity is correlated with phosphorylation of PKB on serine. Finally, we show that a constructed Gag-PKB fusion protein, homologous to the v-akt oncogene, displays significantly increased ligand-independent kinase activity. Furthermore, this activity is sufficient to activate the p70 S6-kinase (p70S6K). These results suggest a role for PKB in PI(3)K-mediated signal transduction.
Nerve growth factor (NGF) induces both differentiation and survival of neurons by binding to the Trk receptor protein tyrosine
kinase. Although Ras is required for differentiation, it was not required for NGF-mediated survival of rat pheochromocytoma
PC-12 cells in serum-free medium. However, the ability of NGF to prevent apoptosis (programmed cell death) was inhibited by
wortmannin or LY294002, two specific inhibitors of phosphatidylinositol (Pl)-3 kinase. Moreover, platelet-derived growth factor
(PDGF) prevented apoptosis of PC-12 cells expressing the wild-type PDGF receptor, but not of cells expressing a mutant receptor
that failed to activate Pl-3 kinase. Cell survival thus appears to be mediated by a Pl-3 kinase signaling pathway distinct
from the pathway that mediates differentiation.
The serine/threonine protein kinase encoded by the Akt proto-oncogene is catalytically inactive in serum-starved primary and immortalized fibroblasts. Here we show that Akt and the Akt-related kinase AKT2 are activated by PDGF. The activation was rapid and specific, and it was abrogated by mutations in the Akt Pleckstrin homology (PH) domain. The Akt activation was also shown to depend on PDGFR beta tyrosines Y740 and Y751, which bind phosphatidylinositol 3-kinase (PI 3-kinase) upon phosphorylation. Moreover, Akt activation was blocked by the PI 3-kinase-specific inhibitor wortmannin and the dominant inhibitory N17Ras. Conversely, Akt activity was induced following the addition of phosphatidylinositol-3-phosphate to Akt immunoprecipitates from serum-starved cells in vitro. These results identify Akt as a novel target of PI 3-kinase and suggest that the Akt PH domain may be a mediator of PI 3-kinase signaling.
Diapause hormone (DH) is a neurohormone which is secreted from suboesophageal ganglion (SG) and responsible for induction of embryonic diapause in the silkworm, Bombyx mori. DH is generated along with four other functionally different neuropeptides including pheromone biosynthesis-activating neuropeptide from the common polyprotein precursor, DH-PBAN (DHP), which is translated by a single species of mRNA. In this paper, the site of the gene expression was determined by reverse transcription-polymerase chain reaction and in situ hybridization using cDNA probe. The transcript of the DHP gene was found in SG of pupae and pharate adults, but no positive sign was detected in other tissues such as brain, thoracic ganglia, abdominal ganglia, and midgut. In situ hybridization with the cDNA clearly stained 12 cells near the ventral midline of SG which were aggregated into three clusters. The clusters were respectively localized in the mandibular, maximally, and labial neuromere of SG. The similar staining profile was observed in the SG cells at the larval, pupal, and adult stages, indicating that the DHP gene is expressed in the same set of cells throughout the postembryonic development.
Under conditions of high population density and low food, Caenorhabditis elegans forms an alternative third larval stage, called the dauer stage, which is resistant to desiccation and harsh environments. Genetic analysis of some dauer constitutive (Daf-c) and dauer defective (Daf-d) mutants has revealed a complex pathway that is likely to function in particular neurons and/or responding tissues. Here we analyze the genetic interactions between three genes which comprise a branch of the dauer formation pathway that acts in parallel to or downstream of the other branches of the pathway, the Daf-c genes daf-2 and daf-23 and the Daf-d gene daf-16. Unlike mutations in other Daf-c genes, mutations in both daf-2 and daf-23 cause non-conditional arrest at the dauer stage. Our epistasis analysis suggests that daf-2 and daf-23 are functioning at a similar point in the dauer pathway. First, mutations in daf-2 and daf-23 are epistatic to mutations in the same set of Daf-d genes. Second, daf-2 and daf-23 mutants are suppressed by mutations in daf-16. Mutations in daf-16 do not suppress any of the other Daf-c mutants as efficiently as they suppress daf-2 and daf-23 mutants. Third, double mutants between either daf-2 or daf-23 and several other daf-d mutants exhibit an unusual interaction. Based on these results, we present a model for the function of daf-2, daf-23 and daf-16 in dauer formation.
Currently, a central question in biology is how signals from the cell surface modulate intracellular processes. In recent years phosphoinositides have been shown to play a key role in signal transduction. Two phosphoinositide pathways have been characterized, to date. In the canonical phosphoinositide turnover pathway, activation of phosphatidylinositol-specific phospholipase C results in the hydrolysis of phosphatidylinositol 4,5-bisphospate and the generation of two second messengers, inositol 1,4,5-trisphosphate and diacylglycerol. The 3-phosphoinositide pathway involves protein-tyrosine kinase-mediated recruitment and activation of phosphatidylinositol 3-kinase, resulting in the production of phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate. The 3-phosphoinositides are not substrates of any known phospholipase C, are not components of the canonical phosphoinositide turnover pathway, and may themselves act as intracellular mediators. The 3-phosphoinositide pathway has been implicated in growth factor-dependent mitogenesis, membrane ruffling and glucose uptake. Furthermore the homology of the yeast vps34 with the mammalian phosphatidylinositol 3-kinase has suggested a role for this pathway in vesicular trafficking.
In this review the different mechanisms employed by protein-tyrosine kinases to activate phosphatidylinositol 3-kinase, and its involvement in the signaling cascade initiated by tyrosine phosphorylation, are examined.
Wortmannin (WT) and its derivative 17-hydroxywortmannin (HWT) inhibit at nanomolar concentrations superoxide formation and exocytosis in neutrophils stimulated with chemotactic agonists. Treatment of neutrophils with radiolabeled [3H]HWT resulted in specific and saturable binding that paralleled the inhibition of the respiratory burst. Both half-maximal binding and half-maximal inhibition were observed at 5 nM, and > 90% of maximal binding and inhibition was observed at 20 nM HWT. Fluorography of subcellular fractions that were separated on NaDodSO4/PAGE showed that [3H]HWT binds covalently to a 110-kDa cytosolic protein. The WT-binding protein was purified from human neutrophils and bovine brain homogenates by column chromatography. The pure protein was eluted from gel filtration columns with an apparent molecular mass of 200 kDa and showed a heterodimeric structure on Coomassie-stained NaDodSO4/PAGE. In addition to the 110 kDa wortmannin binding protein an equally intense band was seen migrating at 85 kDa. This band was identified on Western blots as p85 alpha, the regulatory subunit of phosphatidylinositol (PI) 3-kinase (ATP:1-phosphatidyl-1D-myo-inositol 3-phosphotransferase, EC 2.7.1.137). The purified protein contained PI 3-kinase activity that was enriched > 20,000-fold from human neutrophil cytosol during preparation. The data impose a key role for PI 3-kinase-mediated signal transduction through guanine nucleotide-binding protein-coupled receptors and suggest that 3-phosphorylated inositol phospholipids are important second messengers for immediate responses in neutrophils. Furthermore, the results show that WT is a powerful and selective tool to study the function of PI 3-kinase.
We have found that mutations in the gene daf-2 can cause fertile, active, adult Caenorhabditis elegans hermaphrodites to live more than twice as long as wild type. This lifespan extension, the largest yet reported in any organism, requires the activity of a second gene, daf-16. Both genes also regulate formation of the dauer larva, a developmentally arrested larval form that is induced by crowding and starvation and is very long-lived. Our findings raise the possibility that the longevity of the dauer is not simply a consequence of its arrested growth, but instead results from a regulated lifespan extension mechanism that can be uncoupled from other aspects of dauer formation. daf-2 and daf-16 provide entry points into understanding how lifespan can be extended.
Mutations in the age-1 gene double both the mean and maximum life span of Caenorhabditis elegans. They also result in an age-specific increase of catalase and Cu/Zn superoxide dismutase activity levels. The higher superoxide dismutase activity levels in age-1 mutants confer hyperresistance to the superoxide-anion-generating drug paraquat. The rate of superoxide anion production by microsome fractions declines linearly with age in age-1(+) worms, but, after an initial decline, is stabilized at a higher level in senescent age-1 mutant nematodes. These results clearly show that oxidative stress resistance and potential life span are correlated in this organism, and they suggest that the natural product of age-1 either directly or indirectly downregulates the activities of several other genes as a function of age.
The dauer larva state and the age-1 mutation, both of which extend life-span in Caenorhabditis elegans, were tested for hyperresistance to cellular damage that may be relevant to aging. The age-1 strain TJ401 displayed hyperresistance to oxidative stress relative to its parental strain. The activities of two enzymes that protect cells from oxidative damage, superoxide dismutase (SOD) and catalase, showed an age-dependent increase in mutant animals, which was not seen in the parental strain. These increases in activities paralleled the time course of the hyperresistance. The results are consistent with the age-1 gene product functioning as a negative regulator of SOD and catalase activities. In wild-type and age-1 dauer larvae, elevated levels of SOD activity, but not of catalase activity, were present when compared with young adults. The common increase in SOD activity prompted cloning the C. elegans Cu/Zn SOD gene. Its position on the physical map of the genome was in the region to which the age-1 gene has been genetically mapped, but it is unlikely that a mutation at the SOD locus confers the Age phenotype. Results support the free radical theory of aging by suggesting that the increased resistance to oxidative stress may be among the causes of increased longevity in both strain TJ401 and in the dauer larva.