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Tetrahymena Mob1 localizes preferentially at the posterior pole basal bodies. (A) Tetrahymena cells expressing GFP were stained only with anti-GFP antibody. (B-E) Immunofluorescence microscopy of Tetrahymena cells expressing Mob1-GFP using anti-GFP (all images), anti-a-tubulin (B) and anti-centrin (C-E) antibodies. Mob1-GFP accumulates preferentially at the posterior pole basal bodies, co-localizing with centrin (C,E). Panoramic view of the posterior region of Mob1-GFP-expressing cells is shown in D; arrowhead indicates where contractile vacuole pores are visible. Mob1-GFP could also be detected at the oral apparatus (OA), at the posterior pole transversal microtubules (indicated by arrowheads in B and C1) and at the asymmetric anterior crown (arrows in B and C). Scale bars: 10 mm (A,B,C,E); 2 mm (C1,C2,D).
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Mob1 is a component of both the mitotic exit network and Hippo pathway, being required for cytokinesis, control of cell proliferation and apoptosis. Cell division accuracy is crucial in maintaining cell ploidy and genomic stability and relies on the correct establishment of the cell division axis, which is under the control of the cell's environmen...
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... order to further define the function of Tetrahymena Mob1, we analyzed its cellular distribution. For that purpose we constructed a Tetrahymena strain expressing Mob1-GFP through the introduction, by DNA homologous recombination, of a Mob1- GFP construct into a b-tubulin locus, under the control of the cadmium (Cd 2+ )-inducible promoter metallothionein 1 (MTT1) (supplementary material Fig. S2A). The levels of Mob1-GFP in response to Cd 2+ addition for different times were evaluated by western blot using an anti-GFP antibody (supplementary material Fig. S2B). Mob1-GFP was detected at 15 minutes and reached the highest levels after 30 minutes of Cd 2+ induction. As a control, a Tetrahymena strain expressing just GFP was also ...
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... order to further define the function of Tetrahymena Mob1, we analyzed its cellular distribution. For that purpose we constructed a Tetrahymena strain expressing Mob1-GFP through the introduction, by DNA homologous recombination, of a Mob1- GFP construct into a b-tubulin locus, under the control of the cadmium (Cd 2+ )-inducible promoter metallothionein 1 (MTT1) (supplementary material Fig. S2A). The levels of Mob1-GFP in response to Cd 2+ addition for different times were evaluated by western blot using an anti-GFP antibody (supplementary material Fig. S2B). Mob1-GFP was detected at 15 minutes and reached the highest levels after 30 minutes of Cd 2+ induction. As a control, a Tetrahymena strain expressing just GFP was also ...
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... ( Fig. 2B-E). We therefore investigated whether the localization of basal bodies and oral apparatus in Tetrahymena expressing Mob1-GFP was dependent on microtubules by treating the cells with the microtubule-depolymerizing agent nocodazole. In nocodazole-treated Tetrahymena cells, Mob1- GFP had the same localization pattern as in non-treated cells, indicating that this specific localization of Tetrahymena Mob1 is independent of intracytoplasmic and cortical nocodazole- sensitive microtubules (Fig. ...
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... immunofluorescence confocal microscopy analysis of control cells expressing GFP alone showed it to be distributed in the cytoplasm ( Fig. 2A). Unexpectedly, Mob1-GFP, was clearly accumulated in posterior pole basal bodies ( that progressively and substantially decreases towards the anterior pole ( Fig. 2B-E). Therefore, in Tetrahymena, distinct basal bodies clearly present different molecular compositions and abilities to recruit and/or concentrate pools of proteins involved in establishing cell polarity, which suggests that in addition to cilia assembly they might present specialized functions inside a single cell. Mob1-GFP was also detected in some posterior transversal microtubules, contractile vacuole pores and in the oral (B-E) Immunofluorescence microscopy of Tetrahymena cells expressing Mob1-GFP using anti-GFP (all images), anti-a-tubulin (B) and anti-centrin (C-E) antibodies. Mob1-GFP accumulates preferentially at the posterior pole basal bodies, co-localizing with centrin (C,E). Panoramic view of the posterior region of Mob1-GFP-expressing cells is shown in D; arrowhead indicates where contractile vacuole pores are visible. Mob1-GFP could also be detected at the oral apparatus (OA), at the posterior pole transversal microtubules (indicated by arrowheads in B and C1) and at the asymmetric anterior crown (arrows in B and C). Scale bars: 10 mm (A,B,C,E); 2 mm (C1,C2,D). ...
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... immunofluorescence confocal microscopy analysis of control cells expressing GFP alone showed it to be distributed in the cytoplasm ( Fig. 2A). Unexpectedly, Mob1-GFP, was clearly accumulated in posterior pole basal bodies ( that progressively and substantially decreases towards the anterior pole ( Fig. 2B-E). Therefore, in Tetrahymena, distinct basal bodies clearly present different molecular compositions and abilities to recruit and/or concentrate pools of proteins involved in establishing cell polarity, which suggests that in addition to cilia assembly they might present specialized functions inside a single cell. Mob1-GFP was also detected in some posterior transversal microtubules, contractile vacuole pores and in the oral (B-E) Immunofluorescence microscopy of Tetrahymena cells expressing Mob1-GFP using anti-GFP (all images), anti-a-tubulin (B) and anti-centrin (C-E) antibodies. Mob1-GFP accumulates preferentially at the posterior pole basal bodies, co-localizing with centrin (C,E). Panoramic view of the posterior region of Mob1-GFP-expressing cells is shown in D; arrowhead indicates where contractile vacuole pores are visible. Mob1-GFP could also be detected at the oral apparatus (OA), at the posterior pole transversal microtubules (indicated by arrowheads in B and C1) and at the asymmetric anterior crown (arrows in B and C). Scale bars: 10 mm (A,B,C,E); 2 mm (C1,C2,D). ...
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... in eukaryotic cells the cell division plane, where the cleavage furrow forms and ultimately cytokinesis occurs, bisects the preformed mitotic spindle ( Oliferenko et al., 2009). In Tetrahymena, macronuclear chromosomes lack centromeres and the MAC divides amitotically without a typical spindle being assembled. However, intranuclear microtubules that organize perpendicularly to the cleavage region have been implicated in MAC division ( Smith et al., 2004;Fujiu and Numata, 2000;Wunderlich and Speth, 1970;Tamura et al., 1969). These microtubules seem to be nucleated at a large number of sites inside of the nucleus (Fujiu and Numata, 2000). By contrast, the MIC divides mitotically and the spindle also assembles perpendicularly to the furrow but does not present organized structures at its poles (Frankel, 2000). Also, Tetrahymena cell division involves several morphological events at the cell cortex, beginning with the formation of an oral primordium, which starts with an anarchic field of basal bodies that will develop into the new oral apparatus (Fig. 5A-C) (Frankel, 1967). In dividing cells, we detected Tetrahymena Mob1-GFP in the oral apparatus immediately at the beginning of its assembly ( Fig. 5B1), where it remained ( Fig. 5B-F). As the cell cycle progressed, Mob1-GFP started to accumulate in the midzone basal bodies, just above the region where the cleavage furrow would form (between the old oral apparatus and the new one) (Fig. 5B-F). Therefore, Mob1-GFP accumulates where the new posterior pole of one of the siblings is to be formed (Fig. 5G). These observations, together with the knockdown results, strongly suggest that Tetrahymena Mob1 is involved in the establishment and maintenance of the anterior-posterior polarity of the cell. Next, we created a Tetrahymena Mob1-GFP ShuttON/OFF strain (supplementary material Fig. S2C) for two different purposes: firstly, to confirm that the Tetrahymena Mob1-KD phenotypes were specific and due to the downregulation of Mob1; and secondly, to investigate whether Mob1-GFP recruitment to the cleavage furrow is crucial for defining the cell division plane. For this, the Tetrahymena Mob1-GFP-expressing strain previously described was transformed with the Tetrahymena Mob1-KD DNA construct (supplementary material Fig. S1B). With this strategy, we were able to induce or repress Mob1-GFP expression in an endogenous Mob1 depletion background by addition or removal of Cd 2+ (Fig. 6A). We observed that in the presence of Cd 2+ (ShuttON), the cells were indistinguishable from wild- type cells (Fig. 6B,C). On the other hand, cells growing in Cd 2+ - depleted medium (ShuttOFF) showed the same phenotypes as Tetrahymena Mob1-KD cells (Fig. 6B,D-G), clearly demonstrating that the phenotypes result from low levels or absence of Mob1. In abnormally dividing cells, low levels of Mob1-GFP could be seen in old posterior poles. In addition, the abnormal establishment of the division plane and failure of cytokinesis clearly correlated with the absence or trace levels of Mob1-GFP at the oral apparatus and cell midzone where the cleavage furrow should be formed (Fig. 6D-G). Whenever ShuttOFF cells showed some Mob1-GFP at the equatorial region, cell division seemed to occur symmetrically (Fig. 6D). These results strongly reinforce the idea that the polarized distribution of Tetrahymena Mob1 plays a crucial role in the definition of the division plane and, consequently, in cytokinesis. ...
Citations
... Importantly, Mob proteins have been demonstrated to be involved in defining cell polarity both in humans and in Tetrahymena [44,45]. The importance of cell polarity in a number of physiological processes, including cell differentiation, cell migration, asymmetric cell division, cancer progression and immune response, has been extensively described and reviewed in [46]. ...
... In Tetrahymena, a unicellular organism, the single Mob protein encoded in the genome, is required for correct division-plane placement by establishing the anteriorposterior axis. The downregulation of Mob in Tetrahymena induces the misplacement of the division plane with consequent abscission failure; daughter cells fail to separate and form trails of interconnected abnormal cells [44]. Interestingly, the authors found that the Mob protein accumulates at the future site of cell division prior to constriction start, thereby defining the anterior and posterior ends of the future new daughter cells. ...
... See text for references. [44,45]. The importance of cell polarity in a number of physiological processes, including cell differentiation, cell migration, asymmetric cell division, cancer progression and immune response, has been extensively described and reviewed in [46]. ...
Signaling pathways that integrate a large set of inputs (both extra- and intracellular) to control cell proliferation are essential during both development and adult stages to guarantee organism homeostasis. Mobs are small adaptor proteins that participate in several of these signaling pathways. Here, we review recent advances unravelling Mob4 cellular functions, a highly conserved non-catalytic protein, that plays a diversity of roles in cell proliferation, sperm cell differentiation and is simultaneously involved in synapse formation and neural development. In addition, the gene is often overexpressed in a large diversity of tumors and is linked to poor clinical outcomes. Nevertheless, Mob4 molecular functions remain poorly defined, although it integrates the core structure of STRIPAK, a kinase/phosphatase protein complex, that can act upstream of the Hippo pathway. In this review we focus on the recent findings of Mob4 functions, that have begun to clarify its critical role on cell proliferation and the development of tissues and individuals.
... Recently, reverse and forward genetic approaches (Galati et al., 2014) have enabled identification of a number of gene products that contribute to patterning in ciliates (reviewed in Cole and Gaertig, 2022). On the anterior-posterior axis, several highly conserved kinases and kinase regulators control the positions of forming cortical structures, including Elo1 (Lats kinase) (Jiang et al., 2019a), CdaI (Hippo kinase) (Jiang et al., 2017), Mob1 (Slabodnick et al., 2014;Tavares et al., 2012) and CdaA (cyclin E) (Jiang et al., 2020). These proteins appear to form a signaling 'prepattern' that acts by localized inhibition: forming structures are excluded from the cortical areas where these prepatterning factors are enriched. ...
... Before the stage of cortical subdivision, the posteriorly enriched 'early Hippo circuit' (with Elo1) positions the entire division plane including the OP and DB (Jiang et al., 2019a). Subsequently, a mutually antagonistic pair of the anterior 'late Hippo circuit' (with CdaI) and the posterior CdaA induce and position the DB (Jiang et al., 2017(Jiang et al., , 2020Tavares et al., 2012). In addition, at the time of the DB appearance, CdaI maintains the subequatorial OP position by preventing its anterior displacement (Jiang et al., 2017). ...
Ciliates assemble numerous microtubular structures into complex cortical patterns. During ciliate division, the pattern is duplicated by intracellular segmentation that produces a tandem of daughter cells. In Tetrahymena thermophila, the induction and positioning of the division boundary involves two mutually-antagonistic factors: posterior CdaA/cyclin E and anterior CdaI/Hippo kinase. Here, we characterize the related cdaH-1 allele, which confers a pleiotropic patterning phenotype including an absence of the division boundary and an anterior-posterior mispositioning of the new oral apparatus. CdaH is a Fused/Stk36 kinase that localizes to multiple sites that correlate with the effects of its loss, including the division boundary and the new oral apparatus. CdaH acts downstream of CdaA to induce the division boundary and drives asymmetric cytokinesis at the tip of the posterior daughter. CdaH both maintains the anterior-posterior position of the new oral apparatus and interacts with CdaI to pattern ciliary rows within the oral apparatus. Thus, CdaH acts at multiple scales, from induction and positioning of structures on the cell-wide polarity axis to local organelle-level patterning.
... Importantly, MOB proteins have been demonstrated to be involved in defining cell polarity both in humans and in Tetrahymena [44,45]. The importance of cell polarity in a number of physiological processes, including cell diferentiation, cell migration, asymmetric cell division, cancer progression and immune response, has been extensively described [reviewed in [46]]. ...
... In Tetrahymena, an unicellular organism, the single Mob protein encoded in the genome, is required for correct division plane placement by establishing the anterior-posterior axis. Downregulation of Mob in Tetrahymena induces a misplacement of the division plane with consequent abcission failure; daughter cells fail to separate and form trails of interconnected abnormal cells [44]. Interestingly, the authors found that the Mob protein accumulates at the future site of cell division prior to constriction start, this way defining the anterior and posterior end of the future new daughter cells. ...
Signaling modules that integrate the diverse extra- and intracellular inputs to control cell proliferation are essential during both development and adult stages to guarantee organism homeostasis. Mobs are small adaptor proteins that participate in several of these signalling pathways. Here we review recent advances unraveling Mob4 cellular functions, a highly conserved non-catalytic protein, that plays a diversity of roles in cell proliferation, sperm cell differentiation and simultaneously is involved in synapse formation and neural development. In addition, the gene is often overexpressed in a wide range of tumors and is linked to poor clinical outcomes. Nevertheless, Mob4 molecular functions remain poorly defined, although it integrates the core structure of STRIPAK, a kinase/phosphatase protein complex, that can act upstream of the Hippo pathway. In this review we focus on the recent findings of Mob4 functions, that have begun to clarify its critical role on cell proliferation and development of tissues and individuals.
... In addition, many surface antigens, inner membrane complex proteins and antioxidant proteins, such as thioredoxin and superoxide dismutase, were also upregulated ( Figure 4C, Supplementary Dataset S5). However, many cell division-related proteins are downregulated, such as MOB kinase activator-like 1 (EVM0001798) [22,23] and NEK kinase (EVM0001492) [24] ( Figure 4D). Mob1 protein has been shown to be important for both mitotic completion and cell plate formation in yeast [25]. ...
Intestinal coccidiosis is a common parasitic disease in livestock, caused by the infection of Eimeria and Cystoisospora parasites, which results in great economic losses to animal husbandry. Triazine compounds, such as toltrazuril and diclazuril, are widely used in the treatment and chemoprophylaxis of coccidiosis. Unfortunately, widespread drug resistance has compromised their effectiveness. Most studies have focused on prophylaxis and therapeutics with toltrazuril in flocks, while a comprehensive understanding of how toltrazuril treatment alters the transcriptome of E. tenella remains unknown. In this study, merozoites of E. tenella were treated in vitro with 0.5 μg/mL toltrazuril for 0, 1, 2 and 4 h, respectively. The gene transcription profiles were then compared by high-throughput sequencing. Our results showed that protein hydrolysis genes were significantly upregulated after drug treatment, while cell cycle-related genes were significantly downregulated, suggesting that toltrazuril may affect parasite division. The expression of redox-related genes was upregulated and elevated levels of ROS and autophagosomes were detected in the parasite after toltrazuril treatment, suggesting that toltrazuril may cause oxidative stress to parasite cells and lead to its autophagy. Our results provide basic knowledge of the response of Eimeria genes to toltrazuril and further analysis of the identified transcriptional changes can provide useful information for a better understanding of the mechanism of action of toltrazuril against Eimeria.
... Despite the fact that cell cycle progression is a collective function of Hippo-related kinases across many eukaryotic species, exceptions remain. The Hipporelated pathway in ciliates was notably reported to contribute to the regulation of cilia biology as well as to the establishment of cell polarity (Tavares et al., 2012;Soares et al., 2019). However, there is no clear evidence that Hippo-related kinases in ciliates regulate cell cycle progression the way it was reported in other species such as yeast and denotes a certain degree of functional variability in this otherwise conserved pathway. ...
Centrosomes are best known as the microtubule organizing centers (MTOCs) of eukaryotic cells. In addition to their classic role in chromosome segregation, centrosomes play diverse roles unrelated to their MTOC activity during cell proliferation and quiescence. Metazoan centrosomes and their functional doppelgängers from lower eukaryotes, the spindle pole bodies (SPBs), act as important structural platforms that orchestrate signaling events essential for cell cycle progression, cellular responses to DNA damage, sensory reception and cell homeostasis. Here, we provide a critical overview of the unconventional and often overlooked roles of centrosomes/SPBs in the life cycle of eukaryotic cells.
... Frankel viewed these surgical data as evidence for a potential gradient of some oral development signal molecule emitted from the posterior region of the cell (Frankel, 1989). We will review evidence indicating that in Tetrahymena the posterior region also expresses an inhibitory influence that prevents the OP from developing too close to the posterior cell end (see below) and the gene products associated with this activity (Elo1 and Mob1) present in genuine decreasing posterior-to-anterior gradients (Jiang et al., 2019a;Tavares et al., 2012). Remarkably, these findings in both Tetrahymena and Stentor indicate the presence of two posterior-to-anterior gradients, one inhibitory and one stimulatory, in single celled organisms resembling those documented in the multicellular Hydra (Figure 3). ...
... More recently, Jiang and colleagues used similar comparative NGS to identify CdaI, Elo1 and CdaA proteins that clearly play a role in global (cellwide) patterning along the A/P axis (Jiang et al., 2017(Jiang et al., , 2019a(Jiang et al., , 2020. In addition, reverse genetic approaches have implicated Mob1 (Tavares et al., 2012) and Sas4 (Ruehle et al., 2020) in the A/P patterning in Tetrahymena. The known gene products, and the yet-to-be-identified loci involved in Tetrahymena A/P patterning are summarized in Table 2, with detailed descriptions to follow. ...
... Mob was discovered in yeast as a protein required for completion of M phase (Luca & Winey, 1998). Tavares and colleagues were first to implicate the Hippo pathway in the A/P positioning in Tetrahymena based on their studies of Mob1 (Tavares et al., 2012). The pattern of localization of Mob1 closely resembles that of Elo1-GFP (Jiang et al., 2019a;Tavares et al., 2012). ...
As single cells, ciliates build, duplicate and even regenerate complex cortical patterns by largely unknown mechanisms that precisely position organelles along two cell-wide axes: anterior-posterior and circumferential (left-right). We review our current understanding of intracellular patterning along the anterior-posterior axis in ciliates, with emphasis on how the new pattern emerges during cell division. We focus on the recent progress at the molecular level that has been driven by the discovery of genes whose mutations cause organelle positioning defects in the model ciliate Tetrahymena thermophila. These investigations have revealed a network of highly conserved kinases that are confined to either anterior or posterior domains in the cell cortex. These pattern-regulating kinases create zones of cortical inhibition that by exclusion determine the precise placement of organelles. We discuss observations and models derived from classical microsurgical experiments in large ciliates (including Stentor) and interpret them in light of recent molecular findings in Tetrahymena. In particular, we address the involvement of intracellular gradients as vehicles for positioning organelles along the anterior-posterior axis.
... MOB proteins were first characterized as regulators of ploidy maintenance, helping to ensure proper chromosome segregation before mitotic exit and allowing the transition from mitosis to cytokinesis [1]. This family is also necessary for maintaining cell polarity and morphology during cell division [6,7]. In multicellular organisms, MOBs have been mostly characterized as tumor suppressors and agents of morphogenesis, frequently by regulating GCKII STE20 and NDR kinases in the Hippo signaling pathway. ...
... The depletion of Mob1 in Tetrahymena causes the abnormal establishment of the cell division plane and cytokinesis arrest. In these cells, as far as the division continues, Mob1 progressively accumulates with CdaI protein at the region where the furrow will be established and the future posterior pole of the anterior daughter cell develops [7,142]. Notably, the CdaI protein is absent in non-dividing cells and starts to localize at the ciliary rows of the anterior half of the cell when division initiates. ...
... In fact, loss-of-function of Elo1 gene moves the division plane to the posterior pole [32], whereas the depletion of CdaI displaces it to the anterior pole of the cell [32]. Resembling the Mob1 localization, the ELO1 protein localizes at the posterior basal bodies in non-dividing cells and is recruited to the midline when division starts [7,32]. The Tetrahymena CdaI and ELO1 proteins are orthologues of the human MST1/2 kinases and the NDR/Lats kinases, respectively, showing that Tetrahymena possesses the core kinase module of the human Hippo signaling, which is coincident with the recent data obtained by Chen et al., 2020 [98]. ...
The MOB family proteins are constituted by highly conserved eukaryote kinase signal adaptors that are often essential both for cell and organism survival. Historically, MOB family proteins have been described as kinase activators participating in Hippo and Mitotic Exit Network/ Septation Initiation Network (MEN/SIN) signaling pathways that have central roles in regulating cytokinesis, cell polarity, cell proliferation and cell fate to control organ growth and regeneration. In metazoans, MOB proteins act as central signal adaptors of the core kinase module MST1/2, LATS1/2, and NDR1/2 kinases that phosphorylate the YAP/TAZ transcriptional co-activators, effectors of the Hippo signaling pathway. More recently, MOBs have been shown to also have non-kinase partners and to be involved in cilia biology, indicating that its activity and regulation is more diverse than expected. In this review, we explore the possible ancestral role of MEN/SIN pathways on the built-in nature of a more complex and functionally expanded Hippo pathway, by focusing on the most conserved components of these pathways, the MOB proteins. We discuss the current knowledge of MOBs-regulated signaling, with emphasis on its evolutionary history and role in morphogenesis, cytokinesis, and cell polarity from unicellular to multicellular organisms.
... Recently, Hippo signaling proteins have been linked to the A/P positioning of the division boundary in ciliates (Jiang et al., 2017(Jiang et al., , 2019aSlabodnick et al., 2014;Tavares et al., 2012). In T. thermophila, posterior Elo1 (Lats/Ndr kinase) and Mob1 and anterior CdaI (Hippo/Mst kinase) contribute to placement of the division boundary at the cell's equator (Jiang et al., 2017(Jiang et al., , 2019aTavares et al., 2012). ...
... Recently, Hippo signaling proteins have been linked to the A/P positioning of the division boundary in ciliates (Jiang et al., 2017(Jiang et al., , 2019aSlabodnick et al., 2014;Tavares et al., 2012). In T. thermophila, posterior Elo1 (Lats/Ndr kinase) and Mob1 and anterior CdaI (Hippo/Mst kinase) contribute to placement of the division boundary at the cell's equator (Jiang et al., 2017(Jiang et al., , 2019aTavares et al., 2012). However, the mechanisms that induce the formation of the division boundary remain unknown. ...
Not much is known about how organelles organize into patterns. In ciliates, the cortical pattern is propagated during "tandem duplication," a cell division that remodels the parental cell into two daughter cells. A key step is the formation of the division boundary along the cell's equator. In Tetrahymena thermophila, the cdaA alleles prevent the formation of the division boundary. We find that the CDAA gene encodes a cyclin E that accumulates in the posterior cell half, concurrently with accumulation of CdaI, a Hippo/Mst kinase, in the anterior cell half. The division boundary forms between the margins of expression of CdaI and CdaA, which exclude each other from their own cortical domains. The activities of CdaA and CdaI must be balanced to initiate the division boundary and to position it along the cell's equator. CdaA and CdaI cooperate to position organelles near the new cell ends. Our data point to an intracellular positioning mechanism involving antagonistic Hippo signaling and cyclin E.
... Tetrahymena Hippo pathway mutants exhibit mispositioned division furrows in either the anterior (mob1Δ and cdaI-1[Hippo/Mst]) or posterior (elo1-1 [Lats/Ndr]) direction. This suggests the Hippo pathway uses antagonistic activities to control the cortical pattern required for division furrow placement (Jiang et al., 2017(Jiang et al., , 2019Tavares et al., 2012). It is not known how Hippo pathway proteins associate with BBs and if they depend on BB components for localization and proper division furrow position. ...
... This was generally characterized by larger posterior cells and smaller anterior cells that were often tilted relative to the anterior-posterior axis. This cell division morphology is referred to as the "hammerhead" phenotype and is consistent with Tetrahymena mutants in the Hippo signaling pathway (Frankel, 2008;Jiang et al., 2017Jiang et al., , 2019Tavares et al., 2012). To understand the role that Sas4 plays in cell division, we quantified the percentage of cells with division furrows in WT and sas4Δ cells (Fig. 3 B). ...
... The latter observation led to the conclusion that cortical organization is dispensable for proper cell division (Jerka-Dziadosz et al., 1995). On the other hand, Tetrahymena Mob1, CdaI, and Elo1 localize to BBs and to BBappendages in WT cells (Fig. 4, A and C; Tavares et al., 2012;Jiang et al., 2017Jiang et al., , 2019. Additionally, the homologues of these Hippo factors localize to spindle pole bodies and centrosomes in other cell types, and to the cell cortex in the ciliate, Stentor coeruleus (Bolgioni and Ganem, 2016;Hergovich and Hemmings, 2012;Slabodnick et al., 2014). ...
Basal bodies (BBs) are macromolecular complexes required for the formation and cortical positioning of cilia. Both BB assembly and DNA replication are tightly coordinated with the cell cycle to ensure their accurate segregation and propagation to daughter cells, but the mechanisms ensuring coordination are unclear. The Tetrahymena Sas4/CPAP protein is enriched at assembling BBs, localizing to the core BB structure and to the base of BB-appendage microtubules and striated fiber. Sas4 is necessary for BB assembly and cortical microtubule organization, and Sas4 loss disrupts cell division furrow positioning and DNA segregation. The Hippo signaling pathway is known to regulate cell division furrow position, and Hippo molecules localize to BBs and BB-appendages. We find that Sas4 loss disrupts localization of the Hippo activator, Mob1, suggesting that Sas4 mediates Hippo activity by promoting scaffolds for Mob1 localization to the cell cortex. Thus, Sas4 links BBs with an ancient signaling pathway known to promote the accurate and symmetric segregation of the genome.
... The cortical subdivision is placed at the cell's midpoint by the joint actions of two opposing Hippo kinase signaling pathways ( Figure 9B). The Hippo/MST2-like kinase, CDA1, and its putative binding partner and substrate, MOB1, exclude divisional activities in the anterior half of the cell, while a second Hippo kinase, ELO1, prevents division in the posterior half (Tavares et al., 2012;Jiang et al., 2017Jiang et al., , 2019. Beneath the cortex at the division site, is a contractile ring containing actin, but no myosin II or septins (Yasuda et al., 1980;Hirono et al., 1987;Wloga et al., 2008). ...
Cytokinesis, or the division of the cytoplasm, following the end of mitosis or meiosis, is accomplished in animal cells, fungi, and amoebae, by the constriction of an actomyosin contractile ring, comprising filamentous actin, myosin II, and associated proteins. However, despite this being the best-studied mode of cytokinesis, it is restricted to the Opisthokonta and Amoebozoa, since members of other evolutionary supergroups lack myosin II and must, therefore, employ different mechanisms. In particular, parasitic protozoa, many of which cause significant morbidity and mortality in humans and animals as well as considerable economic losses, employ a wide diversity of mechanisms to divide, few, if any, of which involve myosin II. In some cases, cell division is not only myosin II-independent, but actin-independent too. Mechanisms employed range from primitive mechanical cell rupture (cytofission), to motility- and/or microtubule remodeling-dependent mechanisms, to budding involving the constriction of divergent contractile rings, to hijacking host cell division machinery, with some species able to utilize multiple mechanisms. Here, I review current knowledge of cytokinesis mechanisms and their molecular control in mammalian-infective parasitic protozoa from the Excavata, Alveolata, and Amoebozoa supergroups, highlighting their often-underappreciated diversity and complexity. Billions of people and animals across the world are at risk from these pathogens, for which vaccines and/or optimal treatments are often not available. Exploiting the divergent cell division machinery in these parasites may provide new avenues for the treatment of protozoal disease.
