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BHF accurately predicts new fusibility outcomes and has expression patterns and function consistent with a Botryllus allorecognition determinant. (A) Known and predicted fusion or rejection outcomes among all 23 B. schlosseri colonies analyzed (table S4), including exploratory (n = 17) and validation cohorts (n = 6). All " blind " predictions were confirmed (6 of 6). (B) Expression analysis of BHF, sFuHC, and mFuHC under the conditions preceding fusion or rejection ( " challenged " ; n = 6) compared with unchallenged control colonies ( " naïve " ; n = 4) (*P = 0.009, two-tailed unequal variance t test;
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A Gene for Early Acceptance
One of the fundamental properties of the immune system is the ability to distinguish self- from nonself–histocompatibility. To gain insight into the evolution and molecular basis of histocompatibility, Voskoboynik et al. (p. 384 ) sought to determine the genetic basis for a natural transplantation reaction that occurs in...
Citations
... Allorecognition systems often consist of two tightly linked genes (25). Genetic analyses of vegetative incompatibility in filamentous fungi, such as Neurospora crassa, Podospora anserina, Aspergillus nidulans, and the plant pathogen Cryphonectria parasitica, have shown that incompatibility is genetically controlled by multiple, unlinked het or vcg (vegetative compatibility group) loci (28). GSDM homologs are abundant and widely distributed in the fungal kingdom, with approximately 1900 identified members encoded in the genomes of 400 different species, particularly within the Ascomycota phylum. ...
The gasdermin protein family and its homologs in microorganisms have gained significant attention due to their roles in programmed cell death, immune defense, and microbial infection. This review summarizes the current research status of gasdermin proteins, their structural features, and functional roles in fungi, bacteria, and viruses. The review presents evolutionary parallels between mammalian and microbial defense systems, highlighting the conserved role of gasdermin proteins in regulating cell death processes and immunity. Additionally, the structural and functional characteristics of gasdermin homologs in microorganisms are summarized, shedding light on their potential as targets for therapeutic interventions. Future research directions in this field are also discussed to provide a roadmap for further investigation.
... This includes behaviors in single celled organisms such as swarming behaviors in bacteria [1], flocculation in yeast [2], and altruism in the amoeba Dictyostelium [3][4][5]. Additionally, behaviors in more complex organisms are also thought to be reliant on kin-recognition including cooperation in insects [6,7] and lizards [8,9], colony fusions events in tunicates [10,11], cannibalism in several amphibian species [12,13], as well as nest mate preference in rodents [14,15]. In nematodes a kin-recognition system was also recently identified in Pristionchus pacificus. ...
Kin-recognition is observed across diverse species forming an important behavioral adaptation influencing organismal interactions. In many species, the molecular mechanisms involved are difficult to characterize, but in the nematode Pristionchus pacificus molecular components regulating its kin-recognition system have been identified. These determine its predatory behaviors towards other con-specifics which prevents the killing and cannibalization of kin. Importantly, their impact on other interactions including collective behaviors is unknown. Here, we explored a high altitude adapted clade of this species which aggregates abundantly under laboratory conditions, to investigate the influence of the kin-recognition system on their group behaviours. By utilizing pairwise aggregation assays between distinct strains of P . pacificus with differing degrees of genetic relatedness, we observe aggregation between kin but not distantly related strains. In assays between distantly related strains, the aggregation ratio is frequently reduced. Furthermore, abolishing predation behaviors through CRISPR/Cas9 induced mutations in Ppa-nhr-40 result in rival strains successfully aggregating together. Finally, as Caenorhabditis elegans are found naturally occurring with P . pacificus , we also explored aggregation events between these species. Here, aggregates were dominated by P . pacificus with the presence of only a small number of predators proving sufficient to disrupt C . elegans aggregation dynamics. Thus, aggregating strains of P . pacificus preferentially group with kin, revealing competition and nepotism as previously unknown components influencing collective behaviors in nematodes.
... Our data show that morula cells and phagocytes are involved in neurodegeneration at takeover, as they clearly infiltrate into (or are in strict contact with) the cerebral ganglion. Morula cells are the mediators of the inflammatory (rejection) reaction that occurs in the form of a series of necrotic spots along the contacting borders when genetically incompatible colonies are juxtaposed [43,85,86]. In both vertebrates and invertebrates, phagocytes are known to recognize dying cells as corpses and ingest them [78] thanks to a variety of "eat-me" signals, such as phosphatidylserine [87]. ...
Human neuronal loss occurs through different cellular mechanisms, mainly studied in vitro. Here, we characterized neuronal death in B. schlosseri, a marine colonial tunicate that shares substantial genomic homology with mammals and has a life history in which controlled neurodegeneration happens simultaneously in the brains of adult zooids during a cyclical phase named takeover. Using an ultrastructural and transcriptomic approach, we described neuronal death forms in adult zooids before and during the takeover phase while comparing adult zooids in takeover with their buds where brains are refining their structure. At takeover, we found in neurons clear morphologic signs of apoptosis (i.e., chromatin condensation, lobed nuclei), necrosis (swollen cytoplasm) and autophagy (autophagosomes, autolysosomes and degradative multilamellar bodies). These results were confirmed by transcriptomic analyses that highlighted the specific genes involved in these cell death pathways. Moreover, the presence of tubulovesicular structures in the brain medulla alongside the over-expression of prion disease genes in late cycle suggested a cell-to-cell, prion-like propagation recalling the conformational disorders typical of some human neurodegenerative diseases. We suggest that improved understanding of how neuronal alterations are regulated in the repeated degeneration–regeneration program of B. schlosseri may yield mechanistic insights relevant to the study of human neurodegenerative diseases.
... If so, studying invertebrate allorecognition could help resolve the evolutionary history of immunity and perhaps lead to novel therapies in immunity and transplantation. Together, these interests have motivated the study of allorecognition genes in several species, including the poriferan Amphimedon queenslandica (8), the protochordate Botryllus schlosseri (9)(10)(11), and the cnidarian Hydractinia symbiolongicarpus (12)(13)(14)(15). ...
Most colonial marine invertebrates are capable of allorecognition, the ability to distinguish between themselves and conspecifics. One long-standing question is whether invertebrate allorecognition genes are homologous to vertebrate histocompatibility genes. In the cnidarian Hydractinia symbiolongicarpus, allorecognition is controlled by at least two genes, Allorecognition 1 ( Alr1 ) and Allorecognition 2 ( Alr2 ), which encode highly polymorphic cell-surface proteins that serve as markers of self. Here, we show that Alr1 and Alr2 are part of a family of 41 Alr genes, all of which reside in a single genomic interval called the Allorecognition Complex (ARC). Using sensitive homology searches and highly accurate structural predictions, we demonstrate that the Alr proteins are members of the immunoglobulin superfamily (IgSF) with V-set and I-set Ig domains unlike any previously identified in animals. Specifically, their primary amino acid sequences lack many of the motifs considered diagnostic for V-set and I-set domains, yet they adopt secondary and tertiary structures nearly identical to canonical Ig domains. Thus, the V-set domain, which played a central role in the evolution of vertebrate adaptive immunity, was present in the last common ancestor of cnidarians and bilaterians. Unexpectedly, several Alr proteins also have immunoreceptor tyrosine-based activation motifs and immunoreceptor tyrosine-based inhibitory motifs in their cytoplasmic tails, suggesting they could participate in pathways homologous to those that regulate immunity in humans and flies. This work expands our definition of the IgSF with the addition of a family of unusual members, several of which play a role in invertebrate histocompatibility.
... When two colonies of B. schlosseri come into contact, they recognize each other on a friend-foe principle [92]. If they have at least one common allele of the polymorphic histocompatibility gene, the Botryllus histocompatibility factor (BHF), they merge their vessels, forming a natural parabiont [93]. When creating a common vascular system, cells can freely flow from one chimera partner to another, resembling mammalian chimerism at the somatic level. ...
... When creating a common vascular system, cells can freely flow from one chimera partner to another, resembling mammalian chimerism at the somatic level. If the colonies are genetically incompatible, they undergo an immune rejection reaction, in which inflammatory and cytotoxic cells participate, creating zones of necrosis at points of contacts [93]. The cytotoxic morula (MK) cells form the basis of the rejection reaction and cytotoxicity, resembling human natural killer (NK) cells. ...
The innate immune system provides an adequate response to stress factors and pathogens through pattern recognition receptors (PRRs), located on the surface of cell membranes and in the cytoplasm. Generally, the structures of PRRs are formed by several domains that are evolutionarily conserved, with a fairly high degree of homology in representatives of different species. The orthologs of TLRs, NLRs, RLRs and CLRs are widely represented, not only in marine chordates, but also in invertebrates. Study of the interactions of the most ancient marine multicellular organisms with microorganisms gives us an idea of the evolution of molecular mechanisms of protection against pathogens and reveals new functions of already known proteins in ensuring the body’s homeostasis. The review discusses innate immunity mechanisms of protection of marine invertebrate organisms against infections, using the examples of ancient multicellular hydroids, tunicates, echinoderms, and marine worms in the context of searching for analogies with vertebrate innate immunity. Due to the fact that mucous membranes first arose in marine invertebrates that have existed for several hundred million years, study of their innate immune system is both of fundamental importance in terms of understanding molecular mechanisms of host defense, and of practical application, including the search of new antimicrobial agents for subsequent use in medicine, veterinary and biotechnology.
... Interestingly, the same molecular mechanism has also been suggested to explain the allorecognition response of the ascidian B. schlosseri (De Tomaso 2009). For instance, the blocking of the Botryllus BHF protein has suggested that this is an inhibitory ligand within a missingself model (Voskoboynik et al. 2013;Rosental et al. 2018). In this direction, a recent preprint identified homologs genes of Syk, Shark, SHP, and SHIP in the Hydractinia genome, which are involved in the signaling pathways of NK-cells (Huene et al. 2022), supporting the idea that the missing-self model could be the mechanism that explains allorecognition in Hydractinia. ...
The genetics of allorecognition has been studied extensively in inbred lines of Hydractinia symbiolongicarpus, in which genetic control is attributed mainly to the highly polymorphic loci allorecognition 1 (Alr1) and allorecognition 2 (Alr2), located within the Allorecognition Complex (ARC). While allelic variation at Alr1 and Alr2 can predict the phenotypes in inbred lines, these two loci do not entirely predict the allorecognition phenotypes in wild-type colonies and their progeny, suggesting the presence of additional uncharacterized genes that are involved in the regulation of allorecognition in this species. Comparative genomics analyses were used to identify coding sequence differences from assembled chromosomal intervals of the ARC and from genomic scaffold sequences between two incompatible H. symbiolongicarpus siblings from a backcross population. New immunoglobulin superfamily (Igsf) genes are reported for the ARC, where five of these genes are closely related to the Alr1 and Alr2 genes, suggesting the presence of multiple Alr-like genes within this complex. Complementary DNA sequence evidence revealed that the allelic polymorphism of eight Igsf genes is associated with allorecognition phenotypes in a backcross population of H. symbiolongicarpus, yet that association was not found between parental colonies and their offspring. Alternative splicing was found as a mechanism that contributes to the variability of these genes by changing putative activating receptors to inhibitory receptors or generating secreted isoforms of allorecognition proteins. Our findings demonstrate that allorecognition in H. symbiolongicarpus is a multigenic phenomenon controlled by genetic variation in at least eight genes in the ARC complex.
... If so, studying invertebrate allorecognition could help resolve the evolutionary history of immunity and perhaps lead to novel therapies in immunity and transplantation. Together, these interests have motivated the study of allorecognition genes in several species, including the poriferan Amphimedon queenslandica (8), the protochordate Botryllus schlosseri (9)(10)(11), and the cnidarian Hydractinia symbiolongicarpus (12)(13)(14)(15). ...
Most colonial marine invertebrates are capable of allorecognition, the ability to distinguish between themselves and conspecifics. One long-standing question is whether invertebrate allorecognition genes are homologous to vertebrate histocompatibility genes. In the cnidarian Hydractinia symbiolongicarpus , allorecognition is controlled by at least two genes, Allorecognition 1 ( Alr1 ) and Allorecognition 2 ( Alr2 ), which encode highly polymorphic cell surface proteins that serve as markers of self. Here, we show that Alr1 and Alr2 are part of a family of 41 Alr genes, all of which reside a single genomic interval called the Allorecognition Complex (ARC). Using sensitive homology searches and highly accurate structural predictions, we demonstrate that the Alr proteins are members of the immunoglobulin superfamily (IgSF) with V-set and I-set Ig domains unlike any previously identified in animals. Specifically, their primary amino acid sequences lack many of the motifs considered diagnostic for V-set and I-set domains, yet they adopt secondary and tertiary structures nearly identical to canonical Ig domains. Thus, the V-set domain, which played a central role in the evolution of vertebrate adaptive immunity, was present in the last common ancestor of cnidarians and bilaterians. Unexpectedly, several Alr proteins also have immunoreceptor tyrosine-based activation motifs (ITAMs) and immunoreceptor tyrosine-based inhibitory motifs (ITIMs) in their cytoplasmic tails, suggesting they could participate in pathways homologous to those that regulate immunity in humans and flies. This work expands our definition of the IgSF with the addition of a family of unusual members, several of which play a role in invertebrate histocompatibility.
Significance Statement
The immunoglobulin superfamily (IgSF) is one of the largest and most functionally versatile domain families in animal genomes. Although their amino acid sequences can vary considerably, IgSF domains have been traditionally defined by conserved residues at several key positions in their fold. Here, we sequenced an invertebrate histocompatibility complex and discovered a family of IgSF genes with amino acid sequences that lack most of these residues yet are predicted to adopt folds virtually identical to canonical V-set and I-set IgSF domains. This work broadens the definition of the IgSF and shows that the V-set domain was present earlier in animal evolution than previously appreciated.
... It is difficult to identify homologs for the Hydractinia allorecognition genes in other cnidarian genomes and more distantly related taxa. This includes the allorecognition genes that have been identified to date in the sponge Amphimedon queenslandica (Grice et al. 2017) and the protochordate Botryllus schlosseri (De Tomaso et al. 2005;Nyholm et al. 2006;McKitrick et al. 2011;Voskoboynik et al. 2013). It seems, therefore, that the molecules responsible for self/nonself discrimination have evolved independently in different metazoan lineages. ...
Hydractinia symbiolongicarpus is a colonial hydroid and a long-standing model system for the study of invertebrate allorecognition. The Hydractinia allorecognition system allows colonies to discriminate between their own tissues and those of unrelated conspecifics that co-occur with them on the same substrate. This recognition mediates spatial competition and mitigates the risk of stem cell parasitism. Here, I review how we have come to our current understanding of the molecular basis of allorecognition in Hydractinia. To date, two allodeterminants have been identified, called Allorecognition 1 (Alr1) and Allorecognition 2 (Alr2), which occupy a genomic region called the allorecognition complex (ARC). Both genes encode highly polymorphic cell surface proteins that are capable of homophilic binding, which is thought to be the mechanism of self/non-self discrimination. Here, I review how we have come to our current understanding of Alr1 and Alr2. Although both are members of the immunoglobulin superfamily, their evolutionary origins remain unknown. Moreover, existing data suggest that the ARC may be home to a family of Alr-like genes, and I speculate on their potential functions.
... The fester and uncle fester proteins both contain sushi domains (also known as complement control protein domains), which are common in vertebrate proteins that regulate complement activity and protect host cells from damage (83). Finally, analyses of recently available genome and transcriptome data from genetically defined B. schlosseri lines have identified a third polymorphic gene known as BHF (84). BHF is an intracellular protein that lacks recognizable domain structure. ...
The ongoing arms race between hosts and microbes has fueled the evolution of novel strategies for diversifying the molecules involved in immune responses. Characterization of immune systems from an ever-broadening phylogenetic range of organisms reveals that there are many mechanisms by which this diversity can be generated and maintained. Diversification strategies operate at the level of populations, genomes, genes, and even individual transcripts. Lineage-specific innovations have been cataloged within the immune systems of both invertebrates and vertebrates. Furthermore, somatic diversification of immune receptor genes has now been described in jawless vertebrates and some invertebrate species. In addition to pathogen detection, immunological diversity plays important roles in several distinct allorecognition systems. In this Brief Review, we highlight some of the evolutionary innovations employed by a variety of metazoan species to generate the molecular diversity required to detect a vast array of molecules in the context of both immune response and self/nonself-recognition.
... Scofield et al. 1982;Rinkevich et al. 1993Stoner and Weissman 1996;Stoner et al. 1999;Laird et al. 2005a ;Corey et al. 2016). Additional milestones in the research on Botryllus schlos seri are the publication of its draft genome, followed by the sequence of the histocompatibility locus (Voskoboynik et al. 2013a(Voskoboynik et al. , 2013b. ...
Ascidians are solitary or colonial marine invertebrates that share a common ancestor with vertebrates and belong to the phylum Chordata. Colonial ascidians include more than 1,700 species and are a highly varied group in terms of sizes, shapes, colors and geographical locations. Here we discuss one of the most-studied model species, Botryllus schlosseri, as a most suitable representative of colonial ascidians. Botryllus was first described four centuries ago but has been studied extensively just in the past seven decades, revealing a promising model for diverse biological disciplines. This chapter details the history of the research, biology and geographical distributions of this cosmopolitan species. Special attention is devoted to several unique phenomena staging this species as a model system in biology, such as the continuous life and death cycles of colonial modules (blastogenesis), the capacity for whole-body regeneration and the unique self/non-self recognition (histocompatibility) resulting in either natural immunological rejection or chimerism. The description is followed by with current applications, the development of tools and the description of several leading scientific challenges. Following the wide range of phenomena developing in Botryllus, it is anticipated that this species will become a central model in biology. Working with B. schlosseri may reform and shift dogmas in biology.
