For the past 20 years Ayelet has been researching development, stem cell mediating regeneration processes, and immunology in the colonial tunicate Botryllus schlosseri. As a PHD student in the Technion and IOLR (Israel) Ayelet discovered a method to extend the life span of the Botryllus colonies and suggested that this treatment affects the stem cells of the treated colonies. She became a post-doctoral fellow at the Tunicate lab of Irv Weissman in Stanford Hopkins Marine Station and studied stem cell mediating developmental processes. She isolated the first adult stem cell niche and the first germline stem cell niche in this organism. Since 2009 Ayelet has been leading and supervising the Botryllus studies in HMS and directed the Botryllus genome project with teams from the labs of Irv Weissman, Steve Quake and several international laboratories. In processing the Botryllus genome they developed a novel method for high-throughput sequencing of repeat-rich genomes (called Moleculo / LRseq; acquired by Illumina). Having the genome in hand Ayelet and her collaborators looked for the gene that controls immune recognition in the colonies and allows or prevents fusion of blood vessels between colonies. They isolated the BHF, a single polymorphic gene that allows Botryllus colonies to distinguish self from non-self. Recently, Ayelet and her collaborators began characterizing the Botryllus hematopoietic and immune system at the cellular and molecular levels and succeeded in identifying the hematopoietic stem cells (HSCs), myeloid cell lineage progenitors, cytotoxic cells that induce cellular tissue rejection, and the hematopoietic organ.
Using the resources and tools she and others developed Ayelet continues studying the BHF, the evolution of blood borne immune system, and stem cell mediated regeneration programs.
Current Role at Stanford
Advising and Mentoring
(1) 831-224-2187 Postdoctoral Fellow, Weissman Lab.
Mark Alec Kowarsky
Doctoral program physics, Quake Lab.
Pre Major Advisees
Ratteray, Alida Nicole
1 (603) 921-7328Undergrad, ENGR-BS, Junior
Philp, Charlotte Victoria
1 (650) 391-3140Undergrad, BIOE-BS, Junior
Stevens, Lydia Rose
(805) 440-9115Undergrad, UNDCL-B, Sophomore
Lim, Joseph Patrick
(501) 305-1504Undergrad, UNDCL-B, Sophomore
Kumarasinghe, Raveen Lashlen
(510) 766-5999Undergrad, UNDCL-B, Sophomore
Education & Certifications
Postdoctoral Fellow, Stanford University, Stanford, California, Stem Cell Biology (2006)
Ph.D, Technion, Israel institute of technology, Haifa, Cell Biology (2001)
M.Sc, Tel-Aviv University, Tel-Aviv, Israel, Zoology (1995)
B.Sc, The Hebrew University of Jerusalem, Israel, Animal science (1991)
Ayelet Voskoboynik; Dmitry Pushkarev, Stephen Quake. "United States Patent 61/532,882; International application No. PCT/US2012/054461 Methods for obtaining a sequence. US 61/532,882, filed September 9, 2011(Pending); International application No. PCT/US2012/054461, filled September 10, 2012 (Pending); United Kingdom patent application 1216076.8 filed September 10, 2012 (Pending)"
The B. schlosseri genome project
Urochordates like B. schlosseri are considered to be the closest living invertebrate relatives of vertebrates. Using a novel method for high-throughput sequencing of eukaryotic genomes, we sequenced and assembled 580 Mbp of the B. schlosseri genome. The genome assembly is comprised of nearly 14,000 intron-containing predicted genes, and 13,500 intron-less predicted genes, 40% of which could be confidently parceled into 13 (of 16 haploid) chromosomes. A comparison of homologous genes between B. schlosseri and other diverse taxonomic groups revealed genomic events underlying the evolution of vertebrates and lymphoid-mediated immunity. The B. schlosseri genome is a community resource for studying alternative modes of reproduction, natural transplantation reactions, and stem cell-mediated regeneration (Voskoboynik et al., 2013).
BHF and the evolution of allorecognition
This study focuses on genes, cells, and pathways that regulate allogeneic recognition and tolerance induction in B. schlosseri. Botryllus colonies have a defined vasculature with circulating blood cells. Self-recognition between compatible colonies leads to formation of parabionts with a common vasculature, whereas incompatible colonies will reject one another. As described above we identified the single gene that determine the fusion vs. rejection reaction, BHF. The BHF sequence suggests that it is neither a membrane-bound nor secreted protein, as would be expected of a gene that controls self–nonself recognition (e.g., MHC). Therefore study of this gene will likely reveal new mechanisms of recognition. We developed BHF monoclonal antibodies and recombinant BHF proteins and are currently using flow cytometry, diverse immunological essays, whole-transcriptome sequencing, and computational methods to characterize the BHF pathway (Voskoboynik and Newman et al., 2013). Recently we began characterizing the B. schlosseri hematopoietic and immune system at the cellular and molecular levels. We did it by deploying advanced genomics, live imaging and classical immunological methods including multi-parameter flow cytometric isolation of cellular populations, cell sorting, transplantation assays as well as phagocytosis and cytotoxicity measurement. We identified the hematopoietic stem cells (HSCs), myeloid cell lineage progenitors, cytotoxic cells that induce cellular tissue rejection, and discovered the Botryllus hematopoietic niche showing that it is homologous to human hematopoietic bone marrow (Rosental and Kowarsky et al. 2018).
Sexual and asexual development: two distinct programs producing the same tunicate.
2021; 34 (4): 108681
Colonial tunicates are the only chordate that possess two distinct developmental pathways to produce an adult body: either sexually through embryogenesis or asexually through a stem cell-mediated renewal termed blastogenesis. Using the colonial tunicate Botryllus schlosseri, we combine transcriptomics and microscopy to build an atlas of the molecular and morphological signatures at each developmental stage for both pathways. The general molecular profiles of these processes are largely distinct. However, the relative timing of organogenesis and ordering of tissue-specific gene expression are conserved. By comparing the developmental pathways of B. schlosseri with other chordates, we identify hundreds of putative transcription factors with conserved temporal expression. Our findings demonstrate that convergent morphology need not imply convergent molecular mechanisms but that it showcases the importance that tissue-specific stem cells and transcription factors play in producing the same mature body through different pathways.
View details for DOI 10.1016/j.celrep.2020.108681
View details for PubMedID 33503429
Complex mammalian-like haematopoietic system found in a colonial chordate.
Haematopoiesis is an essential process that evolved in multicellular animals. At the heart of this process are haematopoietic stem cells (HSCs), which are multipotent and self-renewing, and generate the entire repertoire of blood and immune cells throughout an animal's life1. Although there have been comprehensive studies on self-renewal, differentiation, physiological regulation and niche occupation in vertebrate HSCs, relatively little is known about the evolutionary origin and niches of these cells. Here we describe the haematopoietic system of Botryllus schlosseri, a colonial tunicate that has a vasculature and circulating blood cells, and interesting stem-cell biology and immunity characteristics2-8. Self-recognition between genetically compatible B. schlosseri colonies leads to the formation of natural parabionts with shared circulation, whereas incompatible colonies reject each other3,4,7. Using flow cytometry, whole-transcriptome sequencing of defined cell populations and diverse functional assays, we identify HSCs, progenitors, immune effector cells and an HSC niche, and demonstrate that self-recognition inhibits allospecific cytotoxic reactions. Our results show that HSC and myeloid lineage immune cells emerged in a common ancestor of tunicates and vertebrates, and also suggest that haematopoietic bone marrow and the B. schlosseri endostyle niche evolved from a common origin.
View details for PubMedID 30518860
Identification of a colonial chordate histocompatibility gene.
2013; 341 (6144): 384-387
Histocompatibility is the basis by which multicellular organisms of the same species distinguish self from nonself. Relatively little is known about the mechanisms underlying histocompatibility reactions in lower organisms. Botryllus schlosseri is a colonial urochordate, a sister group of vertebrates, that exhibits a genetically determined natural transplantation reaction, whereby self-recognition between colonies leads to formation of parabionts with a common vasculature, whereas rejection occurs between incompatible colonies. Using genetically defined lines, whole-transcriptome sequencing, and genomics, we identified a single gene that encodes self-nonself and determines "graft" outcomes in this organism. This gene is significantly up-regulated in colonies poised to undergo fusion and/or rejection, is highly expressed in the vasculature, and is functionally linked to histocompatibility outcomes. These findings establish a platform for advancing the science of allorecognition.
View details for DOI 10.1126/science.1238036
View details for PubMedID 23888037
Repeated, Long-Term Cycling of Putative Stem Cells between Niches in a Basal Chordate
2013; 24 (1): 76-88
The mechanisms that sustain stem cells are fundamental to tissue maintenance. Here, we identify "cell islands" (CIs) as a niche for putative germ and somatic stem cells in Botryllus schlosseri, a colonial chordate that undergoes weekly cycles of death and regeneration. Cells within CIs express markers associated with germ and somatic stem cells and gene products that implicate CIs as signaling centers for stem cells. Transplantation of CIs induced long-term germline and somatic chimerism, demonstrating self-renewal and pluripotency of CI cells. Cell labeling and in vivo time-lapse imaging of CI cells reveal waves of migrations from degrading CIs into developing buds, contributing to soma and germline development. Knockdown of cadherin, which is highly expressed within CIs, elicited the migration of CI cells to circulation. Piwi knockdown resulted in regeneration arrest. We suggest that repeated trafficking of stem cells allows them to escape constraints imposed by the niche, enabling self-preservation throughout life.
View details for DOI 10.1016/j.devcel.2012.11.010
View details for Web of Science ID 000316305200007
View details for PubMedID 23260626
The genome sequence of the colonial chordate, Botryllus schlosseri.
Botryllus schlosseri is a colonial urochordate that follows the chordate plan of development following sexual reproduction, but invokes a stem cell-mediated budding program during subsequent rounds of asexual reproduction. As urochordates are considered to be the closest living invertebrate relatives of vertebrates, they are ideal subjects for whole genome sequence analyses. Using a novel method for high-throughput sequencing of eukaryotic genomes, we sequenced and assembled 580 Mbp of the B. schlosseri genome. The genome assembly is comprised of nearly 14,000 intron-containing predicted genes, and 13,500 intron-less predicted genes, 40% of which could be confidently parceled into 13 (of 16 haploid) chromosomes. A comparison of homologous genes between B. schlosseri and other diverse taxonomic groups revealed genomic events underlying the evolution of vertebrates and lymphoid-mediated immunity. The B. schlosseri genome is a community resource for studying alternative modes of reproduction, natural transplantation reactions, and stem cell-mediated regeneration. DOI:http://dx.doi.org/10.7554/eLife.00569.001.
View details for DOI 10.7554/eLife.00569
View details for PubMedID 23840927
View details for PubMedCentralID PMC3699833
Identification of the Endostyle as a Stem Cell Niche in a Colonial Chordate
CELL STEM CELL
2008; 3 (4): 456-464
Stem cell populations exist in "niches" that hold them and regulate their fate decisions. Identification and characterization of these niches is essential for understanding stem cell maintenance and tissue regeneration. Here we report on the identification of a novel stem cell niche in Botryllus schlosseri, a colonial urochordate with high stem cell-mediated developmental activities. Using in vivo cell labeling, engraftment, confocal microscopy, and time-lapse imaging, we have identified cells with stemness capabilities in the anterior ventral region of the Botryllus' endostyle. These cells proliferate and migrate to regenerating organs in developing buds and buds of chimeric partners but do not contribute to the germ line. When cells are transplanted from the endostyle region, they contribute to tissue development and induce long-term chimerism in allogeneic tissues. In contrast, cells from other Botryllus' regions do not show comparable stemness capabilities. Cumulatively, these results define the Botryllus' endostyle region as an adult somatic stem cell niche.
View details for DOI 10.1016/j.stem.2008.07.023
View details for Web of Science ID 000260149800015
View details for PubMedID 18940736
Striving for normality: whole body regeneration through a series of abnormal generations
2007; 21 (7): 1335-1344
Embryogenesis and asexual reproduction are commonly considered to be coordinated developmental processes, which depend on accurate progression through a defined sequence of developmental stages. Here we report a peculiar developmental scenario in a simple chordate, Botryllus schlosseri, wherein a normal colony of individuals (zooids and buds) is regenerated from the vasculature (vascular budding) through a sequence of morphologically abnormal developmental stages. Vascular budding was induced by surgically removing buds and zooids from B. schlosseri colonies, leaving only the vasculature and the tunic that connects them. In vivo imaging and histological sections showed that the timing and morphology of developing structures during vascular budding deviated significantly from other asexual reproduction modes (the regular asexual reproduction mode in this organism and vascular budding in other botryllid species). Subsequent asexual reproduction cycles exhibited gradual regaining of normal developmental patterns, eventually leading to regeneration of a normal colony. The conversion into a normal body form suggests the activation of an alternative pathway of asexual reproduction, which involves gradual regaining of normal positional information. It presents a powerful model for studying the specification of the same body plan by different developmental programs.
View details for DOI 10.1096/fj.06-7337com
View details for Web of Science ID 000246117000009
View details for PubMedID 17289924
Botryllus schlosseri as a Unique Colonial Chordate Model for the Study and Modulation of Innate Immune Activity.
2021; 19 (8)
Understanding the mechanisms that sustain immunological nonreactivity is essential for maintaining tissue in syngeneic and allogeneic settings, such as transplantation and pregnancy tolerance. While most transplantation rejections occur due to the adaptive immune response, the proinflammatory response of innate immunity is necessary for the activation of adaptive immunity. Botryllus schlosseri, a colonial tunicate, which is the nearest invertebrate group to the vertebrates, is devoid of T- and B-cell-based adaptive immunity. It has unique characteristics that make it a valuable model system for studying innate immunity mechanisms: (i) a natural allogeneic transplantation phenomenon that results in either fusion or rejection; (ii) whole animal regeneration and noninflammatory resorption on a weekly basis; (iii) allogeneic resorption which is comparable to human chronic rejection. Recent studies in B. schlosseri have led to the recognition of a molecular and cellular framework underlying the innate immunity loss of tolerance to allogeneic tissues. Additionally, B. schlosseri was developed as a model for studying hematopoietic stem cell (HSC) transplantation, and it provides further insights into the similarities between the HSC niches of human and B. schlosseri. In this review, we discuss why studying the molecular and cellular pathways that direct successful innate immune tolerance in B. schlosseri can provide novel insights into and potential modulations of these immune processes in humans.
View details for DOI 10.3390/md19080454
View details for PubMedID 34436293
Stem Cells and Innate Immunity in Aquatic Invertebrates: Bridging Two Seemingly Disparate Disciplines for New Discoveries in Biology.
Frontiers in immunology
2021; 12: 688106
The scopes related to the interplay between stem cells and the immune system are broad and range from the basic understanding of organism's physiology and ecology to translational studies, further contributing to (eco)toxicology, biotechnology, and medicine as well as regulatory and ethical aspects. Stem cells originate immune cells through hematopoiesis, and the interplay between the two cell types is required in processes like regeneration. In addition, stem and immune cell anomalies directly affect the organism's functions, its ability to cope with environmental changes and, indirectly, its role in ecosystem services. However, stem cells and immune cells continue to be considered parts of two branches of biological research with few interconnections between them. This review aims to bridge these two seemingly disparate disciplines towards much more integrative and transformative approaches with examples deriving mainly from aquatic invertebrates. We discuss the current understanding of cross-disciplinary collaborative and emerging issues, raising novel hypotheses and comments. We also discuss the problems and perspectives of the two disciplines and how to integrate their conceptual frameworks to address basic equations in biology in a new, innovative way.
View details for DOI 10.3389/fimmu.2021.688106
View details for PubMedID 34276677
Evolutionary perspective on the hematopoietic system through a colonial chordate: allogeneic immunity and hematopoiesis.
Current opinion in immunology
2020; 62: 91–98
Evolution and selection have shaped diverse immune systems throughout phylogeny, the vast majority of which remain unexplored. Botryllus schlosseri is a colonial tunicate, a sister group to vertebrates, that develops as a chordate, then metamorphoses to an asexually reproductive invertebrate that every week makes the same body plan from budded stem cells. Genetically distinct B. schlosseri colonies can fuse to form a chimera, or reject each other based on allogeneic recognition. In chimeras, circulating germline and somatic stem cells participate in development; stem cells compete in all individuals in the fused colonies, with rejection preventing germline parasitism. Here we review the isolation and characterization of B. schlosseri hematopoietic stem cells (HSC) and their niches, and the role of the immune effector cells in allorecognition.
View details for DOI 10.1016/j.coi.2019.12.006
View details for PubMedID 31954962
- Sixty years of experimental studies on the blastogenesis of the colonial tunicate Botryllus schlosseri DEVELOPMENTAL BIOLOGY 2019; 448 (2): 293–308
- Natural Chimerism and Tolerance Induction in a Colonial Chordate Advances in Comparative Immunology Springer . 2018: 18
Developmental cell death programs license cytotoxic cells to eliminate histocompatible partners
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2016; 113 (23): 6520-6525
In a primitive chordate model of natural chimerism, one chimeric partner is often eliminated in a process of allogeneic resorption. Here, we identify the cellular framework underlying loss of tolerance to one partner within a natural Botryllus schlosseri chimera. We show that the principal cell type mediating chimeric partner elimination is a cytotoxic morula cell (MC). Proinflammatory, developmental cell death programs render MCs cytotoxic and, in collaboration with activated phagocytes, eliminate chimeric partners during the "takeover" phase of blastogenic development. Among these genes, the proinflammatory cytokine IL-17 enhances cytotoxicity in allorecognition assays. Cellular transfer of FACS-purified MCs from allogeneic donors into recipients shows that the resorption response can be adoptively acquired. Transfer of 1 × 10(5) allogeneic MCs eliminated 33 of 78 (42%) recipient primary buds and 20 of 76 (20.5%) adult parental adult organisms (zooids) by 14 d whereas transfer of allogeneic cell populations lacking MCs had only minimal effects on recipient colonies. Furthermore, reactivity of transferred cells coincided with the onset of developmental-regulated cell death programs and disproportionately affected developing tissues within a chimera. Among chimeric partner "losers," severe developmental defects were observed in asexually propagating tissues, reflecting a pathologic switch in gene expression in developmental programs. These studies provide evidence that elimination of one partner in a chimera is an immune cell-based rejection that operates within histocompatible pairs and that maximal allogeneic responses involve the coordination of both phagocytic programs and the "arming" of cytotoxic cells.
View details for DOI 10.1073/pnas.1606276113
View details for Web of Science ID 000377155400052
View details for PubMedID 27217570
- Characterization of Ambra1 in asexual cycle of a non-vertebrate chordate, the colonial tunicate Botryllus schlosseri, and phylogenetic analysis of the protein group in Bilateria MOLECULAR PHYLOGENETICS AND EVOLUTION 2016; 95: 46-57
- Botryllus schlosseri, an emerging model for the study of aging, stem cells, and mechanisms of regeneration INVERTEBRATE REPRODUCTION & DEVELOPMENT 2015; 59: 33-38
Guidelines for the Nomenclature of Genetic Elements in Tunicate Genomes
2015; 53 (1): 1-14
Tunicates are invertebrate members of the chordate phylum, and are considered to be the sister group of vertebrates. Tunicates are composed of ascidians, thaliaceans, and appendicularians. With the advent of inexpensive high-throughput sequencing, the number of sequenced tunicate genomes is expected to rise sharply within the coming years. To facilitate comparative genomics within the tunicates, and between tunicates and vertebrates, standardized rules for the nomenclature of tunicate genetic elements need to be established. Here we propose a set of nomenclature rules, consensual within the community, for predicted genes, pseudogenes, transcripts, operons, transcriptional cis-regulatory regions, transposable elements, and transgenic constructs. In addition, the document proposes guidelines for naming transgenic and mutant lines.
View details for DOI 10.1002/dvg.22822
View details for Web of Science ID 000348656800001
View details for PubMedID 25220678
Botryllus schlosseri, an emerging model for the study of aging, stem cells, and mechanisms of regeneration.
Invertebrate reproduction & development
2015; 59 (sup1): 33–38
The decline of tissue regenerative potential with the loss of stem cell function is a hallmark of mammalian aging. We study Botryllus schlosseri, a colonial chordate which exhibits robust stem cell-mediated regeneration capacities throughout life. Larvae, derived by sexual reproduction and chordate development, metamorphose to clonal founders that undergo weekly formation of new individuals by budding from stem cells. Individuals are transient structures which die through massive apoptosis, and successive buds mature to replicate an entire new body. As a result, their stem cells, which are the only self-renewing cells in a tissue, are the only cells which remain through the entire life of the genotype and retain the effects of time. During aging, a significant decrease in the colonies' regenerative potential is observed and both sexual and asexual reproductions will eventually halt. When a parent colony is experimentally separated into a number of clonal replicates, they frequently undergo senescence simultaneously, suggesting a heritable factor that determines lifespan in these colonies. The availability of the recently published B. schlosseri genome coupled with its unique life cycle features promotes the use of this model organism for the study of the evolution of aging, stem cells, and mechanisms of regeneration.
View details for PubMedID 26136618
Ontology for the Asexual Development and Anatomy of the Colonial Chordate Botryllus schlosseri
2014; 9 (5)
Ontologies provide an important resource to integrate information. For developmental biology and comparative anatomy studies, ontologies of a species are used to formalize and annotate data that are related to anatomical structures, their lineage and timing of development. Here, we have constructed the first ontology for anatomy and asexual development (blastogenesis) of a bilaterian, the colonial tunicate Botryllus schlosseri. Tunicates, like Botryllus schlosseri, are non-vertebrates and the only chordate taxon species that reproduce both sexually and asexually. Their tadpole larval stage possesses structures characteristic of all chordates, i.e. a notochord, a dorsal neural tube, and gill slits. Larvae settle and metamorphose into individuals that are either solitary or colonial. The latter reproduce both sexually and asexually and these two reproductive modes lead to essentially the same adult body plan. The Botryllus schlosseri Ontology of Development and Anatomy (BODA) will facilitate the comparison between both types of development. BODA uses the rules defined by the Open Biomedical Ontologies Foundry. It is based on studies that investigate the anatomy, blastogenesis and regeneration of this organism. BODA features allow the users to easily search and identify anatomical structures in the colony, to define the developmental stage, and to follow the morphogenetic events of a tissue and/or organ of interest throughout asexual development. We invite the scientific community to use this resource as a reference for the anatomy and developmental ontology of B. schlosseri and encourage recommendations for updates and improvements.
View details for DOI 10.1371/journal.pone.0096434
View details for Web of Science ID 000335510600101
View details for PubMedID 24789338
Ascidian Mitogenomics: Comparison of Evolutionary Rates in Closely Related Taxa Provides Evidence of Ongoing Speciation Events
GENOME BIOLOGY AND EVOLUTION
2014; 6 (3): 591-605
Ascidians are a fascinating group of filter-feeding marine chordates characterized by rapid evolution of both sequences and structure of their nuclear and mitochondrial genomes. Moreover, they include several model organisms used to investigate complex biological processes in chordates. To study the evolutionary dynamics of ascidians at short phylogenetic distances, we sequenced 13 new mitogenomes and analyzed them, together with 15 other available mitogenomes, using a novel approach involving detailed whole-mitogenome comparisons of conspecific and congeneric pairs. The evolutionary rate was quite homogeneous at both intraspecific and congeneric level, and the lowest congeneric rates were found in cryptic (morphologically undistinguishable) and in morphologically very similar species pairs. Moreover, congeneric nonsynonymous rates (dN) were up to two orders of magnitude higher than in intraspecies pairs. Overall, a clear-cut gap sets apart conspecific from congeneric pairs. These evolutionary peculiarities allowed easily identifying an extraordinary intraspecific variability in the model ascidian Botryllus schlosseri, where most pairs show a dN value between that observed at intraspecies and congeneric level, yet consistently lower than that of the Ciona intestinalis cryptic species pair. These data suggest ongoing speciation events producing genetically distinct B. schlosseri entities. Remarkably, these ongoing speciation events were undetectable by the cox1 barcode fragment, demonstrating that, at low phylogenetic distances, the whole mitogenome has a higher resolving power than cox1. Our study shows that whole-mitogenome comparative analyses, performed on a suitable sample of congeneric and intraspecies pairs, may allow detecting not only cryptic species but also ongoing speciation events.
View details for DOI 10.1093/gbe/evu041
View details for Web of Science ID 000334578100014
View details for PubMedID 24572017
Chimerism a natural ability to tolerate kin, evolutionary traits connecting mammalian and protochordates
ISJ-INVERTEBRATE SURVIVAL JOURNAL
2009; 6 (1): S9-S20
View details for Web of Science ID 000208472800003
Stem Cells, Chimerism and Tolerance: Lessons from Mammals and Ascidians
Stem Cells in Marine Organisms
Springer Netherlands. 2009: 281–308
View details for DOI 10.1007/978-90-481-2767-2_12
A conserved role of the VEGF pathway in angiogenesis of an ectodermally-derived vasculature
2008; 315 (1): 243-255
Angiogenesis, the growth and remodeling of a vascular network, is an essential process during development, growth and disease. Here we studied the role of the vascular endothelial growth factor receptor (VEGFR) in experimentally-induced angiogenesis in the colonial ascidian Botryllus schlosseri (Tunicata, Ascidiacea). The circulatory system of B. schlosseri is composed of two distinct, but interconnected regions: a plot of sinuses and lacunae which line the body, and a transparent, macroscopic extracorporeal vascular network. The vessels of the extracorporeal vasculature are morphologically inverted in comparison to the vasculature in vertebrates: they consist of a single layer of ectodermally-derived cells with the basal lamina lining the lumen of the vessel. We found that when the peripheral circulatory system of a colony is surgically removed, it can completely regenerate within 24 to 48 h and this regeneration is dependent on proper function of the VEGF pathway: siRNA-mediated knockdown of the VEGFR blocked vascular regeneration, and interfered with vascular homeostasis. In addition, a small molecule, the VEGFR kinase inhibitor PTK787/ZK222584, phenocopied the siRNA knockdown in a reversible manner. Despite the disparate germ layer origins and morphology of the vasculature, the developmental program of branching morphogenesis during angiogenesis is controlled by similar molecular mechanisms, suggesting that the function of the VEGF pathway may be co-opted during the regeneration of an ectoderm-derived tubular structure.
View details for DOI 10.1016/j.ydbio.2007.12.035
View details for Web of Science ID 000253750300019
View details for PubMedID 18234178
View details for PubMedCentralID PMC2292797
BS-Cadherin in the colonial urochordate Botryllus schlosseri: One protein, many functions
2007; 304 (2): 687-700
Botryllus schlosseri is a colonial urochordate composed of coexisting modules of three asexually derived generations, the zooids and two cohorts of buds, each at disparate developmental stage. Functional zooids are replaced weekly by the older generation of buds through a highly synchronized developmental cycle called blastogenesis (which is, in turn, divided into four major stages, A to D). In this study, we examined the mode of expression of BS-cadherin, a 130-kDa transmembrane protein isolated from this species, during blastogenesis. BS-Cadherin is expressed extensively in internal organs of developing buds, embryos, ampullae and, briefly, in the digestive system of zooids at early blastogenic stage D (in contrast to low mRNA expression at this stage). In vitro trypsin assays on single-cell suspensions prepared from blastogenic stage D zooids, confirmed that BS-cadherin protein is expressed on cell surfaces and is, therefore, functional. BS-Cadherin expression is also upregulated in response to various stress conditions, such as oxidative stress, injury and allorecognition. It plays an important role in colony morphogenesis, because siRNA knockdown during D/A blastogenic transition causes chaotic colonial structures and disrupts oocytes homing onto their bud niches. These results reveal that BS-cadherin protein functions are exerted through a specific spatiotemporal pattern and fluctuating expression levels, in both development/regular homeostasis and in response to various stress conditions.
View details for DOI 10.1016/j.ydbio.2007.01.018
View details for Web of Science ID 000245819600019
View details for PubMedID 17316601
fester, a Candidate allorecognition receptor from a primitive chordate
2006; 25 (1): 163-173
Histocompatibility in the primitive chordate, Botryllus schlosseri, is controlled by a single, highly polymorphic locus, the FuHC. By taking a forward genetic approach, we have identified a locus encoded near the FuHC, called fester, which is polymorphic, polygenic, and inherited in distinct haplotypes. Somatic diversification occurs through extensive alternative splicing, with each individual expressing a unique repertoire of splice forms, both membrane bound and potentially secreted, all expressed in tissues intimately associated with histocompatibility. Functional studies, via both siRNA-mediated knockdown and direct blocking by monoclonal antibodies raised against fester, were able to disrupt predicted histocompatibility outcomes. The genetic and somatic diversity, coupled to the expression and functional data, suggests that fester is a receptor involved in histocompatibility.
View details for DOI 10.1016/j.immuni.2006.04.011
View details for Web of Science ID 000239713000019
View details for PubMedID 16860765
Macrophage involvement for successful degeneration of apoptotic organs in the colonial urochordate Botryllus schlosseri
JOURNAL OF EXPERIMENTAL BIOLOGY
2004; 207 (14): 2409-2416
Apoptosis is an important tool for shaping developing organs and for maintaining cellular homeostasis. In the colonial urochordate Botryllus schlosseri, apoptosis is also the hallmark end point in blastogenesis, a cyclical and weekly developmental phenomenon. Then the entire old generation of zooids are eliminated (resorbed) by a process that lasts 24-36 h. Administration of the antioxidant butylated hydroxytoluene (BHT) resulted in resorption being arrested by 1-8 days on average. At high doses (2.5-15.0 mg BHT l(-1)) resorption was completed only after removal of BHT. Colonies that were not removed in time, died. In treated colonies, although DNA fragmentation was high, tissues and organs that would normally have died, survived, and the general oxidative levels of lipids were reduced. Blood vessels were widened, containing aggregates of blood cells with a significantly increased proportion of empty macrophage-like cells without inclusion. In colonies rescued from BHT treatment, resorption of zooids started immediately and was completed within a few days. We propose three possible mechanisms as to how BHT may affect macrophage activity: (1) by interrupting signals that further promote apoptosis; (2) through the respiratory burst initiated following a phagocytic stimulus; and (3) by reducing lipid oxidation and changing cell surface markers of target cells. Our results point, for the first time, to the role of phagocytic cells in the coordination of death and clearance signals in blastogenesis.
View details for DOI 10.1242/jeb.01045
View details for Web of Science ID 000222883000010
View details for PubMedID 15184513
Rejuvenescence and extension of an urochordate life span following a single, acute administration of an anti-oxidant, butylated hydroxytoluene
MECHANISMS OF AGEING AND DEVELOPMENT
2002; 123 (9): 1203-1210
Two commonly accepted metabolic theories of aging interpret senescence either in terms of the rate of living, where a fixed total metabolic potential is consumed over an expected lifetime (after which the organism wears out and dies) or, in terms of accumulative oxidative damage resulting in progressive and irreversible changes in metabolic pathways. Protocols based on restricted diets, chronically administered anti-oxidants and the use of established lines of organisms resistant to free radical damage support the metabolic theories of aging by revealing, in many cases, significant extensions of life spans or dramatic anti-aging effects. To test the universality of these metabolic hypotheses of aging, we acutely treated ramets (clonal replicates) from old, long-lived colonies of the urochordate Botryllus schlosseri with lethal doses of the anti-oxidant butylated hydroxytoluene (BHT). This group of organisms has a weekly cyclical and highly synchronized developmental process (blastogenesis), during which all existing zooids are removed by massive apoptosis and phagocytosis processes. In animals treated with BHT, blastogenesis was completely arrested and colonies deteriorated to a morphologically chaotic state. Rescued ramets resorbed BHT treated zooids, regenerated entirely new sets of zooids and then revealed: (1) rejuvenescence and enhanced growth rates and in many cases, (2) up to 4.6 times extension of post-treatment life expectancy. Both metabolic theories for senescence were therefore falsified in B. schlosseri. The possible existence of an aging clock that can be set by the environment is suggested.
View details for Web of Science ID 000177238800001
View details for PubMedID 12020943