Please join us for Marine Biology Seminar this Friday, May 11th for a talk by:
Dr. Anthony De Tomaso, Associate Professor, University of California Santa Barbara
Stem cells and regeneration in the colonial ascidian, Botryllus schlosseri
We are studying the molecular mechanisms of regeneration in the colonial ascidian, Botryllus schlosseri. Ascidians are basal chordates and represent the transition phylum between invertebrates and vertebrates. Ascidian embryogenesis results in a motile chordate tadpole larvae which later metamorphoses into a sessile invertebrate adult. In addition, B. schlosseri belongs to a subset of ascidians which are colonial and grow, not by increasing in size, but via a budding process which results in a colony of genetically identical individuals (called zooids) united by a common vasculature. Each zooid is an independent body, with its own somatic and germline tissues, and each week undergoes an asexual reproductive process during which all somatic and germline tissues are regenerated. We are trying to understand both the source of budding as well as the developmental processes which underlie regenerative development.
We are focused on understanding the source of germline regeneration during this budding process. Recent results suggest that long-lived germline stem cells (GSCs) are specified during embryogenesis and contribute to germline formation each week for the life of a genotype (6 mo- >2 yrs). Following metamorphosis, colonies undergo 6-12 budding cycles prior to the appearance of gonads, and in addition adults often cycle between fertile and infertile states. GSCs isolated from juvenile or non-fertile colonies can contribute to germline formation immediately following transplant to a sexually mature recipient. In addition, it has been found that allogeneic transplantation of GSCs can lead to competition between genetically distinct stem cell lineages within a chimera, often leading to complete replacement of the germline over time by a single genotype. This process, called germ cell parasitism, is a repeatable and heritable trait, and winner and loser genotypes can be found in lab-reared strains and natural populations. Parasitic abilities are autonomous to the GSCs themselves, and retained upon experimental transplantation. We have recently found that > 90% of the testes isolated from individual zooids within a chimeric colony are clonal, and analyzed the kinetics of chimerism over time. We have also found that fertility can be induced in a juvenile colony following parabiosis to a fertile adult, and that the outcome depends on the size ratio of the two individuals. Together, these results suggest GSCs are present in an infertile colony, that fertility in a colony is likely due to niche formation and/or GSC activation due to a global signal, and that the basis of stem cell parasitism is homing. We are currently identifying differentially expressed genes between fertile and infertile colonies as well as characterizing GSCs prospectively enriched from winner and loser parasitic genotypes using mRNA-seq. Current results will be presented.
Refreshments will be served at 12pm, and the talk will begin at 12:15pm in 4500 Hubbs Hall.