Meeting Abstract
122.3 Monday, Jan. 7 Spider vasa is required for early embryogenesis but not for germline specification SCHWAGER, E.E.*; MENG, Y; EXTAVOUR, C.G.; Harvard University; Harvard University; Harvard University eschwager@oeb.harvard.edu
Metazoans specify their germline either early in development by maternally transmitted cytoplasmic factors (inheritance), or later in development by signaling factors from neighboring tissues (induction). The molecular principles of the inheritance mode have been thoroughly studied in model organisms such as flies, worms and fish, whereas the molecular basis of induction is only known from two vertebrates, mouse and salamander. Nevertheless, induction is hypothesized to be the ancestral mechanism of germline determination. Still currently we are lacking molecular and functional descriptions of inductive germ cell specification from protostomes. Arthropods are one of the metazoan clades that exhibit both induction and inheritance. We therefore examined germ line development in the spider Parasteatoda tepidariorum, an emerging chelicerate model organism. Even though spiders have repeatedly been the subject of classical embryological research, there have been only vague descriptions of putative spider germ cells to date. Our results, based on gene expression patterns of the germline marker genes vasa and piwi, and using spider-specific antibodies against Vasa and Piwi proteins, show that germ cells in the spider are likely formed by induction: neither Vasa nor Piwi protein appear localized before primordial germ cell clusters emerge as paired segmental clusters in opisthosomal segments 2-6. To investigate the molecular basis of the inductive germ cell specification in the spider, we next examined the function of the vasa gene in this process. Maternal vasa knockdown led to embryos that died shortly after initiating gastrulation. To circumvent this maternal effect of the vasa gene, we next knocked down vasa zygotically. Our experiments show that these embryos develop normally and still form germ cells, implicating that vasa is not required for germ line specification.
