PANG, K.*; MATUS, D.Q.; MARTINDALE, M.Q.; Univ. Hawaii; Univ. Hawaii; Univ. Hawaii: Germ line development in basal metazoans.

The segregation of the germ line from somatic lineages is one of the most fundamental events in metazoan development. Surveys throughout the Metazoa indicate that the timing of germ line determination varies considerably among different phyla. We are examining germ line development in two basal metazoans, the starlet sea anemone Nematostella vectensis with a late segregation, and the lobate ctenophore, Mnemiopsis leidyi with early cell fate segregation. We have cloned two nanos and VASA orthologs from each species and studied their expression. Both of these genes have been implicated in the development of the germ line in a wide variety of metazoans including protostomes, deuterostomes, and other cnidarians. In Nematostella vectensis one of the two nanos genes is maternally expressed and the transcript is uniformly expressed. The second nanos gene and the two VASA genes are not expressed until gastrulation. At polyp stages the VASA genes are expressed in a small number of cells in a discreet region in the entodermal mesenteries, suggesting that these maybe the presumptive germ cells. Ctenophores and cnidarians provide an important opportunity to understand the contrast in the origins of germ line.