Vasa and nanos are coexpressed in somatic and germ line tissue from early embryonic cleavage stages through adulthood in the polychaete Capitella sp. I

Abstract

Members of the vasa and nanos gene families are involved in germ line development in a number of diverse animals. As a polychaete annelid model for studies of the germ line, Capitella sp. I has several advantages including the presence of dedicated gonads, individuals that reproduce multiple times, and the presence of males, females, and hermaphrodites. Germ line development has not been characterized in Capitella sp. I, nor is the mechanism of germ line specification generally well understood in annelids. We have cloned vasa and nanos orthologues from Capitella sp. I and found that both CapI-vasa and CapI-nanos transcripts are expressed in developing gametes of sexually mature adults. Characterization of both these genes during embryonic, larval, and juveniles stages reveals expression in multiple somatic tissues for CapI-vasa and CapI-nanos with largely overlapping but not identical expression patterns. In early cleavage stages, both transcripts are broadly expressed; following gastrulation, expression is observed in the presumptive brain, mesodermal bands, and developing foregut. Using CapI-nanos and CapI-vasa as markers, we have identified putative primordial germ cells (PGCs) in larvae, which are initially present as small bilateral clusters in segment 4 and as a single cluster at late larval stages. In adults, a single large cluster of putative PGCs is present in segments 5 and 6. In addition to highlighting differences in expression profiles for these two genes among lophotrochozoans, we present a hypothesis concerning the origin and development of PGCs in Capitella sp. I.