Germ line specific expression of a vasa homologue gene in turbot (Scophthalmus maximus): evidence for vasa localization at cleavage furrows in euteleostei.

Specification of primordial germ cells during early embryogenesis is a critical biological issue in reproduction and development. Yet, little is known in marine economic fish species. Vasa, a component of germ plasm, is the most-documented germ cell marker in teleosts. We isolated a full-length vasa cDNA (Smvas) from turbot (Scophthalmus maximus), a marine Euteleostei species, and investigated its expression patterns by RT-PCR and in situ hybridization during embryogenesis and gametogenesis to identify the germ cell lineage in this species. The deduced amino acid sequence of the isolated cDNA shared typical characteristics of Vasa protein and high identity to Vasa homologues in medaka (76.9%) and zebrafish (68.5%). The Smvas transcripts were exclusively detected in germ cells of testis and ovary, and exhibited an interesting dynamic localization pattern during oogenesis. The distribution pattern of Smvas during embyogenesis in this Euteleostei closely resembled the pattern observed in zebrafish (belonging to Osteriophysans) rather than medaka (belonging to Euteleostei). Thus, it is concluded that Smvas isolated in this study is a germ cell specific molecular marker in turbot. Furthermore, we hypothesize that Euteleostei could localize vasa mRNA by a special mode. The results not only facilitate the germ cell manipulation of the turbot, but also improve our understanding of germline development and evolution of vasa localization in teleost.