Identification of a vasa homologue gene in grass carp and its expression pattern in tissues and during embryogenesis

The RNA helicase Vasa is a member of the DEAD box protein family that plays an indispensable role in germ cell determination in eukaryotes such as in Drosophila and Xenopus species. In this study, the grass carp homologue of the Drosophila vasa gene, Civasa (Ctenopharyngodon idella vasa) was obtained using degenerate primers in RT-PCR and 5' and 3' rapid amplification of cDNA end polymerase chain reaction from the grass carp ovary SMART cDNA. This cDNA sequence encodes a 670 amino acid residue protein that contains eight consensus regions for the DEAD box protein family, 9 arginine-glycine repeats and 9 arginine-glycine-glycine repeats, a common character of known Vasa homologues. CiVasa shows high identity to that of zebrafish and other animals, suggesting Vasa is highly conserved through evolution. RT-PCR analysis reveals that in grass carp tissues, both ovaries and testes contain large amounts of vasa gene transcripts whereas no Civasa transcript is detected in somatic tissues examined. The Civasa transcripts are present at a high level from the 2 cell stage to gastrula stages which indicated that Cicasa transcripts are maternally inherited. The predicted protein sequence, localization and conserved pattern of gene expression suggest that Civasa plays an important role in the germ cell determinant and development in grass carp as proposed for other teleost species.