Characterization of the vasa gene in the Chinese mitten crab Eriocheir sinensis: a germ line molecular marker.

The vasa gene first identified in Drosophila encodes an ATP-dependent RNA helicase belonging to the DEAD-box family and is specifically expressed in germ line cells. In this study a full-length vasa gene homolog from the Chinese mitten crab (Eriocheir sinensis) was characterized, comprising of 2369 bp nucleotides with an open reading frame of 1866 bp encoding 621 amino acids. The putative protein was shown to contain eight conserved motifs belonging to the DEAD-box protein family and two zinc-finger domains (CCHC) and a Q-motif. Its sequence showed high similarity to vasa homologs of other species. The E. sinensis vasa (Es-vasa) mRNA expression was specific to the gonad and its temporal expression in the ovary and testes were significantly different between various developmental periods. By real-time qPCR analysis, Es-vasa mRNA transcripts were at the highest levels during periods of rapid development in the gonads (stage III-2 in ovaries and spermatocyte stage in testes) and gradually decreased as the gonads matured. In conclusion, we first identified the vasa gene from Chinese mitten crab. The specificity and pattern of Es-vasa expression in gonads indicates that it may be used as molecular marker for germ line in E. sinensis.