cDNA cloning and expression analysis of a vasa -like gene in Pacific bluefin tuna Thunnus orientalis

摘要

In this study, a Pacific bluefin tuna (Thunnus orientalis) homolog of the Drosophila vasa gene, BtVLG (bluefin tuna vasa-like gene), was cloned and characterized for use as a molecular marker for germ cells in this species. Analysis of the nucleotide sequence revealed that BtVLG comprises 2,394 bps with an open reading frame of 1,932 bps encoding 644 amino acids. The deduced amino acid sequence contained arginine-glycine or arginine-glycine-glycine motifs and eight conserved motifs belonging to the DEAD-box protein family. The BtVLG sequence showed high similarity to Drosophila vasa (69.1%), zebrafish vasa homolog (80.5%), and tilapia vasa homolog (91.2%). In adult tissues, the BtVLG transcripts were specifically detected in ovary and testis. In situ hybridization analysis showed that BtVLG messenger RNA (mRNA) was detected in oogonia and previtellogenic oocytes in the ovary. In the testis, while BtVLG mRNA was detected in spermatogonia, it was not detected in the primary and secondary spermatocytes, spermatids, spermatozoa or gonadal somatic cells. Consequently, consensus sequences, sequence similarity, and specific localization of BtVLG mRNA in the germ cells all suggest that BtVLG is the bluefin tuna vasa homolog of the Drosophila vasa gene. Further, BtVLG can be used as a molecular marker for bluefin tuna germ cells.