Characterization and Localization of 2 in Both the Testis and Ovary of the Japanese Flounder ().

Although its function in mammalian gonads has been gradually recognized, the expression and function of calretinin (CALB2)-a Ca-binding protein-in the testis and ovary of fish are still unclear. Here, we identified the cDNA sequences of 2 in (); analyzed its gene structure and phylogenetic and syntenic relationship by bioinformatics; and investigated its tissue distribution and localization in the gonads by real-time PCR, western blotting, and immunohistochemistry. The 2 gene has 11 exons and 10 introns, and the full-length cDNA is 1457 bp, including an open reading frame (ORF) of 816 bp encoding 271 amino acids. The CALB2 of has a higher homology with (99%) compared with other species. The conserved synteny of 2 neighboring gene loci was also detected in fish. Real-time PCR showed that the expression of 2 mRNA is abundant not only in the brain, but also in the gonads, and exhibits a higher expression in the testis than in the ovary. Western blotting indicated that the CALB2 protein has a higher expression in the testis compared with the ovary. Immunohistochemistry demonstrated that the CALB2 protein appears in Leydig cells and the ovarian germ epithelium. These results reveal that 2 plays an important role in the gonads of .