Molecular characterization and expression analysis of strbp in Chinese tongue sole (Cynoglossus semilaevis)

Spermatid perinuclear RNA-binding protein (Strbp) is a kind of double-stranded (ds) RNA specific binding protein that plays important roles in mammalian spermatogenesis. In this study, we have isolated and characterized the strbp gene of Chinese tongue sole, Cynoglossus semilaevis, termed as CS-strbp. The CS-strbp genomic sequence contained fifteen exons and fourteen introns. Its cDNA was 2655 bp in length, encoding a 666-amino-acid protein with two conserved ds binding motifs. Using quantitative PCR, we found that CS-strbp mRNA exhibited sex-biased and tissue-specific distribution, predominantly expressed in the fertile male testis, though the expression levels varied throughout different developmental stages. Comparison of methylation profile in different sexual genotypes demonstrated the low methylation level of CS-strbp promoter in male and pseudo-male, which is consistent with the high expression levels in those genotypes. In situ hybridization revealed that CS-strbp mRNA mainly localized in male germ cells, especially in spermatids and spermatozoa. Given these findings, we postulate that CS-strbp might function in spermatogenesis of Chinese tongue sole.