The csdazl gene is a sex related gene of half-smooth tongue sole (Cynoglossus semilaevis). Our research group have cloned full length cDNA of csdazl, and studied its expression pattern. To get the further information of csdazl, we constructed a prokaryotic expression plasmid, pET-32a-CSDAZL, expressed in Escherichia coli BL21 and purified the fusion protein by His Trap. In order to detect the biological activity of the fusion protein, we injected the protein with liposome into fish, and detected other sex-related genes' mRNA expression. The results showed that the expression levels of half-smooth tongue sole female-related genes Cyp19a and Foxl2 significantly decreased between 6 and 24 h; however, both genes' expressions returned to their normal levels 72 h after injection, indicating that recombinant CSDAZL protein could down-regulated the expression of female-related genes, Foxl2 and Cyp19a genes, implying that the fusion protein has biological activity and csdazl plays a role in sex differentiation by regulating sex related genes' expression. (C) 2014 Elsevier Inc. All rights reserved.