Three Copies of zbed1 Specific in Chromosome W Are Essential for Female-Biased Sexual Size Dimorphism in Cynoglossus semilaevis .

The sex chromosome, especially specific in one sex, generally determines sexual size dimorphism (SSD), a phenomenon with dimorphic sexual difference in the body size. For Cynoglossus semilaevis , a flatfish in China, although the importance of chromosome W and its specific gene zbed1 in female-biased SSD have been suggested, its family members and regulation information are still unknown. At present, three zbed1 copies gene were identified on chromosome W, with no gametologs. Phylogenetic analysis for the ZBED family revealed an existence of ZBED9 in the fish. Nine members were uncovered from C. semilaevis , clustering into three kinds, ZBED1, ZBED4 and ZBEDX, which is less than the eleven kinds of ZBED members in mammals. The predominant expression of zbed1 in the female brain and pituitary tissues was further verified by qPCR. Transcription factor c/ebpα could significantly enhance the transcriptional activity of zbed1 promoter, which is opposite to its effect on the male determinant factor- dmrt1 . When zbed1 was interfered with, piwil1 , esr2 and wnt7b were up-regulated, while cell-cycle-related genes, including cdk4 and ccng1, were down-regulated. Thus, zbed1 is involved in cell proliferation by regulating esr2 , piwil1 , cell cycle and the Wnt pathway. Further research on their interactions would be helpful to understand fish SSD.