Three Copies of Izbed1/I Specific in Chromosome W Are Essential for Female-Biased Sexual Size Dimorphism in ICynoglossus semilaevis/I

The sex chromosome, especially specific in one sex, is considered to determine the sexual size dimorphism (SSD), a dimorphic sexual difference in the body size. For Cynoglossus semilaevis, a flatfish unique in China, the important role of female-specific chromosome W in its female-biased SSD was previously implied. Furthermore, a W chromosome-specific gene zbed1 was identified to potentially regulate female-biased SSD in C. semilaevis. However, the chromosome’s location, family members, and detailed network information are still unknown. At present, the genome-wide identification of ZBED family members and dPCR experiment both confirm that three copies of the zbed1 gene are located in chromosome W, with no zbed1 gene in chromosome Z. Phylogenetic analysis for 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. For the chromosome-W-specific zbed1, qPCR verified its predominant expression in the female brain and pituitary tissues. The dual luciferase activity test showed that 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. In addition, after zbed1 interfered in the brain cells, piwil1, esr2 and wnt7b were up-regulated, while cell-cycle-related genes (tbp, cdk2, cdk4, cdk6, ccng1 and ccndx) were down-regulated. It is suggested that the cell proliferation function of zbed1 may be realized by regulating esr2, piwil1, cell cycle and the Wnt pathway. 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.