The gonadal endocrine network regulating sex reversal in the gilthead seabream (Sparus aurata)

The objective of the present study was to expand our understanding of the endocrine regulation during the sex reversal process of the gilthead seabream, a protandrous hermaphrodite. We isolated four cDNAs derived from seabream gonad, encoding FSHR, LHR, CYP19A1 and CYP11B and developed a highly sensitive and specific real-time fluorescence-based quantitative PCR assay to investigate the differential expression and regulation of each gene during sex reversal. Our results reveal: (1) the differential expressions of FSHR and LHR in both the ovarian and testicular portions of the ambisexual gonad are associated with the process of sex reversal; (2) a strong association of CYP19A1 expression with LHR expression, rather than FSHR expression, is present in the ovarian portion of the ambisexual gonad; (3) the expression of testicular CYP11B is well correlated to testicular development and associated with testicular FSHR expression during the early stage of sex reversal, and with testicular LHR expression during the later stage of sex reversal; (4) E 2 (at a low level) promotes the expression of ovarian LHR and CYP19A1, and 11beta-OHT enhances the expression of testicular LHR and CYP11B. Accordingly, results from this study suggest that either the action of LH on the ovarian portion of the ambisexual gonad promotes the expression of CYP19A1, ultimately driving female development, or the action of FSH on the testicular portion of the ambisexual enhances expression of CYP11B, ultimately promoting male development (i.e., blocking sex reversal). E2 and 11beta-OHT serve as the major steroids regulating expression of the genes related to the promotion of gonadal differentiation. The other important finding in this work is the discovery of the expression of both LH and FSH at the transcript and peptide levels, as well as the presence of the gonadal GnRH-GtH axis in seabream gonadal tissues. These factors may participate in the regulation of gonadal development, including the process of sex reversal. The immediate challenge for understanding the control mechanisms of sex reversal is not only discerning the action and regulation of the gonadal GnRH-GtH axis, but also resolving how this local axis integrates and interacts with the HPG axis to regulate gonadal development.