The Involvement of Follicle-Stimulating Hormone in Testis Differentiation in Nile Tilapia

In Nile tilapia, one of the most important aquaculture species, males are larger than females, and an all-male monosex culture offers significant economic benefits. Although the pituitaries of genetic female (XX) and genetic male (XY) tilapia have identical expression levels of follicle-stimulating hormone (fsh), FSH receptor (fshr) expression remains relatively low in XY-undifferentiated gonads and then increases following morphological sex differentiation. The expression patterns of genes related to androgen biosynthesis in XY-undifferentiated gonads are similar to those of fshr during testis differentiation. This might imply that FSH has a potential function in testis differentiation through regulating the expression of genes related to androgen biosynthesis. To determine whether FSH signaling regulated androgen biosynthesis, we microinjected recombinant FSH (rFsh) into XY larvae during the early sex-differentiation stage. We compared the expression of various genes related to testis differentiation after injection. The genes hsd3b, cyp17a1, dmrt1, and gsdf were found to have higher expression in the rFsh treatment group. These results suggest that FSH signaling can activate androgen biosynthesis by regulating steroidogenic enzymes, including hsd3b and cyp17a1. Moreover, injected rFsh can upregulate dmrt1, which has a positive effect on the expression of gsdf. Therefore, during testis differentiation and development, FSH plays a role in both androgen synthesis and the expression of genes related to testis differentiation in Nile tilapia.