Ontogeny of testicular inhibin and activin in ducks: An immunocytochemical analysis

The ontogeny of testicular inhibin/activin in ducks was investigated. Testicular localization of three inhibin/activin subunits (alpha, betaA and betaB) was determined in embryonic and newly hatched ducks from 12 days of incubation to 1 day of age, in immature ducks and in adult ducks. In the duck embryonic testis, positive alpha-subunit immunostaining was first detected in the Leydig cells and Sertoli cells on day 15 of incubation, whereas betaA-subunit and betaB-subunit immunostaining were found in Sertoli cells and primary germ cells on day 18 of incubation. In 1 month old ducks, intense staining of alpha-subunit was present in the seminiferous epithelium consistent with localization in Sertoli cells and primary germ cells, and the immunostaining of the betaA- and betaB-subunit was also present in Sertoli cells and primary germ cells. Specific immunostaining with inhibin/activin alpha-, betaA- and betqB-subunits antisera occurred in Sertoli cells in the adult duck testes. In conclusion, it was shown that, in the duck testis, the majority of alpha-, betaA- and betaB-subunits are colocalized in Sertoli cells with a certain degree of staining in germ cells and the alpha-subunit is present in Leydig cells of embryonic testes before day 18 of incubation. These results indicate that Sertoli cells and possibly germ cells in the embryonic testes of late stage of incubation and newly hatched ducks, immature ducks and mature ducks may produce bioactive inhibin dimers, inhibin A and inhibin B, as a possible regulator of follicle-stimulating hormone secretion. Free inhibin/activin subunits and their dimers may also play an autocrine/paracrine role in the development of the testis and spermatogenesis. Furthermore, early onset of the alpha-subunit in duck testes indicates that it may have an autocrine/paracrine effect on steroid hormones, which is important for sex differentiation.