ACTION OF ESTRADIOL AND TAMOXIFEN ON THE TESTIS-INDUCING ACTIVITY OF THE CHICK EMBRYONIC TESTIS GRAFTED TO THE FEMALE EMBRYO

The implantation of two testes from 13-day-old male chick donor embryo s into the extra-embryonic celom of 3-day-old female embryos induces t he masculinization of their ovaries up to a total and definitive inver sion of their gonadal sex, i.e., the differentiation of testes in the female hosts. Pretreatment of the donors with estradiol (E2) between d ay 11 and 13 counteracts the testis-inducing activity of the implants, while co-treatment of donors with both tamoxifen (TAM) and E2 at the same stage restores the initially observed activity. The treatment of 3-day-old male donor embryos with E2 causes the differentiation of the ir left gonad into an ovotestis totally devoid of testis-inducing acti vity once grafted in the same conditions as above. An additional treat ment with TAM of the grafted host embryos does not modify the results obtained when E2-treated male gonads are grafted to normal host embryo s. This shows that the lack of testis-inducing activity exhibited by t he E2-treated grafts can not be attributed to a protecting action of e ndogenous estrogens on the gonads of the host. On account of previous work showing the inhibition by E2 of the Mullero-regressive activity o f the chick embryonic testis, our present results can be interpreted i n terms of E2-down regulation of Anti-Mullerian Hormone (AMH or MIS), which appears to be a good candidate as testis-inducer. The relevance of our results to the phenomenon of gonad differentiation is discussed .