Androgens regulate ovomucoid and ovalbumin gene expression independently of estrogen

Administration of dihydrotestosterone to estrogen-stimulated chicks induces a synergistic increase in ovomucoid mRNA synthesis and accumulation in the oviduct without affecting the synthesis of ovalbumin mRNA. This synergism is accompanied by an increase in nuclear estrogen receptors which could not be produced by simply increasing the maintenance dose of estrogen. Synergistic interactions between estrogen and dihydrotestosterone are also observed when they are added to oviduct explants in vitro. In addition to these synergistic effects, dihydrotestosterone is capable of maintaining the synthesis of ovalbumin and ovomucoid mRNAs after estrogen withdrawal in vivo. Analysis of total biologically active estrogen in the serum indicates that dihydrotestosterone does not interfere with estrogen elimination. Dihydrotestosterone also reinduces ovalbumin and ovomucoid gene transcription when injected into birds withdrawn from estrogen for less than 5 days; however, after several weeks of estrogen withdrawal, dihydrotestosterone is ineffective. Dihydrotestosterone alone acts directly on cultured oviduct explants to restimulate transcription of the ovalbumin and ovomucoid genes. Moreover, dihydrotestosterone effectively induces ovalbumin mRNA in the presence of the anti-estrogen, tamoxifen. These results indicate that androgen receptors can act either in concert with or independently of estrogen receptors to mediate specific gene transcription.