Developmental and cyclic adenosine 3',5'monophosphate-dependent regulation of inhibin subunit messenger ribonucleic acids in human fetal testes.

Abstract

Inhibin subunit messenger ribonucleic acids (mRNAs) are expressed during the gonadal development of rodent, ovine, and bovine fetuses. We investigated the expression of inhibin subunit mRNAs in human fetal gonads between 13 and 25 weeks of gestational age. In testes, the alpha-subunit mRNA was highly expressed at the beginning of the second trimester and its expression level slightly decreased thereafter. Also the beta B-subunit mRNA was detected throughout this time period but no significant developmental change could be observed. Northern analysis showed a 1.6-kilobase (kb) transcript for alpha-chain, as well as two bands of about 5.0 and 4.5 kb for the beta B-subunit. A human Leydig cell tumor also expressed the 1.6-kb alpha-subunit. By filter hybridization studies, the beta A-chain mRNA could not be observed in testes and none of the three inhibin subunits were detectable in the ovaries at this developmental stage. However, reverse-transcription polymerase chain reaction analysis revealed the expression of all three inhibin subunit mRNAs in testes. As studied by in situ hybridization, inhibin alpha-subunit hybridization signal was most intense in seminiferous tubules and weaker hybridization was observed in interstitial cells of the fetal testis. In primary cultures of fetal testicular cells, dibutyryl cAMP (0.2 mmol/L) stimulated alpha- and beta B-mRNAs. It augmented alpha- and beta B-mRNA accumulation up to 6- and 2.5-fold, respectively. Thus, we conclude that: 1) during the second trimester of gestation, human fetal testes express all three inhibin subunit mRNAs, although the beta A-chain expression appears to be low; 2) during this developmental stage inhibin subunit mRNAs are not detectable in ovaries; 3) in human fetal testes, the alpha-chain mRNA is localized to both intratubular and interstitial cells; 4) in cultured human testicular cells, inhibin alpha- and beta B-subunit mRNAs are regulated by a cAMP-dependent pathway.