Characterization and regulation of testicular inhibin beta-subunit mRNA

To understand the possible structures of testicular inhibin, we have isolated cDNAs coding for inhibin subunits from human testicular cDNA libraries. In this study we report that the nucleotide and predicted amino acid sequences for human testicular inhibin beta-B-subunit are similar to those of human ovary. In rat testis two species of beta-B-subunit mRNA [4.4 and 3.3 kilobases (kb)] appeared to be present in equal concentration, as opposed to rat ovary where a predominant band of 4.4 kb and a minor band of 3.3 kb were observed. One major species of beta-A-subunit mRNA (6.5 kb) was identified in both testis and ovary. The concentration of beta-A-subunit mRNA in the testis was very low, representing only 0.5% of that in rat ovary. The accumulation of beta-B-subunit mRNA peaked at 20 days of age and declined thereafter in a pattern similar to that of the alpha-subunit gene. Hypophysectomy caused a marked increase in the concentration as well as the total content of beta-B-subunit but no change in beta-A-subunit mRNA in rat testis. We have previously reported that FSH markedly increased alpha-subunit mRNA levels both in vivo and in vitro. By contrast, neither FSH nor testosterone has any significant effect on the accumulation of beta-A- or beta-B-subunit mRNAs in hypophysectomized animals or Sertoli cell primary cultures. We conclude that 1) the mRNAs for both beta-subunits are not regulated by FSH; and 2) hypophysectomy does not change and increases, respectively, the mRNAs for the beta-A- and beta-B-subunits. We conclude that the inhibin subunit mRNAs are differentially regulated in rat testis.