Rat Inhibin: Molecular Cloning of α- and β-Subunit Complementary Deoxyribonucleic Acids and Expression in the Ovary

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Abstract
Inhibin is a gonadal protein hormone that suppresses the secretion of FSH from pituitary gonadotrophs. It has previously been characterized as a heterodimer of two dissimilar subunits (.alpha., 18 kilodaltons and .beta., 14 kilodaltons) the smaller of which exists in two forms (.beta.A and .beta.B) and can form dimers that stimulate the secretion of FSH. In the present work, cDNA clones encoding the inhibitin .alpha.- and .beta.A-subunits have been isolated from rat ovary and characterized. The .alpha.-inhibin cDNA predicts a precursor protein of 366 amino acids containing the 133 amino acid mature .alpha.-subunit at its COOH-terminus. The .beta.A-inhibin cDNA predicts a precursor protein of 424 amino acids containing the 116 amino acid .beta.A-subunit at its COOH-terminus. Analysis of rat ovarian RNA indicates that .alpha.-inhibin mRNA levels are stimulated by PMSG treatment in vivo. In cultured granulosa cells, FSH also stimulates .alpha.-inhibin mRNA, and the FSH effect is suppressed by cotreatment with GnRH. Hybridization in situ to rat ovarian tissue demonstrates that both the .alpha.-inhibin and .beta.A-inhibin mRNAs are specifically expressed in granulosa cells of the developing follicles.