INHIBIN ACTIVIN SUBUNIT MESSENGER-RNA EXPRESSION IN HUMAN GRANULOSA-LUTEAL CELLS

We studied the expression of inhibin/activin subunit mRNAs in granulos a-luteal cells of preovulatory ovarian follicles obtained from women u ndergoing in vitro fertilization, and in corpus luteum tissue samples of early pregnancy. Northern analysis of granulosa-luteal cell and cor pus luteum RNA with single-stranded cDNA or cRNA probes revealed an 1. 6-kb mRNA for the alpha subunit and about 6.0-, 4.0-, 2.8-, and 1.7-kb transcripts for the beta(A) subunit. No clear hybridization signal fo r the beta(B) subunit could be detected. The relative expression level s of alpha and beta(A) subunit mRNAs were determined at 2-day interval s in granulosa-luteal cells cultured for 5 to 11 days. The levels of a lpha subunit mRNAs declined steadily with increasing culture age, wher eas those of beta(A) remained unchanged. Reverse transcription-polymer ase chain reaction analysis with 35 amplification cycles confirmed the expression of alpha and beta(A) subunit mRNAs in cultured granulosa-l uteal cells. The beta(B) transcripts were also weakly detectable by th is sensitive assay. In situ hybridization of human early pregnancy cor pus luteum revealed intense hybridization with the alpha cRNA probe an d a weaker signal for the beta(A) subunit in the granulosa cell compar tment. We conclude that: (1) the inhibin alpha and beta(A) subunits (a nd to a lesser extent beta(B)) are expressed in cultured human granulo sa-luteal cells; (2) during extended culture periods the alpha/beta(A) mRNA expression ratio decreases; and that (3) the alpha and beta(A) s ubunit mRNA expression is observed in the granulosa cell compartment o f early pregnancy corpora lutea.