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

We studied the expression of inhibin/activin subunit mRNAs in granulosa-luteal cells of preovulatory ovarian follicles obtained from women undergoing in vitro fertilization, and in corpus luteum tissue samples of early pregnancy. Northern analysis of granulosa-luteal cell and corpus 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 for the beta(B) subunit could be detected. The relative expression levels of alpha and beta(A) subunit mRNAs were determined at 2-day intervals in granulosa-luteal cells cultured for 5 to 11 days. The levels of alpha subunit mRNAs declined steadily with increasing culture age, whereas those of beta(A) remained unchanged. Reverse transcription-polymerase chain reaction analysis with 35 amplification cycles confirmed the expression of alpha and beta(A) subunit mRNAs in cultured granulosa-luteal cells. The beta(B) transcripts were also weakly detectable by this sensitive assay. In situ hybridization of human early pregnancy corpus luteum revealed intense hybridization with the alpha cRNA probe and a weaker signal for the beta(A) subunit in the granulosa cell compartment. We conclude that: (1) the inhibin alpha and beta(A) subunits (and to a lesser extent beta(B)) are expressed in cultured human granulosa-luteal cells; (2) during extended culture periods the alpha/beta(A) mRNA expression ratio decreases; and that (3) the alpha and beta(A) subunit mRNA expression is observed in the granulosa cell compartment of early pregnancy corpora lutea.