Inhibins and Activins

Publisher Summary This chapter discusses the isolation, structure, characterization, and biosynthesis of inhibins and activins. The two pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) which regulate the development and maturation of the gonad, are identified. The ability to quantitate FSH and LH in serum revives the inhibin concept, which offers an explanation for the differential regulation of FSH and LH release often observed in humans and experimental animals. Inhibin activity is monitored by an in vitro bioassay using rat anterior pituitary cells in monolayer culture. The message encoding each of the subunits of the inhibins is cloned from porcine and bovine ovarian complementary DNA (cDNA) libraries. DNA sequence analysis shows that the inhibin a subunit is initially synthesized as a large precursor protein with potential N-linked glycosylation sites. The two β subunits are also found to be derived from large polypeptide precursors and cleavage at the processing sites to yield the mature β subunits at the carboxy termini of the precursors. Using the porcine cDNAs as hybridization probes, the human and murine inhibin subunit precursors are also cloned and sequenced.