PARENT SESSION
STATE-OF-THE-ART LECTURES
Tuesday, July 31, 2001, 4:15 PM-6:15 PM
Westin-Ballroom
Chair: Barbara Sanborn, President, SSR
Speakers: Robert E Braun, Teresa K Woodruff
SA2
MECHANISMS OF INHIBIN AND ACTIVIN ACTION.
Woodruff, Teresa1, 1
ABSTRACT- Activin and inhibin are important molecules that regulate hormonogenesis, cellular homeostasis (divide or die pathways), and differentiation programs (developmentally and in adult cells). The cellular mechanisms that integrate inhibin or activin signals into a physiological response include a multi-component receptor complex, intracellular signal mediators, and nuclear transcription factors. Correct execution of inhibin and activin cues permits actions as fundamental as embryonic mesoderm development, neuronal survival, hematopoietic function, and reproductive cyclicity. Absent or incorrect ligand signaling results in phenotypes as catastrophic as embryonic lethality, tumor formation, and infertility. The general ways in which a cell senses and responds to both inhibin and activin signals are becoming more clear as receptors and accessory proteins are identified and characterized. For example, a membrane-anchored proteoglycan with affinity for inhibin has been identified. The full-length cDNA predicts a 1336 amino acid glycoprotein. Full-length inhibin binding protein (InhBP) cDNAs were isolated from human testis RNA. Two InhBP mRNA transcripts of 4.6 kb and 2 kb are detected in rat pituitary by RNA blot analysis. InhBP immunostaining is coincident with FSHb immunopositive gonadotrope cells in rat pituitary and is regulated in a cycle-dependent manner. InhBP staining is intense in the testicular Leydig cells. This cell type binds iodinated inhibin but not iodinated activin. In summary, key components in the signal transduction pathway for inhibin and activin have been identified and can now be used to determine the mechanism of hormone action in a variety of target tissues.
KEY WORDS: activin, inhibin, pituitary, ovary