Alison Moore

Activins, Inhibins, and Follistatins: Further Thoughts on a Growing Family of Regulators

Abstract Inhibin, a feedback inhibitor of pituitary FSH secretion, and its homodimer, activin, have been the subject of a growing body of literature in the last 5 years. These factors play a role not only in endocrine feedback in the reproductive system but also in paracrine and autocrine regulation of both reproductive and nonreproductive organs, including the liver, kidney, and brain. Additionally, the messages coding for both subunits and their receptors are exquisitely regulated, both spatially and temporally, during embryonic development. The cloning of a family of activin receptors; the development of specific immunoassays for inhibins A and B, and activins A and B; the description of α subunit, β subunit, and receptor loss of function transgenic mouse models; and the cloning of two new β subunit homologs have increased our understanding of the possible roles this complex family of proteins plays in development and endocrine function. This review largely confines itself to the roles of inhibins and activins in the male and female reproductive system, and is intended as an update to a 1992 review published in this journal.

Effects of temperature shift on cell cycle, apoptosis and nucleotide pools in CHO cell batch cultues

Temperature reduction in CHO cell batch culture may be beneficial in the production of recombinant protein and in maintenance of viability. The effects on cell cycle, apoptosis and nucleotide pools were studied in cultures initiated at 37°C and temperature shifted to 30 °C after 48 hours. In control cultures maintained at 37 °C, viable cells continued to proliferate until the termination of the culture, however, temperature reduction caused a rapid decrease in the percent of cells in S phase and accumulation of cells in G-1. This was accompanied by a concurrent reduction in U ratio (UTO/UDP-GNAc), previously shown to be a sensitive indicator of growth rate. Culture viability was extended following temperature shift, as a result of delayed onset of apoptosis, however, once initiated, the rate and manner of cell death was similar to that observed at 37 °C. All nucleotide pools were similarly degraded at the time of apoptotic cell death. Temperature reduction to 30 °C did not decrease the energy charge of the cells, however, the overall rate of metabolism was reduced. The latter may be sufficient to extend culture viability via a reduction in toxic metabolites and/or limitation of nutrient deprivation. However, the possibility remains that the benefits of temperature reduction in terms of both viability and productivity are more directly associated with cultures spending extended time in G-1.

Apoptosis in CHO cell batch cultures: examination by flow cytometry.

Chinese hamster ovary cells grown under conditions which are optimal for the production of a genetically engineered protein in batch culture, lose significant viability shortly after entering the stationary phase. This cell death was investigated morphologically and was found to be almost exclusively via apoptosi. Furthermore, cells were analyzed by flow cytometry using a fluorescent DNA end-labeling assay to label apoptotic cells, in conjunction with cell cycle analysis using propidium iodide. Apoptotic cells could be detected by this method, and by the radioactive end-labeling of extracted DNA, on all days of culture from day 1 to day 7; however, the degree of apoptotic cell death increased dramatically when the cells entered the stationary phase, rising to 50–60% of the total cell number at the termination of the culture. Flow cytometric analysis showed that the majority of cells underwent apoptosis whilst in G1/G0 and formed an apoptotic population with high DNA FITC end-labeling and hypodiploid propidium iodide binding. Additionally, the ability or inability to secrete specific protein products did not appear to interfere with the development of the apoptotic population with time.

Inhibins, activins, their binding proteins and receptors: Interactions underlying paracrine activity in the testis

The inhibin-related peptides are present in the testis from early gestation through adulthood. They are produced from multiple testicular sites in a highly regulated manner, suggesting important paracrine roles. Similarly, receptors for these peptides are located in specific stages of the seminiferous tubule and on particular cell types, and an additional level of control is afforded by specific binding proteins, such as follistatin, which may regulate bioavailability. The actions of these factors include the modulation of interstitial cell function and the increase of spermatogonial proliferation in vitro. It thus appears that activin and inhibin are significant factors in the local control of testicular function.

Inhibin and Activin as Paracrine Regulators of Gonadal Function: In Vitro Model Systems

Inhibin and activin were first described as feedback inhibitors of pituitary function. However, a range of data now supports the hypothesis that these factors play a major role in the paracrine regulation of gonadal function (1, 2). Activin seems to act as a mitogen and morphogen during development. Both inhibin and activin, and their receptors and binding proteins, are also expressed during the normal cycling of the adult ovary (3) and testis. The exact response to these hormones, however, may vary with the developmental stage of the testis or ovary and the stage of the seminiferous or follicular cycle.