Proliferative phase Sertoli cells display a developmentally regulated response to activin in vitro

We have used cultures of highly purified, proliferating rat Sertoli cells collected from d3, 6, and 9 rat pups to investigate the role of activin A on Sertoli cell division. These studies demonstrate that activin A acts directly on d6 and 9, but not d3, Sertoli cells to induce proliferation, both alone and synergistically with FSH. In addition to stimulating proliferation, activin A induces secretion of inhibins A and B as determined by specific ELISAs. We demonstrate that the synergy between activin A and FSH is not due to local actions of secreted inhibin or follistatin. We have used real-time fluorometric RT-PCR to demonstrate that activin regulates expression of activin receptor and follistatin mRNA by Sertoli cells. Saturation binding studies using I-125-activin A indicate that synergy between activin and FSH may be due to increased numbers of activin receptors on the Sertoli cell. Finally, we show that activin A was secreted at high levels by cultured peritubular cells but was undetectable in high purity proliferating Sertoli cell cultures, suggesting that activin A functions as a paracrine factor during postnatal testis development.