Induction of Cyclin D2 in Rat Granulosa Cells Requires FSH-dependent Relief from FOXO1 Repression Coupled with Positive Signals from Smad

Ovarian follicles undergo exponential growth in response to follicle-stimulating hormone (FSH), largely as a result of the proliferation of granulosa cells (GCs). In vitro under serum-free conditions, rat GCs differentiate in response to FSH but do not proliferate unless activin is also present. In the presence of FSH plus activin, GCs exhibit enhanced expression of cyclin D2 as well as inhibin-α, aromatase, steroidogenic factor-1 (SF-1),...