Inhibitory effects of bone morphogenetic proteins (BMPs) on hen granulosa cell differentiation

Prior to follicle selection, granulosa cells are actively maintained in an undifferentiated state by epidermal growth factor ligands (EGFL) that signal via the mitogen activated protein kinase (MAPK)/extracellular regulated kinase (Erk) pathway inhibiting follicle stimulating hormone receptor (FSHR). At the time of follicle selection, there is a release from inhibitory MAPK/Erk signaling initiating granulosa cell differentiation, causing an increase in FSHR in one selected follicle. The present study was conducted in cultured granulosa cells from prehierarchal follicles, and it was found that the effects of bone morphogenetic protein 2 (BMP2) on granulosa cells promote EGFL expression while inhibiting Fshr expression, by either promoting or inhibiting indvidual Id isoform expression. The inhibitory actions of BMP2 on Fshr expression were neutralized by treatment of granulosa cells with the BMP antagonist, Noggin. In conclusion, prior to follicle selection, BMP2 and EGFL act cooperatively to prevent the premature differentiation of hen granulosa cells.