Oocyte-thecal Cell Regulatory Loop in the Control of Preantral Follicle Development

Abstract: Oocyte-somatic cell interaction plays a crucial role in preantral folliculogenesis. Although topical research has focused on oocyte-granulosa cell interaction over the past decade, an oocyte-thecal cell regulatory loop may also play an important role during the preantral stage. Formation of the thecal cell layer is a key event that occurs during preantral folliculogenesis. Granulosal factors (e.g. IGF-I and KL) appear to stimulate the recruitment of thecal cells from stromal cells. Oocyte-derived GDF9 appears to indirectly modulate thecal cell differentiation, perhaps through regulating the granulosa/IGF-I and KL expression. Theca-produced androgens stimulate granulosa cell proliferation and preantral follicle growth. GDF9 enhances preantral follicle growth by up-regulating thecal androgen production, suggesting that a threshold level of androgens derived from thecal cells is necessary for preantral follicle growth, and that the androgen production may be controlled by the oocyte-derived GDF9. T...