Gonadotropin Signaling in the Ovary

In this chapter we review current knowledge about the signaling pathways by which FSH promotes ovarian follicle maturation and LH promotes ovulation, oocyte maturation, and corpus luteum formation. We focus on FSH signaling pathways identified in granulosa cells of immature preantral follicles, addressing the question of the sufficiency of protein kinase A as the mediator of the actions of FSH. We also focus on LH signaling pathways identified in granulosa and theca cells of mature preovulatory follicles. We review how FSH and LH signaling pathways activate or inhibit transcriptional factors to regulate gene expression. Throughout this chapter we highlight the observations that these gonadotropins are structurally related, act on similar G- protein-coupled receptors, and signal predominantly through cAMP-dependent mechanisms, yet FSH and LH elicit very different responses in preantral versus preovulatory granulosa cells. We also indicate gaps in knowledge of the mechanisms by which FSH and LH regulate follicle maturation. Emphasis is placed on studies of the rodent, although examples from other species are also discussed.