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Gonadotropin-releasing hormone (GnRH) and activin regulate synthesis of FSH and ultimately fertility. Recent  in vivo  studies cast SMAD4 and FOXL2 as master transcriptional mediators of activin signaling that act together and independently of GnRH to regulate  Fshb  gene expression and female fertility. Ovarian hormones regulate GnRH and its receptor (GNRHR) through negative and positive feedback loops. In contrast, the role of ovarian hormones in regulating activin, activin receptors, and components of the activin signaling pathway, including SMAD4 and FOXL2, remains understudied. The widespread distribution of activin and many of its signaling intermediates complicates analysis of the effects of ovarian hormones on their synthesis in gonadotropes, one of five pituitary cell types. We circumvented this complication by using a transgenic model that allows isolation of polyribosomes selectively from gonadotropes of intact females and ovariectomized females treated with or without a GnRH antagonist. This paradigm allows assessment of ovarian hormonal feedback and distinguishes responses that are either independent or dependent on GnRH. Surprisingly, our results indicate that  Foxl2  levels in gonadotropes decline significantly in the absence of ovarian input and independently of GnRH. Expression of the genes encoding other members of the activin signaling pathway are unaffected by loss of ovarian hormonal feedback, highlighting their selective effect on  Foxl2 . Expression of  Gnrhr , a known target of FOXL2, also declines upon ovariectomy consistent with reduced expression of  Foxl2  and loss of ovarian hormones. In contrast,  Fshb  mRNA increases dramatically post-ovariectomy due to increased compensatory input from GnRH. Together these data suggest that ovarian hormones regulate expression of  Foxl2  thereby expanding the number of genes controlled by the hypothalamic-pituitary-gonadal axis that ultimately dictate reproductive fitness.

Maximal Expression of Foxl2 in Pituitary Gonadotropes Requires Ovarian Hormones