A FoxL in the Smad house: activin regulation of FSH

Follicle-stimulating hormone (FSH), produced by pituitary gonadotrope cells, is required for maturation of ovarian follicles. The FSHβ subunit is the limiting factor for production of mature hormone and provides biological specificity. Activin dramatically induces FSHβ transcription and the secondary rise in FSH, important for follicular development, is dependent on this induction. Thus, regulation of FSHβ levels by activin is crucial for female reproductive fitness. This review discusses activin signaling pathways, transcription factors and FSHβ promoter elements required for activin responsiveness. Because FoxL2, a forkhead transcription factor, was recently shown to be instrumental in relaying activin signaling to the FSHβ promoter, we focus in this paper on its role and the inter-relatedness of several key players in activin responsiveness on the FSHβ promoter.