Regulation of the FSH receptor in the ovary

The follicle-stimulating hormone receptor (FSHR) is found exclusively on gr anulosa cells from as early as the two-layer or primary stage of folliculog enesis. Up to four alternatively spliced transcripts have been described. A n increase in steady-state levels of FSHR mRNA as well as a change in alter native splicing appear to be important during early folliculogenesis. FSHRs remain on the granulosa cells of healthy follicles until they become atret ic or luteinize, with relatively little change in receptor number per cell. Factors that increase expression are FSH itself, cAMP and its analogs, act ivin and transforming growth factor beta (TGF-beta), whereas epidermal grow th factor (EGF)/TGF-alpha decrease expression. The regulatory regions of th e FSHR gene are more akin to 'housekeeping' genes than to a highly regulate d gene, and there is an E box in the promoter region. Regulation of the ini tial expression of FSHR mRNA at the two-granulosa cell layer stage of folli culogenesis is not understood. It will also be important to understand whet her the alternatively spliced FSHR transcripts and their prevalence in the ovary during early folliculogenesis represent a biologically important phen omenon.