Oocyte-expressed TGF-beta superfamily members in female fertility

Folliculogenesis is regulated by the interplay of extraovarian and intraova rian factors, and the importance of each type of regulation varies dependin g on the developmental stage of the follicle. Preantral follicle developmen t is regulated predominantly by factors produced locally within the ovary a nd within the follicle itself. The oocyte has been shown to produce soluble factor(s), which regulate a number of processes in follicular development, including cumulus expansion in the periovulatory period. Members of the TG F beta superfamily are potent regulators of cell proliferation and differen tiation in a number of organ systems, and three members, growth differentia tion factor 9 (GDF-9), bone morphogenetic protein 15 (BMP-15) and BMP-6 are expressed by the oocyte and may mediate effects attributed to the oocyte. Based on knockout mouse models BMP-6 does not play an essential role in ova rian function, but GDF-9 is absolutely required for preantral follicle deve lopment. GDF-9 also alters the periovulatory expression of granulosa cell g enes and stimulates cumulus expansion. Although BMP-15 is expressed identic ally to GDF-9, its role in regulating ovarian function is still unknown. Th is review examines the similarities and differences in sequence, expression , and function of the oocyte-expressed TGF beta family members with respect to regulating folliculogenesis. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.