Synergistic roles of BMP15 and GDF9 in the development and function of the oocyte–cumulus cell complex in mice: genetic evidence for an oocyte–granulosa cell regulatory loop

Abstract

Bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are oocyte-specific growth factors that appear to play key roles in granulosa cell development and fertility in most mammalian species. We have evaluated the role(s) of these paracrine factors in the development and function of both the cumulus cells and oocytes by assessing cumulus expansion, oocyte maturation, fertilization, and preimplantation embryogenesis in Gdf9+/-Bmp15-/- [hereafter, double mutant (DM)] mice. We found that cumulus expansion, as well as the expression of hyaluronon synthase 2 (Has2) mRNA was impaired in DM oocyte-cumulus cell complexes. This aberrant cumulus expansion was not remedied by coculture with normal wild-type (WT) oocytes, indicating that the development and/or differentiation of cumulus cells in the DM, up to the stage of the preovulatory luteinizing hormone (LH) surge, is impaired. In addition, DM oocytes failed to enable FSH to induce cumulus expansion in WT oocytectomized (OOX) cumulus. Moreover, LH-induced oocyte meiotic resumption was significantly delayed in vivo, and this delayed resumption of meiosis was correlated with the reduced activation of mitogen-activated protein kinase (MAPK) in the cumulus cells, thus suggesting that GDF9 and BMP15 also regulate the function of cumulus cells after the preovulatory LH surge. Although spontaneous in vitro oocyte maturation occurred normally, oocyte fertilization and preimplantation embryogenesis were significantly altered in the DM, suggesting that the full complement of both GDF9 and BMP15 are essential for the development and function of oocytes. Because receptors for GDF9 and BMP15 have not yet been identified in mouse oocytes, the effects of the mutations in the Bmp15 and Gdf9 genes on oocyte development and functions must be produced indirectly by first affecting the granulosa cells and then the oocyte. Therefore, this study provides further evidence for the existence and functioning of an oocyte-granulosa cell regulatory loop.

Temporal regulation of BMP2, BMP6, BMP15, GDF9, BMPR1A, BMPR1B, BMPR2 and TGFBR1 mRNA expression in the oocyte, granulosa and theca cells of developing preovulatory follicles in the pig

“…However, the upregulation of BMPR1B mRNA in the GC and TC during the same period, accompanied by a similar increase in BMPR1B protein in follicle hemisections, suggests that the oocyte-derived BMP15 may play a key role in the periovulatory period in the pig follicle. This is in accordance with the phenotype observed in Bmp15 null mice where no apparent defects in follicular development were observed; but ovulation rate was lower and the ovulated oocytes showed reduced developmental potential (Yan et al 2001, Su et al 2004. Interestingly, the Bmpr1b null mice exhibited defects in cumulus expansion which, in turn, prevented in vivo fertilization (Yi et al 2001).…”

The promoter of the oocyte-specific gene, Gdf9, is active in population of cultured mouse embryonic stem cells with an oocyte-like phenotype

“…Gdf9 is an oocyte-specific gene that is expressed in ovarian follicles beginning at the primary follicle stage, when the oocyte is surrounded by a single layer of cuboidal granulosa cells [17]. To establish the ability of this oocyte-specific gene promoter to drive expression of eGFP specifically in oocytes of ES cell-derived ovarian follicles, we transfected a plasmid [14] , in which eGFP is expressed under control of a 3.1 kilobase (kb) region of the Gdf9 promoter, into JM21 XX ES cells.…”

Selected molecular and physiological aspects of mammalian ovarian granulosa cells in primary culture

“…Cumulus expansion is tightly connected with production of a mucified matrix that is crucial for ovulation (7). The OC is responsible for induction of cumulus expansion after the LH surge by secretion of cumulus expansion enabling factors (CEEFs), which likely include GDF-9 and/or BMP-15 (47). Expansion of cumulus GCs is tightly connected with formation of the cumulus-oocyte complex (COC).…”