Multiple ovulations are uncommon in humans, cattle and many breeds of sheep. Pituitary gonadotrophins and as yet unidentified ovarian factors precisely regulate follicular development so that, normally, only one follicle is selected to ovulate. The Inverdale (FecXI) sheep, however, carries a naturally occurring X-linked mutation that causes increased ovulation rate and twin and triplet births in heterozygotes (FecXI/FecX+; ref. 1), but primary ovarian failure in homozygotes (FecXI/FecXI; ref. 2). Germ-cell development, formation of the follicle and the earliest stages of follicular growth are normal in FecXI/FecXI sheep, but follicular development beyond the primary stage is impaired. A second family unrelated to the Inverdale sheep also has the same X-linked phenotype (Hanna, FecXH). Crossing FecXI with FecXH animals produces FecXI/FecXH infertile females phenotypically indistinguishable from FecXI/FecXI females. We report here that the FecXI locus maps to an orthologous chromosomal region syntenic to human Xp11.2-11.4, which contains BMP15, encoding bone morphogenetic protein 15 (also known as growth differentiation factor 9B (GDF9B)). Whereas BMP15 is a member of the transforming growth factor beta (TGFbeta) superfamily and is specifically expressed in oocytes, its function is unknown. We show that independent germline point mutations exist in FecXI and FecXH carriers. These findings establish that BMP15 is essential for female fertility and that natural mutations in an ovary-derived factor can cause both increased ovulation rate and infertility phenotypes in a dosage-sensitive manner.

The aim of this study was to test the hypothesis that both growth differential factor 9 (GDF9) and bone morphogenetic protein (BMP15; also known as GDF9B) are essential for normal ovarian follicular development in mammals with a low ovulation rate phenotype. Sheep (9-10 per group) were immunized with keyhole limpet hemocyanin (KLH; control), a GDF9-specific peptide conjugated to KLH (GDF9 peptide), a BMP15-specific peptide conjugated to KLH (BMP15 peptide), or the mature region of oBMP15 conjugated to KLH (oBMP15 mature protein) for a period of 7 mo and the effects of these treatments on various ovarian parameters such as ovarian follicular development, ovulation rate, and plasma progesterone concentrations evaluated. Also in the present study, we examined, by immunohistochemistry, the cellular localizations of GDF9 and BMP15 proteins in the ovaries of lambs. Both GDF9 and BMP15 proteins were localized specifically within ovarian follicles to the oocyte, thereby establishing for the sheep that the oocyte is the only intraovarian source of these growth factors. Immunization with either GDF9 peptide or BMP15 peptide caused anovulation in 7 of 10 and 9 of 10 ewes, respectively, when assessed at ovarian collection. Most ewes (7 of 10) immunized with oBMP15 mature protein had a least one observable estrus during the experimental period, and ovulation rate at this estrus was higher in these ewes compared with those immunized with KLH alone. In both the KLH-GDF9 peptide- and KLH-BMP15 peptide-treated ewes, histological examination of the ovaries at recovery (i.e., approximately 7 mo after the primary immunization) showed that most animals had few, if any, normal follicles beyond the primary (i.e., type 2) stage of development. In addition, abnormalities such as enlarged oocytes surrounded by a single layer of flattened and/or cuboidal granulosa cells or oocyte-free nodules of granulosa cells were often observed, especially in the anovulatory ewes. Passive immunization of ewes, each given 100 ml of a pool of plasma from the GDF9 peptide- or BMP15 peptide-immunized ewes at 4 days before induction of luteal regression also disrupted ovarian function. The ewes given the plasma against the GDF9 peptide formed 1-2 corpora lutea but 3 of 5 animals did not display normal luteal phase patterns of progesterone concentrations. The effect of plasma against the BMP15 peptide was more dramatic, with 4 of 5 animals failing to ovulate and 3 of 5 ewes lacking surface-visible antral follicles at laparoscopy. By contrast, administration of plasma against KLH did not affect ovulation rate or luteal function in any animal. In conclusion, these findings support the hypothesis that, in mammals with a low ovulation rate phenotype, both oocyte-derived GDF9 and BMP15 proteins are essential for normal follicular development, including both the early and later stages of growth.

The oocyte-secreted polypeptide growth factors, growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15, also known as GDF9B) have both been shown to be essential for ovarian follicular growth and function. The effects of murine (m) and ovine (o) GDF9 as well as oBMP15, alone or together, on 3 H-thymidine uptake and progesterone and inhibin production by granulosa cells from rats were determined. Murine GDF9 stimulated thymidine incorporation by granulosa cells whereas oGDF9 and oBMP15 alone had no effect. However, oBMP15 given together with mGDF9 or oGDF9 was very potent in stimulating 3 H-thymidine incorporation by granulosa cells with a greater than 3-fold stimulation compared with any growth factor alone. The synergistic effect of oBMP15 and oGDF9 was almost completely blocked by antibodies generated against these growth factors when administered either alone or in combination. While neither GDF9 (murine or ovine) nor oBMP15 were able to modulate FSH-stimulated progesterone production on their own, FSH-stimulated progesterone production by granulosa cells was potently inhibited when BMP15 and GDF9 were administered together. Immunoreactive ainhibin levels increased more than 15-fold from granulosa cells when BMP15 and GDF9 were given together whereas consistent stimulatory effects of either growth factor alone were not observed. The effects of GDF9 and BMP15, when added together, were different than those observed for the growth factors alone. Therefore, we hypothesize that within the ovary, these oocyte-secreted growth factors co-operate to regulate proliferation and gonadotropin-induced differentiation of granulosa cells in mammals.Reproduction (

The oocyte-secreted polypeptide growth factors, growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15, also known as GDF9B) have both been shown to be essential for ovarian follicular development and ovulation rate. In addition, it is known from both in vivo and in vitro studies that these factors co-operate in some manner. To date, most studies examining the in vitro effects of these growth factors have used the rodent model. However, the evidence suggests that these growth factors have somewhat different roles between rodents and ruminants. Therefore, the objectives of these studies were to examine the effects of GDF9 and BMP15, alone and together, on the functions of ovine and bovine granulosa cells under in vitro conditions. Ovine (o)BMP15 given together with murine (m)GDF9 or oGDF9 was more potent in stimulating 3 H-thymidine incorporation by ovine granulosa cells compared with each growth factor alone. For bovine granulosa cells, there appeared to be little or no co-operativity between oBMP15 and oGDF9 as oBMP15 alone was as potent as any combination of the two growth factors in stimulating 3 H-thymidine uptake. The species of origin of GDF9 affected the progesterone response in ovine granulosa cells with mGDF9 stimulating and oGDF9 inhibiting progesterone production. Ovine BMP15 alone had no effect on progesterone production by ovine granulosa cells and these growth factors did not appear to co-operate. FSH-stimulated progesterone production by bovine granulosa cells was most potently inhibited when oBMP15 and murine or ovine GDF9 were administered together. As was observed for progesterone, the species of origin of GDF9 affected inhibin production by ovine granulosa cells where mGDF9 inhibited while oGDF9 stimulated production. Murine GDF9 also inhibited inhibin production from bovine granulosa cells. For both ovine and bovine granulosa cells, BMP15 alone had no effect on inhibin production and there did not appear to be any co-operation between GDF9 and BMP15. These results indicate that the effects of BMP15 and GDF9 varied with respect to the species of origin of the growth factor. Moreover, the effects of GDF9 and BMP15 together were often co-operative and not always the same as those observed for these growth factors alone.Reproduction (

Growth differentiation factor-9 (GDF-9) is a transforming growth factor-b (TGF-b) family member which is expressed in the oocytes in mouse ovaries (McGrath, S.A., Esquela, A.F., Lee, S.J., 1995. Oocyte-specific expression of growth/differentiation factor-9. Mol. Endocrinol. 9, 131-136). GDF-9 is indispensable for normal folliculogenesis since female mice deficient for the GDF-9 gene are infertile due to an arrest of follicular growth at the primary follicle stage (Dong, J., Albertini, D.F., Nishimori, K., Kumar, T.R. , Lu, N., Matzuk, M.M., 1996. Growth differentiation factor-9 is required during early ovarian folliculogenesis. Nature 383, 531-535). We searched the GenBank Expressed Sequence Tag (EST) database with the mouse GDF-9 cDNA sequence, and identified from a mouse 2-cell embryo library an EST cDNA that encodes a putative member of the TGF-b superfamily, and named it as GDF-9B. Northern blot hybridization analyses of mouse ovaries revealed a single transcript of approximately 4.0 kilobases (kb) for GDF-9B and of 2.0 kb for GDF-9. We cloned by reverse transcription-polymerase chain reaction from mouse ovarian RNA a partial 821-base pair GDF-9B cDNA that spans the sequence encoding the putative mature region of GDF-9B. The COOH-terminal region of GDF-9B appears to be 53% homologous to GDF-9. Moreover, like GDF-9, GDF-9B lacks the cysteine residue needed for the covalent dimerization of several TGF-b family members. Using in situ hybridization analysis, we demonstrate that GDF-9B and GDF-9 mRNAs are co-localized in the oocyte. We also show that GDF-9B and GDF-9 genes are co-ordinately expressed during follicular development.