RESUMEN

The advancement of folliculogenesis is coincident with the sequential acquisition of oocyte developmental competence. In practical bovine/porcine ART, cumulus-oocyte complexes (COCs) aspirated from small antral follicles have low developmental competence relative to COCs from medium/large antral follicles, as evidenced by a poor capacity to support embryogenesis up to the blastocyst stage. This is in part because of incomplete differentiation of cumulus cells in small antral follicles, in particular under-developed functionality of EGF signalling. Gonadotrophins and oocyte-secreted paracrine factors cooperate to establish EGF receptor functionality in cumulus cells, which appears to be involved in the acquisition of oocyte developmental competence. Here we review the modification of follicular cumulus cells during antral folliculogenesis involved in oocyte developmental competence.

RESUMEN

CONTEXT: Bone morphogenetic protein (BMP)15 is an oocyte-specific growth factor, which, together with growth differentiation factor (GDF) 9, regulates folliculogenesis and ovulation rate. Multiple mutations in BMP15 have been identified in women with primary ovarian insufficiency (POI), supporting a pathogenic role; however, the underlying biological mechanism of many of these mutants remains unresolved. OBJECTIVES: To determine how mutations associated with ovarian dysfunction alter the biological activity of human BMP15. DESIGN: The effects of 10 mutations in BMP15 on protein production, activation of granulosa cells, and synergy with GDF9 were assessed. RESULTS: Sequencing of 35 patients with POI identified both an unrecognized BMP15 variant (c.986G>A, R329H) and a variant (c.581T>C, F194S) previously associated with the condition. Assessing expression and activity of these and 8 other BMP15 mutants identified: (1) multiple variants, including L148P, F194S, and Y235C, with reduced mature protein production; (2) three variants (R138H, A180T, and R329H) with ∼fourfold lower activity than wild-type BMP15; and (3) 3 variants (R68W, F194S, and N196K) with a significantly reduced ability to synergize with GDF9. CONCLUSIONS: Mutations in BMP15 associated with POI reduce mature protein production, activity, or synergy with GDF9. The latter effect is perhaps most interesting given that interactions with GDF9 most likely underlie the physiology of BMP15 in the human ovary.

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RESUMEN

Bone morphogenetic protein 15 (BMP15) and members of the fibroblast growth factor (FGF) family are expressed by the oocyte and are involved in the control of cumulus cell function. We tested the hypothesis that FGF17, alone or combined with BMP15 in the maturation medium, enhances cumulus expansion, meiosis progression, embryonic development, and expression of mRNA encoding key genes regulating expansion (prostaglandin-endoperoxide synthase 2 [PTGS2], hyaluronan synthase 2 [HAS2], tumor necrosis factor-stimulated gene 6 [TNFAIP6], and pentraxin 3 [PTX3]) and markers of oocyte developmental competence (phosphofructokinase [PFKP], gremlin [GREM1], versican [VCAN], and the genomic progesterone receptor [nPR]) in cumulus cells. Fibroblast growth factor 17 and BMP15 increased the percentage of fully expanded cumulus-oocyte complexes (COCs), but there was no additive effect when both were combined. Neither FGF17 nor BMP15 altered the percentage of oocytes reaching meiosis II at the end of COC culture or cleavage and blastocyst rates after IVF. However, embryo quality, as assessed by the number of cells in the inner cell mass, was improved by the combination of FGF17 with BMP15. Fibroblast growth factor 17 alone did not alter gene expression in cumulus cells at the end of IVM, whereas BMP15 increased PTGS2 and PTX3 mRNA levels. The combination of FGF17 and BMP15 increased nPR mRNA abundance in cumulus cells but did not change the expression of other markers of developmental competence. This study provides novel evidence that FGF17 enhances cumulus expansion in bovine COCs submitted to IVM and that the supplementation of the IVM medium with FGF17 and BMP15 may improve embryo quality.

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RESUMEN

Oocyte-secreted factors (OSFs) regulate differentiation of cumulus cells and are of pivotal relevance for fertility. Bone morphogenetic protein 15 (BMP15) and fibroblast growth factor 10 (FGF10) are OSFs and enhance oocyte competence by unknown mechanisms. We tested the hypothesis that BMP15 and FGF10, alone or combined in the maturation medium, enhance cumulus expansion and expression of genes in the preovulatory cascade and regulate glucose metabolism favouring hyaluronic acid production in bovine cumulus-oocyte complexes (COCs). BMP15 or FGF10 increased the percentage of fully expanded COCs, but the combination did not further stimulate it. BMP15 increased cumulus cell levels of mRNA encoding a disintegrin and metalloprotease 10 (ADAM10), ADAM17, amphiregulin (AREG), and epiregulin (EREG) at 12 h of culture and of prostaglandin (PG)-endoperoxide synthase 2 (PTGS2), pentraxin 3 (PTX3) and tumor necrosis factor alpha-induced protein 6 (TNFAIP6 (TSG6)) at 22 h of culture. FGF10 did not alter the expression of epidermal growth factor-like factors but enhanced the mRNA expression of PTGS2 at 4 h, PTX3 at 12 h, and TNFAIP6 at 22 h. FGF10 and BMP15 stimulated glucose consumption by cumulus cells but did not affect lactate production or levels of mRNA encoding glycolytic enzymes phosphofructokinase and lactate dehydrogenase A. Each growth factor increased mRNA encoding glucosamine:fructose-6-PO4 transaminases, key enzymes in the hexosamine pathway leading to hyaluronic acid production, and BMP15 also stimulated hyaluronan synthase 2 (HAS2) mRNA expression. This study provides evidence that BMP15 and FGF10 stimulate expansion of in vitro-matured bovine COCs by driving glucose metabolism toward hyaluronic acid production and controlling the expression of genes in the ovulatory cascade, the first acting upon ADAM10, ADAM17, AREG, and EREG and the second on downstream genes, particularly PTGS2.

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