Mode of oocyte maturation affects EGF-like peptide function and oocyte competence

Abstract

The function and impact of epidermal growth factor (EGF)-like peptide signalling during ovulation and in vivo oocyte maturation (IVV) has been recently characterized, however, little is currently known about the effect of oocyte in vitro maturation (IVM) on this pathway. The aim of this study was to examine expression and functional aspects of three EGF-like peptides (amphiregulin, epiregulin and betacellulin) and their common receptor (EGFR) in cumulus cells during mouse oocyte IVM compared with IVV. Cumulus–oocyte complexes (COCs) were collected from prepubertal mice either 46 h post-eCG (IVM) or 46 h post-eCG plus 0.5–12 h post-hCG (IVV). Time course experiments showed mRNA expression of all three EGF-like peptides and amphiregulin protein in IVM media were significantly lower for the majority of FSH-supplemented IVM compared with IVV. The supplementation of EGF during IVM yielded EGF-like peptide expression levels comparable with IVV and amphiregulin/epiregulin supplemented IVM. However, despite this, EGF activation of the COC EGFR remained significantly lower at 3 and 6 h of IVM than in vivo, and levels were similar to those observed during FSH-supplemented IVM. The addition of exogenous epiregulin during IVM significantly increased blastocyst rates, and epiregulin and amphiregulin improved blastocyst quality, compared with FSH or EGF. In conclusion, findings from this study suggest that the widely used IVM additives, FSH and EGF, are inadequate propagators of the essential EGF-like peptide signalling cascade. In contrast, the use of epiregulin and/or amphiregulin during IVM leads to improved oocyte developmental competence and therefore may be preferable IVM additives than FSH or EGF.