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.

Failure to launch: aberrant cumulus gene expression during oocyte in vitro maturation

“…Amphiregulin promotes receptor recycling to epithelial cell membranes, while EGF and BTC traffic the receptor to lysosomes for degradation (Roepstorff et al 2009), which will truncate signal duration and blunt the cell's capacity to respond to other EGF-L whether exogenously added or endogenously produced. This outcome is consistent with what has been described for EGFR Tyr 1068 phosphorylation in IVM COC, which show a sharp rapid induction, but premature downregulation (Richani et al 2013). Finally, some of the EGF-L ligand's signalling is modulated by heparan sulphate proteoglycans on the cell surface or the local ECM environment.…”

“…Deficient expression of EGF-L factors in IVM has been confirmed in a number of subsequent studies (Richani et al 2013(Richani et al , 2014b. Additionally, Versican is another factor with demonstrated EGFlike activity in COC , which was also reduced in IVM compared to in vivo COCs as has been previously demonstrated (Dunning et al 2007).…”

“…This may promote a specific temporal pattern of signalling in the COC which is difficult to replicate in IVM and the physiological importance of this sequence for full oocyte developmental potential is unknown. Supplementation of IVM cultures with EGF promotes EGF-L mRNA expression to levels quantitatively similar to in vivo COCs, yet levels of EGF receptor phosphorylation at Tyrosine Tyr 1068 remain generally lower than in vivo and differ in temporal kinetics (Richani et al 2013). Variable responses to the different EGF-L ligands are mediated in part through interaction with distinct receptors or receptor complexes.…”

“…An alternative IVM technology that uses a prematuration treatment to elevate cAMP before stimulating COC with FSH and/or EGF, improved oocyte competence in cows (Albuz et al 2010) and mice (Zeng et al 2014) and enhances EGF-L peptide expression (Richani et al 2013(Richani et al , 2014b. However, ERK1/2 phosphorylation, which is a downstream consequence of EGF-L activity, was not different (Richani et al 2013(Richani et al , 2014b.…”

Oocyte maturation and quality: role of cyclic nucleotides

“…The increased developmental competence of cAMP-mediated IVM oocytes may in part be attributable to the impact of cAMP on EGF pathway signalling in CCs. Standard IVM conditions (including with FSH) exhibit perturbed CC expression of EGF-p relative to those matured in vivo (Richani et al 2013), leading to alterations in COC glucose metabolism and decreased oocyte mitochondrial activity (Richani et al 2014a). Cyclic AMP elevation using forskolin leads to a large, but very transient, increased expression of CC amphiregulin, epiregulin and betacellulin compared with unstimulated or IBMX-treated COCs (Richani et al 2014b).…”