Figure 1. Hypothetical mechanism of cooperation between endocrine FSH priming and oocyte paracrine signals to promote EGFR signaling in cumulus cells. The acquisition of EGFR signaling capability by cumulus cells is a developmental hallmark for the COC. Cumulus-oocyte complexes derived from small antral follicles, which have low developmental competence, exhibit under-developed EGFR signaling as they are unresponsive to EGF-peptides (EGF-p). As folliculogenesis progresses, EGFR functionality is induced in COCs by the concerted actions of FSH/cAMP and oocyte-secreted factors (of which BMP15 and GDF9/cumulin have been identified), and is associated with increased oocyte developmental competence. Improved oocyte developmental competence may be facilitated by EGF-peptide stimulation of cumulus cell glycolysis and provision of metabolites (e.g. NAD(P)H) to the oocyte facilitating oocyte mitochondrial activity and energy production needed for development. Figure from Richani and Gilchrist (2018) adapted from Sugimura et al. (2015) with permission.