Oocyte-cumulus cell interaction: a key factor in early embryo development.

The evaluation of oocyte competence is a fundamental step in achieving successful outcomes following assisted reproduction techniques (ART). At present, however, conventional oocyte maturation assessment is carried out by morphological observation, which is a subjective method that does not consider molecular features. For this reason, many authors have proposed cumulus cells (CCs) as biomarkers for oocyte quality, mainly due to their role in the modulation of the physiology and competence of the female gamete. This review summarises our current understanding of the influence of CCs on oocyte physiology and also on the first stages of embryo development. Thus, it includes studies carried out in mammalian species evaluating DNA integrity, viability, gene expression, and profiles of the metabolome and proteome in CCs. While previous research has proposed different CC molecules and features as biomarkers of oocyte functionality and competence, data are, in some cases, inconsistent. For instance, contradictory data have been published regarding the impact of DNA fragmentation, mitochondrial DNA content, or apoptosis in CCs on oocyte maturation and embryo development. On the other hand, looking into gene expression profiles in CCs may reflect oocyte quality, as the expression of several transcripts has been positively associated with oocyte growth and embryo development. Finally, we also point out areas in which more research should be carried out, as is the case for proteomics, telomere length, and metabolomics. This review discusses the most relevant findings not only to better understand the existing relationship between cell types but also to pinpoint the most promising characteristics that could be used as biomarkers.