Abstract
Cumulus cells play an essential role during oocyte maturation and the acquisition of fertilizability and developmental competence. Micro(mi)RNAs can post-transcriptionally regulate mRNA expression, and we hypothesized that miRNA profiles in cumulus cells could serve as an indicator of oocyte quality. Cumulus cell biopsies from cumulus−oocyte−complexes that either yielded a blastocyst or failed to cleave after exposure to sperm cells were analyzed for miRNA expression. On average, 332 miRNA species with more than 10 reads and 240 miRNA species with more than 50 reads were identified in cumulus cells; this included nine previously undescribed microRNAs. The most highly expressed miRNAs in cumulus cells were miR-21, members of the let-7 family and miR-155. However, no repeatable differences in miRNA expression between the cumulus cells from oocytes that became blastocysts versus those from non-cleaved oocytes were identified. Further examination of individual cumulus cell samples showed a wide variability in miRNA expression level. We therefore conclude that miRNA expression in cumulus cells cannot be used as an oocyte quality marker.
Highlights
Mammalian oocytes acquire the capacity to become fertilized and acquire developmental competence during their final maturation within the ovary
In order to identify miRNA species expressed in cumulus cells that could potentially predict quality of the enclosed oocyte, cumulus biopsies were obtained from COCs after in vitro maturation
Cumulus cells surrounding an oocyte that did not cleave after sperm exposure or developed into a blastocyst were chosen, to have the two most different stages to see a change in miRNA expression
Summary
Mammalian oocytes acquire the capacity to become fertilized and acquire developmental competence during their final maturation within the ovary. These oocytes originate from female primordial germ cells that proliferated while migrating towards the gonadal ridges and continue to proliferate until gonadal sex differentiation. After the resumption of meiosis and in addition to chromosome segregation, the oocyte needs to redistribute organelles and proteins in a process known as cytoplasmic maturation [4]. For these processes, the oocyte relies on molecules present within the follicular fluid and on intimate contact with the somatic cells that surround the oocyte, known as cumulus cells. From in vitro maturation and fertilization experiments, it has become clear that large differences exist between the quality of oocytes, and it seems likely that cumulus cells are at least partly responsible for the oocyte quality
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