Tight gene co-expression between oocyte and surrounding cumulus is critical for oocyte developmental competence

The BCB+ oocytes are twice as likely to produce a blastocyst in vitro compared to BCB- oocytes (P<0.01). We analyzed mitochondrial DNA (mtDNA) copy number in single oocytes and determined that BCB- oocytes have 1.3-fold more copies than BCB+ oocytes (P=0.004). We also interrogated the transcriptome of oocytes and surrounding cumulus cells of BCB+ versus BCB- oocytes. There was no differential transcript abundance of genes expressed in oocytes, but we identified 172 genes in cumulus cells with differential transcript abundance (FDR<0.05) based on the BCB staining of their oocyte. Differential gene co-expression analysis between BCB+ and BCB- oocytes and their surrounding cumulus cells revealed dynamic coordination of transcript abundance between both compartments of the cumulus-oocyte complex. We identified a subset of genes whose co-expression in fully grown oocytes (n=75) and their surrounding cumulus cells (n=108) compose a unique profile of the cumulus-oocyte complex. In conclusion, as oocytes transition from growing to fully grown, there is an increase in the likelihood of producing a blastocyst, a reduction of mtDNA copies and no systematic variation of transcript abundance. Cumulus cells present changes in transcript abundance, which reflects in a dynamic co-expression between oocyte and cumulus cells.