Characterization of the human cumulus cell transcriptome during final follicular maturation and ovulation

Purpose: The goal of this study was to identify differentially expressed genes and pathways between the cumulus of compact/unstimulated cumulus-oocyte-complex (COC) and the cumulus of expanded/stimulated COC. Methods: mRNA profiles of Compact/unstimulated cumulus cells (CCs) from germinal vesicle (GV) COC obtained from two patients undergoing unstimulated IVM procedure and expanded/stimulated CCs from metaphase 2 (MII) COC obtained from three patients undergoing IVF/ICSI were generated by deep sequencing using Illumina HiSeq 2000. The sequence reads that passed quality filters were mapped to the human genome (hg19) using Tophat software. Differential expression analysis was done using DESeq bioconductor package. qRT–PCR validation was performed using SYBR Green assays. Results: A total of 40-80 million sequence reads per sample were mapped to the human genome (hg19). A total of 1746 differentially expressed genes between compact and expanded CCs with fold change > 2, and adjusted p value < 0.05 were identified. Gene ontology analysis of differentially expressed genes revealed a number of cellular processes regulated during the periovulatory interval including cellular movement, inflammatory response, immune cell trafficking, tissue development, lipid metabolism, tissue morphology, DNA replication and cell cycle. A total of 116 of the differentially expressed genes were annotated as long non-coding RNAs, 10 of them coded from introns of genes known to be involved in granulosa cell processes suggesting that unique non coding RNA transcripts may contribute to the regulation of cumulus expansion and oocyte maturation. Results were validated using qRT-PCR. Conclusions: Using global transcriptome sequencing we identified new important genes and non coding RNAs involved in COC maturation and cumulus expansion, which may contribute to improve the process of in vitro maturation of immature oocytes utilized in IVM cycles Overall design: mRNA profiles of Compact/unstimulated cumulus cells (CCs) from germinal vesicle (GV) COC obtained from two patients undergoing unstimulated IVM procedure and expanded/stimulated CCs from metaphase 2 (MII) COC obtained from three patients undergoing IVF/ICSI were generated by deep sequencing using Illumina HiSeq 2000.