ABSTRACT
During folliculogenesis, the granulosa cells differentiate into two cell types: cumulus cells (CCs) and mural granulosa cells (MGCs). The objective of the study was to generate and compare the transcriptomes of MGCs and CCs from the pre-ovulatory follicle to characterize the detailed profile of the two cell populations shortly before ovulation. Twenty-one IVF/ICSI patients undergoing controlled ovarian stimulation (COS) donated CCs and MGCs from individual follicles containing metaphase II oocytes. Cells were prepared immediately after recovery and mRNA was isolated for whole-genome gene expression analysis and reverse transcriptase-polymerase chain reactions. Paired (within the individual follicle) comparisons between the CC and MGC expression profiles were performed and corrected for multiple comparisons. A total of 1562 genes were differentially expressed by >2-fold (P < 0.01) in the two cell types. Of these, 156 genes were >8-fold changed and represented specialized cellular functional categories such as inflammatory response, extracellular matrix and cell-cell communication, whereas the 1406 genes were 2-8-fold changed and represented functional categories such as proliferation and lipid metabolism. Transcripts not previously linked to the follicle were found to be differentially expressed between CCs and MGCs, suggesting specialized function in these compartments, e.g. pepsinogen A was selectively expressed in MGCs, whereas ryanodine receptor-2 (RYR2) was selectively expressed in CCs. Positive correlations were present between expression levels of RYR2 and the amphiregulin and gap-junction proteins. In conclusion, the transcriptomes of corresponding CCs and MGCs from individual pre-ovulatory follicles clearly revealed two distinct cell types. New as well as known genes representing specific cell functions close to ovulation were highlighted.
