Oocyte competence and cumulus cells gene expression

Oocyte competence is the ability of the oocyte to fulfil maturation, undergo successful fertilization, reach the blastocyst stage and yield a healthy baby. Cumulus cells are indispensable for this process. Their removal significantly impairs oocyte maturation and therefore the development outcome. Moreover, the properties and functions of cumulus cells are regulated by the oocyte and thought to reflect its degree of maturation. We believe that the cumulus compartment of a competent oocyte is the site of specific signalling and gene expression events which support and reflect the gamete's quality. Using state of the art molecular biology technologies as microarrays and quantitative real time PCR, as well as gene pathways software analysis, we have focused on the study of cumulus cells gene expression and their relationship with oocyte competence. The first objective of my thesis was to find differentially expressed genes in bovine CCs between three IVM treatments (FSH, PMA, FSH+PMA) collected at 6h of IVM in vitro (GVBD) and associated to variable blastocyst yields. Besides the confirmation of PKC pathway as main player involved in oocyte competence, we report herein a list of commonly overexpressed candidates between the three treatments that have serious chances to be associated with the molecular process of acquisition of competence. The second objective was the analysis of cumulus cells' gene expression induced by LH in vivo. Since the LH surge is crucial to the in vivo final maturation and improves oocyte quality, we have analyzed differentially expressed genes associated with oocyte final maturation at 6 hours after the LH surge (around GVBD). Afterwards, the gene expression at this stage was compared to its corresponding stage in vitro and a common list of potential markers of oocyte competency both in vivo and in vitro was established. The identification of these biomarkers would increase knowledge about gene expression patterns in cumulus cells and would serve as a preamble to understand the crucial events of the oocyte competence acquisition process. These findings could be valuable tool to increase IVF yields in vitro and to optimize ovarian stimulation in vivo for both the bovine and human species. Interestingly and following a comparative analysis of the transcriptional effects of FSH in vitro versus LH in vivo, we report for the first time a possibility of compensation/substitution of LH action by FSH in vitro. The third part of this thesis concern the analysis of gene expression in human cumulus cells harvested prior to ICSI in order to identify reliable genomic biomarkers that accurately and noninvasively predict the oocyte developmental competence and reinforce the already used morphological criteria. Seven genes were differentially (p < 0.05) associated to both successful pregnancy and implantation under similar morphological and zona pellucidae birefringence parameters. These biomarkers are quantitative and non-invasive tools that could be used to discriminate amongst good morphology embryos the one that has best chances to achieve a successful pregnancy. Ultimately, these biochemical markers and their associated signalling pathways in both bovine and human species increased the knowledge of gene expression patterns in cumulus cells, which would yield insights into the molecular pathways controlling oocyte competence and would serve as a preamble to the understanding of crucial events in subsequent fertilization and early embryonic development.