A human/bovine comparative approach to identify transcripts related to oocyte maturation: from fertility to aging

Decline aging-oocyte competence and premature ovarian failure (POF) are common factors in human female infertility. In both conditions, follicular senescence and ovarian dysfunctions occur at different speed. Understanding how an immature oocyte transforms into an egg during oocyte maturation is critical for knowledge of fertility and decline-oocyte aging. This process guides the achievement of the final competence essential to fertilization and zygote division, through evolutionary conserved nuclear and cytoplasmatic events. The maturation of mammalian oocyte requires a co-ordinated programme of gene expression events that itself regulates the development of ovarian follicles. Starting from selected genes involved in POF disorders and oocyte aging, we are carrying out a project directed to characterize the expression level of bovine ortologous genes during oocyte maturation. The cow constitutes the best surrogate model for studying reproductive human disorders given the great similarity between the two reproduction systems (such as reproduction cycle, ovulation rate, ovarian maturation, gamete biology, etc.). We assayed systematically the expression level of each transcript in bovine oocytes at different stage of maturation (immature-MI stage and mature-MII stage) coming from young (12 months old) and older animals (13 years old). Oocyte pools (20-100) were collected by puncturing follicles from ovaries of cows and RNA extraction methods were carried out using high recovery rate methods. This presentation showed our preliminary results on those transcripts expressed during meiosis I and II. We believe that they may represent a good starting point to investigate on the presence of specific mRNAs in the former maturation stages and assay how they vary during decline- competence in aging oocyte.