NUCLEAR AND CYTOPLASMIC DETERMINANTS INVOLVED IN THE REGULATION OF MAMMALIAN OOCYTE MATURATION

The requisite endpoint of mammalian oocyte maturation, whether in vivo or in vitro,is a metaphase II oocyte which is able to be fertilized a nd which can eventually support normal embryonic development. Oocytes which have been matured in vivo basically fulfil these criteria. On th e other hand, a completely different situation exists when these cells are isolated from the ovaries and cultured in vitro. If they are too small (growing oocytes), they do not undergo maturation, or, if more a dvanced, will mature only to the metaphase I stage. Even in fully grow n oocytes which are able to mature to metaphase Il, the developmental potential after fertilization is disappointingly low, for reasons whic h remain unknown. The complexity of certain factors (nuclear, cytoplas mic or arising from our current culture systems) undoubtedly influence s both the ability of oocytes to mature fully, as well as their develo pmental potential after fertilization.