Causes of developmental failure of in-vitro and matured rhesus monkey oocytes: Impairments in embryonic genome activation

Abstract

Background: Understanding the causes of developmental failure of in-vitro matured primate oocytes may lead to viable strategies for improving their developmental competence. The aims of this study were to determine whether the timely onset of embryonic genome activation among individual blastomeres of preimplantation macaque embryos is impaired by in-vitro maturation (IVM) of oocytes and whether these impairments are associated with developmental failure during the embryonically controlled period of preimplantation development. Methods: Genome activation among individual blastomeres was assessed using expression of fibrillarin as a marker of nucleolar transcription. Immature oocytes were obtained from rhesus monkeys following treatment with recombinant human FSH and matured in-vitro in one of two IVM media (CMRLa or CMRLb). In-vivo matured oocytes were obtained from FSH treated monkeys following administration of hCG. Oocytes were fertilized in vitro and either cultured for developmental studies or processed at the 8-12-cell stage for expression of fibrillarin. Results: Developmental competence of embryos derived from in-vitro matured CMRLa oocytes was markedly (P < 0.05) impaired compared with those derived from in-vivo matured or in-vitro matured CMRLb oocytes. Developmental profiles were similar among the groups prior to the 8-cell stage. However, in embryos derived from in-vitro matured CMRLa oocytes, developmental failure increased significantly (P < 0.05) after the time of genome activation compared with those derived from in-vivo matured or in-vitro matured CMRLb oocytes. The mean percentages of non-activated blastomeres per embryo, as well as the proportions of embryos with at least one non-activated blastomere, or with no activated blastomeres, were all significantly (P < 0.05) greater in embryos derived from in-vitro matured CMRLa oocytes than in those derived from in-vivo matured or CMRLb oocytes. Conclusions: The relatively poor developmental competence of in-vitro matured primate oocytes is likely caused in part by failure in the timely onset of embryonic genome activation resulting from incomplete cytoplasmic maturation.