[Freezing effects on the in vitro development of mice preantral follicles]. / Influence du type de congélation sur les courbes de croissance in vitro de follicules ovariens murins.

OBJECTIVES: Comparison of in vitro development, survival and oocyte maturation rates of mice preantral follicles frozen by various methods. MATERIALS AND METHODS: Cryopreservation of the germinal cells using the slow freezing method for entire ovary (Ova Cong) or isolated preantral follicles (Iso Cong) and vitrification in a closed system of isolated preantral follicles (Iso Vitr). Non-freezing follicles were considered as the control group. The four groups were simultaneous cultured for 12 days in a microdrop system. At each day of the culture, mean diameter was measured and at the end of the culture, follicular survival and mature oocyte rates were compared. RESULTS: Iso Cong and Ova Cong follicles achieved a smaller diameter (423.0 ± 47.1 µm et 450.3 ± 15.7 µm, respectively) than control group (680.7 ± 12.3 µm) at the 12th day of culture. At the end of the culture 6.21 % of Iso Cong follicles, 53.41 % of Ova Cong follicles and 83,77 % of Control follicles were alive. Mature oocyte rates were similar for the cryopreserved groups, 44.4 % for Iso Cong group and 44.7 % for Ova Cong group, but smaller than the Control group with 90 % of mature oocytes. Only 1/171 of the Iso Vitr follicles survived to the culture. DISCUSSION AND CONCLUSIONS: This study shows that mice's ovarian follicles can grow in vitro after cryopreservation but their diameter, survival and oocytes maturation rates are smaller than in the control group.

[Site specific mutagenesis by homologous recombination in embryonic stem cells]. / Mutagenèse dirigée par recombinaison homologue dans les cellules ES.

Twenty years ago, the production of mice whose genomes have been deliberatly modified revolutionised biology. Indeed, it is now possible to eliminate a gene's expression to various levels in desired locations, and also to broadcast these genetic modifications created in vitro to the progeny. The isolation and culture of embryonic stem cells (ES) and the discovery of the mechanism of homologous recombination between two sequences of DNA in the 80's, have contributed to the development of site-directed mutagenesis. Today, site specific mutagenesis by homologous recombination in embryonic stem cells is a powerful technique and is widely used throughout the world. In parallel, new techniques to invalidate targeted genes are emerging. These genetics tools, which we will introduce, allow for a better understanding of a gene's function both in fundamental and clinical research. It is now possible to create murine models of human genetic diseases including Lesch-Nhyan syndrome, Adenomatous Polyposis and Duchenne muscular dystrophy which we will discuss as examples.