A 5-fold reduction in sister-chromatid exchange following implantation of mouse embryos is not directly related to the expression of embryonic genese responsible for oxygen radical metabolism

Abstract

We studied the spontaneous sister chromatid exchange (SCE) frequencies in mice at different stages of development; early preimplantation: 2 days post conception (p.c.); late preimplantation: 4 days p.c.; post implantation: day 10 and 13 p.c. The SCE level in preimplantation embryos is 5 times higher than any of the stages following implantation. The explantation for such observations may include a direct impact of maternal circulatory system as a result of implantation or onset of expression of a set embryonic genes. Here, we studied the expression and development profile of the three enzymes of oxygen radical metabolism (superoxide dismutase, glutathione peroxidase, and catalase) during development. Our results suggest that the onset and increase in the activity of these enzymes with in-utero differentiation, development and growth is not directly associated with the drop in SCEs/cell following implantation of the embryos. This unique developmental phenomenon may be mediated by the maternal circulatory system or expression of some other embryonic genes, possibly the genes involved in DNA repair.