Cytotoxic and genotoxic effects of bromodeoxyuridine during in vitro labelling for sister-chromatid differentiation in preimplantation mouse embryos.

Exposure of preimplantation mouse embryos in culture to bromodeoxyuridine (BrdU) in the concentration range of 10(-9) to 2 x 10(-6) M allows sister-chromatid differentiation at the morula and blastocyst stage. The same BrdU concentrations induced no chromosomal aberrations, but a prolongation of the cell cycle and an increase of the SCE frequency. Even at the lowest BrdU concentration for sister-chromatid differentiation (10(-9) M the background level for SCE was found to be significantly higher in early embryos than in fetal or adult tissues of the mouse. Therefore, the high SCE frequency seems to be characteristic of undifferentiated embryonic cells. Methodological recommendations are also given for SCE assay in preimplantation mouse embryos.