DNA strand breaks in embryonic mouse limbs exposed to methylnitrosourea

The alkaline elution assay was used to monitor DNA single strand breaks in hindlimbs of embryonic mice exposed to methylnitrosourea (MNU) on day 13 of gestation, a stage of development at which the embryotoxicity of MNU was minimal. DNA breakage was maximal by 1 h after exposure, and rapidly declined to control levels by 8 h. There was a reduction of fetal weights in the MNU-treated litters, but no increase in embryomortality. No malformations of the limbs were observed. The data are discussed in relation to an earlier study, where the same dose of MNU administered on day 11 of gestation was highly teratogenic and produced a substantially different pattern of DNA breakage in hindlimbs.