Single-strand DNA breaks in nuclei of early mouse embryos detected by in situ nick translation.

The nick translation procedure without external addition of nicking enzymes was performed in situ on fixed nuclei of mouse preimplantation, and postimplantation embryos, as well as bone marrow in order to detect possible DNA single-strand breaks. All preparations of nuclei were made using the same technique. Nick translation of nuclear DNA with DNA polymerase I in the presence of biotinylated-dUTP demonstrated a characteristic absence of label on nuclei of postimplantation embryos and bone marrow. The nuclear reactivity varied according to the cleavage divisions of the zygote, being highest at the four-cell stage.