[Utilization of mononuclear DNA by regeneration epidermis]

In four series of experiments on random-bred mice, ten animals received 3H-thymidine in a dose of 1 micro Ci/g. An hour later 10 intact mice were subjected to cross allotransplantation of dorsal skin. The animals of both groups were sacrificed after 4 days. Twenty mice were injected with thymidine in the same way and sacrificed after one hour or after four days. The skin was subjected to histological examination using autoradiography. It has been found that proliferation of the epidermis around the allotransplant is not followed by substantial dilution of the label over the nuclei of its cells, so that in fact the total content of labeled thymidine in the allotransplant nuclei increases. At the same time the regenerating epidermis is infiltrated with mononuclears a quarter of which contain the label. It is suggested that mononuclears might be the source of additional thymidine for the regenerating epithelium.