DNA strand breaks in rat tissues as detected by in situ nick translation

The nick-translation procedure without external addition of DNase was performed in situ on sections of various rat organs to detect possible DNA single-strand breaks (nicks) in normal tissues. The freshly frozen sections were briefly fixed in ethanol/acetone and nick-translated in the presence of E. coli DNA polymerase I. A significant difference in the amount of nuclear reaction was found among the different cell populations as detected by autoradiography following incorporation of tritiated TTP as well as by histochemical staining following incorporation of biotin-dUTP into nuclei. Such incorporation of triphosphates was localized in the DNA and was entirely dependent on E. coli DNA polymerase I. The nuclei with the highest reactivity were found in skeletal muscle cells, lymphocytes in various lymphatic organs, the proliferative cells in the gastrointestinal tract, stratified squamous epithelial cells, duct epithelial cells of salivary gland and the maturing spermatids in the seminiferous tubules. These results suggest that, under the conditions adopted, the cells in various tissues reveal different chromatin structures resulting in varying rates of nick translation reaction. Such difference(s) in chromatin structure, presumably including that in the number of DNA single-strand breaks or in the level of endogenous nuclease activity, may be associated with the mechanisms involved in cell growth and differentiation.