Age associated increase of single-stranded regions in the DNA of mouse brain and liver cells.

The touch smears of brain cells and hepatocytes of young and senescent mice were stained with antibody to cytidine nucleoside by an indirect immunofluorescence technique and subsequently combined with fluorescence cresyl violet staining of DNA. Nuclear binding of the antibody which reacts only with denatured or single-stranded regions in the DNA was seen only in the tissues of an aging animal. No such DNA lesion was detected in the epithelial cells of the gastrointestinal tract at any age. This type of DNA alteration is supposed to accumulate in the slowly renewing and non-replenishing tissues as a function of aging. The antibody was found not to react with the cells in S phase as demonstrated by 3H-thymidine autoradiography on a smear of newborn hepatocytes after the double fluorescence staining with cresyl violet and anti-cytidine antibody.