A search for DNA alterations in the aging mammalian genome: an experimental strategy.

In order to experimentally test the hypothesis that at the basal level senescence is caused by instabilities in DNA, techniques are required that allow the sensitive detection, quantification and characterization of DNA damage and DNA sequence changes in various organs and tissues of naturally aging mammals. In this article a strategy is presented that should allow the analysis of DNA damage metabolism in aging mammals from the original changes in the chemical structure of DNA (DNA damages) via their processing (DNA repair) to the molecular endpoints in terms of gene mutations and DNA rearrangements. With respect to the detection of DNA damage, a short overview is provided of recently emerged biochemical and immunochemical methods that can be applied immediately to study the spectrum of DNA damages in various organs and tissues of aging animals or humans. By contrast, before one is able to study low frequency changes in DNA sequence organization in somatic tissues, formidable problems have yet to be overcome. This is mainly due to the fact that the scale of highly advanced recombinant DNA techniques recently developed is almost totally devoted to the analysis of heritable genetic factors. In order to be able to study low frequency changes in DNA sequence organization in somatic tissues, we have initiated experimental approaches based on recently emerged shuttle vector technology in combination with transgenic mice, and on new electrophoretic separation principles. These approaches and their potentialities for testing somatic mutation theories of aging are discussed.