Dysdifferentiative nature of aging: age-dependent expression of mouse mammary tumor virus and casein genes in brain and liver tissues of the C57BL/6J mouse strain.

Many aspects of the aging process could be the result of cells slowly drifting away from their proper state of differentiation. This possibility has been studied by searching for an age-dependent increase in the expression of specific genes in tissues where expression of these genes would not normally be expected. In these studies, cDNA probes of specific genes are used in a DNA X NA hybridization assay to detect possible complementary RNA sequences in tissues of different-aged animals. Using this technique in past experiments, a qualitative increase in the RNA sequence complexity of mouse leukemia virus (MuLV) and a quantitative increase in the amount of alpha- and beta-globin RNA were found with increasing age in the brain and liver of the C57BL/6J mouse strain. We report here a similar age-dependent qualitative increase in the RNA sequence complexity for mouse mammary tumor virus (MMTV) but no quantitative or qualitative age-dependent change in casein RNA sequences for the same tissues and mouse strain.