Loss of Genes coding for Ribosomal RNA in Ageing Brain Cells

Abstract

ALTHOUGH recent investigations of genetic damage in the ageing process suggest that tissues made up of cells which are continually replaced will not be harmed by mutational events because the most vigorous cell lines are perpetuated selectively, information loss in DNA will be particularly harmful in non-replenishing tissues such as the nervous and muscular systems. Evidence of this effect comes from observations of abnormal mitotic chromosomes in increasing numbers in the cells of regenerating liver in old animals¹, which clearly reflects damage to DNA accumulating during ageing. The importance of chromosomal aberrations in ageing has, however, been discounted somewhat because the exposure of young animals to a dose of X-irradiation sufficient to produce more chromosomal breaks than normally occur during the lifetime of unexposed animals does not shorten the life span of the irradiated animals². Other investigators have suggested an age-dependent increase in protein crosslinking (reviewed in ref. 3), and there is evidence for the accumulation of single strand scissions in the DNA of ageing mouse neurones⁴.