Changes in frequency and localization of human X- and Y-chromatin bodies at interphase during in vitro cellular aging.

We have investigated the degree of hypodiploidy of human X (inactive) and Y chromosomes and their relative localization in the interphase nuclei during in vitro aging of diploid fibroblasts. It is found that significant proportions of both female and male cells lose the inactive X and Y chromosome, respectively during cellular aging. Our results from fibroblasts are consistent with comparable findings of other investigators utilizing lymphocytes and bone marrow cells. However, we have observed a relatively higher proportion of X and Y chromosomal hypodiploidy in older fibroblasts than the frequencies reported for lymphocytes or bone marrow cells from aged people. Significant changes in the relative localization pattern of the inactive X and Y chromosomes in the nuclei are also noted during in vitro aging of female and male cells, respectively, and these changes in localization pattern are not identical in both sexes. We believe that, during cellular aging, the analysis of sex chromosomal aneuploidy at interphase is highly likely to provide more accurate results as opposed to the analysis of metaphase chromosomes since the latter is dependent upon the divisional capacity of cells which declines with age. Analysis of interphase cells also avoids the artifacts that accompany metaphase chromosome preparations.