Histone variant synthesis patterns in confluent populations of human diploid cells of different in vitro ages.

Histone variant synthesis patterns have been used to determine the cell cycle state of cultured cells. H2A and H3 histone variant synthesis patterns from confluent populations of human diploid fibroblast-like cells of different in vitro ages were determined and compared as ratios. In the absence of significant levels of DNA synthesis, there was an age related increase in the H2A ratio while the H3 ratio remained constant. These results indicate that confluent populations of older HDF are either in a different state of the cell cycle than younger cells or that they are synthesizing a different set of histone components while being maintained in the same cell cycle state at confluence. The synthesis and deposition of inappropriate histone components may alter chromatin structure in older cells and inhibit their subsequent progression through the cell cycle.