Histone variants of H2A and H3 families are regulated during in vitro aging in the same manner as during differentiation

In a previous communication, we showed that the H2A.1/H2A.2 histone variant ratio decreases in a linear manner during the in vitro aging of human dipl oid fibroblasts. This ratio is known to decrease in the same manner in prog ressive stages of development and in the process of differentiation, and is thus considered to be a biochemical marker for differentiation. A detailed analysis of the synthesis of H2A and H3 histone variants as a function of cumulative population doublings in the same in vitro cell system is present ed in this study. Quantitative analysis of these variants in the GO phase, synchronized fibroblasts has shown that their relative amount in chromatin, as well as their biosynthesis rate, change during in vitro aging of human diploid fibroblasts, revealing both up-and down-regulation of certain varia nts as a function of cumulative population doublings. Furthermore, we show by morphometric studies employing the seven distinct fibroblast morphotypes , as described by the Bayreuther classification, that this regulation is at tributable to the replicative sub-populations. These results reveal that hi stone variants of the H2A and H3 families are regulated during in vitro agi ng in the same manner as that during differentiation. (C) 1999 Elsevier Sci ence Inc. All rights reserved.