Chromatin organization and transcriptional activity in human embryonic lung fibroblasts aged in vitro

Chromatin organization was examined in confluent cultures of embryonic lung fibroblasts in the middle and at the end of their replicative lifespan. Age-related modifications resulted in an unusually wide spacing of the chromatin threads induced by a mild loosening treatment and an increased sensitivity of the nucleosomes to the Joy-containing hypotonic medium used in Miller's spreads. The profound changes in chromatin response to various hypotonic solutions were not associated with the disappearance of RNA synthesis in old type nuclei as demonstrated by high-resolution autoradiographical studies.