title: Replicative activity and actinomycin binding in mouse diploid fibroblasts (in vitro ageing).
abstract: Populations of embryonic mouse fibroblasts undergo 10 +/- 2 doublings in vitro prior to cessation of growth. We have studied various properties of the DNA of such cells as they undergo this process of in vitro ageing. Following a 1-h pulse with [3H]thymidine the labelling of growing cell populations decreases progressively with serial subcultivation. At early passage levels, the decrease in labelling between passages is rapid, but after about five passages the decline is much slower. Following a long pulse with [3H]thymidine (up to 4 days), up to 50% of the cells in the final passage become labelled. The binding of [3H]actinomycin to nuclei decreases progressively during serial subcultivation. Under conditions of quiescence, induced by serum deprivation, the cells withdraw from the S-phase. Feulgen cytophotometry reveals a wide spectrum of cellular DNA contents in terminal cultures, with 38% of cells possessing more DNA than equivalent early passage cells. Under these conditions, 40% of the fibroblasts bind less actinomycin than any early passage cells. Neither variations in DNA amount nor differences in cell-cycle phases can explain these alterations, which are thought to be related to age-dependent changes in chromatin condensation.
mesh_terms: D000818:Animals; D002455:Cell Division; D002470:Cell Survival; D002478:Cells, Cultured; D004261:DNA Replication; D003609:Dactinomycin / Q000378:metabolism*; D051379:Mice
chemical_list: D003609:Dactinomycin