Overall changes in chromatin sensitivity to DNase I during differentiation

Gábor Szabó, Sandor Damjanovich, János Sümegi, George Klein

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Abstract

The DNase I sensitivity of total chromatin was studied in fixed cells and nuclei isolated from proliferating and terminally differentiated cells, by measuring the incorporation of labelled nucleotides into DNase-sensitive sites, and electrophoresis of DNA isolated from DNase-treated nuclei. The unfixed nuclei were sensitive to digestion at around 10 μg/ml, the fixed cells at 30 μg/ml DNase I concentration. Proliferating Rauscher leukemia cells were more digestible than normal spleen cells. The DNase I sensitivity of the human HL60 leukemia line decreased upon DMSO-induced differentiation but still exceeded the digestability of nuclei from normal human peripheral blood. A novel flow-cytometric technique was developed to study DNase sensitivity at the cell level. It confirmed the relative resistance of differentiated cells to DNase I and ruled out the possibility that this could be due to an altered distribution of cell cycle phases. The overall DNase I sensitivity of chromatin was compared with the sensitivity of the c-myc gene and the myc-associated hypersensitive sites. The latter sites were detected at 1 μg/ml DNase I in HL60 nuclei. They disappeared partially upon DMSO-induced differentiation. At 10 μg/ml, myc was degraded in both growing and differentiating HL60, but not in HPB cells. These data suggest that a progressive condensation of the chromatin occurs during terminal differentiation which gradually involves specific genes that need to be inactivated.

Original languageEnglish
Pages (from-to)158-168
Number of pages11
JournalExperimental Cell Research
Volume169
Issue number1
DOIs
Publication statusPublished - Mar 1987

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ASJC Scopus subject areas

  • Cell Biology

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