Effects of 5-azacytidine on the centromeric region of human fibroblasts studied by CREST staining and in situ hybridization on cytokinesis-blocked cells.

Several interphase methodologies have been applied in this study to investigate whether chemically induced undercondensation of the pericentromeric region of human fibroblast chromosomes promotes structural or numerical aberrations at the cell cycles following treatment. To achieve this aim, the effects of the hypomethylating agent 5-azacytidine (5- azaC) were studied on cytokinesis-blocked binucleated fibroblasts. This approach allowed the distribution of whole chromosomes or chromosome fragments in the daughter nuclei and micronuclei of treated cells to be followed, since the daughter nuclei of a single mitosis are maintained in one cytoplasm by treatment with the actin inhibitor cytochalasin B. Antikinetochore staining and in situ hybridization with an alpha-satellite probe capable of detecting all human centromeres on 5-azaC-induced micronuclei in binucleated fibroblasts indicated that the predominant effect of the chemical is to induce micronuclei lacking centromeres, suggestive of induced chromosome aberrations. Double in situ hybridization with alphoid and classical satellite DNA probes specific for chromosome 1 on binucleated fibroblasts was used to discriminate induced aneuploidy from breakage effects in the target area of hybridization. The results showed that undercondensation of the pericentromeric heterochromatin of human fibroblast chromosomes by treatment with 5-azaC produces structural chromosome aberrations involving the classical satellite DNA, whereas there was no evidence that the chemical induced chromosomal aneuploidy.