Sequence of centromere separation: effect of 5-azacytidine-induced epigenetic alteration

Abstract

The factors which control the sequential separation of the various chromosomes in a genome at the meta-anaphase junction are not well understood. In genomes in which separation is correlated with the quantity of pericentric heterochromatin one factor appears to be the epigenetic nature, namely condensation, of pericentric heterochromatin. When we induced decondensation of pericentric heterochromatin in mouse cells with 10(-6), 4x 10(-6) and 6x10(-6) M 5-azacytidine (5-AC) for 8 h, it resulted in alteration of the sequence of centromere separation. The centromeres which lacked pericentric heterochromatin appeared not to have been affected because there could not be an epigenetic alteration induced by 5-AC. The major effect was on chromosomes with the largest quantity of pericentric heterochromatin. These chromosomes separated at significantly higher frequency than in the untreated population. We also treated human cells, in which separation does not depend upon the quantity of heterochromatin, with 2x10(-5) and 6x10(-6) M 5-AC for 5 and 8 h. Compared with the control, 5-AC treatment resulted in an increased frequency of separated centromeres of acrocentric chromosomes in relation to those of non-acrocentric chromosomes. In the control the acrocentric chromosomes are the last to separate; in the treated population there was almost random separation of the two types of chromosomes. This epigenetic alteration might be another factor which results in genesis of aneuploidy.

Unusual chromosome cleavage dynamic in rodent neonatal germ cells

“…This leads to the morphological differences observed between Sertoli and germ cells and also between germ cells at first and further divisions after birth. Premature centromere division was observed in vitro, after demethylating treatment of mouse cells in culture (Rodriguez et al 2001). We also obtained a tenfold increase in the rate of PCD after two different demethylating treatments in a human breast cancer cell line (unpublished data).…”

Permissive Transcriptional Activity at the Centromere through Pockets of DNA Hypomethylation

“…Previous studies have shown that ICF-syndrome patients with a mutation of the DNMT3b gene show centromeric and pericentric chromatin decondensation [26,44], and the possible re-enactment of this phenotype in cells treated with the methylation inhibitor, 5-aza-dC [45]. We investigated the functional significance of DNA hypermethylation at the neocentromere using 5-aza-dC and observed increased anaphase lagging or bridging of chromosomes, indicative of centromere instability caused by 5-aza-dC–induced inhibition of DNA methylation.…”

Increased Frequency of Micronuclei in Adults with a History of Childhood Sexual Abuse: A Discordant Monozygotic Twin Study

“…Evidence that methylation changes influence acquired chromosomal abnormality frequencies comes from studies of hypomethylated cells obtained following either: (1) in vitro induction (primarily using 5-azacytidine); or (2) as a result of mutation (cells from patients having immunonodeficiency, centromeric heterochromatin instability, and facial anomalies [ICF] syndrome, which is a condition in which the individuals have a mutation in the DNA methyltransferase 3b gene). The results of these investigation have shown increases in the rate of micronuclei associated with methylation alterations (particularly chromosomes 1, 9, and 16 in the samples from people having ICF), with observed delays in centromere separation being suggested as at least one means whereby the observed increase in somatic chromosomal abnormalities was acquired [59], [60], [61], [62], [63], [64].…”