Variations in DNA Methylation Patterns During the Cell Cycle of HeLa Cells

TLDR

DNA methylation is traditionally viewed as a stable epigenetic mark established during development and remaining fixed thereafter. The study aims to show that DNA methylation patterns change during a single cell cycle in HeLa cells. Using nearest‑neighbor analysis, immunocytochemistry, high‑performance capillary electrophoresis, and CpG‑island microarrays, the authors examined methylation of unique sequences across the cell cycle. They found that global methylation decreases in G1 and rises in S, with 174 CG‑containing loci differentially methylated—most showing hypomethylation at G0—confirmed by bisulfite mapping, demonstrating dynamic methylation in a mature somatic cell and highlighting its instability.

Abstract

AbstractDNA methylation has been viewed as a stable component of the epigenome, which is established during development and fixed thereafter. We show here using nearest neighbor analysis, immunocytochemistry, and high performance capillary electrophoresis that the DNA methylation pattern varies in HeLa cells during a single cell cycle. Immunocytochemical analysis in primary human fibroblasts shows similar variations. The global levels of DNA methylation decreased in G1 and increase during the S phase of the cell cycle. Since there was little change in the DNA methylation levels in repetitive sequences throughout the cell cycle, we examined the DNA methylation pattern of unique sequences using a human CpG island microarray. Hybridization with methylated DNA from G1 and S phase of the cell cycle revealed that 174 CG-containing sequences were differentially methylated between G1 and S. 75% of all the variations in DNA methylation detected in unique sequences represented hypomethylation at G0, with changes occurring in both CpG islands and non-CpG islands. Bisulfite mapping confirmed these changes in methylation in the regions identified by the microarray. This is the first demonstration of a dynamic DNA methylation pattern within a single cell cycle of a mature somatic cell. These data are important for our understanding of the stability of DNA methylation patterns in somatic cells.