M. Chopei, A. Piven, K. Afanasieva, A. Sivolob*

ESC “Institute of Biology and Medicine”,
Taras Shevchenko National University of Kyiv, Ukraine;
*e-mail: sivolob@knu.ua

Received: 21 April 2025; Revised: 26 May 2025;
Accepted: 11 June 2025; Available on-line: 07 July 2025

Tissue-specific DNA methylation plays an important role in the regulation of many functional processes. The methylation level in single cells can be assessed using the comet assay (single-cell gel electrophoresis), a simple and cost-effective technique. The methyl-sensitive comet assay approach has been widely used under the assumption that methylation in the context of CpG dinucleotides is the only type of this modification. However, although CpG is the main methylation target, non-CpG methylation is also widespread. We used the methyl-sensitive comet assay to demonstrate that, in human lymphocytes, non-CpG methylation significantly contributes to the global methylation level. The activation of lymphocyte proliferation results in an increase in non-CpG methylation, and the methyl-sensitive comet assay can be used to assess the ratio between CpG and non-CpG methylation levels.