Correlation of DNA methylation with histone modifications across the HNRPA2B1-CBX3 ubiquitously-acting chromatin open element (UCOE).

The methylation-free CpG island encompassing the divergently transcribed promoters of the HNRPA2B1 and CBX3 housekeeping genes possesses a dominant ubiquitously-acting chromatin opening element (UCOE) capability. This element allows reproducible and stable transgene expression including from within centromeric heterochromatin. We present an investigation of DNA methylation and histone modification marks across the HNRPA2B1-CBX3 locus in primary peripheral blood mononuclear cells (PBMCs) to characterise the chromatin structure that underlies UCOE activity. The CpG methylation-free region associated with the UCOE extends into the central areas of HNRPA2B1 and CBX3, with a total length of approximately 5 kb. However, the DNA in the 3' half of both genes is methylated. Histone H4 lysine (K) acetylation shows a broad distribution across both genes, whilst histone H3 lysine acetylation peaks around the transcriptional start sites and drops to background levels at the 3' ends. Higher levels of H3K4 di-methylation are present at the 3' end of the genes in contrast to H3K4 tri-methylation which peaks around the transcriptional start sites. Therefore, methylated DNA in transcribed regions of these genes has been shown here to co-exist with active histone modification marks, indicating that these functionally opposing epigenetic signatures can overlap. This suggests that an extended large region of unmethylated DNA in combination with distinct histone modification patterns are at the basis of UCOE function.