Characterization of H3K9me3 and DNA methylation co-marked CpG-rich regions during mouse development.

BACKGROUND: H3K9me3 and DNA methylation co-marked CpG-rich regions (CHMs) are functionally important in mouse pre-implantation embryos, but their characteristics in other biological processes are still largely unknown. RESULTS: In this study, we performed a comprehensive analysis to characterize CHMs during 6 mouse developmental processes, identifying over 2,600 CHMs exhibiting stable co-mark of H3K9me3 and DNA methylation patterns at CpG-rich regions. We revealed the distinctive features of CHMs, including elevated H3K9me3 signals and a significant presence in euchromatin and the potential role in silencing younger long terminal repeats (LTRs), especially in some ERVK subfamilies. The results highlight the distinct nature of universal CHMs compared to CpG-rich nonCHMs in terms of location, LTR enrichment, and DNA sequence features, enhancing our understanding of CpG-rich regions' regulatory roles. CONCLUSIONS: This study characterizes the features of CHMs in multiple developmental processes and broadens our understanding of the regulatory roles of CpG-rich regions.