Role of DNA Methylation in Liquid-liquid Phase Separation-mediated Heterochromatin Formation

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Project Summary/Abstract The structure and dynamics of chromatin control the accessibility of DNA to regulatory factors during transcription, replication, recombination and DNA damage repair. PTMs of chromatin-associated proteins and DNA methylation are complex epigenetic mechanisms that regulate gene expression and chromatin organization. The interplay between these mechanisms generate synergistic or antagonistic interactions that partition chromatin into (i) euchromatin: lightly packed chromatin, enriched in genes often under active transcription or (ii) heterochromatin: tightly packed and condensed chromatin, containing mostly silenced genes. The molecular mechanisms underlying this partition is not fully understood. Recent studies demonstrate that heterochromatin can assemble through liquid-liquid phase separation (LLPS) driven by multivalent interactions between modified histone tails and the proteins that bind these epigenetic modifications. However, heterochromatin is also highly enriched in methylated DNA, which is reciprocally regulating, and regulated by the surrounding histone modification binding proteins and enzymes. How methylated DNA binding proteins and the patterns of DNA methylation co-ordinate with the histone modification machinery in the LLPS-mediated assembly of heterochromatin is not fully understood. This proposal will address these gaps in knowledge.