Epigenome Maintenance on Sister Chromatids

DNA replication not only involves the copying of the genome to propagate cell identity to daughter cells but also of the epigenome, where histones and their post-translational modifications (PTM) are accurately maintained in replicated chromatin. This is achieved by a strikingly coordinated process that ensures accurate, symmetric recycling of H3-H4 tetramers to both daughter strands, thus forming the basis of epigenetic memory. Recently, I identified H2A-H2B PTMs to be also symmetrically recycled in a H3-H4-independent manner. The underlying mechanism and their role in epigenetic memory remain unclear. Moreover, whether the asymmetric nature of DNA replication (leading vs. lagging strand) leads to asymmetric chromatin landscapes on daughter strands per se remains unexplored due to the current lack of technologies.I hypothesize that propagation of cell identity to daughter cells requires crosstalk of conserved “memory modules” (on H3-H4 and H2A-H2B) to equilibrate the asymmetric mode of DNA replication. We will use both stem cell culture and fission yeast to define evolutionarily conserved concepts of chromatin restoration after replication. To this end, we will extend state-of-the-art sequencing, proteomics, genome editing, as well as established and novel nucleotide labelling approaches. First, we will address the molecular mechanism of H2A-H2B PTMs recycling during replication. Second, we will test the role of active chromatin PTMs in maintaining chromatin states, 3D chromatin organization, and gene expression after replication. Third, we will develop a novel strand-specific labelling technology to determine the composition and restoration principles of leading and lagging strand-replicated chromatin.This proposal will directly dissect the function and relevance of epigenetic memory on H2A-H2B and active chromatin PTMs post-replication and define new concepts of how chromatin maintenance mechanisms promote symmetric cell division and support cell identity.