Functional analysis of the histone variant H2A.Z during lineage commitment

Abstract

remained enigmatic. In this thesis, we dissect the role of H2A.Z during lineage commitment. In particular, we focused on the Polycomb-mediated mono-ubiquitylation of H2A.Z. We found that this modification regulates the differentiation potential of mouse embryonic stem cells (mESCs). Loss of H2A.Z ubiquitylation leads to a disrupted chromatin state and derepression of key developmental regulators in mESCs. Furthermore, we show that H2A.Zub is a crucial component required for regulating canonical Wnt signaling, a key pathway in early embryogenesis. Consistent with hyperactivation of Wnt signaling, ESCs lacking H2A.Zub fail to differentiate into neuronal lineages. Therefore, we suggest that modification of H2A.Z is crucial for the response to stimuli. Using quantitative proteomics, we uncovered a role for H2A.Z ubiquitylation in modulating the protein interaction landscape of H2A.Z. H2A.Zub impacts a specific subset of protein interactions. By investigating several of these differential interactions, we revealed a role for H2A.Zub in regulation of DNA methylation, the deposition of repressive histone modifications, as well as a potential connection between H2A.Zub and DNA damage. Therefore, ubiquitin may serve as a binding platform for subsequent recruitment of chromatin-associated factors. These data suggest a mechanism by which post-translation modification of H2A.Z can allow for rapid changes in cell state in a context dependent manner. On a broader level, our work contributes mechanistic insights into the essential requirement of H2A.Z across eukaryotes. Collectively, this work sets the stage for understanding how post-translation modifications can contribute to further specialization of H2A.Z in a context-dependent manner.