Deciphering the Mechanism of G9a Spreading Genome-wide

Abstract

The cell differentiation process is associated with activation and repression of different genes, whereby the formation of heterochromatin is mediated by spreading of repressor proteins along large chromatin domains. Some of these proteins are methyltransferases, including GLP and G9a that are implicated in the addition of mono- and dimethyl groups to lysine 9 at Histone 3. Despite extensive research the exact mechanism of binding and spreading of G9a and GLP is unclear. To better understand the molecular mechanisms through which G9a and GLP bind to chromatin we tested the in vivo binding of a mutant G9a that is unable to bind to H3K9me2 histone marks via its Ankyrin domain. Murine erythroleukemia (MEL) cell line with expression of mutant G9a was generated using recombinant DNA technologies; G9a binding targets genome-wide were detected by the analysis of ChIP-sequencing data. We validated ChIP-sequencing data providing a reliable tool to visualize G9a targets in MEL cells. We also found that G9a Ankyrin mutant bound to all tested regions suggesting that the Ankyrin domain is not the only factor that contributes to the binding of G9a on chromatin in vivo.