Histone variant H3.3 is incorporated into various chromatin domains by distinct chaperones including HIRA, ASF1A, ATRX and DAXX. We have shown that a pool of neo-synthesized H3.3 is recruited to PML bodies (NBs) before deposition into chromatin. In PML NBs H3.3 is colocalized with DAXX, ATRX, HIRA and ASF1A, suggesting a view of PML NBs acting as regulatory centers of H3.3 loading. Here we by assess the impact of PML on the association of epitope-tagged H3.3 with chromatin. ChIP-seq analysis of epitope-tagged H3.3-3xFlag transfected into wild-type MEFs reveals H3.3 enrichment in expressed genes. H3.3 is largely excluded from domains occupied by PML (PML-interacting domains, or PMLIDs), which are in contrast found in gene-poor regions. Genes within PMLIDs are overall weakly or not expressed. Strikingly, in Pml-null MEFs, H3.3 is enriched in regions marked by PML in wild-type cells, suggesting that PML directly or indirectly influences H3.3 loading. We also note a loss of heterochromatin marks in these domains in Pml-null cells, without, however, marked changes in gene expression in these domains. Our results suggest that PML may impose site-specificity in the loading of H3.3 on chromatin. SOURCE: Philippe Collas University of Oslo

Pluto Bioinformatics

GSE66364: Role of PML on histone variant H3.3 loading on chromatin