Regional identity of human neural stem cells determines oncogenic responses to histone H3.3 mutants [ChIP-Seq]

Point mutations within the histone H3.3 are frequent in aggressive childhood brain tumours known as paediatric high-grade gliomas (pHGGs). Intriguingly, different mutations arise in discrete anatomical regions: H3.3-G34R within the forebrain and H3.3-K27M preferentially within the hindbrain. The reasons for this contrasting aetiology are unknown. By engineering human foetal neural stem cell cultures from distinct regions, we demonstrate here that cell-intrinsic regional identity provides differential responsiveness to each mutant that mirrors the origins of pHGGs. Focusing on H3.3-G34R, we find that the oncohistone supports proliferation of forebrain cells, while inducing a cytostatic response in the hindbrain. Mechanistically, H3.3-G34R does not impose widespread transcriptional or epigenetic changes, but impairs recruitment of ZMYND11, a transcriptional repressor of highly expressed genes. We therefore propose that H3.3-G34R promotes tumorigenesis by stabilising the expression of key progenitor genes and, thus, locking initiating forebrain cells into their preexisting immature state. Overall design: Mapping genome-wide distribtuition of H3K4me3, H3HK27me3, H3K36me3, H3.3-G34R (endogenous) and V5-H3.3 (wild-type and G34R-mutant, ectopically expressed) in the H3F3A G34R-mutant paeditric glioblastoma cells (Parental pGBM002 and H3F3A-G34R CRISPR ablated pair)