Cell autonomous regional differences in oligodendrocyte lineage development and responses to oncohistone H3.3 K27M.

Diffuse midline glioma, H3K27-altered (DMG), is a lethal midline brain tumor. Most DMG, unlike glioma arising in other regions, harbor histone H3.3 K27M (K27M) mutations. The basis for this anatomical selectivity remains unclear. Stem-like DMG cell transcriptomes most resemble oligodendrocyte precursor cells (OPCs). Using conditional K27M knock-in mice, we show that K27M reduces oligodendrocyte differentiation, altering the proportions of oligodendrocytic cell states in a region-specific manner. In vivo EdU labeling in tissue-cleared whole brains revealed greater K27M-driven increases in proliferation within pons, midline, and hindbrain regions than in telencephalon. In vitro, wild-type brainstem OPCs proliferate more slowly and differentiate later than telencephalic OPCs. K27M enhances brainstem OPC proliferation and disrupts regional transcriptional programs, selectively restraining full maturation of brainstem OPCs while inducing brainstem-selective upregulation of bivalent Bmp, Wnt, and Notch pathway genes. These findings suggest that K27M exploits intrinsic regional differences in oligodendrocyte development, creating a brainstem-selective window for gliomagenesis.