Novel genetically engineered H3.3G34R model reveals cooperation with ATRX loss in upregulation of PRC2 targets, NOTCH activation, promotion of neuronal lineage

Pediatric high-grade gliomas (pHGGs) are an aggressive pediatric CNS tumor, often characterized by mutations in H3F3A, the gene that encodes Histone H3.3 (H3.3). Substitution of the Glycine at position 34 of H3.3 with either Arginine or Valine (H3.3G34R/V), was recently described and characterized in a large cohort of pHGG samples as occurring in 5-20% of pHGGs. We developed a genetically engineered mouse model (GEMM) that incorporates PDGF-A activation, TP53 loss and the H3.3G34R mutation both in the presence and loss of Alpha thalassemia/mental retardation syndrome X-linked (ATRX), which is commonly mutated in H3.3G34 mutant pHGGs. Nestin Tv-a; p53 fl/fl and Nestin Tv-a; p53 fl/fl; ATRX fl/fl mice were injected with DF-1 cells transfected with RCAS-Cre, RCAS-PDGFA, and either RCAS-H3.3WT-GFP or RCAS-H3.3G34R-GFP. By 210 days old, a majority of mice develop symptoms of tumor growth (erratic behavior, domed head, ataxia) or have 20% weight loss and are euthanized. Our goal is to develop a biologically relevant animal model of pHGG in order to probe the downstream effects of the H3.3G34R mutation in the context of vital co-occurring mutations. Overall design: Examination of gene expression differences in mouse frontal Cortex of H3.3G34R expression and ATRX loss