Diffuse Intrinsic Pontine Glioma (DIPG) is a rare pediatric brain tumor for which no cure or efficacious therapies exist. Recently, novel mutations in ACVR1, a BMP pathway receptor, were discovered that commonly co-occur with a K27M mutation in the gene encoding histone H3.1 (H3.1 K27M) in DIPG patient samples. The overall objectives of this proposal are to identify the mechanisms by which mutant ACVR1 and H3.1 K27M contribute to DIPG pathogenesis and to uncover strategies to pharmacologically target these mutations or downstream signaling molecules. Our central hypothesis is that mutant ACVR1 and H3.1 K27M contribute to brainstem gliomagenesis by activating the Stat3 and Notch signaling pathways, respectively. We plan to use novel genetically engineered mouse models representing primary tumors growing in their native microenvironment to interrogate the effects of both mutant ACVR1 and H3.1 K27M on gliomagenesis, proliferation, apoptosis, cell differentiation, self- renewal, cell motility, and angiogenesis in vitro and in vivo. We will also use both genetic and pharmacologic tools to determine the contributions of Stat3 and Notch to ACVR1-mediated functions and to H3.1 K27M-mediated functions, respectively. Finally, we will test a panel of ACVR1, Stat3, and Notch inhibitors in vitro and in vivo in both human and murine DIPG models. Once it is understood how ACVR1 mutations and H3.1 K27M contribute to DIPG pathogenesis, the relevant developmental pathways can be manipulated pharmacologically, resulting in new and innovative therapeutic approaches that are based upon the basic biology inherent, and specific, to DIPG. We anticipate these outcomes will have a positive impact by 1) laying the foundation for future pre-clinical and clinical trials for DIPG, 2) characterizing the first genetically engineered mouse models of DIPG driven by mutant ACVR1 and H3.1 K27M, and 3) advancing our understanding of signaling pathway activities that are essential for DIPG growth.