Neural stem cells (NSCs) hold promise for the treatment of a wide range of neurological disorders common to Veterans such as traumatic brain injury (TBI) and Parkinson's disease. In addition to providing cells for transplantation-based therapies, NSCs are also an important source of human neurons and glia for drug discovery and development. To realize the full potential of NSCs for human therapy, it is important to understand the molecular mechanisms that regulate the production of specific neural cell types. Our long-term goal is to understand the cellular and molecular mechanisms by which NSCs produce specific types of neurons and glia. The postnatal and adult mammalian brain harbors NSCs in the ventricular-subventricular zone (V- SVZ). Importantly, V-SVZ NSCs retain distinct regional identities that underlie the production of different neuronal subtypes. For instance, NSCs in the ventral V-SVZ produce neuron subtypes different from those born from NSCs in the dorsal V-SVZ. Furthermore, such NSC regional identity is largely cell-intrinsic, and we have shown that NSCs “remember” their regional identity through serial cell divisions. The expression of Nkx2.1 defines a population of NSCs in the ventral V-SVZ. While sonic hedgehog (SHH) is required to induce Nkx2.1 expression in ventral NSCs of the early embryonic brain, our Preliminary Studies indicate that SHH- signaling is not required for the maintenance of Nkx2.1 expression in ventral V-SVZ NSCs, suggesting that these cells epigenetically “remember” their regional identity. Mixed lineage leukemia-1 (Mll1) encodes a chromatin regulator that is part of an evolutionarily conserved transcriptional memory system, and MLL1 is required for normal V-SVZ neurogenesis. We found MLL1 protein enriched at Nkx2.1 regulatory elements, and disruption of MLL1 activity with either conditional Mll1 deletion or an MLL1-specific chemical inhibitor resulted in the loss of Nkx2.1 expression in ventral V-SVZ NSCs. After reversal of MLL1 inhibition, Nkx2.1 expression remained low, but neuronal production was restored. Based on these findings, our central hypothesis is that MLL1 is required to maintain NSC regional identity via specific chromatin state changes. In this renewal application, we propose to investigate the role of MLL1 in NSC regional identity and determine the molecular mechanisms by which MLL1 maintains region-specific gene expression. Given that NSC regional identity is a critical aspect of their neurogenic potential, results obtained will have important implications for our ability to produce specific types of neurons for human translational research and transplantation therapies. Furthermore, these studies advance new basic, neurodevelopmental concepts regarding NSC regional identity, which may be important to understanding how mutations in human MLL1 cause Weidemann-Steiner Syndrome, a developmental disorder that includes intellectual disability and autism. Finally, discovering MLL1-dependent mechani...