Abstract / Project Summary The brain extracellular matrix (ECM) is a complex three-dimensional milieu that has a profound influence on synaptic plasticity and myelination during development. The pathways and cell types driving ECM generation during brain development are poorly understood. This proposal investigates a recently identified cellular pathway that controls ECM composition from the oligodendrocyte progenitor cells (OPCs). This discovery was made through studies of the transcription factor THAP1, which is mutated in the neurodevelopmental movement disorder DYT-THAP1 (DYT6) dystonia. Previous work identified a critical role for THAP1 in developmental myelination. Loss of THAP1 in the oligodendrocyte (OL) lineage impairs the progression of OPC into mature myelinating OLs. Recent work has established that THAP1 mediates OL differentiation in large part by controlling the composition of secreted chondroitin sulfate (CS) GAGs, a class of long unbranched polysaccharides and core-constituents of the ECM, which are inhibitory to OL differentiation. The hypothesis that OPCs regulate ECM composition is new, and the transcription factor THAP1, together with its partner YY1, provides an inroad to delineating the cellular mechanisms that regulate ECM composition during CNS development. The proposed studies will establish a molecular understanding of the regulation of ECM and myelination by THAP1. Aim 1 will use ChIP-seq and transcriptomic studies to test the hypothesis that THAP1 and its co-regulatory transcription factor YY1 regulate GAG metabolism through a shared pathway in differentiating OPCs. Both transcription factors have established roles in myelination and cause human dystonia when mutated. Aim 2 will test the hypothesis that OPCs are important contributors to developmentally regulated CS-GAG composition of the brain ECM and define the relative contribution of other CNS cell types, and the role of THAP1 in this process. Aim 3 test the hypothesis that THAP1- dependent OL maturation is required for normal motor learning and define THAP1-dependent changes in ECM pathway genes induced by motor learning. These studies will advance our understanding of the mechanisms by which glia and ECM contribute to CNS motor function and will shed light on how disruption of these processes contribute to pathogenesis of dystonia and other neurodevelopmental disorders.