Project Summary/Abstract Large-scale studies have identified thousands of genetic variants linked to developmental defects, together with the regulatory elements harboring these variants and the cell types in which these variants likely function. This diversity of variants, regulatory elements, and cell types indicates that multiple mechanisms contribute to developmental defects. One key challenge to our understanding of these mechanisms is that the molecular, cellular, and functional phenotypes of each variant remain largely uncharacterized. Until these critical gaps in knowledge are addressed, the underlying molecular and cellular determinants of developmental disease susceptibility will remain incomplete. To bridge these gaps, we propose to establish the “UT Southwestern Center for Regulatory Element Variation and Function”. The primary goal of this Center is to systematically catalog molecular and cellular phenotypes for disease-associated enhancers in human development, with a focus on gaining insights into mechanisms of non-canonical human genetics and gene regulation. To build a generalizable framework to understanding the impact of human genetic variation on function, we propose a high throughput perturbation platform with three primary goals: (1) Contribute to a variant/element/phenotype catalog with relevance to diseases of human development, focusing on elements genetically associated with congenital heart disease (cardiomyocytes), autism (neurons), and placental defects (trophoblasts); (2) Contribute to a variant/element/phenotype catalog for non-canonical human genetics, focusing on two understudied topics in human genetics: pleiotropic effects and non-cell autonomous effects; and (3) Contribute to a variant/element/phenotype catalog with relevance to mechanisms of gene regulation, focusing on enhancer RNAs. The Center will take advantage of recent technological innovations in genome engineering, single-cell genomics, and high content screening to enable the multiscale functional characterization of genomic variation in human developmental disorders. Several of these techniques have been pioneered by investigators contributing to this project, including: the development of novel tools for enhancer perturbation and the coupling of endogenous enhancer perturbations with a single-cell RNA-Seq readout (Mosaic-Seq). Impact and Significance: The efforts on this project will lead to a number of key outcomes and deliverables, including (1) greater understanding of the relationships between sequence variation and genome function, (2) an extensive variant/element/phenotype catalog for the community, (3) tools for generating predictive models for the community, and (4) resources to enable future functional genomics studies. Together, our multifaceted and combinatorial approaches will open new horizons to understanding the impact of regulatory variants on developmental disease phenotypes.