Studies funded by DK43806 have led to discoveries that have illuminated how the unliganded thyroid hormone receptor represses basal transcription. We have determined the role of corepressors NCoR (Nuclear Receptor Corepressor) and SMRT (Silencing Mediator of Retinoid and Thyroid receptors) for TRs and other NRs, discovered general mechanisms as well as specificity factors governing corepressor interactions, and elucidated the core NCoR/SMRT corepressor complex, which contains the chromatin-modifying enzyme, histone deacetylase 3 (HDAC3), in stoichiometric amounts. HDAC3 derives its catalytic activity from its interaction with NCoR and/or SMRT, via the Deacetylase Activation Domain (DAD) that is unique to NCoR/SMRT. With strong evidence for the function of the DAD-dependent NCoR/SMRTHDAC3 complex in cell culture models, we are excited that state of the art methods of gene targeting and mouse phenotyping allow us to test for the first time the physiological relevance of the NCoRHDAC3 and SMRTHDAC3 corepressor complexes, which is the main objective of the parent grant. The main objective of the parent grant activities is to determine the physiological relevance of the NCoR-HDAC3 and SMRT-HDAC3 corepressor complexes. This is being accomplished through 3 specific aims: 1) Determine the physiological function of the NCoR DAD domain;2) Determine the physiological function of the SMRT DAD domain;and 3) Determine the physiological, tissue-specific functions of HDAC3. Here we request to expand these studies to include an additional aim that will be accomplished in two years and will greatly enhance the importance and impact of this work: Determine and characterize the genomic locations of HDAC3 corepressor complexes. These studies will identify the regions of the genome where HDAC3 is located and potentially functioning with NCoR and SMRT to regulate gene expression through interaction with various transcription factors. Once genomic regions of association have been identified, motif analysis tools will be utilized to identify the transcription factors potentially cooperating with HDAC3 at those locations. We will also evaluate the effect of tissue specific knockout of HDAC3 (generated in Aim 3) on genome-wide histone acetylation. Relational analysis of the identified HDAC3-associated regions with epigenetic changes in chromatin modification and HDAC3-dependent gene expression will provide novel insight into the mechanism of how HDAC3-NCoR/SMRT complexes regulate gene transcription. The goals of this aim are achievable within a two year period because the liver, macrophage, and adipocyte-specific HDAC3 mice are available in the laboratory, and the gene expression profiling and genome-wide ChIP-seq analysis are up and running in the laboratory. Thus this is an ideal addition to a productive project that illuminates relationships between nuclear receptor coregulators, epigenetic changes, gene expression, and metabolic physiology. PUBLIC HEALTH RELEVANCE: Project narrative not required for this submission. No change from original proposal.