ABSTRACT Genetic analyses of patients have associated transcription factors (TFs), proteins which regulate gene expression, with atrial fibrillation (AF). AF is a major healthcare burden with associated healthcare costs exceeding 26 billion dollars in the US annually. AF exacerbates many forms of heart disease and is among the leading causes of stroke. Since AF incidence increases with age, the human and financial toll of AF is anticipated to continue to increase. Current therapies mitigate the consequences of AF, but there are no therapies that prevent or specifically treat AF. New treatment modalities are urgently needed. Genome-wide association studies have linked AF to several TFs, among them TBX5. TFs maintain gene expression programs in healthy cells, and errors in the behavior of the TF network result in inappropriate levels of gene expression that promote atrial remodeling and AF. Although significant progress has been made in identifying TFs and downstream targets that comprise the gene regulatory networks (GRNs) of atrial cardiomyocytes (CMs), many of the regulatory mechanisms of atrial CMs in health and AF remain unknown. Our preliminary data reveal a previously unappreciated interaction between TBX5 and TEAD1. TEAD1 is a TF currently best known as a major partner of the transcriptional co-activator YAP1, which regulates cell growth and responses to mechanical forces through the Hippo signaling pathway. Furthermore, the preliminary data show that we have successfully generated a murine AF model by inactivating Tbx5 in atrial CMs by delivering an Nppa promoter-driven Cre recombinase transgene using adeno-associated virus. Building on these results, here we propose to test the hypothesis that the TBX5-TEAD1 complex maintains rhythm homeostasis in healthy atria, while the loss of TBX5 causes AF in part by permitting inappropriate transcriptional activation by pYAP-TEAD1. In Aim 1, we implement biochemical and genetic approaches to determine how TBX5, TEAD1, and YAP interact to modulate AF pathogenesis. In Aim 2, using TEAD1 ChIP-seq, single nucleus RNA-seq, and single nucleus ATAC-seq, we will uncover changes in transcriptional regulation that drive AF pathogenesis. The proposed research will contribute to our understanding of AF pathogenesis and provide a great opportunity for the PI to become trained in molecular cardiology and functional genomics approaches to study gene regulation. Integral to this training, the PI will become well-versed in the latest cutting-edge approaches and technologies that are essential for an independent career as an investigator. The second aim of the proposal particularly focuses on obtaining and analyzing NGS data, and the training environment offered by the Pu lab group (which includes 2 dedicated bioinformaticians) and the affiliated Harvard Medical School offers a unique opportunity to develop these skills by exploration of the data, supported by didactic training in the classroom and by collaborativ...