Transcriptional Regulation of the Postnatal Cardiac Conduction System Heterogeneity

The cardiac conduction system (CCS) is a network of specialized cardiomyocytes coordinating electrical impulse propagation for synchronized heart contractions. Although the components of the CCS, including the sinoatrial node, atrioventricular node, His bundle, bundle branches, and Purkinje fibers, were anatomically discovered more than 100 years ago, their molecular constituents as well as regulators remain not fully understood. Here, we demonstrated the transcriptomic landscape of the postnatal mouse CCS at a single-cell resolution with spatial information. Integration of single-cell and spatial transcriptomics uncovered region-specific markers and zonation patterns of gene expression across the CCS, which were histologically validated. Network inference showed heterogeneous gene regulatory networks across the CCS. Notably, CCS region-specific gene regulation was recapitulated in a dish using neonatal mouse atrial and ventricular myocytes overexpressing CCS-specific transcription factors, Tbx3 and/or Irx3. This finding was supported by ATAC-seq of different CCS regions, Tbx3-ChIP-seq, and the identification of Irx motifs. Overall, this study demonstrates comprehensive molecular profiles within the postnatal CCS and provides evidence of the regulatory mechanisms contributing to its heterogeneity.