A novel transgenic Cre allele to label mouse cardiac conduction system.

The cardiac conduction system is a network of heterogeneous cell population that initiates and propagates electric excitations in the myocardium. Purkinje fibers, a network of specialized myocardial cells, comprise the distal end of the conduction system in the ventricles. The developmental origins of Purkinje fibers and their roles during cardiac physiology and arrhythmia have been reported. However, it is not clear if they play a role during ischemic injury and heart regeneration. Here we introduce a novel tamoxifen-inducible Cre allele that specifically labels a broad range of components in the cardiac conduction system while excludes other cardiac cell types and vital organs. Using this new allele, we investigated the cellular and molecular response of Purkinje fibers to myocardial injury. In a neonatal mouse myocardial infarction model, we observed significant increase in Purkinje cell number in regenerating myocardium. RNA-Seq analysis using laser-captured Purkinje fibers showed a unique transcriptomic response to myocardial infarction. Our finds suggest a novel role of cardiac Purkinje fibers in heart injury.