Epicardial epithelial-to-mesenchymal transition in injured heart

Cre-LoxP-mediated genetic lineage trace has been used to illuminate the cell fate of progenitor cells in vivo. Application of this strategy to the epicardium, a sheet of cells covering the surface of heart, revealed that it dynamically participates in both heart development and postnatal heart repair and regeneration. After myocardial infarction, epicardial cells undergo epithelial-to-mesenchymal transition (EMT) and mainly adopt myofibroblast, fibroblast and smooth muscle cell fates. Here we present the wholemount images that map epicardial EMT following myocardial infarction, taking advantage of an inducible epicardial Cre line and a double fluorescence reporter. While remote epicardium retained its epithelial cell shape, reactivated epicardium in the infarcted region showed significant EMT. This image supports active involvement of the epicardium in repair and regeneration of infarcted myocardium.