The contribution of the proepicardium to avian cardiovascular development

The embryonic epicardial layer of the heart, which originates from the proe picardium, gives rise to a set of invasive pluripotent epicardially-derived cells (EPDCs) that contribute to the development of 1) subepicardial mesen chyme, 2) coronary vessels, 3) intermyocardial fibrous tissue, and 4) mesen chyme of the atrioventricular cardiac valve primordia. Here we report that chimeric tracing of proepicardial cells as well as a new experimental proce dure reveal a non-proepicardial origin for the epicardial-like cells of the more distal part of the outflow tract of the heart (OFT). This observation is supported by the fact that the expression pattern of mesothelial antige ns in the epicardial-like cells of the distal outflow tract is different fr om the expression pattern in the pro epicardially-derived epicardium. The d elay of epicardium and EPDC development using diverse microsurgical procedu res leads to abnormal cardiac phenotypes in all cardiac areas colonized by proepicardially-derived epicardium and EPDCs. These results suggest the exi stence of a signaling role for epicardium and EPDCs in cardiac development and support the hypothesis that ontogenetical diversity of cardiac epicardi um is involved in heart chamber morphogenesis and remodeling.