Abstract
The mammalian heart contains multiple cell types that appear progressively during embryonic development. Advance in determining cardiac lineage diversification has often been limited by the unreliability of genetic tracers. Here we combine clonal analysis, genetic lineage tracing, tissue transplantation, and mutant characterization to investigate the lineage relationships between epicardium, arterial mesothelial cells (AMCs), and the coronary vasculature. We report a contribution of the second heart field (SHF) to a vasculogenic niche composed of AMCs and sub-mesothelial cells at the base of the pulmonary artery. Sub-mesothelial cells from this niche differentiate into lymphatic endothelial cells and, in close association with AMC-derived cells, contribute to and are essential for the development of ventral cardiac lymphatics. In addition, regionalized epicardial/mesothelial retinoic acid signaling regulates lymphangiogenesis, contributing to the niche properties. These results uncover a SHF vasculogenic contribution to coronary lymphatic development through a local niche at the base of the great arteries.