Irx4 Marks a Multipotent, Ventricular-Specific Progenitor Cell

While much progress has been made in the resolution of the cellular hierarchy underlying cardiogenesis, our understanding of chamber-specific myocardium differentiation remains incomplete. To better understand ventricular myocardium differentiation, we targeted the ventricle-specific gene, Irx4, in mouse embryonic stem cells to generate a reporter cell line. Using an antibiotic-selection approach, we purified Irx4⁺ cells in vitro from differentiating embryoid bodies. The isolated Irx4⁺ cells proved to be highly proliferative and presented Cxcr4, Pdgfr-alpha, Flk1, and Flt1 on the cell surface. Single Irx4⁺ ventricular progenitor cells (VPCs) exhibited cardiovascular potency, generating endothelial cells, smooth muscle cells, and ventricular myocytes in vitro. The ventricular specificity of the Irx4⁺ population was further demonstrated in vivo as VPCs injected into the cardiac crescent subsequently produced Mlc2v⁺ myocytes that exclusively contributed to the nascent ventricle at E9.5. These findings support the existence of a newly identified ventricular myocardial progenitor. This is the first report of a multipotent cardiac progenitor that contributes progeny specific to the ventricular myocardium. Stem Cells 2016;34:2875-2888.