Notch Signaling Commits Mesoderm to the Cardiac Lineage

During development multiple progenitor populations contribute to the formation of the four-chambered heart and its diverse lineages. However, the underlying mechanisms that result in the specification of these progenitor populations are not yet fully understood. We have previously identified a population of cells that gives rise selectively to the heart ventricles but not the atria. Here, we have used this knowledge to transcriptionally profile subsets of cardiac mesoderm from the mouse embryo and have identified an enrichment for Notch signaling components in ventricular progenitors. Using directed differentiation of human pluripotent stem cells, we next investigated the role of Notch in cardiac mesoderm specification in a temporally controlled manner. We show that transient Notch induction in mesoderm increases cardiomyocyte differentiation efficiency, while maintaining cardiomyocytes in an immature state. Finally, our data suggest that Notch interacts with WNT to enhance commitment to the cardiac lineage. Overall, our findings support the notion that key signaling events during early heart development are critical for proper lineage specification and provide evidence for early roles of Notch and WNT during mouse and human heart development. Summary statement Early fate decisions are dictated by the embryonic signaling environment. We show that Notch signaling is active during early mouse development and that activating Notch in human cardiac mesoderm enhances cardiomyocyte differentiation efficiency.