The heart field transcriptional landscape at single-cell resolution

Organogenesis requires the orchestrated development of multiple cell lineages that converge, interact, and specialize to generate coherent functional structures, exemplified by transformation of the cardiac crescent into a four-chambered heart. Cardiomyocytes originate from the first and second heart fields, which make different regional contributions to the definitive heart. In this review, a series of recent single-cell transcrip-tomic analyses, together with genetic tracing experiments, are discussed, providing a detailed panorama of the cardiac progenitor cell landscape. These studies reveal that first heart field cells originate in a juxtacar-diac field adjacent to extraembryonic mesoderm and contribute to the ventrolateral side of the cardiac pri-mordium. In contrast, second heart field cells are deployed dorsomedially from a multilineage-primed pro-genitor population via arterial and venous pole pathways. Refining our knowledge of the origin and developmental trajectories of cells that build the heart is essential to address outstanding challenges in car-diac biology and disease.