Abstract
During vertebrate heart development two progenitor populations, first and second heart fields (FHF, SHF), sequentially contribute to longitudinal subdivisions of the heart tube (HT), with the FHF contributing the left ventricle and most of the atria, and the SHF the rest of the heart. Here we study the dynamics of cardiac differentiation by tracking individual cells in live analysis of mouse embryos. We report unexpected temporal regulation of cardiac differentiation and its coordination with heart tube morphogenesis. During an initial phase, FHF precursors differentiate rapidly to form a cardiac crescent, while limited morphogenesis takes place. In a second phase, no differentiation occurs while extensive morphogenesis results in HT formation. In a third phase, cardiac precursor differentiation resumes and contributes to SHF-derived regions and the dorsal closure of the HT. These results reveal tissue-level coordination between morphogenesis and differentiation during HT formation and provide a new framework to understand heart development