Abstract
In embryos, pluripotent stem cells and multipotent progenitors must divide and produce distinct progeny to express their full developmental potential. In vertebrates, mounting evidence point to the existence of multipotent cardiopharyngeal progenitors that produce second-heart-field-derived cardiomyocytes, and branchiomeric skeletal head muscles. However, the cellular and molecular mechanisms underlying these early fate choices remain largely elusive. The tunicate Ciona has emerged as an attractive model to study early cardiopharyngeal development at high spatial and temporal resolution: through two asymmetric and oriented cell divisions, defined multipotent cardiopharyngeal progenitors produce distinct first and second heart precursors, and pharyngeal muscle (aka atrial siphon muscle, ASM) precursors. Here, we demonstrate that differential FGF-MAPK signaling distinguishes between MAPK-negative heart precursors, and MAPK-positive multipotent progenitors and ASM precursors. We characterize an FGF-MAPK-driven feed-forward circuit that promotes the successive activations of essential cardiopharyngeal determinants, Tbx1/10 and Ebf. Finally, we show that coupling FGF-MAPK restriction and cardiopharyngeal network deployment with cell divisions permits the emergence of diverse cell types from common multipotent progenitors.
