Abstract 19676: A Molecular Switch Regulating Heart and Pancreatic Development

The mesendoderm is thought to be a population of the intermediate and transient common progenitors prior to the emergence of the mesoderm (Me) and the endoderm (En) in vitro; however, it is unclear whether it exists in vivo, and if so, what are the molecular mechanisms that establish the subsequent Me or En fate of the mesendoderm. Here we show that Mesp1 transiently marks a subset of the epiblast at the primitive streak (PS) initiation site at gastrulation in vivo. It is also evidenced by the cell fate mapping that the progeny of Mesp1+ progenitors gives rise to both the Me and the definitive En, but neither the primitive En nor the ectoderm, suggesting that Mesp1+ cells are the bio-potent mesendodermal progenitors. Mesp1-fated dorsal foregut En (derived from the definitive En) subsequently contributes exclusively to the Pdx1+/Foxa2+ progenitors in the pancreatic bud (PB), and ultimately to the endocrine cells in the pancreas. RNA-seq and chromatin-immunoprecipitation of Mesp1-fated cells show that Mesp1...