Endoderm and cardiogenesis new insights.

Classic studies of vertebrate heart development have implicated the endoderm in an inductive role, based on its ability to induce rhythmic beating in explants of presumptive heart mesoderm. Recent experiments, aided by the use of heart-specific molecular markers, have defined discrete phases of cardiogenesis that depend on endodermal signals for functional contractility. In addition, the ability of the endoderm to generate a beating heart from tissues fated to form other cell types suggests that endoderm may also be involved in the initial specification of the early heart field.