Figure 2.

Early segregation of the cardiogenic and haemogenic roads. A likely existing bipotent early progenitor in the epiblast gives rise to both a Flk1+ /Brachyury+ and a Flk1-/Brachyury+ cell population, under the action of BMP4 secreted by the extraembryonic ectoderm (ExE) and BMP2 in the visceral endoderm (VE), respectively. This early event already segregates the future haemogenic and cardiogenic (i.e. myocardial) cell populations. A parallel route used by a Flk1+ lineage re-emerging from a Flk1- cell population, and also possibly part from the hemangioblast lineage leads to the endocardial cell population.