Fig. 11

Model of early RA requirements in patterning the zebrafish heart. RA signaling restricts the cardiac progenitor populations within the ALPM. Normally, FHF (green) and anterior SHF (purple) lie adjacent to each other within bilateral populations. Posterior RA signaling limits the boundary of the cardiac progenitor field. As the tube forms, SHF-derived cells are added to the arterial pole of the heart tube, giving rise to ventricular CMs and smooth muscle in the bulbus arteriosus (yellow). At the venous pole, pacemaker CMs (blue) differentiate. In the absence of RA, the FHF progenitors are expanded, while the number of SHF progenitors are actually not initially affected, they may be expanded posteriorly within the ALPM. However, the SHF progenitors that will give rise to the OFT prematurely differentiate, leading to a loss of the SHF-derived-arterial pole and OFT in the enlarged hearts. Pacemaker CMs fail to differentiate at the venous pole of the enlarged hearts in RA-deficient embryos.