Fig. 3

The OFT cushions in chicken HH28. The endocardial outflow tract (OFT) cushions from proximal to distal in adjacent sister sections. The septal (sc) and parietal cushion (pc) are indicated. a Both cushions appose each other in the proximal OFT. b, c They come close to each other, the Ao and Pu channels are indicated. d The sc and pc have fused showing here the NCC-derived condensed mesenchyme (c*). e The Ao channel is divided into the left visceral (vAo) and right systemic aortic (sAo) channels. f The pc shows 2 segments on both sides of the condensed mesenchyme, WT1-positive cells dorsally to the AP septum (arrow). g, h Chicken HH31. The left PAA4 has completely regressed from the OFT. Only both PAA3, PAA4R and PAA6 are present. Pu indicates the stem of both PAA6, of which PAA6R is present in g and PAA6L in h. WT1 staining reveals the mesenchyme cells surrounding the negative tunica media of the arteries. Thin arrows indicate the WT1-positive mesenchyme between the arteries. The different positions of the left and right PAA6 leave an asymmetric pericardial recesses dorsal to the arterial pole (bold arrow). Ao aortic trunk, AP aorto-pulmonary septum, AV atrioventricular cushions, FS folding septum, ic intercalated cushion, MB main bronchi, Oes oesophagus, pc parietal cushion, Pu pulmonary trunk, sAo right systemic aorta, sc septal cushion, T trachea, vAo left visceral aorta