Expression of TGFβ type III receptor. (a) Normal left and right atrium of HH20. No TBRIII expression in atrial endocardium. (b) Ligated embryo with ectopic TBRIII expression along the atrial septum and atrial floor (arrows). (c) AV cushions of normal HH22 embryo, TBRIII expression is downregulated. (d) Ligated embryo with prolonged endocardial TBRIII expression (arrows). (e) Normal HH20 embryo, ventricular trabeculations lack TBRIII. (f) Ectopic TBRIII expression of the endocardium lining ventricular trabeculations after ligation (arrows). (g) Higher magnification of the boxed area of (e). (h) Higher magnification of the boxed area of (f). IAV: inferior AV cushion, LA: left atrium, RA: right atrium, SA: superior AV cushion.