Fig. 1

Inflow tract tissue adjacent to the venous pole of the heart tissue expands in adult nr2f1a mutants lacking an atrium.

a Brightfield images of whole hearts from adult WT and nr2f1a^aco−/− fish. Bulbus arteriosus (BA), Ventricle (V), Atrium (A), putative Atrium (“A”). b Brightfield images of sectioned hearts stained with AFOG. Cardiac muscle – brownish-orange, Collagen - blue, fibrin - red. c ISH for amhc on adult WT and nr2f1a^aco mutant hearts. Amhc (arrowhead) in nr2f1a^aco mutant hearts is a relatively small ring adjacent to the ventricle. d, e ISH for amhc and vmhc on sectioned hearts. A restricted ring of CMs expressed both these atrial and ventricular differentiation marker genes adjacent to the venous pole of the heart (black arrowheads) f. Schematic depicting subunits of the zebrafish hearts harvested for bulk RNA-seq. g PCA analysis from the bulk RNA-seq BA, SV, A, and V samples. The SV from nr2f1a^aco mutant fish occupies space between the WT SV and BA. h Heatmap of representative marker genes summarizing SMC, EC progenitor (ECP), arterial EC (AEC), venous EC (VEC), and cardiomyocyte (CM) markers. i Schematic of the preparation procedure of juvenile hearts for wholemount IHC. j, k Confocal images of wholemount IHC of SMC markers Myosin light chain kinase a (Mylka - red) and Elastin b (Elnb - magenta) in 28 dpf hearts. l–n Confocal images of wholemount IHC of BA and SV with transgenic reporters for NC-derived cells Tg(NC:mCherry), SMCs Tg(acta2:EGFP), and vascular ECs Tg(kdrl:EGFP). NC-derived cells within the large chamber-like vessels (arrows). NC-derived contribution to adjacent tissues (arrowhead). Scale bars − 500 μm.