Nr2f1a functions redundantly with Nr2f2 to restrict ventricular CM number.

(A-D) Frontal view of hearts from nr2f1awt; nr2f2wt, nr2f1amut; nr2f2wt, nr2f1amut; nr2f2het, and nr2f1amut; nr2f2mut embryos at 48 hpf with immunohistochemistry (IHC). Atria (AMHC)—green. Ventricles (MHC)—red. (E) CM number from hearts of nr2f1actrl; nr2f2ctrl (n = 24), nr2f1amut; nr2f2wt (n = 10), and nr2f1amut; nr2f2het (n = 16), and nr2f1amut; nr2f2mut (n = 10) embryos with the myl7:h2afva-mCherry transgene at 48 hpf. Although embryos WT for nr2f1a and nr2f2 alleles are shown in all images for comparison to nr2f1a; nr2f2 mutants, other allele combinations were indistinguishable from WT and pooled for data analysis. Therefore, nr2f1actrl; nr2f2ctrl indicates analysis performed with the combination of nr2f1awt; nr2f2wt; nr2f1ahet; nr2f2wt, nr2f1awt; nr2f2het, and nr2f1ahet; nr2f2het embryos.