The cardiomyocyte proliferation effects of the cardiac natriuretic peptides are coordinated by the action of multiple natriuretic peptide receptors in vivo. (A) Lateral views of 48 hpf cmlc2:CFP embryos show significantly altered atrial and ventricular chamber sizes in Nppa/Nppb double knockdown and nppb overexpression embryos. Likewise, double knockdown of both natriuretic peptide guanylate cyclase-linked receptors, Npr1 and Npr2, caused a similar phenotype as the Nppa/Nppb double knockdown and could block the effect of nppb overexpression (npr1/npr2 MO + HS/nppb). Finally, the knockdown of Npr3 caused a significant reduction in both atrial and ventricular chamber sizes that was similar to that observed after overexpression of nppb. (B) Corresponding heart surface areas of all treatment groups shown in A. *P<0.05 compared with control heart size, #P<0.05 compared with HS/nppb alone. (C) Cardiomyocyte proliferation was increased in the Npr1 and Npr2 knockdown embryos, whereas Npr3 knockdown embryos had reduced cardiomyocyte proliferation at 52 hpf as assessed by BrdU labeling of cardiomyocytes. *P<0.01 compared with control. (D) Differentiation of ventricular cardiomyocytes between 30 and 48 hours of heart development was not altered by knockdown of the natriuretic peptide receptors. White arrowhead denotes arterial pole, areas of green tissue were added after 30 hpf (non-photoconverted). Yellow tissue is a mixture of photoconverted red tissue and non-photoconverted green tissue. All data are expressed as mean + s.e.m. Scale bars: 100 μm.
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