Figure 2. Hh signaling acts during gastrulation and early somitogenesis to limit IFT cardiomyocyte production and promote atrial cardiomyocyte production.

(A-C) In situ hybridization depicts amhc expression at 22 somites (s). Dorsal views; anterior toward the top. Embryos treated with CyA at tailbud stage (B) express amhc in fewer cells relative to controls (A). Embryos treated with CyA at 10 s exhibit normal amhc expression (C). Scale bars: 50 μm.

(D-F) In situ hybridization depicts bmp4 at 48 hpf, frontal views. Embryos treated with CyA at tailbud (E; n=12) exhibit expanded bmp4 expression in the IFT, relative to controls (D; n=44), whereas embryos treated at 10 s exhibit a normal pattern of bmp4 expression (F; n=24).

(G) Graph indicates the number of Isl1+ cardiomyocytes in the IFT at 48 hpf. Embryos treated with CyA beginning at dome or tailbud have more Isl1+ IFT cardiomyocytes, compared to ethanol-treated controls. **p<0.01; ****p<0.0001.

(H) Graph indicates the number of amhc-expressing cells at 22 s. See Materials and Methods for cell counting technique. Embryos treated with CyA at dome or tailbud have fewer amhc-expressing cells, compared to controls. ****p<0.0001.