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Fig. 5 Hedgehog signaling activity is required early for the formation of the appropriate number of cardiomyocytes. (A) Quantification of the number of vmhc-expressing cells per bilateral heart field at the 18-somite stage, comparing control embryos with embryos treated with CyA beginning at the indicated stages. Values represent the mean cell number for each category (±s.d.). Asterisks indicate statistically significant differences from controls (P<0.004). (B) Representative images of vmhc expression at the 18-somite stage in control embryos and embryos exposed to CyA beginning at the indicated stages. (C) Quantification of the impact of inhibiting Hh signaling during defined time windows on the number of vmhc-expressing cells. CyA was added at dome stage and removed at indicated stages. CyA control embryos were exposed continually between the dome and 18-somite stages. Asterisks indicate statistically significant differences from ethanol controls (P<0.0024). Double asterisks indicate that a treatment also results in a statistically significant difference from CyA controls (P<0.001). (D) Representative images of vmhc expression in embryos treated as indicated.