Fig. 1

hand2 overexpression increases cardiomyocyte production. (A-D) In situ hybridization depicts cmlc2 expression at 18 somites in (A) wild-type embryos, (B) hand2-overexpressing embryos (hand2 OE), (C) embryos expressing a DNA binding-deficient form of hand2 (hand2 EDE) and (D) embryos expressing a dimerization-deficient form of hand2 (hand2 P); dorsal views, anterior upwards. Broader expression of cmlc2 is found within the ALPM of embryos overexpressing hand2 or hand2 EDE. (E) Average area of cmlc2 expression, in arbitrary units, in wild-type embryos and in embryos overexpressing hand2, hand2 EDE or hand2 P. Error bars indicate s.d.; asterisks indicate significant differences from wild type. Overexpression of hand2 or hand2 EDE increases area of cmlc2 expression (n=13-25; *P<0.001), whereas overexpression of hand2 P does not (n=11; P=0.87). (F) Bar graph compares average number of cardiomyocytes at 36hpf in wild-type embryos and in embryos overexpressing hand2. Error bars indicate s.d.; asterisk indicates a significant increase compared with wild type (n=17-19; *P<0.001).