Fig 9.

The actc1a^s434 mutation disrupts atrioventricular specification events that precede endocardial cushion formation. In situ hybridization was performed for the following markers in both wild-type (A to D and I to L) and mutant (E to H and M to P) embryos at 55 hpf: notch1b, nfatc1, the versican gene, bmp4, amhc, vmhc, klf2a, and actc1a. (A and E) The notch1b transcript is localized to the endocardial AVC by 55 hpf in the wild-type embryos (arrowhead); however, it appears disorganized and downregulated in the mutants. (B and F) nfatc1 is also localized to the endocardial AVC in wild-type embryos (arrowhead), while it appears decreased and not localized in the mutants. (C and G) The versican gene transcript is restricted to the myocardial AVC in the wild-type embryos by 55 hpf (arrowhead), while it is disorganized and decreased in the mutants. (D and H) bmp4 is expressed in the myocardial AVC (arrowhead) and partially within the atrium (asterisk). In the mutant, bmp4 is still restricted to the AVC (arrowhead), but appears upregulated in the atrium (asterisk). (I and M) Wild-type amhc expression is restricted to the atrium at 55 hpf, while the mutant amhc expression is expanded, indicative of dilated atrium. (J and N) vmhc expression is not affected in the mutant embryos. (K and O) Wild-type expression of klf2a is restricted to the endocardial AVC (arrowhead). klf2a expression is mislocalized in the mutant embryos. (L and P) actc1a expression is restricted mostly to the ventricle in both the wild-type and mutant embryos. No significant change in actc1a expression is apparent.