Fig. 5

Fig. 5 Achievement of cardiac A–P pattern does not require cardiac fusion. (A) Ventral view of a 48-hpf Casanova (cas) mutant embryo stained with MF20 (TRITC) and S46 (FITC), anterior at the top. Red fluorescence indicates MF20 staining of ventricular tissue (arrowheads) in the anterior portion of each lateral heart, while yellow fluorescence indicates the overlap of S46 and MF20 staining in atrial tissue (arrrows) in the posterior portion of each lateral heart. Staining of eye musculature with MF20 is also apparent just medial to each eye. (B–J) Dorsal views, anterior at the top, of wild-type and cas mutant embryos. (B, E, H) Expression of cmlc2 in wild-type embryos. (C, F, I) Expression of cmlc2 in cas mutant embryos. (D, G, J) Expression of vmhc in cas mutant embryos. (B, C, D) 18-somite stage; while cardiac fusion begins in wild-type embryos (B), the myocardial precursors in mutant embryos (C) remain stationary. vmhc-expressing cells in mutant embryos are located medially (D). (E, F, G) 21-somite stage; while the cardiac cone forms in wild-type embryos (E), myocardial precursors in mutant embryos (F) bend slightly toward the midline, led by vmhc-expressing cells (G). (H, I, J) 24 hpf; as a tube forms in wild-type embryos (H), myocardial precursors in mutant embryos (I) appear to form modified cones, with vmhc-expressing cells leading the way (J). In both wild-type (H) and mutant (I) embryos, there is an apparent condensation of preventricular tissue (arrowheads) while preatrial tissue (arrows) remains more diffuse.