Fig. 7

The Pandora (pan) mutation affects ventricle formation as well as early expression of cmlc2 and vmhc. (A) Head-on view of a 48-hpf pan mutant embryo stained with MF20 (TRITC) and S46 (FITC), dorsal at the top. A thin stalk of ventricular tissue (red) is attached to the rostral end of a bulbous atrium (yellow). (B, E, H) Expression of cmlc2 in wild-type embryos. (C, F, I, K) Expression of cmlc2 in pan mutant embryos. (D, G, J, L) Expression of vmhc in pan mutant embryos. (B–D) Head-on views, dorsal at the top, of 48-hpf embryos. In pan mutants, the heart is composed of a bulbous atrium (C, arrow) and a thin stalk of ventricular tissue (C, arrowhead). (E–L) Dorsal views, anterior at the top. (E, F, G) 18-somite stage; pan embryos exhibit relatively faint and thin bilateral stripes of cmlc2-expressing cells (F, arrows), in contrast to the robust cmlc2-expressing population of fusing myocardial precursors in wild-type siblings (E). pan embryos do not express vmhc at this stage (G). (H, I, J) 21-somite stage; pan embryos exhibit slightly stronger cmlc2 expression (I, arrows), but still far less than in wild-type embryos (H). Some pan embryos have faint bilateral patches of vmhc expression (J, arrowheads). (K, L) 36 hpf; cardiac cone formation is delayed and abnormal in pan mutants (K). Often, pan mutant cones have a split base (K, arrow). The apex of the pan cone (K, arrowhead) expresses a significant amount of vmhc (L). It is important to note that pan embryos lag behind their wild-type siblings during somitogenesis. For example, pan embryos usually have only 16 somites when their wild-type siblings have 20 somites. In (E–G) and (H–J), we are comparing pan embryos with wild-type embryos with the same number of somites; i.e., the wild-type siblings are fixed a few hours before the pan mutants. Also note that the precise morphology of the developing myocardium in pan mutants can vary; these examples represent typical expression patterns observed in a majority of mutants.