Fig. 2

Myosin expression and giant danio DM heart morphogenesis. Myosin (MYH1) immunoreactivity of DM heart at 24 hpf (A), the fish rotated 45 degrees from the AP midline. MYH1 immunoreactivity in a 48 hpf DM larvae (B) showing segmentation of the heart with the ventricle and atrium shifted more toward the midline compared to 24 hpf. MYH1 immunoreactivity in a 72 hpf DM larvae showing pectoral and jaw skeletal muscle, and the segmented heart (ventricle, atrium, and sinus venosus) with the ventricle shifted to the right of the AP midline plane and the atrium remaining on the left (C). Note abundant luminal cardiac trabeculae projecting into the center of the ventricle while they are absent in the atrium and sinus venosus. Myosin staining of DM heart at 2 wpf (D), framed by pectoral and jaw muscles. Only the ventricle can be observed from the ventral view as the atrium is rotated posteriorly. (E) Graphical representation of morphogenesis and anatomical changes to the developing heart in the first 4 dpf based on DIC live imaging and myosin staining. A = atrium, B = bulbus, SV = sinus venosus, sk. mus = skeletal muscle, V = ventricle.