Heart asymmetry was affected in gsk3β morphants. Normally, bmp4 transcripts accumulate predominantly on the left side of the heart tube at 20 hpf (A, B), and the left-predominant bmp4 asymmetry persists through the stages of jogging (G). However, in gsk3β morphants, the expression of bmp4 becomes symmetrical at 20 hpf (B, D). In gsk3β morphants, in which the heart fails to jog, bmp4 is more evenly distributed in the heart region (H, I). The left-sided lefty-1 domain was greatly reduced in gsk3β morphant hearts at 16 hpf (F). All are dorsal views. B, E are higher magnifications of A, D, respectively. Lines mark the midline. L, embryo left.