The cardiac defects induced by the knockdown of zebrafish GSK3α and GSK3β. Anti-sense morpholino oligonucleotide (MO), which was designed to specifically inhibit the translation of either gsk3α-(gsk3α-MO) or gsk3β-mRNA (gsk3β-MO), was injected into one-celled stage embryos and the heart morphology was observed at the stage as indicated. The elongation of heart tube was normally developed at 24 hpf in the wild-type (A) and in the gsk3β morphants (C); whereas the heart of gsk3α morphant did not elongate to from a heart-tube (B). The wild-type (D) and gsk3β morphant's heart (F) developed normally at 30 hpf, but the heart of gsk3α morphant was still retardant development at 30 hpf (E), and even ceased at heart-cone stage at 36 hpf (F). Compared to the wild-type (G), however, the heart positioning was abnormally in the gsk3β morphant at 36 hpf (I, J). Eventually, both gsk3α and gsk3β morphants displayed an unlooped and stretched heart (L, M). The heart morphology of embryos injected with the control MO was also observed at 72 hpf (N). a: atrium; v: ventricle.