Bmp4 is required for LR patterning. (A, B) Spw expression in the left LPM and ntl expression in the notochord in control MO-injected embryos (A) and bilateral spw expression in bmp4 splice MO-injected embryos (B) at the 18 somite stage. (C, D) pitx2 expression in the posterior LPM (arrow) of control MO-injected embryos at the 22 somite stage (C) is predominantly absent or reduced when embryos are injected with bmp4 splice MO (D). (E, F) Cyclops is broadly expressed but stronger in the left anterior LPM of wt or control MO-injected embryos at the 22 somite stage (arrow in panel E). Although still being expressed, the asymmetry in cyclops expression is lost when embryos have been injected with bmp4 splice MO (F). (G, H) Normal lefty1 expression in the notochord and left cardiac field of 22 somite stage embryos (G) is absent from embryos injected with bmp4 splice MO (H). (I, J) Normal cardiac jogging in control MO-injected embryos (I) and loss of cardiac jogging in embryos injected with bmp4 splice MO (J) revealed by cmlc2 expression. Dorsal view, anterior to the top of 30 hpf embryos. (L, M) Visceral organ laterality revealed by foxa3 expression in control MO-injected embryos (L) and embryos injected with bmp4 splice MO (M) resulting in organ duplications and failed gut looping.
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