Fig. 2

Jogging laterality phenotypes.

Embryos were scored for laterality of cardiac jogging between 24 and 30 hpf. A-C: Dorsal views of the heart at 24 hpf showing jogging laterality phenotypes by RNA in situ hybridizations using the myl7 probe D: WT embryos exhibit primarily left-directed cardiac jog, as do bmp4^Y180 mutants (I) lacking both maternal and zygotic bmp4 (MZbmp4). E,F: While WT embryos injected with spaw morpholino [9] and late-zygotic (LZ) oep mutants display randomized jogging laterality, H: MZbmp4^Y180 mutants injected with spaw morpholino lack significant jogging asymmetries. I: Loss of bmp4 alone does not affect jogging laterality and resembles WT (D) suggesting Bmp is dispensable for correct jogging when asymmetric Nodal signals are present. J: Jogging laterality in the absence of Spaw is highly sensitive to the level of Bmp4 present, as loss of a single functional copy of bmp4 in embryos deficient for Spaw is sufficient to result in predominantly midline jogging phenotypes. K: midway mutants homozygous for a nonsense mutation in the Nodal transcription factor FoxH1 display jogging phenotypes similar to what is observed in embryos lacking both Nodal and Bmp signaling. We note that a discrepancy exists between the randomized jogging of spaw morphants and the predominantly midline jogging of SB-505124-treated embryos (G). As described in more detail in the discussion, these phenotypic differences are likely due to the more global inhibition of TGFβ signaling achieved through drug treatment and we believe reflects the involvement of a second, as yet unidentified, TGFβ ligand in establishing jogging laterality. MO: morpholino. Het: Heterozygotes. Mut: Mutant. Asterisk: jogging data presented supplementary to [9].