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Trajectories and average velocities of migrating cells within the cardiac cone. A–G: First frame of time lapse movies taken from a dorsal view of Tg(myl7:eGFP) embryos overlaid with cell trajectories. Yellow tracks: left cells. White tracks: center cells. Red tracks: right cells. A: All cells exhibit trajectories directed toward the anterior and left in WT embryos. B: Bilateral expression of spaw in ntl morphants leads to loss of L/R asymmetry in cardiac cell migrations. C–G: L/R directionality is also absent in embryos C: lacking the Nodal ligand spaw; D: treated with the SB-505124 Nodal inhibitor drug E: lacking spaw and one functional copy of bmp4; F: injected with both bmp4 and spaw morpholinos; and G: homozygous midway mutants. H: Numbers within each bar indicate the number of cells tracked on the left, center and right for all embryos of each genotype. The number of embryos utilized in analysis is indicated (n = ) for each genotype. WT embryos exhibit differences in average cell velocities along the L/R axis, with left cells migrating significantly faster than right cells. Bilateral exposure to Spaw leads to significant increases in average velocities in left and right cells of ntl morphants, while loss of Spaw and global inhibition of Nodal signaling through drug treatment results in significantly decreased rates of migration. In embryos with diminished Bmp signaling along with loss of Spaw, average cell velocities are significantly increased compared with loss of Spaw alone. Error bars in H indicate standard error of the mean. MO: morpholino. Het: Heterozygotes.
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