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Fig. 6-S4
Nodal activity gradients in under- and over-rescued lefty double mutants.
To examine the tolerance to variation in Nodal signaling gradients, lft1-/-;lft2-/- embryos were exposed to 1 µM (‘under-rescued’, (A–A’’’)), 2 µM (‘rescued’, (B–B’’’)), or 3 µM (‘over-rescued’, (C–C’’’)) of the Nodal inhibitor drug SB-505124 beginning at the 8 cell stage. Embryos were fixed at 50% epiboly and stained for pSmad2 as described in the Materials and methods section. The under-rescue treatment leads to marked expansion of the Nodal signaling gradient (A’, A’’) and phenotypes at 1 day post-fertilization (dpf) consistent with hyperactive Nodal signaling (A’’’). The over-rescue treatment leads to a Nodal gradient with reduced amplitude (C’, C’’) and phenotypes consistent with mild Nodal loss of function (e.g. cyclopia) (C’’’). Images in A’’, B’’, and C’’ are cropped as indicated from A’, B’, and C’, respectively. Note that rescuing concentrations of SB-505124 vary from batch to batch, but are internally consistent within each experiment.