Hedgehog (Hh) level controls Rohon-Beard mechanosensory neurons (RBs) and neural crest formation. A-C: The number of lateral neurons (either elv3-positive [A] or isl1-positive [B inset]) and trunk neural crest [NC] cells [C], foxd3, rectangular domain shown in the photo at the bottom) are counted for groups of embryos (wild-type [WT], MO-tri, smu, shh, twhh, and hsp;shh) and analyzed in mediolateral distance (MLD) time. As in Figure 5, cell count results were expressed as the difference from the uninjected WT controls of the identical MLD stage ({delta}WT, cells/side). P values from statistical analysis by Tukey's multiple comparison test after one-way analysis of variance (A, B inset, and C) are shown with symbols: ***, P < 0.001; **, P < 0.01; *, P < 0.05; and n.s. (not significant) P > 0.05. RB differentiation index (ratio of lateral isl1 cells to lateral elv3 neurons) are calculated from mean values of elv3 and isl1 cells and shown as a bar chart. For application of Ryan's multiple comparison test of proportions, calculated ratios were rounded to the nearest integer, and P values at the significant level of 0.05 are shown with symbols: *, P < 0.05; n.s. (not significant) P > 0.05. Note that the loss-of-function Hh mutant smu showed a decreased RB differentiation index, demonstrating the requirement of Hh signalling in the lateral proneural domains. C: The loss-of-function Hh mutant smu showed significantly increased numbers of foxd3-positive trunk neural crest cells (***, P < 0.001 in Tukey's test after one-way analysis of variance). D: Models of Hh function on lateral neurogenesis and neural crest formation. Hh signalling adds fine adjustment on the established neural fates (neuron vs neural crest). Selec, selection; Spec, specification; Det, determination (the establishment of commitment); Diff, differentiation (onset of differentiation).
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