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. 2010 Aug 18;30(33):11167–11176. doi: 10.1523/JNEUROSCI.1488-10.2010

Figure 1.

Figure 1.

Wnt5a and Wnt7a guide post-crossing commissural axons rostrally. A–D, We used in ovo RNAi to downregulate Wnts in the floor-plate area during commissural axon pathfinding. Neither Wnt11 dsRNA (dsWnt11; A) nor Wnt4 dsRNA (dsWnt4; B) injection and electroporation had an effect on post-crossing commissural axon guidance. In contrast, downregulation of Wnt5a (dsWnt5a; C) resulted in the majority of axons stalling in the floor plate. Those axons that reached the contralateral floor-plate border randomly turned rostrally (filled arrowheads) or caudally (open arrowheads). Similarly, axons failed to turn rostrally in the absence of Wnt7a (dsWnt7a; D). In general, more axons reached the contralateral floor-plate border in the absence of Wnt7a compared with Wnt5a. Injection sites with >50% of the axons stalling in the floor plate or at the floor-plate exit site, or with axons turning caudally, were considered to exhibit a severe phenotype. The percentage of injection sites with severe phenotypes was calculated per embryo (supplemental Table S1, available at www.jneurosci.org as supplemental material). Scale bar, 40 μm. E, At least 11 embryos for each experimental condition were used for quantification. In the absence of Wnt5a, a strong phenotype was observed, on average, at 34.9 ± 7.2% of the injection sites per embryo (n = 11 embryos). In the absence of Wnt7a, a strong phenotype was found, on average, at 27.9 ± 8.1% of the injection sites (n = 16 embryos). The values found after downregulation of Wnt4 (1.5 ± 1.5%, n = 11 embryos) or Wnt11 (3.4 ± 2.7%, n = 11 embryos) were not different from controls (wild type; WT). Untreated control embryos (3.0 ± 1.6%, n = 11 embryos) did not differ from EGFP-expressing embryos (1.1 ± 0.8%, n = 18 embryos). Values are given ±SEM. A two-tailed Student's t test was used for statistical analysis. ***p < 0.001 for Wnt5a versus all control groups; **p < 0.01 for Wnt7a versus EGFP controls. The p value was <0.05 for Wnt7a versus nontreated controls and versus embryos lacking Wnt4 or Wnt11, respectively (supplemental Table S1, available at www.jneurosci.org as supplemental material). R, Rostral; Ca, caudal.