Figure 8.

Draxin-mediated defects on cranial neural crest EMT were rescued by canonical Wnt pathway components. (A) Immunostaining against Pax7 (green) and LRP5 (cyan) in hLRP5 and Draxin-FLAG–coelectroporated (magenta) embryos. (B) Immunostaining against Pax7 (green) and GFP (cyan) in embryos that were coelectroporated with Draxin-FLAG (magenta) and a β-catenin gain-of-function mutant construct, which lacks the first 90 amino acids of the mouse protein, is fused to a C-terminal EGFP and is driven by the FoxD3 NC1 enhancer (NC1-Δ90βcat). Bars, 100 µm. (C) Quantification of relative maximum migration distance indicated coelectroporation of either hLRP5 (n = 6) or NC1-Δ90βcat (n = 8) with Draxin-FLAG significantly rescued emigration of Pax7⁺ neural crest cells from Draxin-FLAG overexpression. Statistical significance was determined using one-way ANOVA with Tukey’s post hoc test. *, P = 0.02, P ≥ 0.50. For ease of visual comparison, the means of relative maximum migration distance for pCI-H2B-RFP and Draxin-FLAG from Fig. 4 are presented in this figure again as gray circles. Each circle represents the average of six measurements per embryo taken over a 300-µm anterior-to-posterior region of cranial neural crest. Black bars, mean ± SEM. (D) Schematic of proposed model for Draxin function. When canonical Wnt signaling is active, Wnt forms a ternary complex with the Frizzled (Fz) and LRP receptors, causing stabilization of β-catenin (B-CAT) and its subsequent localization to the nucleus, where it functions as a transcriptional activator. When Draxin (D) is present, it attenuates canonical Wnt signaling by interacting with LRP extracellularly, occluding Wnt/Fz association and resulting in β-catenin degradation, which can then no longer activate transcription.