(A–C) Grayscale inverted images of gut preparations from E12.5 control (A), Celsr3^–/– (B), and Fzd3^–/– (C) embryos immunostained for TuJ1. Arrows indicate the position of the most caudally located neurons. (D–F) High magnification of equivalent midgut areas from preparations shown in A–C. Red arrows in D indicate the prominent longitudinal tracts found in control midguts, which were absent in mutant embryos. (G–I) Analysis of the distribution of the developing neuronal plexus in either one of the 12 directions (15° wide from –90° to +90°). The gray dotted line indicates the hypothetical case in which TuJ1⁺ neuronal tracts were organized randomly (equal distribution over all bins, 180°/12 = 0.083). A Gaussian fit was used to identify the dominant direction in each genotype. In mutants, the plexus orientation deviates less from the random order and is significantly different from the control (N = 6 per genotype). Two-way ANOVA, P < 0.0001; Bonferroni’s post-hoc test, *P < 0.05, **P < 0.01, and ***P < 0.001. (J–L) DiI tracing in control (J), Celsr3^–/– (K), and Fzd3^–/– (L) E12.5 midguts. Left and right panels indicate the rostral and caudal sides of tracings, respectively. Note the dramatic reduction in the number and length of longitudinal projections and the number of cell bodies (arrows) in mutant preparations. ca, caecum; hg, hindgut; mg, midgut; st, stomach. Scale bars: 500 μm (A–C), 50 μm (D–F), and 100 μm (J–L).