Fig. 6

Fig. 6 Double sdf1a/cxcr7b inactivation partially restored motoneuron migration (A,D). Compared to sdf1a phenotype (A), three examples of double morphants are given: a severe case (B) which is comparable to (A) with cells arrested in r4 and r5 (arrows) and a weak case (C), which corresponds to the major phenotype: cells are retrieved in r4, r5, r6 (B, C embryos were injected at the ratio sdf1a-MO/cxcr7b-MO 1.25/1.5). (D) Typical mixed phenotype with r5 accumulation on the left side (CXCR7b phenotype) and cell accumulation along the midline on the right side with ectopic dendrites (injection at the ratio sdf1a-MO/cxcr7b-MO 0.5/1.5). H: graphic illustration of the phenotype variability from a range of concentration of sdf1a-MO (0-1.25 mM) with constant cxcr7b-MO concentration (1.5 mM). Three categories have been distinguished, the severe phenotype includes strong phenotypes of cxcr7b-MO and sdf1a-MO. The Y axis corresponds to the percentage of embryos in each group. (E–G) Motoneuron migration at 48 hpf after GM6001, MMP inhibitor, ventricular injections of Isl1-GFPembryos (24 hpf). GM6001 injected embryos (n = 25) showed a variability in cell arrest position in r4 (F, G, arrows). (G) #2 embryo displays the more severe phenotype observed (n = 5/25). No specific arrest in r5 ever occurs. (I–K) Ectopic expression of cxcr7b truncated receptor cxcr7b^Δ140 by mRNA injection. cxcr4b expression is not altered in mRNA cxcr7b^Δ140 injected embryos (J), however it reflects a failure of the migration of CXCR4b expressing cells with accumulation in r4 (arrow) at 24 hpf. (K) At 48 hpf, injected Islet1-GFPembryos display a migration defect with cell accumulation in r4 and r5 (K, arrows) and in most severe cases, ectopic dendrites (L, arrow). cxcr7b^Δ140 mRNA injection was performed at 40 pg (J, K) and 80 pg (L).