Fig 7. Syntaxin1A is required for axonal sensitivity to Slit-2 and Netrin-1.

(A-D) Explants of dI1 neurons dissected from chick embryos grown on laminin substrate extend neurites readily in the absence of Slit-2 (A). In the presence of Slit-2, neurite length is strongly reduced (B). In contrast, neurite growth from explants taken from embryos electroporated with dsRNA derived from STX1A did not differ in the absence (C) or presence (D) of Slit-2. Bar: 200 μm. (E-H) Dorsal spinal cord explants obtained from E11 wild-type and STX1A/B knock-out mouse embryos were confronted with HEK293T cells aggregates expressing or not Netrin-1. (E, F) Axons from wild-type explants showed a marked attraction when confronted to Netrin-1 expressing cell aggregates (F), in contrast to explants confronted with control cells which exhibited a radial axonal growth (E). Mutant spinal cord explants (STX1A(-/-)B(-/-)) exhibited a radial pattern of axonal growth in all conditions (G, H). Scale bar: 100μm. (I) Plots showing average neurite lengths in explants of dl1 neurons incubated with Slit-2. Significant difference is exclusively seen in wild-type explants. (two-way ANOVA analysis; * p<0.05, ** p = 0.0011, ****p<0.0001). At least, 37 explants per condition were used for quantification. The average neurite length in control explants was 214 μm in the absence of Slit-2 (A,I; n = 42 explants) and 43 μm in the presence of Slit-2 (B,I; n = 51 explants). Explants taken from embryos after silencing STX1A extended neurites with an average length of 214 μm in the absence (C,I; n = 37) and 158 μm in the presence of Slit-2 (D,I; n = 41). J) Quantification of Proximal/Distal (P/D) ratios in spinal cord mouse explants confronted to Netrin-1 expressing cell aggregates (two-way ANOVA analysis; *p<0.05).