(A) Time-lapse imaging of DIV7 cultured hippocampal neurons before and after Semaphorin stimulation. Upper panel: Axon growth without Semaphorin stimulation. Middle panel: stimulation with Sema3A (0 hours) (1nM, n=669 axons for WT, 761 axons for knockout) causes retraction of both WT and crmp2-/- neurons. Lower panel: stimulation with Sema3F (5 nM, n=602 axons for WT, 955 axons for knockout) causes axon retraction in WT, but not in crmp2-/- neurons. Red triangles depict growing axons, yellow retracting axons and blue asterisks indicate steady non-growing axons. Scale bars: 100 μm (whole image field) and 50 μm (magnified). 