Performing Axon Orientation Assays with Secreted Semaphorins and Other Guidance Cues

The guidance of axons within the developing nervous system is orchestrated by a variety of cues that successively and complementary attract or repel axons to achieve a stereotyped wiring of neural circuits. Here we present a version of a method that has been widely used to identify and characterize the effect of guidance cues on the orientation of axons. We describe the coculture, within a three-dimensional environment, of dorsal spinal cord explants together with a cell aggregate secreting a candidate cue and the method to quantify the effect of this cue on axon orientation.