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. Author manuscript; available in PMC: 2011 Nov 1.
Published in final edited form as: Trends Neurosci. 2010 Sep 21;33(11):485–492. doi: 10.1016/j.tins.2010.08.005

Figure 3. Axon guidance checkpoint.

Figure 3

Commissural axons (CA) cross the midline of the spinal cord to ascend on the opposite side. Their growth cones are initially attracted by a gradient of Netrin-1 secreted by midline cells, which binds to DCC receptors. After crossing the midline, growth cones are repelled by a gradient of Slit secreted by midline cells, which binds to Robo receptors. Insensitivity to Netrin-1 is mediated by interaction of DCC with activated Robo that constitutes a checkpoint for midline crossing. Attraction of growth cones is subsequently mediated by a gradient of Wnt binding to Frizzled receptors.