Figure 9.

Wnt/calcium signaling guides axon growth through the corpus callosum. (A) Schematic of a cortical slice showing cortical axons extending through the corpus callosum (cc) surrounded by Wnt5a secreted by the indusium griseum (IG) and glial wedge (GW). Axons in the contralateral callosum have high frequencies of calcium transients evoked by Wnt5a signaling, which accelerates rates of axon outgrowth. In contrast, ipsilateral axons not yet responsive to Wnt5a, have low levels of calcium activity and thus grow more slowly. LV, lateral ventricle; CP, cortical plate. (B) Schematic of intracellular signaling in the postcrossing axon from (A) showing that Wnt5a gradient from the glial wedge activates RyK receptors to open IP3 receptors and TRP channels causing release of calcium from intracellular stores and calcium influx through the plasma membrane. These calcium transients activate CaMKII to accelerate axon extension and repel growth cones away from the glial wedge toward the contralateral cortex. (Reprinted from Hutchins et al., 2011).