Netrin proteins are a family of laminin-related secreted proteins that provide guidance signals for axonal growth and cell migration during development. Netrin signaling is dependent on the concentration of calcium outside the cell and the level of PKA activity. In axonal cells, a reduction in PKA activity converts the responsiveness of the axons to the netrin proteins as the cells are repelled, rather than attracted, by the netrin gradient. Neogenin serves as the primary guidance receptor for netrin-3. Netrin-2 and the corresponding mouse homolog netrin-3 are expressed primarily in the lower two-thirds of the spinal cord, and, like netrin-1, they can either attract or repel commissural axons at a distance. Netrin-3 proteins are associated with the axon fibers projecting from motor neurons and from neurons within sympathetic and sensory ganglia, suggesting that netrin-3 may be involved in pathfinding and fasciculation of axon projection. Neogenin serves as the primary guidance receptor for netrin-3. During peripheral nerve development, high netrin-3 expression has been detected in mesenchymal cells, sensory ganglia and muscles. In humans, the gene encoding for the netrin-3 protein is localized to chromosome 16p13.3.