Netrin 1 (Ntn1)

Netrin is a class of protein involved in axon guidance, genetically conserved across C. elegans, Drosophila, frogs, and mice. The genes that encode the first discovered netrins was found to be 50% identical to the gene the unc-6 protein that plays a role in the development of neural systems in nematodes.
Netrin-1 is a growth cue which is expressed in neuroepithelial cells in the optic nerve head (ONH). Although it is not required for retinal ganglion cell (RGC) axons to reach the ONH, it does favor their entrance by means of chemoattraction. However, growth of Xenopus RGC's on laminin substrate change the Netrin-1 response to chemorepulsion, which causes the RGC axon to be pushed into the optic nerve head.