Aswith nerve growth factors, they form a family of (diffusible) proteins secretedby target cells, generally having attractive influences on outgrowing axons. They not only attract, but also repel other neurons. Netrin-1 is formed and secreted in thefloor plate of the neural tube and netrin-2 in the lower regions of the neuraltube. Netrin-1 is credited with being aguidance factor that attracts or repels axons growing to target sites. All told, though, they guide cell and axon migration,and are thus crucial in brain development (e.g., a lack of netrin in miceresults in a failure of the corpus callosum or hippocampal commissure to form). Netrin was first identified in thenematode Caenorhabditis elegans in1990 and labeled Unc-6, with the mammalian homologue being discovered in 1994(now five netrins have been revealed).
See Caenorhabditiselegans (C.) elegans (or nematode), Cell migration, Corpus callosum, Dorsal commissural interneurons, Growth cone, Hippocampus, Neural tube, Unc-6