UNC is a set of proteins first identified through a set of screening tests in Caenorhabditis elegans, looking for roundworms with movement problems. Worms with which were un-coordinated (hence UNC) were analysed in order to identify the genetic defect. Such proteins include UNC-5, a receptor for UNC-6 which is one of the netrins. Netrins are a class of proteins involved in axon guidance. UNC-5 uses repulsion (genetics) to direct axons while the other netrin receptor UNC-40 attracts axons to the source of netrin production.