NTF3 and cerebellar ataxia: For example, neurotrophin-3 (NT-3), a critical neurotrophic factor for the survival and maintenance of proprioceptive neurons, serves as a chemoattractant, guiding the proper outgrowth and terminal branching of sensory axons.213, –215 Mice lacking NT-3, its receptor, tyrosine kinases receptor (TrKC) or Runnx3 exhibit severe ataxia and fail to develop muscle spindles as the axons were not able to innervate the target muscles.