Defects in sensory nerve numbers and growth in mutant Kit and Steel mice

The roles in the nervous system of the receptor tyrosine kinase Kit and its ligand, Steel factor, are unclear. We have now found first, that sensory n erve populations are reduced in mutant Kit and Steel mice, implicating Stee l-Kit interactions in neuronal development. Second, sensory axonal regenera tion (which occurs independently of nerve growth factor, or NGF) is impaire d, while collateral sprouting (NGF dependent) is normal. Therefore, there i s a selective involvement of Kit signal transduction pathways in nerve grow th; supporting this, in wild-type animals Kit was up-regulated in regenerat ing, but unchanged in sprouting, sensory neurons. The receptor tyrosine kin ase Kit thus contrasts with the receptor tyrosine kinase trkA, which is act ivated by the sprouting stimulus (NGF) but not by the axonal regeneration s ignal. NeuroReport 11:1159-1165 (C) 2000 Lippincott Williams & Wilkins.