Expression of a chimeric CSF1R-LTK mediates ligand-dependent neurite outgrowth

In an earlier screening, we identified several genes for kinases that might control the extension of neurites. One of these genes encoded a leukocyte tyrosine kinase (LTK), which is a receptor tyrosine kinase whose ligands remain to be identified. To examine the possible role of this LTK in neurite outgrowth, we constructed a chimeric receptor, in which the extracellular domain of the receptor for colony-stimulating factor-1 was fused to the cytoplasmic domain of LTK, which allowed the selective activation of LTK by colony-stimulating factor-1. Our studies using this chimeric receptor suggest that activation of the tyrosine kinase activity of LTK is sufficient to promote neurite outgrowth through pathways that include reactions catalyzed by phosphatidylinositol 3-kinase and MAPK.