Tyrosine phosphorylation and protrusive structures of the growth cone.

Protein-tyrosine kinase, such as those of the trk and Eph families, serve as membrane receptors for extracellular cues which regulate the rate and direction of growth of numerous groups of axons. Certain cytoplasmic protein-tyrosine kinases, such as src, are also abundant in growth cones. But, how protein-tyrosine phosphorylation regulates the growth cone is poorly understood. We discuss here potential roles for tyrosine phosphorylation in the protrusive structures of the growth cone, especially filopodia, which are important in detecting cues. A particular focus is the integrin receptor for substrate-bound growth promoters like laminin. Changes in tyrosine phosphorylation may be important in both facilitating and mediating the interaction of filopodia with these growth promoters.