ErbB Membrane Tyrosine Kinase Receptors: Analyzing Migration in a Highly Complex Signaling System

The erbB membrane tyrosine kinases (EGF receptor, erbB2, erbB3, and erbB4) are a family of structurally similar transmembrane proteins that act as receptors for the EGF and neuregulin (NRG) families of growth factors. ErbB receptors and their ligands are widely expressed by neurons and glia throughout the peripheral and central nervous system, where they promote proliferation, survival, migration, differentiation, and other effects. Precisely which effects are induced by erbB activation depends on a variety of factors. These factors include which erbB receptors are recruited to the signaling complex, whether key non-erbB intramembranous proteins (e.g., mucin 1, CD44, integrins) are present and interact with the erbB kinases and the lineage and developmental state of the cell. Different erbB ligands acting through the same receptors often also elicit distinct or even diametrically opposed effects. In this chapter, we review key aspects of the complexity intrinsic to signaling by erbB kinases and their ligands in the nervous system. We then relate this knowledge to the rational design of experiments examining erbB signaling in migration, a common response induced by erbB receptor activation. The proper performance of Boyden chamber assays is considered, together with the procedures used to identify appropriate migration substrates and to optimize key experimental parameters (cell number, migration time, comparisons of the effects of different erbB ligands, and establishing optimal concentrations of these growth factors). The use of pharmacologic inhibitors and RNA interference to establish whether specific erbB kinases are required for the migration of nervous system cells is also described.