Arg coordinates contractile forces with adhesion dynamics in migrating neurons

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DESCRIPTION (provided by applicant): The precise control of neuronal migration by adhesive cues is essential for proper brain development. Neuron migration initiates via F-actin-rich membrane protrusion of a leading process. Adhesions anchor the protrusion and link the cellular F-actin cytoskeleton to the extracellular matrix. Actomyosin contraction then generates traction force to pull the leading process forward. This migratory apparatus is controlled by cell surface receptors that relay migratory signals to the cytoskeleton machinery. Defects in these migratory signaling pathways are known to cause neuronal migration disorders (NMDs), including cephalic disorders, agyrias, heterotopias, and epilepsy. Abl family non-receptor tyrosine kinases, including Abl and Abl-related gene (Arg), are important regulators of neuron migration in developing animals. abl-/-arg-/- double knockout mice exhibit significant cerebellar deformities caused by aberrant cerebellar granular neuron migration. The Rho inhibitor p190RhoGAP-A is a major Arg substrate in the developing brain. I have shown that integrin engagement localizes Arg to specific regions at the cell periphery, where Arg activates p190A to inhibit Rho-induced cell-matrix adhesions (focal adhesions) and contractile bundles of actin and myosin (stress fibers). Arg inhibition of stress fibers leads to a decrease in cell contractility. The effects of Arg on cell contractility and focal adhesion dynamics attenuate cell migration on adhesive substrates. I found that Arg, not Abl, played the major role in these cell migration phenotypes. I hypothesize that Arg coordinates contractile and adhesive processes in migrating neurons to ensure accurate neuronal positioning. The goal of my proposal is to determine how Arg coordinates contractility and adhesion dynamics in migrating cerebellar granular neurons. In aim 1, I will determine how Arg locally regulates contractility in migrating fibroblasts, as a model system for neuronal migration. In aim 2, I will determine how Arg regulates focal adhesion dynamics in migrating fibroblasts. In aim 3, I will determine how Arg coordinates contractility and adhesion in migrating cerebellar granular neurons. Overall, these experiments should provide a detailed molecular framework for understanding the causes of NMDs and potentially discovering novel therapies or drug treatments that alleviate the symptoms of those suffering from NMDs. Neuronal migration disorders lead to severe developmental and cognitive disorders, but the signaling mechanisms that coordinate migratory machinery in properly-migrating neurons are unknown. I propose a novel signaling pathway that coordinates contractility and adhesion in migrating neurons.