CAREER: Regulation of Growth Cone Dynamics by Actin Depolymerizing Factor

University Of North Dakota Main Campus, Grand Forks ND

Investigators

Abstract

IBN 0093359 PI: Meberg, Peter Abstract During the development of the nervous system individual neurons must extend their axons and form synaptic contacts with other neurons or muscles. The growing tips of axons, the growth cones, are able to navigate to their appropriate synaptic targets by responding to extracellular cues. This growth cone motility and navigation is regulated by the directed assembly of actin filaments. Many extracellular matrix proteins, growth factors and other signaling molecules can regulate actin dynamics, but the intracellular effectors that link signal transduction pathways to actin reorganization in neurons are not well characterized. Actin depolymerizing factor (ADF) and related proteins may be important targets of these signals since: 1) ADF is essential for actin-dependent motility in other simpler systems; 2) ADF is present in growth cones; 3) ADF activity is regulated by many signal pathways; and 4) increased ADF activity increases the extension of axons. The first objective of Dr. Meberg and his students will be to determine how changes in ADF activity affect growth cone structure and dynamics in primary neuronal cultures. Changes in ADF activity will be accomplished though antisense suppression of ADF expression as well as the expression of mutant forms of ADF and LIM kinase using recombinant adenoviruses. LIM kinase inhibits ADF activity by phosphorylation. Dr. Meberg will then ascertain if growth cone responsiveness to extracellular cues involves changes in ADF activity. This will be accomplished first by assaying if changes in the phosphorylation state/activity of ADF are locally or globally induced within growth cones and neurons by guidance cues normally present in the nervous system. Finally, they will perform assays to determine if signaling through ADF is required for responsiveness to discrete extracellular cues, using the ADF and LIMK mutants that prevent signaling through ADF phosphorylation. Such studies are essential for determining whether ADF simply stimulates outgrowth in general or if it is also an integral component for growth cone navigation. These studies will not only extend our understanding of how actin dynamics are regulated in growth cones, but also how neurons grow and are able to form appropriate connections during brain development. The integration of the proposed research activities and facilities with teaching responsibilities will enhance graduate and undergraduate education at the University of North Dakota by direct student involvement in the research project together with increased capabilities in the teaching labs.