Many of the intracellular components that allow neuronal growth cones to interpret and respond to extracellular guidance cues have been identified, but we lack an understanding of how these components function to establish asymmetry in the growth cone. C. elegans provides an excellent system to address this question, because it is possible to observe the localization of proteins within a neuron as it responds to a guidance cue in vivo. In the HSN neuron of C. elegans, UNC-40 (also known as DCC) receptor becomes asymmetrically localized to the side of the cell closest to the source of the UNC-6 (also known as netrin) guidance cue. This in turn, leads to asymmetric recruitment of MIG-10 (also known as lamellipodin), which has an outgrowth-promoting activity, thereby causing outgrowth towards the source of UNC-6 guidance cue. The outgrowth-promoting activity of MIG-10 is thought to result from actin polymerization, but the link between MIG-10 and the actin cytoskeleton is not understood. The objective of this proposal is to determine how MIG-10 links to the actin cytoskeleton to cause a directional outgrowth-promoting activity. Our hypothesis is that MIG-10 (lamellipodin) promotes directional outgrowth by asymmetrically recruiting the WAVE actin regulatory complex. It is expected that the results from these studies will allow us to build an understanding of how signaling complexes can spatially organize actin regulatory proteins to promote growth in response to axon guidance cues. Furthermore, it is likely that the results of these studies will have broader significance because UNC-40 and MIG-10 have been implicated in a wide variety of other morphogenetic events and emerging evidence suggests that asymmetric localization is a key part of their roles in these processes.
Normal axon guidance is required for the development of a functional nervous system and genetically encoded disruptions in this process can underlie mental and neurological disorders. Thus, the proposed research will lead to the development of fundamental knowledge that could impact the diagnosis and treatment of these developmental disorders.
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