The goals of this project are to decipher the mechanisms that regulate the actin and microtubule cytoskeletons, the structures underlying neural cell behaviors including morphology, polarity, adhesion, process elongation, motility, navigation, connectivity, and plasticity. To change their size, shape, and connectivity, neurons require actin and tubulin proteins to assemble together into long polymers (F-actin and microtubules, respectively) ? and numerous extracellular stimuli have now been identified that alter the assembly and organization of these cytoskeletal structures. Yet, we still know little of how these extracellular cues exert their precise effects on the cytoskeleton. To better understand these mechanisms, my lab has been focusing on one of the largest families of extracellular cues, the Semaphorins (Semas) ? which alter neuronal behaviors by eliciting destabilizing effects on both F-actin and microtubules. Our strategy has been to use model organisms and screening approaches to search for proteins that work in the signal transduction cascade utilized by Semas and their Plexin receptors. Among the proteins that we have identified, is a new family of intracellular proteins called the MICALs that are required for Sema/Plexin signal transduction. Now, work in my lab during the previous funding cycle of this R01 has revealed that the MICALs employ a previously unknown Redox signaling system to control the actin cytoskeleton. Namely, we have found that Mical is a novel F-actin disassembly factor ? and our results reveal that Sema/Plexin-mediated reorganizations of the actin cytoskeleton can be precisely achieved in space and time through activation of Mical. We have also found that the MICALs belong to a class of oxidoreductase (Redox) enzymes and that Mical employs its Redox enzymatic activity to alter the properties of F-actin. Our work has gone on to identify that Mical uses F-actin as a direct substrate and post- translationally oxidizes conserved amino acids on actin, simultaneously dismantling F-actin and decreasing polymerization. Moreover, we find that this Sema/Plex/Mical-mediated Redox regulation of actin is reversible (by a protein called SelR/MsrB) ? and that this specific reversible Redox actin regulatory system directs multiple different biological processes in neuronal and non-neuronal tissues. Therefore, I hypothesize that Sema/Plexin guidance cues utilize a reversible Redox signaling mechanism composed of Mical and SelR to directly and spatiotemporally coordinate cytoskeletal remodeling to drive cellular form and function. I propose to test this hypothesis by following-up on several lines of preliminary observations that illuminate critical molecular mechanisms of Sema/Plexin/Mical-mediated cytoskeletal reorganization including 1) specific types of F-actin/networks of F-actin that are most responsive to Sema/Plex/Mical effects, 2) molecular interactions that allow Sema/Plexins to coordinate the disassembly of the actin and microtubule cytoskeletons, 3) ligand/receptor systems that allow Sema/Plex/Mical cytoskeletal effects to be magnified spatiotemporally, and 4) specific actin regulatory proteins that protect actin filaments from Sema/Plex/Mical effects.

Public Health Relevance

Our nervous system controls such remarkable abilities as learning, speaking, and walking only because our neurons communicate in highly organized networks. The goal of this proposal is to characterize the molecular and biochemical mechanisms that enable neurons to find and connect with one another during development and maintain these proper connections throughout adulthood. Understanding how these neuronal networks are assembled, integrated, and maintained will reveal fundamental mechanisms underlying thought, emotion, and behavior, identify therapeutic strategies for neurological diseases and addictive behaviors, and contribute to healthy recovery following traumatic injuries to the brain and spinal cord.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Study Section
Synapses, Cytoskeleton and Trafficking Study Section (SYN)
Program Officer
Riddle, Robert D
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University of Texas Sw Medical Center Dallas
Schools of Medicine
United States
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Alto, Laura Taylor; Terman, Jonathan R (2018) MICALs. Curr Biol 28:R538-R541
Wu, Heng; Yesilyurt, Hunkar Gizem; Yoon, Jimok et al. (2018) The MICALs are a Family of F-actin Dismantling Oxidoreductases Conserved from Drosophila to Humans. Sci Rep 8:937
Alto, Laura Taylor; Terman, Jonathan R (2017) Semaphorins and their Signaling Mechanisms. Methods Mol Biol 1493:1-25
Yoon, Jimok; Hung, Ruei-Jiun; Terman, Jonathan R (2017) Characterizing F-actin Disassembly Induced by the Semaphorin-Signaling Component MICAL. Methods Mol Biol 1493:119-128
Grintsevich, Elena E; Yesilyurt, Hunkar Gizem; Rich, Shannon K et al. (2016) F-actin dismantling through a redox-driven synergy between Mical and cofilin. Nat Cell Biol 18:876-85
Wu, Heng; Hung, Ruei-Jiun; Terman, Jonathan R (2016) A simple and efficient method for generating high-quality recombinant Mical enzyme for in vitro assays. Protein Expr Purif 127:116-124
Wilson, Carlos; Terman, Jonathan R; González-Billault, Christian et al. (2016) Actin filaments-A target for redox regulation. Cytoskeleton (Hoboken) 73:577-595
Gupta, Nidhi; Wu, Heng; Terman, Jonathan R (2016) Data presenting a modified bacterial expression vector for expressing and purifying Nus solubility-tagged proteins. Data Brief 8:1227-31
Terman, Jonathan R; Kashina, Anna (2013) Post-translational modification and regulation of actin. Curr Opin Cell Biol 25:30-8
Hung, Ruei-Jiun; Spaeth, Christopher S; Yesilyurt, Hunkar Gizem et al. (2013) SelR reverses Mical-mediated oxidation of actin to regulate F-actin dynamics. Nat Cell Biol 15:1445-54

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