title: MAP7 Regulates Axon Collateral Branch Development in Dorsal Root Ganglion Neurons.
abstract: Collateral branches from axons are key components of functional neural circuits that allow neurons to connect with multiple synaptic targets. Like axon growth and guidance, formation of collateral branches depends on the regulation of microtubules, but how such regulation is coordinated to ensure proper circuit development is not known. Based on microarray analysis, we have identified a role for microtubule-associated protein 7 (MAP7) during collateral branch development of dorsal root ganglion (DRG) sensory neurons. We show that MAP7 is expressed at the onset of collateral branch formation. Perturbation of its expression by overexpression or shRNA knockdown alters axon branching in cultured DRG neurons. Localization and time-lapse imaging analysis reveals that MAP7 is enriched at branch points and colocalizes with stable microtubules, but enters the new branch with a delay, suggesting a role in branch maturation. We have also investigated a spontaneous mutant mouse that expresses a truncated MAP7 and found a gain-of-function phenotype bothin vitroandin vivoFurther domain analysis suggests that the amino half of MAP7 is responsible for branch formation, suggesting a mechanism that is independent of its known interaction with kinesin. Moreover, this mouse exhibits increased pain sensitivity, a phenotype that is consistent with increased collateral branch formation. Therefore, our study not only uncovers the first neuronal function of MAP7, but also demonstrates the importance of proper microtubule regulation in neural circuit development. Furthermore, our data provide new insights into microtubule regulation during axonal morphogenesis and may shed light on MAP7 function in neurological disorders.SIGNIFICANCE STATEMENTNeurons communicate with multiple targets by forming axonal branches. In search of intrinsic factors that control collateral branch development, we identified a role for microtubule-associated protein 7 (MAP7) in dorsal root ganglion sensory neurons. We show that MAP7 expression is developmentally regulated and perturbation of this expression alters branch formation. Cell biological analysis indicates that MAP7 promotes branch maturation. Analysis of a spontaneous mouse mutant suggests a molecular mechanism for branch regulation and the potential influence of collateral branches on pain sensitivity. Our studies thus establish the first neuronal function of MAP7 and demonstrate its role in branch morphogenesis and neural circuit function. These findings may help in our understanding of the contribution of MAP7 to neurological disorders and nerve regeneration.
authors.affiliation: Department of Neuroscience, Vickie and Jack Farber Institute for Neuroscience, Sydney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
authors.forename: Stephen R
authors.identifier: 0000-0002-6837-0644
authors.initials: SR
authors.lastname: Tymanskyj
authors.affiliation: Department of Neuroscience, Vickie and Jack Farber Institute for Neuroscience, Sydney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
authors.forename: Benjamin
authors.identifier: 0000-0002-9845-0514
authors.initials: B
authors.lastname: Yang
authors.affiliation: Department of Neuroscience, Vickie and Jack Farber Institute for Neuroscience, Sydney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
authors.forename: Aditi
authors.initials: A
authors.lastname: Falnikar
authors.affiliation: Department of Neuroscience, Vickie and Jack Farber Institute for Neuroscience, Sydney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
authors.forename: Angelo C
authors.initials: AC
authors.lastname: Lepore
authors.affiliation: Department of Neuroscience, Vickie and Jack Farber Institute for Neuroscience, Sydney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107 le.ma@jefferson.edu.
authors.forename: Le
authors.identifier: 0000-0003-2769-9416
authors.initials: L
authors.lastname: Ma
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology*; D002478:Cells, Cultured; D005260:Female; D005727:Ganglia, Spinal / Q000378:metabolism*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000096:biosynthesis*; D009474:Neurons / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D008869:Microtubule-Associated Proteins
keywords: DRG; MAP7; axon; collateral branch; microtubule; sensory neuron