title: Exclusion of integrins from CNS axons is regulated by Arf6 activation and the AIS.
abstract: Integrins are adhesion and survival molecules involved in axon growth during CNS development, as well as axon regeneration after injury in the peripheral nervous system (PNS). Adult CNS axons do not regenerate after injury, partly due to a low intrinsic growth capacity. We have previously studied the role of integrins in axon growth in PNS axons; in the present study, we investigate whether integrin mechanisms involved in PNS regeneration may be altered or lacking from mature CNS axons by studying maturing CNS neurons in vitro. In rat cortical neurons, we find that integrins are present in axons during initial growth but later become restricted to the somato-dendritic domain. We investigated how this occurs and whether it can be altered to enhance axonal growth potential. We find a developmental change in integrin trafficking; transport becomes predominantly retrograde throughout axons, but not dendrites, as neurons mature. The directionality of transport is controlled through the activation state of ARF6, with developmental upregulation of the ARF6 GEF ARNO enhancing retrograde transport. Lowering ARF6 activity in mature neurons restores anterograde integrin flow, allows transport into axons, and increases axon growth. In addition, we found that the axon initial segment is partly responsible for exclusion of integrins and removal of this structure allows integrins into axons. Changing posttranslational modifications of tubulin with taxol also allows integrins into the proximal axon. The experiments suggest that the developmental loss of regenerative ability in CNS axons is due to exclusion of growth-related molecules due to changes in trafficking.
authors.affiliation: Cambridge Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, Cambridge CB2 OPY, United Kingdom.
authors.forename: Elske H P
authors.initials: EH
authors.lastname: Franssen
authors.affiliation: Cambridge Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, Cambridge CB2 OPY, United Kingdom.
authors.forename: Rong-Rong
authors.identifier: http://orcid.org/0000-0002-1408-313X
authors.initials: RR
authors.lastname: Zhao
authors.affiliation: Cambridge Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, Cambridge CB2 OPY, United Kingdom.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Koseki
authors.affiliation: Institute of Life Science 1, College of Medicine, Swansea University, Singleton Park, Swansea SA2 8PP, United Kingdom; and.
authors.forename: Venkateswarlu
authors.identifier: http://orcid.org/0000-0002-8739-1483
authors.initials: V
authors.lastname: Kanamarlapudi
authors.affiliation: Cell Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands.
authors.forename: Casper C
authors.initials: CC
authors.lastname: Hoogenraad
authors.affiliation: Cambridge Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, Cambridge CB2 OPY, United Kingdom, jf108@cam.ac.uk re263@cam.ac.uk.
authors.forename: Richard
authors.initials: R
authors.lastname: Eva
authors.affiliation: Cambridge Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, Cambridge CB2 OPY, United Kingdom, jf108@cam.ac.uk re263@cam.ac.uk.
authors.forename: James W
authors.initials: JW
authors.lastname: Fawcett
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D000818:Animals; D001369:Axons / Q000378:metabolism*; D002478:Cells, Cultured; D002490:Central Nervous System / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D002540:Cerebral Cortex / Q000166:cytology* / Q000196:embryology / Q000378:metabolism*; D016023:Integrins / Q000172:deficiency*; D051381:Rats; D012038:Regeneration / Q000502:physiology*
chemical_list: D000089982:ADP-Ribosylation Factor 6; D016023:Integrins; D020727:ADP-Ribosylation Factors; C000715349:Arf6 protein, rat
keywords: Arf6; axon initial segment; axonal transport; integrin; trafficking