title: mRNAs and Protein Synthetic Machinery Localize into Regenerating Spinal Cord Axons When They Are Provided a Substrate That Supports Growth.
abstract: Although intra-axonal protein synthesis is well recognized in cultured neurons and during development in vivo, there have been few reports of mRNA localization and/or intra-axonal translation in mature CNS axons. Indeed, previous work indicated that mature CNS axons contain much lower quantities of translational machinery than PNS axons, leading to the conclusion that the capacity for intra-axonal protein synthesis is linked to the intrinsic capacity of a neuron for regeneration, with mature CNS neurons showing much less growth after injury than PNS neurons. However, when regeneration by CNS axons is facilitated, it is not known whether the intra-axonal content of translational machinery changes or whether mRNAs localize into these axons. Here, we have used a peripheral nerve segment grafted into the transected spinal cord of adult rats as a supportive environment for regeneration by ascending spinal axons. By quantitative fluorescent in situ hybridization combined with immunofluorescence to unambiguously distinguish intra-axonal mRNAs, we show that regenerating spinal cord axons contain β-actin, GAP-43, Neuritin, Reg3a, Hamp, and Importin β1 mRNAs. These axons also contain 5S rRNA, phosphorylated S6 ribosomal protein, eIF2α translation factor, and 4EBP1 translation factor inhibitory protein. Different levels of these mRNAs in CNS axons from regenerating PNS axons may relate to differences in the growth capacity of these neurons, although the presence of mRNA transport and likely local translation in both CNS and PNS neurons suggests an active role in the regenerative process.
  
  
  CONCLUSIONS
  Although peripheral nerve axons retain the capacity to locally synthesize proteins into adulthood, previous studies have argued that mature brain and spinal cord axons cannot synthesize proteins. Protein synthesis in peripheral nerve axons is increased during regeneration, and intra-axonally synthesized proteins have been shown to contribute to nerve regeneration. Here, we show that mRNAs and translational machinery are transported into axons regenerating from the spinal cord into the permissive environment of a peripheral nerve graft. Our data raise the possibility that spinal cord axons may make use of localized protein synthesis for regeneration.
authors.affiliation: Department of Biology, Drexel University, Philadelphia, Pennsylvania 19104.
authors.forename: Ashley L
authors.initials: AL
authors.lastname: Kalinski
authors.affiliation: Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129, and.
authors.forename: Rahul
authors.identifier: http://orcid.org/0000-0001-7972-9344
authors.initials: R
authors.lastname: Sachdeva
authors.affiliation: Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208.
authors.forename: Cynthia
authors.identifier: http://orcid.org/0000-0002-5026-0797
authors.initials: C
authors.lastname: Gomes
authors.affiliation: Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208.
authors.forename: Seung Joon
authors.initials: SJ
authors.lastname: Lee
authors.affiliation: Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208.
authors.forename: Zalak
authors.initials: Z
authors.lastname: Shah
authors.affiliation: Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129, and.
authors.forename: John D
authors.initials: JD
authors.lastname: Houle
authors.affiliation: Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129, and Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208 twiss@mailbox.sc.edu.
authors.forename: Jeffery L
authors.identifier: http://orcid.org/0000-0001-7875-6682
authors.initials: JL
authors.lastname: Twiss
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism; D001369:Axons / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology; D064451:Hepcidins / Q000235:genetics / Q000378:metabolism; D037181:Lectins, C-Type / Q000235:genetics / Q000378:metabolism; D008297:Male; D009416:Nerve Regeneration / Q000502:physiology*; D000073718:Pancreatitis-Associated Proteins; D010442:Peptide Chain Initiation, Translational / Q000235:genetics / Q000502:physiology*; D059348:Peripheral Nerve Injuries / Q000473:pathology; D014176:Protein Biosynthesis / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011984:Sensory Receptor Cells / Q000378:metabolism / Q000473:pathology; D013116:Spinal Cord / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000473:pathology
chemical_list: D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; C578703:Hamp protein, rat; D064451:Hepcidins; D037181:Lectins, C-Type; D000073718:Pancreatitis-Associated Proteins; C000612141:REG3A protein, human; D012333:RNA, Messenger; C000612146:Reg3a protein, rat
keywords: RNA transport; axon regeneration; spinal cord injury; translation