title: Squid Giant Axon Contains Neurofilament Protein mRNA but does not Synthesize Neurofilament Proteins.
abstract: When isolated squid giant axons are incubated in radioactive amino acids, abundant newly synthesized proteins are found in the axoplasm. These proteins are translated in the adaxonal Schwann cells and subsequently transferred into the giant axon. The question as to whether any de novo protein synthesis occurs in the giant axon itself is difficult to resolve because the small contribution of the proteins possibly synthesized intra-axonally is not easily distinguished from the large amounts of the proteins being supplied from the Schwann cells. In this paper, we reexamine this issue by studying the synthesis of endogenous neurofilament (NF) proteins in the axon. Our laboratory previously showed that NF mRNA and protein are present in the squid giant axon, but not in the surrounding adaxonal glia. Therefore, if the isolated squid axon could be shown to contain newly synthesized NF protein de novo, it could not arise from the adaxonal glia. The results of experiments in this paper show that abundant 3H-labeled NF protein is synthesized in the squid giant fiber lobe containing the giant axon's neuronal cell bodies, but despite the presence of NF mRNA in the giant axon no labeled NF protein is detected in the giant axon. This lends support to the glia-axon protein transfer hypothesis which posits that the squid giant axon obtains newly synthesized protein by Schwann cell transfer and not through intra-axonal protein synthesis, and further suggests that the NF mRNA in the axon is in a translationally repressed state.
authors.affiliation: Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA. gainerh@ninds.nih.gov.|Marine Biological Laboratory, Woods Hole, MA, 02543, USA. gainerh@ninds.nih.gov.
authors.forename: Harold
authors.initials: H
authors.lastname: Gainer
authors.affiliation: Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA.|Marine Biological Laboratory, Woods Hole, MA, 02543, USA.
authors.forename: Shirley
authors.initials: S
authors.lastname: House
authors.affiliation: Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA.|Marine Biological Laboratory, Woods Hole, MA, 02543, USA.|Department of Anatomy, College of Medicine, Kyungbuk National University, Daegu, South Korea.
authors.forename: Dong Sun
authors.initials: DS
authors.lastname: Kim
authors.affiliation: Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA.|Marine Biological Laboratory, Woods Hole, MA, 02543, USA.|Division of Extramural Research, National Eye Institute, NIH, Bethesda, MD, 20892, USA.
authors.forename: Hemin
authors.initials: H
authors.lastname: Chin
authors.affiliation: Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA.|Marine Biological Laboratory, Woods Hole, MA, 02543, USA.
authors.forename: Harish C
authors.initials: HC
authors.lastname: Pant
mesh_terms: D000818:Animals; D001345:Autoradiography; D001369:Axons / Q000378:metabolism*; D049832:Decapodiformes / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D047468:Immunoprecipitation; D016900:Neurofilament Proteins / Q000096:biosynthesis* / Q000235:genetics*; D023282:Nuclease Protection Assays; D014176:Protein Biosynthesis; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D016900:Neurofilament Proteins; D021122:Protein Subunits; D012333:RNA, Messenger
keywords: Local protein synthesis; Neurofilament protein; Ribonuclease protection; Schwann cell; Squid axon; mRNA