Abstract
We investigated the localization of components of translational machinery and their regulators in the postsynaptic region. We examined several components, especially those involved in translational regulation: components of (1) MAPK-Mnk-eIF4E, (2) PI3-kinase-PDK-Akt/PKB-FRAP/mTOR-PHAS/4EBP, (3) p70S6K-S6 ribosomal protein and (4) eEF2 kinase/CaMKIII-eEF2 pathways. Western blotting detected all the components examined in the synaptic fractions, and their differential localization to the synaptic subcompartments: initiation or elongation factors, except for eIF5, were detected predominantly in the dendritic lipid raft fraction, which contained ER marker proteins. In contrast, most of their regulatory kinases were distributed to both the postsynaptic density (PSD) and the dendritic lipid raft fractions, or enriched in the former fraction. Localization of eIF4E at synaptic sites was further examined immunohistochemically at the electron microscopic level. The eIF-4E-immunoreactivity was localized to the postsynaptic sites, especially to the microvesicle-like structures underneath the postsynaptic membrane in the spine, some of which were localized in close proximity to PSD. These results suggest that the postsynaptic local translational system, in at least four major regulatory pathways, is similar to those in the perinuclear one, and that it takes place, at least partly, immediately beneath the postsynaptic membrane. The results also suggest the presence of ER-associated type of translational machinery at the postsynaptic sites.
Publication types
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Comparative Study
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Antigens / metabolism
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Blotting, Western / methods
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Brain / anatomy & histology
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Brain / physiology*
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Brain / ultrastructure
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Brain Chemistry
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Calcium-Calmodulin-Dependent Protein Kinases / metabolism
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Carrier Proteins / metabolism
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Cell Cycle Proteins / metabolism
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Cytoskeletal Proteins*
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DNA-Binding Proteins / metabolism
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Dendrites / metabolism
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Egg Proteins / metabolism
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Elongation Factor 2 Kinase
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Eukaryotic Initiation Factors / classification
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Eukaryotic Initiation Factors / metabolism
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Eukaryotic Initiation Factors / ultrastructure
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Immunohistochemistry / methods
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Male
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Membrane Glycoproteins / metabolism
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Membrane Proteins / metabolism
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Microscopy, Immunoelectron / instrumentation
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Mitogen-Activated Protein Kinase 1 / metabolism
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases / metabolism
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Phosphatidylinositol 3-Kinases / metabolism
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Phthalimides / metabolism
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Porphyrins / metabolism
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Protein Biosynthesis / physiology*
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Protein Serine-Threonine Kinases*
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins c-akt
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Rats
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Rats, Wistar
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Receptors, Cell Surface*
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Ribosomal Protein S6 / metabolism
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Ribosomal Protein S6 Kinases, 70-kDa / metabolism
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Signal Transduction / physiology*
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Subcellular Fractions / metabolism
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Subcellular Fractions / ultrastructure
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Synapses / metabolism*
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Synapses / ultrastructure
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Transcription Factors / metabolism
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Zona Pellucida Glycoproteins
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p38 Mitogen-Activated Protein Kinases
Substances
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5,15-bis(N-(Kemp's triacid imido)-2-tolyl)-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin
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Antigens
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Carrier Proteins
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Cell Cycle Proteins
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Cytoskeletal Proteins
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DNA-Binding Proteins
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Egg Proteins
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Eukaryotic Initiation Factors
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IFI44 protein, human
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Membrane Glycoproteins
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Membrane Proteins
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Phthalimides
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Porphyrins
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Proto-Oncogene Proteins
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Receptors, Cell Surface
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Ribosomal Protein S6
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Transcription Factors
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Zona Pellucida Glycoproteins
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flotillins
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EEF2K protein, human
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Eef2k protein, rat
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Akt1 protein, rat
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-akt
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Ribosomal Protein S6 Kinases, 70-kDa
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Calcium-Calmodulin-Dependent Protein Kinases
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Elongation Factor 2 Kinase
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases
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p38 Mitogen-Activated Protein Kinases