Ribosomes in myelinated axons of dorsal root ganglia

Zelená, Jiřina

doi:10.1007/bf00335680

Cited by 73 publications

(43 citation statements)

References 43 publications

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“…Nevertheless other energy-intensive processes such as axonal transport by kinesin motors are readily observed in the extruded axoplasm (Kang et al 2016;Prahlad et al 2000;Vale et al 1985). Another key observation against the idea of intra-axonal protein synthesis in the squid giant axon is the absence of morphological evidence for canonical ribosomes in the giant axon, and in vertebrate axons in general (Conradi 1966;Palay and Palade 1955;Palay et al 1968;Peters et al 1968;Peters et al 1970;Zelena 1972). This is in contrast to well-documented sites of "local protein synthesis" such as in dendrites where canonical ribosomes and polyribosomes have clearly been observed (Steward and Levy 1982;Steward and Schuman 2003).…”

Section: Discussionmentioning

confidence: 99%

Squid Giant Axon Contains Neurofilament Protein mRNA but does not Synthesize Neurofilament Proteins

et al. 2016

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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 is 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.

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Section: Discussionmentioning

confidence: 99%

Squid Giant Axon Contains Neurofilament Protein mRNA but does not Synthesize Neurofilament Proteins

et al. 2016

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“…Although ribosomes are found in the neurites of developing neurons, the number of ribosomes decreases as these neurites develop into axons. This process appears to continue during later development since Zelena (71) has found a small number of ribosomes in the spinal ganglion cell axons of neonatal rats but very few in those of mature animals. The few axonal ribosomes which are found in postembryonic neurons are located near the cell body.…”

Section: Does Protein Synthesis Occur Within the Squid Giant Axon?mentioning

confidence: 96%

“…Ribosomes appear to be confined almost exclusively to the cell body and dendrites of mature neurons (71). Although ribosomes are found in the neurites of developing neurons, the number of ribosomes decreases as these neurites develop into axons.…”

Section: Does Protein Synthesis Occur Within the Squid Giant Axon?mentioning

confidence: 99%

Cell-to-cell transfer of glial proteins to the squid giant axon: The glia- neuron protein transfer hypothesis

Lasek¹,

Gainer²,

Barker³

1977

The Journal of Cell Biology

186

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The hypothesis that glial cells synthesize proteins which are transferred to adjacent neurons was evaluated in the giant fiber of the squid (Loligo pealei). When giant fibers are separated from their neuron cell bodies and incubated in the presence of radioactive amino acids, labeled proteins appear in the glial cells and axoplasm. Labeled axonal proteins were detected by three methods: extrusion of the axoplasm from the giant fiber, autoradiography, and perfusion of the giant fiber. This protein synthesis is completely inhibited by puromycin but is not affected by chloramphenicol. The following evidence indicates that the labeled axonal proteins are not synthesized within the axon itself. (a) The axon does not contain a significant amount of ribosomes or ribosomal RNA. (b) Isolated axoplasm did not incorporate [aH]leucine into proteins. (c) Injection of RNase into the giant axon did not reduce the appearance of newly synthesized proteins in the axoplasm of the giant fiber. These findings, coupled with other evidence, have led us to conclude that the adaxonal glial cells synthesize a class of proteins which are transferred to the giant axon. Analysis of the kinetics of this phenomenon indicates that some proteins are transferred to the axon within minutes of their synthesis in the glial cells. One or more of the steps in the transfer process appear to involve Ca ++, since replacement of extracellular Ca ++ by either Mg § or Co §247 significantly reduces the appearance of labeled proteins in the axon. A substantial fraction of newly synthesized glial proteins, possibly as much as 40%, are transferred to the giant axon. These proteins are heterogeneous and range in size from 12,000 to greater than 200,000 daltons. Comparisons of the amount of amino acid incorporation in glia cells and neuron cell bodies raise the possibility that the adaxonal glial cells may provide an important source of axonal proteins which is supplemental to that provided by axonal transport from the cell body. These findings are discussed with reference to a possible trophic effect of glia on neurons and metabolic cooperation between adaxonal glia and the axon.It has often been suggested that adjacent cells communicate with one another via the actual intercellular transfer of molecules including macromolecules. The possibility that molecular transfer may play a role in intercellular regulation has taken on added credibility since the discovery and

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“…6 A). Because grp78/BiP, calreticulin, and ERp29 are considered ER proteins, it was surprising to find their mRNAs extending into the axons when ultrastructural studies have not detected any rough ER in axons (Zelena, 1970(Zelena, , 1972Peters et al, 1991;Bassell et al, 1998;Spencer et al, 2000;Zheng et al, 2001). Immunolabeling showed a clear signal for grp78/BiP, calreticulin, and ERp29 proteins in neurofilament-positive processes of cultured DRG neurons (Fig.…”

Section: Resident Er Protein Mrnas In the Drg Axonsmentioning

confidence: 99%

Differential Transport and Local Translation of Cytoskeletal, Injury-Response, and Neurodegeneration Protein mRNAs in Axons

Willis¹,

Li²,

Zheng³

et al. 2005

J. Neurosci.

360

391

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Recent studies have begun to focus on the signals that regulate axonal protein synthesis and the functional significance of localized protein synthesis. However, identification of proteins that are synthesized in mammalian axons has been mainly based on predictions. Here, we used axons purified from cultures of injury-conditioned adult dorsal root ganglion (DRG) neurons and proteomics methodology to identify axonally synthesized proteins. Reverse transcription (RT)-PCR from axonal preparations was used to confirm that the mRNA for each identified protein extended into the DRG axons. Proteins and the encoding mRNAs for the cytoskeletal proteins ␤-actin, peripherin, vimentin, ␥-tropomyosin 3, and cofilin 1 were present in the axonal preparations. In addition to the cytoskeletal elements, several heat shock proteins (HSP27, HSP60, HSP70, grp75, ␣B crystallin), resident endoplasmic reticulum (ER) proteins (calreticulin, grp78/BiP, ERp29), proteins associated with neurodegenerative diseases (ubiquitin C-terminal hydrolase L1, rat ortholog of human DJ-1/Park7, ␥-synuclein, superoxide dismutase 1), anti-oxidant proteins (peroxiredoxins 1 and 6), and metabolic proteins (e.g., phosphoglycerate kinase 1 (PGK 1), ␣ enolase, aldolase C/Zebrin II) were included among the axonally synthesized proteins. Detection of the mRNAs encoding each of the axonally synthesized proteins identified by mass spectrometry in the axonal compartment indicates that the DRG axons have the potential to synthesize a complex population of proteins. Local treatment of the DRG axons with NGF or BDNF increased levels of cytoskeletal mRNAs into the axonal compartment by twofold to fivefold but had no effect on levels of the other axonal mRNAs studied. Neurotrophins selectively increased transport of ␤-actin, peripherin, and vimentin mRNAs from the cell body into the axons rather than changing transcription or mRNA survival in the axonal compartment.

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Ribosomes in myelinated axons of dorsal root ganglia

Cited by 73 publications

References 43 publications

Squid Giant Axon Contains Neurofilament Protein mRNA but does not Synthesize Neurofilament Proteins

Squid Giant Axon Contains Neurofilament Protein mRNA but does not Synthesize Neurofilament Proteins

Cell-to-cell transfer of glial proteins to the squid giant axon: The glia- neuron protein transfer hypothesis

Differential Transport and Local Translation of Cytoskeletal, Injury-Response, and Neurodegeneration Protein mRNAs in Axons

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