Electron Microscope and Experimental Investigations of the Neurofilamentous Network in Deiters' Neurons

Metuzals, J.; Mushynski, Walter E.

doi:10.1083/jcb.61.3.701

Cited by 115 publications

(56 citation statements)

References 44 publications

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“…Earlier chemical and ultrastructural data were compatible with the notion that the PSD was formed primarily from microtubules and perhaps microfilaments (2,14,19,20). For example, Gray (19) We can now view the PSD as composed of portions of the fibrous proteins, tubulin, actin, and neurofilament protein, and other unidentified polypeptides joined together at the specialized membrane domain of asymmetric synapses (16).…”

Section: Discussionsupporting

confidence: 65%

Identification of a protein related to tubulin in the postsynaptic density.

Feit¹,

Kelly²,

Cotman³

1977

Proc. Natl. Acad. Sci. U.S.A.

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The postsynaptic density is a unique subcellular organelle associated with the synaptic complex and appears as an electron-dense area immediately subjacent to the postsynaptic plasma membrane. The postsynaptic density was isolated from the synaptosomal fraction and the protein constituents were analyzed by polyacrylamide gel electrophoresis. Polypeptides closely related to tubulin were identified as a major component of the postsynaptic density on the basis of molecular weight, subunit structure, and peptide map criteria.Knowledge of the molecular constituents of the synapse is essential in order to understand the underlying mechanisms in the development, maintenance, and plasticity of synaptic connections. At the synapse in the central nervous system, preand postsynaptic membranes are specialized where they are joined. The presynaptic membrane often displays a set of electron-dense projections on its cytoplasmic surface, while on its inner surface the postsynaptic plasma membrane is often distinguished by the presence of an electron-dense structure called the postsynaptic density (PSD). The PSD is not found in all classes of synapses, but in the central nervous system, a prominent PSD is associated with excitatory axodendritic synapses. Neither the functional role nor the exact composition of the PSD is known at present.Identification of the various components of the synapse is dependent on suitable subcellular fractionation techniques. In recent years techniques have been devised for the isolation of synaptic vesicles, synaptic plasma membranes, and most recently, the PSD (1). The PSD fraction can be isolated by treatment of the synaptic plasma membrane fraction with sodium N-lauroyl sarcosinate, followed by density gradient centrifugation. The product of this procedure is a highly purified fraction of PSDs. In the electron microscope isolated PSDs are devoid of their adherent plasma membrane and appear as fibrous and granular matrix which closely resembles that seen in micrographs of intact tissue. Isolated PSDs also retain their distinctive cytochemical properties (1).Isolated PSDs consist primarily of protein with a small amount of carbohydrate and lipid (2). After sodium dodecyl sulfate (NaDodSO4)-polyacrylamide gel electrophoresis, a single band contains about 40% of the total protein, and therefore this polypeptide(s) probably constitutes the molecular backbone or skeleton of the structure seen in the electron microscope. The apparent molecular weight of this major protein band is 52,000-54,000. On the basis of its molecular weight, which is similar to tubulin, it was suggested that the polypeptide might be tubulin or a very similar protein (2). Tubulin (or a closely related protein) has been identified as a major constituent of both the soluble and insoluble components of the synaptosome (3-5), even though intact microtubules are usually not found at the synapse.In this study we have examined the possibility that tubulin is a major component of the PSD with regard to two criteria: (i) resolution...

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Section: Discussionsupporting

confidence: 65%

Identification of a protein related to tubulin in the postsynaptic density.

Feit¹,

Kelly²,

Cotman³

1977

Proc. Natl. Acad. Sci. U.S.A.

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“…Helical relationships in neurofilament structure have been previously indicated from X-ray defraction patterns of annelidan axoplasm (4) and from electron microscope observation of mammalian (10,16), moluscan, and annelidan filaments (6). It has been proposed that neurofilaments comprise two protofilaments twisted helically together.…”

Section: Filament Structurementioning

confidence: 99%

Antibody decoration of neurofilaments.

Willard¹,

Simon²

1981

The Journal of Cell Biology

225

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We have decorated neurofilaments with antibodies against three polypeptides (designated here as H [mol wt = 195,000], 45[mol wt = 145,000], and 46[mol wt = 73,000]) in an effort to understand the arrangement of these polypeptides within neurofilaments. The three polypeptides were purified and antibodies were raised against each. The cross-reactivity of the antibodies suggested that each polypeptide contains both shared and unique antigenic determinants. The differential reactivities of each antibody preparation were enhanced by adsorption with the two heterologous polypeptides, and the resulting preparations were used to decorate purified neurofilaments, which were then negatively stained and examined in an electron microscope. The appearance of the antibody-decorated structures led to the following conclusions: All three polypeptides are physically associated with the same neurofilament. However, the disposition of H and 46 within a filament is different; 46 antigens appear to be associated with a "central core" of the filament, whereas H antigens compose a structure more loosely and peripherally attached to the central core and periodically arranged along its axis. The antibody-decorated H-containing structure assumes variable configurations; in some cases it appears asa bridge connecting two filaments; in other cases it appears as a helix wrapping the central core with a period of approximately 1,000 A and an apparent unit length of approximately 1.5 periods. These configurations suggest several functional implications, including the possibility that H is a component of the cross-bridges observed between filaments in situ. We also note that the central core-helix relationship could be used in the design of an intracellular transport motor.

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“…They are linked to each other by cross-bridges and form a network (43,44). The cross-bridges apparently are dynamic (i.e., they can detach from adjacent neurofilaments and reattach) (44,45). Despite the dynamic nature of the individual cross-bridges, the hundreds or thousands of cross-bridges that are located along the length of the neurofilaments may restrict the capacity of neurofilaments to slide past each other.…”

Section: The Journal Of (Tell Biologymentioning

confidence: 99%

Axonal transport of the cytoplasmic matrix.

Lasek¹,

Garner²,

Brady³

1984

The Journal of Cell Biology

284

155

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The cytoplasmic matrix is often highly specialized, making it possible to clearly relate particularaspects ofthe cytoplasmic matrix to the specialized functions of cells . For example, in striated muscle cells the contractile components of the cytoplasmic matrix dominate the cell structurally and functionally. Neurons are another example of cells in which specializations of structure and function can be clearly related to particular aspects of the cytoplasmic matrix (36, 37). The primary function of neurons is to convey information from one location in the organism to another. Pathways for information transfer in the nervous system are provided by specialized neuronal extensions, the axons and the dendrites . Axons, in particular, are specialized to convey information over very long distances, meters in some cases. Accordingly, in the axon the cytoplasmic matrix is specialized to generate and support the extremely elongate shape ofthe axon during development, regeneration, and maturity.To generate and maintain the great volume of cytoplasm within the axon, neurons must produce tremendous amounts of protein (32). Essentially all axonal proteins are synthesized in the neuron cell body and then conveyed into the axon by axonal transport, which provides a lifeline for the axon and its terminus (25,36). Axonal transport is a process that is initiated when the axon first develops and that continues throughout the life of the neuron. To meet the needs of large animals, which require long axons, axonal transport has become one of the most highly developed mechanisms for the intracellular transport of materials in metazoan cells .

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Electron Microscope and Experimental Investigations of the Neurofilamentous Network in Deiters' Neurons

Cited by 115 publications

References 44 publications

Identification of a protein related to tubulin in the postsynaptic density.

Identification of a protein related to tubulin in the postsynaptic density.

Antibody decoration of neurofilaments.

Axonal transport of the cytoplasmic matrix.

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