Identification of a novel force-generating protein, kinesin, involved in microtubule-based motility

https://www.cell.com/cell/pdf/S0092-8674(03)00111-9.pdf

The Molecular Motor Toolbox for Intracellular Transport

Glycogen synthase kinase‐3β (GSK‐3β) has been postulated to mediate Alzheimer9s disease tau hyperphosphorylation, β‐amyloid‐induced neurotoxicity and presenilin‐1 mutation pathogenic effects. By using the tet‐regulated system we have produced conditional transgenic mice overexpressing GSK‐3β in the brain during adulthood while avoiding perinatal lethality due to embryonic transgene expression. These mice show decreased levels of nuclear β‐catenin and hyperphosphorylation of tau in hippocampal neurons, the latter resulting in pretangle‐like somatodendritic localization of tau. Neurons displaying somatodendritic localization of tau often show abnormal morphologies and detachment from the surrounding neuropil. Reactive astrocytosis and microgliosis were also indicative of neuronal stress and death. This was further confirmed by TUNEL and cleaved caspase‐3 immunostaining of dentate gyrus granule cells. Our results demonstrate that in vivo overexpression of GSK‐3β results in neurodegeneration and suggest that these mice can be used as an animal model to study the relevance of GSK‐3β deregulation to the pathogenesis of Alzheimer9s disease.

/pdf/decreased-nuclear-b-catenin-tau-hyperphosphorylation-and-1iadvnhhxe.pdf

Decreased nuclear β‐catenin, tau hyperphosphorylation and neurodegeneration in GSK‐3β conditional transgenic mice

The intracellular transport of organelles along an axon is crucial for the maintenance and function of a neuron. Anterograde axonal transport has a role in supplying proteins and lipids to the distal synapse and mitochondria for local energy requirements, whereas retrograde transport is involved in the clearance of misfolded and aggregated proteins from the axon and the intracellular transport of distal trophic signals to the soma. Axonal transport can be affected by alterations to various components of the transport machinery. Here, we review the current state of knowledge about axonal transport defects that might contribute to the pathogenesis of particular neurodegenerative diseases.

Axonal transport deficits and neurodegenerative diseases

The interrelationships of the endoplasmic reticulum (ER), microtubules, and intermediate filaments were studied in the peripheral regions of thin, spread fibroblasts, epithelial, and vascular endothelial cells in culture We combined a fluorescent dye staining technique to localize the ER with immunofluorescence to localize microtubules or intermediate filaments in the same cell Microtubules and the ER are sparse in the lamellipodia, but intermediate filaments are usually completely absent These relationships indicate that microtubules and the ER advance into the lamellipodia before intermediate filaments We observed that microtubules and tubules of the ER have nearly identical distributions in lamellipodia, where new extensions of both are taking place We perturbed microtubules by nocodazole, cold temperature, or hypotonic shock, and observed the effects on the ER distribution On the basis of our observations in untreated cells and our experiments with microtubule perturbation, we conclude that microtubules and the ER are highly interdependent in two ways: (a) polymerization of individual microtubules and extension of individual ER tubules occur together at the level of resolution of the fluorescence microscope, and (b) depolymerization of microtubules does not disrupt the ER network in the short term (15 min), but prolonged absence of microtubules (2 h) leads to a slow retraction of the ER network towards the cell center, indicating that over longer periods of time, the extended state of the entire ER network requires the microtubule system

https://rupress.org/jcb/article-pdf/103/4/1557/1053568/1557.pdf

Microtubules and the endoplasmic reticulum are highly interdependent structures.

Video-enhanced contrast-differential interference contrast microscopy has revealed new features of axonal transport in the giant axon of the squid, where no movement had been detected previously by conventional microscopy. The newly discovered dominant feature is vast numbers of "submicroscopic" particles, probably 30- to 50-nanometer vesicles and other tubulovesicular elements, moving parallel to linear elements, primarily in the orthograde direction but also in a retrograde direction, at a range of steady velocities up to +/- 5 micrometers per second. Medium (0.2 to 0.6 micrometer) and large (0.8 micrometer) particles move more slowly and more intermittently with a tendency at times to exhibit elastic recoil. The behavior of the smallest particles and the larger particles during actual translocation suggests that the fundamental processes in the mechanisms of organelle movement in axonal transport are not saltatory but continuous.

Fast axonal transport in squid giant axon

Ubiquitin is present on the cytokeratin intermediate filaments and Mallory bodies of hepatocytes.

The cytoplasmic-nuclear interface has been investigated by conventional thin sectioning electron microscopy of neurons from frontal lobe biopsies of 13 patients with Alzheimer's disease. Nine patients were in the early and intermediate stages of the disease and four patients in the advanced stage. Fascicles of paired helical filament-like strands and paired helical filaments appose the nuclear envelope, the nuclear pore complexes and the perinuclear polysomes. Paired helical filament profiles have also been identified in the nucleoplasm. These observations indicate that the cytoplasmic-nuclear interface and, consequently, the relationships between the cytoplasm and the nucleus, might be impaired in Alzheimer's disease.

Paired helical filaments and the cytoplasmic-nuclear interface in Alzheimer's disease.

https://aasldpubs.onlinelibrary.wiley.com/doi/pdf/10.1002/hep.1840110315

Role of cytokeratin intermediate filaments in transhepatic transport and canalicular secretion.

The organization of the cortical endoplasmic reticulum in the squid giant axon was investigated by rapid freeze and freeze-substitution electron microscopy, thereby eliminating the effects of fixatives on this potentially labile structure. Juvenile squid, which have thinner Schwann sheaths, were used in order to achieve freezing deep enough to include the entire axonal cortex. The smooth endoplasmic reticulum is composed of subaxolemmal and deeper cisternae, tubules, tethers and vesicles. The subaxolemmal cisternae make junctional contacts with the axolemma which are characterized by filamentous-granular bridging structures approximately 3 nm in diameter. The subaxolemmal junctions with the axolemma resemble the coupling junctions between the sarcoplasmic reticulum and the T-tubules in muscle. Reconstruction of short series of sections showed that a number of the elements of the endoplasmic reticulum were continuous but numerous separate vesicles were present as well. The morphology of endoplasmic reticulum as described here suggests that it is a highly dynamic entity as well as a Ca2+ sequestering organelle.

J. Metuzals

Papers

Fast axonal transport in squid giant axon

Ubiquitin is present on the cytokeratin intermediate filaments and Mallory bodies of hepatocytes.

Paired helical filaments and the cytoplasmic-nuclear interface in Alzheimer's disease.

Role of cytokeratin intermediate filaments in transhepatic transport and canalicular secretion.

Organization of the Cortical Endoplasmic Reticulum in the Squid Giant Axon