Cytoplasmic dynein: tension generation on microtubules and the nucleus

The increase of α-synuclein and alterations of dynein in A53T transgenic and aging mouse

The dynein protein plays a key role in the degradation pathway by attaching to targeted molecules and transporting the autophagosome to the centrosome. Aging plays an important role in the pathogenesis of Parkinson's disease (PD), but its effect on dynein is not clear. In this study we analyzed behavioral characteristics using the rod endurance test and climbing rod time test in different aged mice (3 months, 12 months, 20 months), and measured protein expression of dynein, α-synuclein, Tctex-1, and LC3 in the substantianigra of the mice by Western blot. The mRNA levels of dynein, α-synuclein, LC3 and Tctex-1 were measured by quantitative real time reverse transcription PCR, and detecting expression of dynein and α-synuclein by immunofluorescence. We found the motor functions of A53T mutant mice, in 12 months and 20 months, decreased more significantly compared with normal mice (p < 0.05). In addition, the expression of dynein, LC3-Ⅱ and Tctex-1 proteins in the substantia nigra of the two groups decreased with age. However, α-synuclein protein increased gradually with age, with significantly higher levels in the PD groups compared with age matched controls (p < 0.05). These results were confirmed by immunofluorescence. Our data demonstrates that dynein and other autophagy proteins change with age, and this is associated with increased α-synuclein. Therefore, therapeutics that prevent dynein dysfunction may offer novel treatments for PD and other autophagy related diseases.

Microtubules and Dynein Regulate Human Neutrophil Nuclear Volume and Hypersegmentation During H. pylori Infection

Neutrophils (also called polymorphonuclear leukocytes, PMNs) are heterogeneous and can exhibit considerable phenotypic and functional plasticity. In keeping with this, we discovered previously that Helicobacter pylori infection induces N1-like subtype differentiation of human PMNs that is notable for profound nuclear hypersegmentation. Herein, we utilized biochemical approaches and confocal and super-resolution microscopy to gain insight into the underlying molecular mechanisms. Sensitivity to inhibition by nocodazole and taxol indicated that microtubule dynamics were required to induce and sustain hypersegmentation, and super-resolution Stimulated Emission Depletion (STED) imaging demonstrated that microtubules were significantly more abundant and longer in hypersegmented cells. Dynein activity was also required, and enrichment of this motor protein at the nuclear periphery was enhanced following H. pylori infection. In contrast, centrosome splitting did not occur, and lamin B receptor abundance and ER morphology were unchanged. Finally, analysis of STED image stacks using Imaris software revealed that nuclear volume increased markedly prior to the onset of hypersegmentation and that nuclear size was differentially modulated by nocodazole and taxol in the presence and absence of infection. Taken together, our data define a new mechanism of hypersegmentation that is mediated by microtubules and dynein and as such advance understanding of processes that regulate nuclear morphology.

Mechanistic three-dimensional model to study centrosome positioning in the interphase cell

During the interphase in mammalian cells, the position of the centrosome is actively maintained at a small but finite distance away from the nucleus. The perinuclear positioning of the centrosome is crucial for cellular trafficking and progression into mitosis. Although the literature suggests that the contributions of the microtubule-associated forces bring the centrosome to the center of the cell, the position of the centrosome was merely investigated in the absence of the nucleus. Upon performing a coarse-grained simulation study with mathematical analysis, we show that the combined effect of the forces due to the cell cortex and the nucleus facilitate the centrosome positioning. Our study also demonstrates that in the absence of nucleus-based forces, the centrosome collapses on the nucleus due to cortical forces. Depending upon the magnitudes of the cortical forces and the nucleus-based forces, the centrosome appears to stay at various distances away from the nucleus. Such null force regions are found to be stable as well as unstable fixed points. This study uncovers a set of redundant schemes that the cell may adopt to produce the required cortical and nucleus-based forces stabilizing the centrosome at a finite distance away from the nucleus.

Nanoparticles engineered to bind cellular motors for efficient delivery

Background

Dynein is a cytoskeletal molecular motor protein that transports cellular cargoes along microtubules. Biomimetic synthetic peptides designed to bind dynein have been shown to acquire dynamic properties such as cell accumulation and active intra- and inter-cellular motion through cell-to-cell contacts and projections to distant cells. On the basis of these properties dynein-binding peptides could be used to functionalize nanoparticles for drug delivery applications.

Results

Here, we show that gold nanoparticles modified with dynein-binding delivery sequences become mobile, powered by molecular motor proteins. Modified nanoparticles showed dynamic properties, such as travelling the cytosol, crossing intracellular barriers and shuttling the nuclear membrane. Furthermore, nanoparticles were transported from one cell to another through cell-to-cell contacts and quickly spread to distant cells through cell projections.

Conclusions

The capacity of these motor-bound nanoparticles to spread to many cells and increasing cellular retention, thus avoiding losses and allowing lower dosage, could make them candidate carriers for drug delivery.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0354-1) contains supplementary material, which is available to authorized users.

Analysis of microtubule growth dynamics arising from altered actin network structure and contractility in breast tumor cells

The periphery of epithelial cells is shaped by opposing cytoskeletal physical forces generated predominately by two dynamic force generating systems-growing microtubule ends push against the boundary from the cell center, and the actin cortex contracts the attached plasma membrane. Here we investigate how changes to the structure and dynamics of the actin cortex alter the dynamics of microtubules. Current drugs target actin polymerization and contraction to reduce cell division and invasiveness; however, the impacts on microtubule dynamics remain incompletely understood. Using human MCF-7 breast tumor cells expressing GFP-tagged microtubule end-binding-protein-1 (EB1) and coexpression of cytoplasmic fluorescent protein mCherry, we map the trajectories of growing microtubule ends and cytoplasmic boundary respectively. Based on EB1 tracks and cytoplasmic boundary outlines, we calculate the speed, distance from cytoplasmic boundary, and straightness of microtubule growth. Actin depolymerization with Latrunculin-A reduces EB1 growth speed as well as allows the trajectories to extend beyond the cytoplasmic boundary. Blebbistatin, a direct myosin-II inhibitor, reduced EB1 speed and yielded less straight EB1 trajectories. Inhibiting signaling upstream of myosin-II contractility via the Rho-kinase inhibitor, Y-27632, altered EB1 dynamics differently from Blebbistatin. These results indicate that reduced actin cortex integrity can induce distinct alterations in microtubule dynamics. Given recent findings that tumor stem cell characteristics are increased by drugs which reduce actin contractility or stabilize microtubules, it remains important to clearly define how cytoskeletal drugs alter the interactions between these two filament systems in tumor cells.

In silico synchronization reveals regulators of nuclear ruptures in lamin A/C deficient model cells

The nuclear lamina is a critical regulator of nuclear structure and function. Nuclei from laminopathy patient cells experience repetitive disruptions of the nuclear envelope, causing transient intermingling of nuclear and cytoplasmic components. The exact causes and consequences of these events are not fully understood, but their stochastic occurrence complicates in-depth analyses. To resolve this, we have established a method that enables quantitative investigation of spontaneous nuclear ruptures, based on co-expression of a firmly bound nuclear reference marker and a fluorescent protein that shuttles between the nucleus and cytoplasm during ruptures. Minimally invasive imaging of both reporters, combined with automated tracking and in silico synchronization of individual rupture events, allowed extracting information on rupture frequency and recovery kinetics. Using this approach, we found that rupture frequency correlates inversely with lamin A/C levels, and can be reduced in genome-edited LMNA knockout cells by blocking actomyosin contractility or inhibiting the acetyl-transferase protein NAT10. Nuclear signal recovery followed a kinetic that is co-determined by the severity of the rupture event, and could be prolonged by knockdown of the ESCRT-III complex component CHMP4B. In conclusion, our approach reveals regulators of nuclear rupture induction and repair, which may have critical roles in disease development.

The Hagfish Gland Thread Cell: A Fiber-Producing Cell Involved in Predator Defense

Fibers are ubiquitous in biology, and include tensile materials produced by specialized glands (such as silks), extracellular fibrils that reinforce exoskeletons and connective tissues (such as chitin and collagen), as well as intracellular filaments that make up the metazoan cytoskeleton (such as F-actin, microtubules, and intermediate filaments). Hagfish gland thread cells are unique in that they produce a high aspect ratio fiber from cytoskeletal building blocks within the confines of their cytoplasm. These threads are elaborately coiled into structures that readily unravel when they are ejected into seawater from the slime glands. In this review we summarize what is currently known about the structure and function of gland thread cells and we speculate about the mechanism that these cells use to produce a mechanically robust fiber that is almost one hundred thousand times longer than it is wide. We propose that a key feature of this mechanism involves the unidirectional rotation of the cell’s nucleus, which would serve to twist disorganized filaments into a coherent thread and impart a torsional stress on the thread that would both facilitate coiling and drive energetic unravelling in seawater.

Circovirus transport proceeds via direct interaction of the cytoplasmic dynein IC1 subunit with the viral capsid protein

Microtubule transport of circovirus from the periphery of the cell to the nucleus is essential for viral replication in early infection. How the microtubule is recruited to the viral cargo remains unclear. In this study, we observed that circovirus trafficking is dependent on microtubule polymerization and that incoming circovirus particles colocalize with cytoplasmic dynein and endosomes. However, circovirus binding to dynein was independent of the presence of microtubular α-tubulin and translocation of cytoplasmic dynein into the nucleus. The circovirus capsid (Cap) subunit enhanced microtubular acetylation and directly interacted with intermediate chain 1 (IC1) of dynein. N-terminal residues 42 to 100 of the Cap viral protein were required for efficient binding to the dynein IC1 subunit and for retrograde transport. Knockdown of IC1 decreased virus transport and replication. These results demonstrate that Cap is a direct ligand of the cytoplasmic dynein IC1 subunit and an inducer of microtubule α-tubulin acetylation. Furthermore, Cap recruits the host dynein/microtubule machinery to facilitate transport toward the nucleus by an endosomal mechanism distinct from that used for physiological dynein cargo.

IMPORTANCE

Incoming viral particles hijack the intracellular trafficking machinery of the host in order to migrate from the cell surface to the replication sites. Better knowledge of the interaction between viruses and virus proteins and the intracellular trafficking machinery may provide new targets for antiviral therapies. Currently, little is known about the molecular mechanisms of circovirus transport. Here, we report that circovirus particles enter early endosomes and utilize the microtubule-associated molecular motor dynein to travel along microtubules. The circovirus capsid subunit enhances microtubular acetylation, and N-terminal residues 42 to 100 directly interact with the dynein IC1 subunit during retrograde transport. These findings highlight a mechanism whereby circoviruses recruit dynein for transport to the nucleus via the dynein/microtubule machinery.

Cloning and characterization of cytoplasmic dynein intermediate chain in Fenneropenaeus chinensis and its essential role in white spot syndrome virus infection

To investigate the role of cytoplasmic dynein in white spot syndrome virus (WSSV) infection, the full-length cDNA of cytoplasmic dynein intermediate chain (FcDYNCI) was cloned in Fenneropenaeus chinensis, which consists of 2582 bp and encodes a polypeptide of 660 amino acids. Sequence analysis and multiple sequence alignment displayed that FcDYNCI was a member of cytoplasmic dynein 1 family. The FcDYNCI mRNA was most highly expressed in hemocytes, which was significantly up-regulated post WSSV infection. At 12 h post infection (hpi), confocal microscopic observation showed that WSSV could be co-localized with cytoplasmic dynein in hemocytes. After silencing by specific FcDYNCI dsRNA, the FcDYNCI mRNA level and the protein amount of FcDYNCI in hemocytes both exhibited a significant reduction, and the expression levels of three WSSV genes ie1, wsv477 and vp28 all exhibited the greatest decreases at 24 hpi. These results suggested that cytoplasmic dynein was involved in WSSV infection.

Microtubules and spermatogenesis

Microtubules are dynamic polymers of tubulin subunits that underpin many essential cellular processes, such as cell division and migration. Spermatogenesis is the process by which spermatogenic stem cells undergo mitotic and meiotic division and differentiation to produce streamlined spermatozoa capable of motility and fertilization. This review summarizes the current knowledge of microtubule-based processes in spermatogenesis. We describe the involvement of microtubule dynamics in Sertoli cell shape and function, as well as in the mitotic and meiotic division of germ cells. The roles of microtubules in sperm head shaping, via the development and function of the manchette, and in sperm flagella development are also discussed. The review brings together data from microscopy studies and genetically modified mouse models, and reveals that the regulation of microtubule dynamics is essential for male fertility.