-
International Journal of Biological... Jul 2019In specialized cell types such as neurons, microtubules maintain the integrity of axons by forming stable bundles and facilitate the transport of synaptic vesicles. The... (Review)
Review
In specialized cell types such as neurons, microtubules maintain the integrity of axons by forming stable bundles and facilitate the transport of synaptic vesicles. The cells regulate the stability and dynamics of microtubules using a diverse array of mechanisms. One of the mechanisms involves the interaction of microtubules with its associated proteins. Microtubule-associated proteins (MAPs) may have either stabilizing or destabilizing effects on the microtubules. Tau, a neuronal MAP, promotes the assembly and bundling of microtubules and suppresses microtubule dynamics. Abnormal functioning of tau is implicated in several neuronal disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD), wherein tau forms insoluble aggregates and causes neurotoxicity. In this review, we focus on the effects of tau on neuronal microtubule stability and dynamics. We also discuss the factors that lead to tau aggregation and the resulting destabilization of microtubules and the implications of this phenomenon in the AD and other tauopathies.
Topics: Animals; Humans; Microtubules; Mutation; Neurons; Protein Processing, Post-Translational; Tauopathies; tau Proteins
PubMed: 31004638
DOI: 10.1016/j.ijbiomac.2019.04.120 -
Cells Feb 2020The sensing, integrating, and coordinating features of the eukaryotic cells are achieved by the complex ultrastructural arrays and multifarious functions of the... (Review)
Review
The sensing, integrating, and coordinating features of the eukaryotic cells are achieved by the complex ultrastructural arrays and multifarious functions of the cytoskeleton, including the microtubule network. Microtubules play crucial roles achieved by their decoration with proteins/enzymes as well as by posttranslational modifications. This review focuses on the Tubulin Polymerization Promoting Protein (TPPP/p25), a new microtubule associated protein, on its "regulatory functions by day and pathological functions at night". Physiologically, the moonlighting TPPP/p25 modulates the dynamics and stability of the microtubule network by bundling microtubules and enhancing the tubulin acetylation due to the inhibition of tubulin deacetylases. The optimal endogenous TPPP/p25 level is crucial for its physiological functions, to the differentiation of oligodendrocytes, which are the major constituents of the myelin sheath. Pathologically, TPPP/p25 forms toxic oligomers/aggregates with α-synuclein in neurons and oligodendrocytes in Parkinson's disease and Multiple System Atrophy, respectively; and their complex is a potential therapeutic drug target. TPPP/p25-derived microtubule hyperacetylation counteracts uncontrolled cell division. All these issues reveal the anti-mitotic and α-synuclein aggregation-promoting potency of TPPP/p25, consistent with the finding that Parkinson's disease patients have reduced risk for certain cancers.
Topics: Animals; Humans; Microtubule-Associated Proteins; Models, Biological; Neoplasms; Nervous System Diseases; Photoperiod; Tubulin
PubMed: 32033023
DOI: 10.3390/cells9020357 -
BMC Biology Apr 2020Upon water uptake and release of seed dormancy, embryonic plant cells expand, while being mechanically constrained by the seed coat. Cortical microtubules (CMTs) are key...
BACKGROUND
Upon water uptake and release of seed dormancy, embryonic plant cells expand, while being mechanically constrained by the seed coat. Cortical microtubules (CMTs) are key players of cell elongation in plants: their anisotropic orientation channels the axis of cell elongation through the guidance of oriented deposition of load-bearing cellulose microfibrils in the cell wall. Interestingly, CMTs align with tensile stress, and consistently, they reorient upon compressive stress in growing hypocotyls. How CMTs first organise in germinating embryos is unknown, and their relation with mechanical stress has not been investigated at such an early developing stage.
RESULTS
Here, we analysed CMT dynamics in dormant and non-dormant Arabidopsis seeds by microscopy of fluorescently tagged microtubule markers at different developmental time points and in response to abscisic acid and gibberellins. We found that CMTs first appear as very few thick bundles in dormant seeds. Consistently, analysis of available transcriptome and translatome datasets show that limiting amounts of tubulin and microtubule regulators initially hinder microtubule self-organisation. Seeds imbibed in the presence of gibberellic acid or abscisic acid displayed altered microtubule organisation and transcriptional regulation. Upon the release of dormancy, CMTs then self-organise into multiple parallel transverse arrays. Such behaviour matches the tensile stress patterns in such mechanically constrained embryos. This suggests that, as CMTs first self-organise, they also align with shape-derived tensile stress patterns.
CONCLUSIONS
Our results provide a scenario in which dormancy release in the embryo triggers microtubule self-organisation and alignment with tensile stress prior to germination and anisotropic growth.
Topics: Arabidopsis; Germination; Microtubules; Seeds
PubMed: 32354334
DOI: 10.1186/s12915-020-00774-8 -
Planta Mar 2023STD1 specifically interacts with MAP65-5 in rice and they cooperatively control microtubule bundles in phragmoplast expansion during cell division. Microtubules play...
STD1 specifically interacts with MAP65-5 in rice and they cooperatively control microtubule bundles in phragmoplast expansion during cell division. Microtubules play critical roles during the cell cycle progression in the plant cell. We previously reported that STEMLESS DWARF 1 (STD1), a kinesin-related protein, was localized specifically to the phragmoplast midzone during telophase to regulate the lateral expansion of phragmoplast in rice (Oryza sativa). However, how STD1 regulates microtubule organization remains unknown. Here, we found that STD1 interacted directly with MAP65-5, a member of the microtubule-associated proteins (MAPs). Both STD1 and MAP65-5 could form homodimers and bundle microtubules individually. Compared with MAP65-5, the microtubules bundled by STD1 were disassembled completely into single microtubules after adding ATP. Conversely, the interaction of STD1 with MAP65-5 enhanced the microtubule bundling. These results suggest STD1 and MAP65-5 might cooperatively regulate microtubule organization in the phragmoplast at telophase.
Topics: Microtubule-Associated Proteins; Kinesins; Oryza; Microtubules; Mitosis
PubMed: 36862199
DOI: 10.1007/s00425-023-04106-2 -
Methods in Molecular Biology (Clifton,... 2023Cross-linking of microtubules by microtubule-associated proteins (MAPs) results in the formation of microtubule bundles. It has been shown that a majority of...
Cross-linking of microtubules by microtubule-associated proteins (MAPs) results in the formation of microtubule bundles. It has been shown that a majority of microtubules in interphase plant cells are bundled. Bundling can contribute to maintaining structural stability and sustaining spatial organization of microtubule arrays. While bundling can be readily detected by an electron or fluorescent microscope, quantifying this activity remains technically challenging. Here we describe a method for quantifying microtubule-bundling in vitro using green and red stable microtubules. Furthermore, this method distinguishes between different types of microtubule-microtubule interactions: bundling, annealing, and branching. Our technique can be used to compare bundling activity of different MAPs and generate parameters for modeling their contribution to organization and dynamics of microtubule arrays.
Topics: Microtubule-Associated Proteins; Microscopy; Microtubules; Cytoskeleton
PubMed: 36773221
DOI: 10.1007/978-1-0716-2867-6_1 -
Nature Communications Oct 2015Kinesin-5 slides antiparallel microtubules during spindle assembly, and regulates the branching of growing axons. Besides the mechanical activities enabled by its...
Kinesin-5 slides antiparallel microtubules during spindle assembly, and regulates the branching of growing axons. Besides the mechanical activities enabled by its tetrameric configuration, the specific motor properties of kinesin-5 that underlie its cellular function remain unclear. Here by engineering a stable kinesin-5 dimer and reconstituting microtubule dynamics in vitro, we demonstrate that kinesin-5 promotes microtubule polymerization by increasing the growth rate and decreasing the catastrophe frequency. Strikingly, microtubules growing in the presence of kinesin-5 have curved plus ends, suggesting that the motor stabilizes growing protofilaments. Single-molecule fluorescence experiments reveal that kinesin-5 remains bound to the plus ends of static microtubules for 7 s, and tracks growing microtubule plus ends in a manner dependent on its processivity. We propose that kinesin-5 pauses at microtubule plus ends and enhances polymerization by stabilizing longitudinal tubulin-tubulin interactions, and that these activities underlie the ability kinesin-5 to slide and stabilize microtubule bundles in cells.
Topics: Animals; Dimerization; Drosophila; Drosophila Proteins; In Vitro Techniques; Kinesins; Microtubule-Associated Proteins; Microtubules; Tubulin; Tubulin Modulators; Xenopus Proteins; Xenopus laevis
PubMed: 26437877
DOI: 10.1038/ncomms9160 -
Journal of Thrombosis and Haemostasis :... Mar 2015Blood platelets are tiny cell fragments derived from megakaryocytes. Their primary function is to control blood vessel integrity and ensure hemostasis if a vessel wall... (Review)
Review
Blood platelets are tiny cell fragments derived from megakaryocytes. Their primary function is to control blood vessel integrity and ensure hemostasis if a vessel wall is damaged. Circulating quiescent platelets have a flat, discoid shape maintained by a circumferential microtubule bundle, called the marginal band (MB). In the case of injury platelets are activated and rapidly adopt a spherical shape due to microtubule motor-induced elongation and subsequent coiling of the MB. Platelet activation and shape change can be transient or become irreversible. This depends on the strength of the activation stimulus, which is translated into a cytoskeletal crosstalk between microtubules, their motors and the actomyosin cortex, ensuring stimulus-response coupling. Following microtubule motor-driven disc-to-sphere transition, a strong stimulus will lead to compression of the sphere through actomyosin cortex contraction. This will concentrate the granules in the center of the platelet and accelerate their exocytosis. Once granules are released, platelets have crossed the point of no return to irreversible activation. This review summarizes the current knowledge of the molecular mechanism leading to platelet shape change, with a special emphasis on microtubules, and refers to previously published observations, which have been essential for generating an integrated view of cytoskeletal rearrangements during platelet activation.
Topics: Actin Cytoskeleton; Animals; Blood Platelets; Cell Shape; Cytoplasmic Vesicles; Exocytosis; Humans; Microtubules; Molecular Motor Proteins; Platelet Activation; Secretory Vesicles; Signal Transduction
PubMed: 25510620
DOI: 10.1111/jth.12819 -
Nano Letters Sep 2020In nature, interactions between biopolymers and motor proteins give rise to biologically essential emergent behaviors. Besides cytoskeleton mechanics, active nematics...
In nature, interactions between biopolymers and motor proteins give rise to biologically essential emergent behaviors. Besides cytoskeleton mechanics, active nematics arise from such interactions. Here we present a study on 3D active nematics made of microtubules, kinesin motors, and depleting agent. It shows a rich behavior evolving from a nematically ordered space-filling distribution of microtubule bundles toward a flattened and contracted 2D ribbon that undergoes a wrinkling instability and subsequently transitions into a 3D active turbulent state. The wrinkle wavelength is independent of the ATP concentration and our theoretical model describes its relation with the appearance time. We compare the experimental results with a numerical simulation that confirms the key role of kinesin motors in cross-linking and sliding the microtubules. Our results on the active contraction of the network and the independence of wrinkle wavelength on ATP concentration are important steps forward for the understanding of these 3D systems.
Topics: Computer Simulation; Kinesins; Microtubules
PubMed: 32786934
DOI: 10.1021/acs.nanolett.0c01546 -
FASEB Journal : Official Publication of... May 2023Age-related oocyte aneuploidy occurs as a result of chromosome segregation errors in female meiosis-I and meiosis-II, and is caused by a progressive age-related...
Age-related oocyte aneuploidy occurs as a result of chromosome segregation errors in female meiosis-I and meiosis-II, and is caused by a progressive age-related deterioration of the chromosome segregation machinery. Here, we assess the impact of age upon the kinetochore, the multi-protein structure that forms the link between the chromosome and spindle microtubules. We find that in meiosis-I the outer kinetochore assembles at germinal vesicle breakdown, but that a substantially smaller outer kinetochore is assembled in oocytes from aged mice. We show this correlates with a weaker centromere in aged oocytes and, using nuclear transfer approaches to generate young-aged hybrid oocytes, we show that outer kinetochore assembly always mirrors the status of the centromere, regardless of cytoplasmic age. Finally, we show that weaker kinetochores in aged oocytes are associated with thinner microtubule bundles, that are more likely to be mis-attached. We conclude that progressive loss of the centromere with advancing maternal age underpins a loss of the outer kinetochore in meiosis-I, which likely contributes to chromosome segregation fallibility in oocytes from older females.
Topics: Female; Animals; Mice; Kinetochores; Centromere; Oocytes; Meiosis; Microtubules; Aging; Chromosome Segregation; Spindle Apparatus
PubMed: 37078553
DOI: 10.1096/fj.202300062R -
Current Biology : CB Mar 2021The centrosome is the main organizer of microtubules and as such, its position is a key determinant of polarized cell functions. As the name says, the default position...
The centrosome is the main organizer of microtubules and as such, its position is a key determinant of polarized cell functions. As the name says, the default position of the centrosome is considered to be the cell geometrical center. However, the mechanism regulating centrosome positioning is still unclear and often confused with the mechanism regulating the position of the nucleus to which it is linked. Here, we used enucleated cells plated on adhesive micropatterns to impose regular and precise geometrical conditions to centrosome-microtubule networks. Although frequently observed there, the equilibrium position of the centrosome is not systematically at the cell geometrical center and can be close to cell edge. Centrosome positioning appears to respond accurately to the architecture and anisotropy of the actin network, which constitutes, rather than cell shape, the actual spatial boundary conditions the microtubule network is sensitive to. We found that the contraction of the actin network defines a peripheral margin in which microtubules appear bent by compressive forces. The progressive disassembly of the actin network at distance from the cell edges defines an inner zone where actin bundles were absent, where microtubules were more radially organized and where dynein concentration was higher. We further showed that the production of dynein-based forces on microtubules places the centrosome at the center of this zone. In conclusion, the spatial distribution of cell adhesion and the production of contractile forces define the architecture of the actin network with respect to which the centrosome-microtubule network is centered.
Topics: Actins; Centrosome; Dyneins; Microtubules; Myosins
PubMed: 33609453
DOI: 10.1016/j.cub.2021.01.002