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Cells Feb 2019Eukaryotic cilia are microtubule-based organelles that protrude from the cell surface to fulfill sensory and motility functions. Their basic structure consists of an... (Review)
Review
Eukaryotic cilia are microtubule-based organelles that protrude from the cell surface to fulfill sensory and motility functions. Their basic structure consists of an axoneme templated by a centriole/basal body. Striking differences in ciliary ultra-structures can be found at the ciliary base, the axoneme and the tip, not only throughout the eukaryotic tree of life, but within a single organism. Defects in cilia biogenesis and function are at the origin of human ciliopathies. This structural/functional diversity and its relationship with the etiology of these diseases is poorly understood. Some of the important events in cilia function occur at their distal domain, including cilia assembly/disassembly, IFT (intraflagellar transport) complexes' remodeling, and signal detection/transduction. How axonemal microtubules end at this domain varies with distinct cilia types, originating different tip architectures. Additionally, they show a high degree of dynamic behavior and are able to respond to different stimuli. The existence of microtubule-capping structures (caps) in certain types of cilia contributes to this diversity. It has been proposed that caps play a role in axoneme length control and stabilization, but their roles are still poorly understood. Here, we review the current knowledge on cilia structure diversity with a focus on the cilia distal domain and caps and discuss how they affect cilia structure and function.
Topics: Animals; Axoneme; Biological Evolution; Cilia; Humans; Models, Biological
PubMed: 30769894
DOI: 10.3390/cells8020160 -
Experimental Cell Research Oct 2018The fruit-fly Drosophila melanogaster harbours different types of ciliary structures: ciliary projections associated with neurons of type I and cilium-like regions...
The fruit-fly Drosophila melanogaster harbours different types of ciliary structures: ciliary projections associated with neurons of type I and cilium-like regions (CLRs) found during male gametogenesis. The latter deserve particular attention since they are morphologically similar to vertebrate primary cilia and transform into the sperm axonemes during spermiogenesis. Although, all the centrioles are able to organize the CLRs, we found that the mother centriole docks first to the plasma membrane suggesting a new intrinsic functional asymmetry between the parent centrioles. We also show that the CLRs lack the Y-links that connect the axoneme doublets with the plasma membrane in conventional primary cilia. Moreover, the C-tubules, that are lacking in the axoneme of the primary cilia, persisted along the CLRs albeit modified into longitudinal blades. Remarkably, mutant flies in which the CLRs are devoid of the C-tubules or their number is reduced lack sperm axonemes or have incomplete axonemes. Therefore, the C-tubules are dispensable for the assembly of the CLRs but are essential for sperm axoneme elongation and maintenance in Drosophila.
Topics: Animals; Axoneme; Cell Cycle Proteins; Cell Membrane; Centrioles; Cilia; Drosophila Proteins; Drosophila melanogaster; Gene Expression Regulation, Developmental; Male; Meiosis; Microscopy, Electron, Transmission; Mutation; Pupa; Spermatocytes; Spermatogenesis
PubMed: 30130520
DOI: 10.1016/j.yexcr.2018.08.020 -
Molecular Biology of the Cell Jun 2023Microtubules are noncovalent polymers built from αβ-tubulin dimers. The disordered C-terminal tubulin tails are functionalized with multiple glutamate chains of...
Microtubules are noncovalent polymers built from αβ-tubulin dimers. The disordered C-terminal tubulin tails are functionalized with multiple glutamate chains of variable lengths added and removed by tubulin tyrosine ligases (TTLLs) and carboxypeptidases (CCPs). Glutamylation is abundant on stable microtubule arrays such as in axonemes and axons, and its dysregulation leads to human pathologies. Despite this, the effects of glutamylation on intrinsic microtubule dynamics are unclear. Here we generate tubulin with short and long glutamate chains and show that glutamylation slows the rate of microtubule growth and increases catastrophes as a function of glutamylation levels. This implies that the higher stability of glutamylated microtubules in cells is due to effectors. Interestingly, EB1 is minimally affected by glutamylation and thus can report on the growth rates of both unmodified and glutamylated microtubules. Finally, we show that glutamate removal by CCP1 and 5 is synergistic and occurs preferentially on soluble tubulin, unlike TTLL enzymes that prefer microtubules. This substrate preference establishes an asymmetry whereby once the microtubule depolymerizes, the released tubulin is reset to a less-modified state, while polymerized tubulin accumulates the glutamylation mark. Our work shows that a modification on the disordered tubulin tails can directly affect microtubule dynamics and furthers our understanding of the mechanistic underpinnings of the tubulin code.
Topics: Humans; Tubulin; Microtubules; Glutamic Acid; Axoneme; Protein Processing, Post-Translational
PubMed: 37074962
DOI: 10.1091/mbc.E23-01-0030 -
Journal of Cell Science Aug 2021Axonemal dyneins power the beating of motile cilia and flagella. These massive multimeric motor complexes are assembled in the cytoplasm, and subsequently trafficked to...
Axonemal dyneins power the beating of motile cilia and flagella. These massive multimeric motor complexes are assembled in the cytoplasm, and subsequently trafficked to cilia and incorporated into the axonemal superstructure. Numerous cytoplasmic factors are required for the dynein assembly process, and, in mammals, defects lead to primary ciliary dyskinesia, which results in infertility, bronchial problems and failure to set up the left-right body axis correctly. Liquid-liquid phase separation (LLPS) has been proposed to underlie the formation of numerous membrane-less intracellular assemblies or condensates. In multiciliated cells, cytoplasmic assembly of axonemal dyneins also occurs in condensates that exhibit liquid-like properties, including fusion, fission and rapid exchange of components both within condensates and with bulk cytoplasm. However, a recent extensive meta-analysis suggests that the general methods used to define LLPS systems in vivo may not readily distinguish LLPS from other mechanisms. Here, I consider the time and length scales of axonemal dynein heavy chain synthesis, and the possibility that during translation of dynein heavy chain mRNAs, polysomes are crosslinked via partially assembled proteins. I propose that axonemal dynein factory formation in the cytoplasm may be a direct consequence of the sheer scale and complexity of the assembly process itself.
Topics: Animals; Axonemal Dyneins; Axoneme; Cilia; Cytoplasm; Dyneins; Flagella
PubMed: 34342348
DOI: 10.1242/jcs.258626 -
Current Biology : CB May 2014The cilium is a specialized extension of the cell in which many specific proteins are admitted and retained, while many others are excluded or expelled. In order to...
The cilium is a specialized extension of the cell in which many specific proteins are admitted and retained, while many others are excluded or expelled. In order to maintain the organelle, the cell must possess mechanisms for the selective gating of protein entry, as well as for the targeted transport of proteins to the cilium from their sites of synthesis within the cell [1-4]. We hypothesized that the cell employs cytoplasmic vesicles as vehicles not only for the transport of proteins destined for the ciliary membrane but also for the transport of axonemal proteins to the cilium by means of peripheral association with vesicles. To test this hypothesis, we employed two different experimental strategies: (1) isolation and biochemical characterization of cytoplasmic vesicles that carry ciliary proteins, and (2) in situ localization of ciliary proteins on cytoplasmic vesicle surfaces using gold labeling and electron microscopy. Our findings indicate that structural proteins destined for the ciliary axoneme are attached to the outer surfaces of cytoplasmic vesicles that carry integral ciliary membrane proteins during the process of ciliary growth.
Topics: Algal Proteins; Axoneme; Biological Transport; Blotting, Western; Cell Membrane; Chlamydomonas; Cilia; Cytoplasmic Vesicles; Electrophoresis, Polyacrylamide Gel; Membrane Proteins
PubMed: 24814148
DOI: 10.1016/j.cub.2014.03.047 -
FASEB Journal : Official Publication of... Sep 2010The intracellular amastigote stages of parasites such as Leishmania are often referred to as aflagellate. They do, however, possess a short axoneme of cryptic function....
The intracellular amastigote stages of parasites such as Leishmania are often referred to as aflagellate. They do, however, possess a short axoneme of cryptic function. Here, our examination of the structure of this axoneme leads to a testable hypothesis of its role in the cell biology of pathogenicity. We show a striking similarity between the microtubule axoneme structure of the Leishmania mexicana parasite infecting a macrophage and vertebrate primary cilia. In both, the 9-fold microtubule doublet symmetry is broken by the incursion of one or more microtubule doublets into the axoneme core, giving rise to an architecture that we term here the 9v (variable) axoneme. Three-dimensional reconstructions revealed that no particular doublet initiated the symmetry break, and moreover it often involved 2 doublets. The tip of the L. mexicana flagellum was frequently intimately associated with the macrophage vacuole membrane. We propose that the main function of the amastigote flagellum is to act as a sensory organelle with important functions in host-parasite interactions and signaling in the intracellular stage of the L. mexicana life cycle.
Topics: Animals; Axoneme; Cilia; Flagella; Host-Parasite Interactions; Humans; Leishmania; Microscopy, Electron, Transmission
PubMed: 20371625
DOI: 10.1096/fj.09-151381 -
Journal of Cellular Physiology Jun 2022The microtubular scaffold of motile cilia-the axoneme, is decorated with dynein arms, which are large multiprotein complexes essential for ciliary motility. Dynein arms... (Review)
Review
The microtubular scaffold of motile cilia-the axoneme, is decorated with dynein arms, which are large multiprotein complexes essential for ciliary motility. Dynein arms are arranged along the length of the axoneme in a precise repeating pattern, converting chemical energy from ATP hydrolysis into ciliary mechanical movement. How these complicated molecular machines are assembled coordinately and accurately, starting from mere polypeptide chains in the cytoplasm, remains a fascinating yet perplexing question. Rapidly emerging evidence, from multiple studies carried out with different model organisms and with various methodologies, has highlighted the existence of a dedicated assembly pathway. Here, we summarize recent progress made in clarifying the axonemal dynein arm assembly process, focusing on individual assembly steps, including cytoplasmic preassembly, intraflagellar transport, and axonemal docking.
Topics: Axoneme; Biological Transport; Cilia; Cytoplasm; Dyneins
PubMed: 35128656
DOI: 10.1002/jcp.30689 -
Journal of Cell Science Feb 2023The primary cilium is a microtubule-based organelle that serves as a hub for many signaling pathways. It functions as part of the centrosome or cilium complex, which...
The primary cilium is a microtubule-based organelle that serves as a hub for many signaling pathways. It functions as part of the centrosome or cilium complex, which also contains the basal body and the centriolar satellites. Little is known about the mechanisms by which the microtubule-based ciliary axoneme is assembled with a proper length and structure, particularly in terms of the activity of microtubule-associated proteins (MAPs) and the crosstalk between the different compartments of the centrosome or cilium complex. Here, we analyzed CCDC66, a MAP implicated in cilium biogenesis and ciliopathies. Live-cell imaging revealed that CCDC66 compartmentalizes between centrosomes, centriolar satellites, and the ciliary axoneme and tip during cilium biogenesis. CCDC66 depletion in human cells causes defects in cilium assembly, length and morphology. Notably, CCDC66 interacts with the ciliopathy-linked MAPs CEP104 and CSPP1, and regulates axonemal length and Hedgehog pathway activation. Moreover, CCDC66 is required for the basal body recruitment of transition zone proteins and intraflagellar transport B (IFT-B) machinery. Overall, our results establish CCDC66 as a multifaceted regulator of the primary cilium and provide insight into how ciliary MAPs and subcompartments cooperate to ensure assembly of functional cilia.
Topics: Humans; Cilia; Axoneme; Hedgehog Proteins; Microtubule-Associated Proteins; Centrioles; Eye Proteins
PubMed: 36606424
DOI: 10.1242/jcs.260327 -
Cell Motility and the Cytoskeleton Aug 2009Bending of cilia and flagella results from sliding between the microtubular outer doublets, driven by dynein motor enzymes. This review reminds us that many questions... (Review)
Review
Bending of cilia and flagella results from sliding between the microtubular outer doublets, driven by dynein motor enzymes. This review reminds us that many questions remain to be answered before we can understand how dynein-driven sliding causes the oscillatory bending of cilia and flagella. Does oscillation require switching between two distinct, persistent modes of dynein activity? Only one mode, an active forward mode, has been characterized, but an alternative mode, either inactive or reverse, appears to be required. Does switching between modes use information from curvature, sliding direction, or both? Is there a mechanism for reciprocal inhibition? Can a localized capability for oscillatory sliding become self-organized to produce the metachronal phase differences required for bend propagation? Are interactions between adjacent dyneins important for regulation of oscillation and bend propagation? Cell Motil. Cytoskeleton 2008. (c) 2008 Wiley-Liss, Inc.
Topics: Animals; Axoneme; Cilia; Dyneins; Flagella; Humans; Microtubules
PubMed: 18828155
DOI: 10.1002/cm.20313 -
Journal of Hazardous Materials Oct 2023Organophosphorus flame retardants (OPFRs) are frequently detected in aquatic environments and can potentially amplify the food chain, posing a potential risk to...
Organophosphorus flame retardants (OPFRs) are frequently detected in aquatic environments and can potentially amplify the food chain, posing a potential risk to organisms. Marine invertebrates have primitive nervous systems to regulate behavior, but how they respond to OPFRs that are potentially neurotoxic substances is unclear. This study assessed changes in the feeding behavior of rotifer Brachionus plicatilis exposed to alkyl OPFRs tributyl phosphate (TnBP) (0.376 nM, 3.76 and 22.53 µM) to elucidate the mechanism of behavioral toxicity. TnBP at 22.53 μM reduced the ingestion and filtration rates of rotifers for Chlorella vulgaris and Phaeocystis globosa in a 24-h test and altered rotifer-P. globosa population dynamics in 15-d coculture. Ciliary beat frequency was also reduced, and the expression of genes encoding the cilia axoneme was downregulated. TnBP could inhibit rotifer acetylcholinesterase activity by binding this protein and reduce the expression of the exocytotic membrane protein syntaxin-4, suggesting a disorder in nervous regulation of cilia beat. Moreover, TnBP induced abnormal shape and dysfunction of mitochondria, which caused insufficient energy required for ciliary movement. This study revealed diverse neurotoxicity mechanisms of TnBP, particularly as a potentially competing acetylcholinesterase ligand for aquatic invertebrates. Our research also provides a meaningful reference for OPFR-induced behavioral toxicity assessments.
Topics: Animals; Acetylcholinesterase; Cilia; Chlorella vulgaris; Axoneme; Rotifera; Organophosphates; Feeding Behavior; Flame Retardants; Organophosphorus Compounds
PubMed: 37557041
DOI: 10.1016/j.jhazmat.2023.132224