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Mammalian axoneme central pair complex proteins: Broader roles revealed by gene knockout phenotypes.Cytoskeleton (Hoboken, N.J.) Jan 2016The axoneme genes, their encoded proteins, their functions and the structures they form are largely conserved across species. Much of our knowledge of the function and... (Review)
Review
The axoneme genes, their encoded proteins, their functions and the structures they form are largely conserved across species. Much of our knowledge of the function and structure of axoneme proteins in cilia and flagella is derived from studies on model organisms like the green algae, Chlamydomonas reinhardtii. The core structure of cilia and flagella is the axoneme, which in most motile cilia and flagella contains a 9 + 2 configuration of microtubules. The two central microtubules are the scaffold of the central pair complex (CPC). Mutations that disrupt CPC genes in Chlamydomonas and other model organisms result in defects in assembly, stability and function of the axoneme, leading to flagellar motility defects. However, targeted mutations generated in mice in the orthologous CPC genes have revealed significant differences in phenotypes of mutants compared to Chlamydomonas. Here we review observations that support the concept of cell-type specific roles for the CPC genes in mice, and an expanded repertoire of functions for the products of these genes in cilia, including non-motile cilia, and other microtubule-associated cellular functions.
Topics: Animals; Axoneme; Cytoskeletal Proteins; Gene Knockout Techniques; Humans; Mice; Microtubule Proteins; Microtubule-Associated Proteins
PubMed: 26785425
DOI: 10.1002/cm.21271 -
The Journal of Cell Biology Nov 2023Cilia are essential organelles that protrude from the cell body. Cilia are made of a microtubule-based structure called the axoneme. In most types of cilia, the ciliary...
Cilia are essential organelles that protrude from the cell body. Cilia are made of a microtubule-based structure called the axoneme. In most types of cilia, the ciliary tip is distinct from the rest of the cilium. Here, we used cryo-electron tomography and subtomogram averaging to obtain the structure of the ciliary tip of the ciliate Tetrahymena thermophila. We show that the microtubules at the tip are highly crosslinked with each other and stabilized by luminal proteins, plugs, and cap proteins at the plus ends. In the tip region, the central pair lacks typical projections and twists significantly. By analyzing cells lacking a ciliary tip-enriched protein CEP104/FAP256 by cryo-electron tomography and proteomics, we discovered candidates for the central pair cap complex and explained the potential functions of CEP104/FAP256. These data provide new insights into the function of the ciliary tip and the mechanisms of ciliary assembly and length regulation.
Topics: Axoneme; Cilia; Microtubules; Tetrahymena thermophila
PubMed: 37756660
DOI: 10.1083/jcb.202301129 -
Nature Communications Apr 2023Cilia are ubiquitous eukaryotic organelles responsible for cellular motility and sensory functions. The ciliary axoneme is a microtubule-based cytoskeleton consisting of...
Cilia are ubiquitous eukaryotic organelles responsible for cellular motility and sensory functions. The ciliary axoneme is a microtubule-based cytoskeleton consisting of two central singlets and nine outer doublet microtubules. Cryo-electron microscopy-based studies have revealed a complex network inside the lumen of both tubules composed of microtubule-inner proteins (MIPs). However, the functions of most MIPs remain unknown. Here, we present single-particle cryo-EM-based analyses of the Tetrahymena thermophila native doublet microtubule and identify 42 MIPs. These data shed light on the evolutionarily conserved and diversified roles of MIPs. In addition, we identified MIPs potentially responsible for the assembly and stability of the doublet outer junction. Knockout of the evolutionarily conserved outer junction component CFAP77 moderately diminishes Tetrahymena swimming speed and beat frequency, indicating the important role of CFAP77 and outer junction stability in cilia beating generation and/or regulation.
Topics: Tetrahymena thermophila; Cryoelectron Microscopy; Microtubules; Axoneme; Cytoskeleton; Cilia; Microtubule Proteins; Tetrahymena
PubMed: 37061538
DOI: 10.1038/s41467-023-37868-0 -
Nature Communications Nov 2020Axonemal dynein ATPases direct ciliary and flagellar beating via adenosine triphosphate (ATP) hydrolysis. The modulatory effect of adenosine monophosphate (AMP) and...
Axonemal dynein ATPases direct ciliary and flagellar beating via adenosine triphosphate (ATP) hydrolysis. The modulatory effect of adenosine monophosphate (AMP) and adenosine diphosphate (ADP) on flagellar beating is not fully understood. Here, we describe a deficiency of cilia and flagella associated protein 45 (CFAP45) in humans and mice that presents a motile ciliopathy featuring situs inversus totalis and asthenospermia. CFAP45-deficient cilia and flagella show normal morphology and axonemal ultrastructure. Proteomic profiling links CFAP45 to an axonemal module including dynein ATPases and adenylate kinase as well as CFAP52, whose mutations cause a similar ciliopathy. CFAP45 binds AMP in vitro, consistent with structural modelling that identifies an AMP-binding interface between CFAP45 and AK8. Microtubule sliding of dyskinetic sperm from Cfap45 mice is rescued with the addition of either AMP or ADP with ATP, compared to ATP alone. We propose that CFAP45 supports mammalian ciliary and flagellar beating via an adenine nucleotide homeostasis module.
Topics: Adenine Nucleotides; Adolescent; Adult; Animals; Asthenozoospermia; Axoneme; CRISPR-Cas Systems; Cilia; Cytoskeletal Proteins; DNA Mutational Analysis; Disease Models, Animal; Epididymis; Female; Flagella; Humans; Loss of Function Mutation; Male; Mice; Mice, Knockout; Middle Aged; Planarians; Respiratory Mucosa; Situs Inversus; Sperm Motility; Tomography, X-Ray Computed; Exome Sequencing
PubMed: 33139725
DOI: 10.1038/s41467-020-19113-0 -
Cytoskeleton (Hoboken, N.J.) Oct 2020Loss of the cilium is important for cell cycle progression and certain developmental transitions. Chytrid fungi are a group of basal fungi that have retained centrioles...
Loss of the cilium is important for cell cycle progression and certain developmental transitions. Chytrid fungi are a group of basal fungi that have retained centrioles and cilia, and they can disassemble their cilia via axoneme internalization as part of the transition from free-swimming spores to sessile sporangia. While this type of cilium disassembly has been observed in many single-celled eukaryotes, it has not been well characterized because it is not observed in common model organisms. To better characterize cilium disassembly via axoneme internalization, we focused on chytrids Rhizoclosmatium globosum and Spizellomyces punctatus to represent two lineages of chytrids with different motility characteristics. Our results show that each chytrid species can reel in its axoneme into the cell body along its cortex on the order of minutes, while S. punctatus has additional faster ciliary compartment loss and lash-around mechanisms. S. punctatus retraction can also occur away from the cell cortex and is partially actin dependent. Post-internalization, the tubulin of the axoneme is degraded in both chytrids over the course of about 2 hr. Axoneme disassembly and axonemal tubulin degradation are both partially proteasome dependent. Overall, chytrid cilium disassembly is a fast process that separates axoneme internalization and degradation.
Topics: Axoneme; Cilia; Fungi
PubMed: 33103844
DOI: 10.1002/cm.21637 -
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 -
Journal of Cell Science Dec 2022The assembly and maintenance of most cilia and eukaryotic flagella depends on intraflagellar transport (IFT), the bidirectional movement of multi-megadalton IFT trains... (Review)
Review
The assembly and maintenance of most cilia and eukaryotic flagella depends on intraflagellar transport (IFT), the bidirectional movement of multi-megadalton IFT trains along the axonemal microtubules. These IFT trains function as carriers, moving ciliary proteins between the cell body and the organelle. Whereas tubulin, the principal protein of cilia, binds directly to IFT particle proteins, the transport of other ciliary proteins and complexes requires adapters that link them to the trains. Large axonemal substructures, such as radial spokes, outer dynein arms and inner dynein arms, assemble in the cell body before attaching to IFT trains, using the adapters ARMC2, ODA16 and IDA3, respectively. Ciliary import of several membrane proteins involves the putative adapter tubby-like protein 3 (TULP3), whereas membrane protein export involves the BBSome, an octameric complex that co-migrates with IFT particles. Thus, cells employ a variety of adapters, each of which is substoichiometric to the core IFT machinery, to expand the cargo range of the IFT trains. This Review summarizes the individual and shared features of the known cargo adapters and discusses their possible role in regulating the transport capacity of the IFT pathway.
Topics: Dyneins; Flagella; Protein Transport; Axoneme; Cilia; Biological Transport; Membrane Proteins
PubMed: 36533425
DOI: 10.1242/jcs.260408 -
Cells Jul 2018During ciliogenesis, centrioles convert to membrane-docked basal bodies, which initiate the formation of cilia/flagella and template the nine doublet microtubules of the... (Review)
Review
During ciliogenesis, centrioles convert to membrane-docked basal bodies, which initiate the formation of cilia/flagella and template the nine doublet microtubules of the flagellar axoneme. The discovery that many human diseases and developmental disorders result from defects in flagella has fueled a strong interest in the analysis of flagellar assembly. Here, we will review the structure, function, and development of basal bodies in the unicellular green alga , a widely used model for the analysis of basal bodies and flagella. Intraflagellar transport (IFT), a flagella-specific protein shuttle critical for ciliogenesis, was first described in A focus of this review will be on the role of the basal bodies in organizing the IFT machinery.
PubMed: 30018231
DOI: 10.3390/cells7070079 -
FAP106 is an interaction hub for assembling microtubule inner proteins at the cilium inner junction.Nature Communications Aug 2023Motility of pathogenic protozoa depends on flagella (synonymous with cilia) with axonemes containing nine doublet microtubules (DMTs) and two singlet microtubules....
Motility of pathogenic protozoa depends on flagella (synonymous with cilia) with axonemes containing nine doublet microtubules (DMTs) and two singlet microtubules. Microtubule inner proteins (MIPs) within DMTs influence axoneme stability and motility and provide lineage-specific adaptations, but individual MIP functions and assembly mechanisms are mostly unknown. Here, we show in the sleeping sickness parasite Trypanosoma brucei, that FAP106, a conserved MIP at the DMT inner junction, is required for trypanosome motility and functions as a critical interaction hub, directing assembly of several conserved and lineage-specific MIPs. We use comparative cryogenic electron tomography (cryoET) and quantitative proteomics to identify MIP candidates. Using RNAi knockdown together with fitting of AlphaFold models into cryoET maps, we demonstrate that one of these candidates, MC8, is a trypanosome-specific MIP required for parasite motility. Our work advances understanding of MIP assembly mechanisms and identifies lineage-specific motility proteins that are attractive targets to consider for therapeutic intervention.
Topics: Cilia; Flagella; Microtubules; Acclimatization; Axoneme; Microtubule Proteins
PubMed: 37633952
DOI: 10.1038/s41467-023-40230-z -
Journal of Parasitic Diseases :... Dec 2015Kinetoplastids, the evolutionary ancient organisms exhibit a rich and diverse biology which epitomizes many of the fascinating topics of recent interest and study. These... (Review)
Review
Kinetoplastids, the evolutionary ancient organisms exhibit a rich and diverse biology which epitomizes many of the fascinating topics of recent interest and study. These organisms possess a multifunctional organelle, the flagellum containing a canonical 9 + 2 axoneme which is involved in vital roles, viz. parasite cell division, morphogenesis, motility and immune evasion. Since Antony Van Leeuwenhoek's innovative explanation of 'little legs' helping the movements of microbes in 1975, this biological nanomachine has captured the thoughts of scientists. The core structure of kinetoplastid flagellum is embroidered with a range of extra-axonemal structures such as paraflagellar rod (PFR), a large lattice like structure which extends alongside the axoneme from the flagellar pocket to the flagellar tip. The coding sequences for significant components of PFR are highly conserved throughout the Kinetoplastida and Euglenida. The high order organization and restricted evolutionary distribution of the PFR components and structure makes the PFR a particularly valuable therapeutic and prophylactic target. This review focuses on the recent developments in identification of ultra structural components of PFR in order to understand the function of this intriguing organelle and devising strategies for therapeutic interventions.
PubMed: 26688619
DOI: 10.1007/s12639-014-0422-x