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Yanagisawa HA, Mathis G, Oda T, Hirono M, Richey EA, Ishikawa H, Marshall WF, Kikkawa M, Qin H. FAP20 is an inner junction protein of doublet microtubules essential for both the planar asymmetrical waveform and stability of flagella in Chlamydomonas. Mol Biol Cell 2014; 25:1472-83. [PMID: 24574454 PMCID: PMC4004596 DOI: 10.1091/mbc.e13-08-0464] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
The question of what proteins compose the junctions between two tubules in doublet microtubules is long-standing. Here a conserved flagellar protein, FAP20, is shown to be an inner junction component important for stabilizing the axoneme and scaffolding intra–B-tubular structures required for a planar asymmetrical waveform. The axoneme—the conserved core of eukaryotic cilia and flagella—contains highly specialized doublet microtubules (DMTs). A long-standing question is what protein(s) compose the junctions between two tubules in DMT. Here we identify a highly conserved flagellar-associated protein (FAP), FAP20, as an inner junction (IJ) component. The flagella of Chlamydomonas FAP20 mutants have normal length but beat with an abnormal symmetrical three-dimensional pattern. In addition, the mutant axonemes are liable to disintegrate during beating, implying that interdoublet connections may be weakened. Conventional electron microscopy shows that the mutant axonemes lack the IJ, and cryo–electron tomography combined with a structural labeling method reveals that the labeled FAP20 localizes at the IJ. The mutant axonemes also lack doublet-specific beak structures, which are localized in the proximal portion of the axoneme and may be involved in planar asymmetric flagellar bending. FAP20 itself, however, may not be a beak component, because uniform localization of FAP20 along the entire length of all nine DMTs is inconsistent with the beak's localization. FAP20 is the first confirmed component of the IJ. Our data also suggest that the IJ is important for both stabilizing the axoneme and scaffolding intra–B-tubular substructures required for a planar asymmetrical waveform.
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Affiliation(s)
- Haru-aki Yanagisawa
- Department of Cell Biology and Anatomy, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Department of Biology, Texas A&M University, College Station, TX 77843 Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158
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52
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Bush A, Hogg C. Primary ciliary dyskinesia: recent advances in epidemiology, diagnosis, management and relationship with the expanding spectrum of ciliopathy. Expert Rev Respir Med 2014; 6:663-82. [DOI: 10.1586/ers.12.60] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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53
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Jana SC, Marteil G, Bettencourt-Dias M. Mapping molecules to structure: unveiling secrets of centriole and cilia assembly with near-atomic resolution. Curr Opin Cell Biol 2013; 26:96-106. [PMID: 24529251 DOI: 10.1016/j.ceb.2013.12.001] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Revised: 11/21/2013] [Accepted: 12/02/2013] [Indexed: 11/25/2022]
Abstract
Centrioles are microtubule (MT)-based cylinders that form centrosomes and can be modified into basal bodies that template the axoneme, the ciliary MT skeleton. These MT-based structures are present in all branches of the eukaryotic tree of life, where they have important sensing, motility and cellular architecture-organizing functions. Moreover, they are altered in several human conditions and diseases, including sterility, ciliopathies and cancer. Although the ultrastructure of centrioles and derived organelles has been known for over 50 years, the molecular basis of their remarkably conserved properties, such as their 9-fold symmetry, has only now started to be unveiled. Recent advances in imaging, proteomics and crystallography, allowed the building of 3D models of centrioles and derived structures with unprecedented molecular details, leading to a much better understanding of their assembly and function. Here, we cover progress in this field, focusing on the mechanisms of centriole and cilia assembly.
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Meng D, Cao M, Oda T, Pan J. The conserved ciliary protein Bug22 controls planar beating of Chlamydomonas flagella. J Cell Sci 2013; 127:281-7. [PMID: 24259666 DOI: 10.1242/jcs.140723] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Eukaryotic flagella and cilia can exhibit planar and non-planar beating, and the mechanism controlling these beating patterns is not well understood. Chlamydomonas reinhardtii flagella beat in approximately the same plane with either an asymmetric ciliary-type or symmetric flagellar-type waveform. Each B-tubule of the number 1, 5 and 6 doublets of the flagellar axoneme possesses a beak-like structure. The number 5 and 6 beak structures are implicated in conversion of ciliary motion into flagellar motion. Here, we show that in a null mutant of Bug22, the asymmetric ciliary waveform is converted into a three-dimensional (non-planar) symmetric flagellar waveform. Bug22 is localized to approximately the proximal half to two-thirds of the flagellum, similar to localization of beak-like structures. However, as shown by immunogold labeling, Bug22 associates with axonemal microtubules without apparent preference for any particular doublets. Interestingly, bug22 mutants lack all beak-like structures. We propose that one function of Bug22 is to regulate the anchoring of the beak-like structures to the doublet microtubules and confine flagellar beating to a plane.
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Affiliation(s)
- Dan Meng
- MOE Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China
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55
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Ishikawa T. 3D structure of eukaryotic flagella/cilia by cryo-electron tomography. Biophysics (Nagoya-shi) 2013; 9:141-8. [PMID: 27493552 PMCID: PMC4629670 DOI: 10.2142/biophysics.9.141] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2013] [Accepted: 09/25/2013] [Indexed: 12/01/2022] Open
Abstract
Flagella/cilia are motile organelles with more than 400 proteins. To understand the mechanism of such complex systems, we need methods to describe molecular arrange-ments and conformations three-dimensionally in vivo. Cryo-electron tomography enabled us such a 3D structural analysis. Our group has been working on 3D structure of flagella/cilia using this method and revealed highly ordered and beautifully organized molecular arrangement. 3D structure gave us insights into the mechanism to gener-ate bending motion with well defined waveforms. In this review, I summarize our recent structural studies on fla-gella/cilia by cryo-electron tomography, mainly focusing on dynein microtubule-based ATPase motor proteins and the radial spoke, a regulatory protein complex.
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Affiliation(s)
- Takashi Ishikawa
- Laboratory of Biomolecular Research, Paul Scherrer Institute, Villigen PSI, CH5232, Switzerland
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56
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Diniz MC, Pacheco ACL, Farias KM, de Oliveira DM. The eukaryotic flagellum makes the day: novel and unforeseen roles uncovered after post-genomics and proteomics data. Curr Protein Pept Sci 2013; 13:524-46. [PMID: 22708495 PMCID: PMC3499766 DOI: 10.2174/138920312803582951] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Revised: 05/22/2012] [Accepted: 05/23/2012] [Indexed: 12/21/2022]
Abstract
This review will summarize and discuss the current biological understanding of the motile eukaryotic flagellum,
as posed out by recent advances enabled by post-genomics and proteomics approaches. The organelle, which is crucial
for motility, survival, differentiation, reproduction, division and feeding, among other activities, of many eukaryotes,
is a great example of a natural nanomachine assembled mostly by proteins (around 350-650 of them) that have been conserved
throughout eukaryotic evolution. Flagellar proteins are discussed in terms of their arrangement on to the axoneme,
the canonical “9+2” microtubule pattern, and also motor and sensorial elements that have been detected by recent proteomic
analyses in organisms such as Chlamydomonas reinhardtii, sea urchin, and trypanosomatids. Such findings can be
remarkably matched up to important discoveries in vertebrate and mammalian types as diverse as sperm cells, ciliated
kidney epithelia, respiratory and oviductal cilia, and neuro-epithelia, among others. Here we will focus on some exciting
work regarding eukaryotic flagellar proteins, particularly using the flagellar proteome of C. reinhardtii as a reference map
for exploring motility in function, dysfunction and pathogenic flagellates. The reference map for the eukaryotic flagellar
proteome consists of 652 proteins that include known structural and intraflagellar transport (IFT) proteins, less well-characterized
signal transduction proteins and flagellar associated proteins (FAPs), besides almost two hundred unannotated
conserved proteins, which lately have been the subject of intense investigation and of our present examination.
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Affiliation(s)
- Michely C Diniz
- Programa de Pós-Graduação em Biotecnologia-RENORBIO-Rede Nordeste de Biotecnologia, Universidade Estadual do Ceará-UECE, Av. Paranjana, 1700, Campus do Itaperi, Fortaleza, CE 60740-000 Brasil
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57
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Affiliation(s)
- U B Kaupp
- Department of Molecular Sensory Systems, Center of Advanced European Studies and Research, 53175 Bonn, Germany
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58
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Native Architecture of the Centriole Proximal Region Reveals Features Underlying Its 9-Fold Radial Symmetry. Curr Biol 2013; 23:1620-8. [DOI: 10.1016/j.cub.2013.06.061] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Revised: 06/04/2013] [Accepted: 06/27/2013] [Indexed: 12/31/2022]
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59
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Olivier-Mason A, Wojtyniak M, Bowie RV, Nechipurenko IV, Blacque OE, Sengupta P. Transmembrane protein OSTA-1 shapes sensory cilia morphology via regulation of intracellular membrane trafficking in C. elegans. Development 2013; 140:1560-72. [PMID: 23482491 DOI: 10.1242/dev.086249] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The structure and function of primary cilia are critically dependent on intracellular trafficking pathways that transport ciliary membrane and protein components. The mechanisms by which these trafficking pathways are regulated are not fully characterized. Here we identify the transmembrane protein OSTA-1 as a new regulator of the trafficking pathways that shape the morphology and protein composition of sensory cilia in C. elegans. osta-1 encodes an organic solute transporter alpha-like protein, mammalian homologs of which have been implicated in membrane trafficking and solute transport, although a role in regulating cilia structure has not previously been demonstrated. We show that mutations in osta-1 result in altered ciliary membrane volume, branch length and complexity, as well as defects in localization of a subset of ciliary transmembrane proteins in different sensory cilia types. OSTA-1 is associated with transport vesicles, localizes to a ciliary compartment shown to house trafficking proteins, and regulates both retrograde and anterograde flux of the endosome-associated RAB-5 small GTPase. Genetic epistasis experiments with sensory signaling, exocytic and endocytic proteins further implicate OSTA-1 as a crucial regulator of ciliary architecture via regulation of cilia-destined trafficking. Our findings suggest that regulation of transport pathways in a cell type-specific manner contributes to diversity in sensory cilia structure and might allow dynamic remodeling of ciliary architecture via multiple inputs.
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Affiliation(s)
- Anique Olivier-Mason
- Department of Biology and National Center for Behavioral Genomics, Brandeis University, Waltham, MA 02454, USA
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60
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Briggs JAG. Structural biology in situ--the potential of subtomogram averaging. Curr Opin Struct Biol 2013; 23:261-7. [PMID: 23466038 DOI: 10.1016/j.sbi.2013.02.003] [Citation(s) in RCA: 175] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2012] [Revised: 02/12/2013] [Accepted: 02/13/2013] [Indexed: 12/27/2022]
Abstract
Cryo-electron tomography provides low-resolution 3D views of cells, organelles, or viruses. Macromolecular complexes present in multiple copies can be subsequently identified within the 3D reconstruction (the tomogram), computationally extracted, and averaged to obtain higher resolution 3D structures, as well as a map of their spatial distribution. This method, called subtomogram averaging or subvolume averaging, allows structures of macromolecular complexes to be resolved in situ. Recent applications have provided in situ structural data at resolutions of 2-4 nm on samples including polysomes, nuclear pores, vesicle coats, and viral surface proteins. Here I describe the method and discuss limitations, advances and recent applications. I speculate how the method will solve more structures at higher resolution, allowing in situ structural biology.
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Affiliation(s)
- John A G Briggs
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
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61
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Bower R, Tritschler D, Vanderwaal K, Perrone CA, Mueller J, Fox L, Sale WS, Porter ME. The N-DRC forms a conserved biochemical complex that maintains outer doublet alignment and limits microtubule sliding in motile axonemes. Mol Biol Cell 2013; 24:1134-52. [PMID: 23427265 PMCID: PMC3623635 DOI: 10.1091/mbc.e12-11-0801] [Citation(s) in RCA: 89] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The nexin–dynein regulatory complex (N-DRC) is implicated in the control of dynein activity as a structural component of the nexin link. This study identifies several new subunits of the N-DRC and demonstrates for the first time that it forms a discrete biochemical complex that maintains outer doublet integrity and regulates microtubule sliding. The nexin–dynein regulatory complex (N-DRC) is proposed to coordinate dynein arm activity and interconnect doublet microtubules. Here we identify a conserved region in DRC4 critical for assembly of the N-DRC into the axoneme. At least 10 subunits associate with DRC4 to form a discrete complex distinct from other axonemal substructures. Transformation of drc4 mutants with epitope-tagged DRC4 rescues the motility defects and restores assembly of missing DRC subunits and associated inner-arm dyneins. Four new DRC subunits contain calcium-signaling motifs and/or AAA domains and are nearly ubiquitous in species with motile cilia. However, drc mutants are motile and maintain the 9 + 2 organization of the axoneme. To evaluate the function of the N-DRC, we analyzed ATP-induced reactivation of isolated axonemes. Rather than the reactivated bending observed with wild-type axonemes, ATP addition to drc-mutant axonemes resulted in splaying of doublets in the distal region, followed by oscillatory bending between pairs of doublets. Thus the N-DRC provides some but not all of the resistance to microtubule sliding and helps to maintain optimal alignment of doublets for productive flagellar motility. These findings provide new insights into the mechanisms that regulate motility and further highlight the importance of the proximal region of the axoneme in generating flagellar bending.
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Affiliation(s)
- Raqual Bower
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA
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62
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Bui KH, Yagi T, Yamamoto R, Kamiya R, Ishikawa T. Polarity and asymmetry in the arrangement of dynein and related structures in the Chlamydomonas axoneme. ACTA ACUST UNITED AC 2013; 198:913-25. [PMID: 22945936 PMCID: PMC3432765 DOI: 10.1083/jcb.201201120] [Citation(s) in RCA: 131] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cryoelectron tomography and subtomogram averaging reveal a high degree of structural asymmetry and polarization in dynein localization in the Chlamydomonas flagella. Understanding the molecular architecture of the flagellum is crucial to elucidate the bending mechanism produced by this complex organelle. The current known structure of the flagellum has not yet been fully correlated with the complex composition and localization of flagellar components. Using cryoelectron tomography and subtomogram averaging while distinguishing each one of the nine outer doublet microtubules, we systematically collected and reconstructed the three-dimensional structures in different regions of the Chlamydomonas flagellum. We visualized the radial and longitudinal differences in the flagellum. One doublet showed a distinct structure, whereas the other eight were similar but not identical to each other. In the proximal region, some dyneins were missing or replaced by minor dyneins, and outer–inner arm dynein links were variable among different microtubule doublets. These findings shed light on the intricate organization of Chlamydomonas flagella, provide clues to the mechanism that produces asymmetric flagellar beating, and pose a new challenge for the functional study of the flagella.
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Affiliation(s)
- Khanh Huy Bui
- Laboratory of Biomolecular Research, Paul Scherrer Institute, CH-5232 Villigen, Switzerland
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63
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Carbajal-González BI, Heuser T, Fu X, Lin J, Smith BW, Mitchell DR, Nicastro D. Conserved structural motifs in the central pair complex of eukaryotic flagella. Cytoskeleton (Hoboken) 2013; 70:101-120. [PMID: 23281266 PMCID: PMC3914236 DOI: 10.1002/cm.21094] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2012] [Revised: 11/19/2012] [Accepted: 11/21/2012] [Indexed: 11/11/2022]
Abstract
Cilia and flagella are conserved hair-like appendages of eukaryotic cells that function as sensing and motility generating organelles. Motility is driven by thousands of axonemal dyneins that require precise regulation. One essential motility regulator is the central pair complex (CPC) and many CPC defects cause paralysis of cilia/flagella. Several human diseases, such as immotile cilia syndrome, show CPC abnormalities, but little is known about the detailed three-dimensional (3D) structure and function of the CPC. The CPC is located in the center of typical [9+2] cilia/flagella and is composed of two singlet microtubules (MTs), each with a set of associated projections that extend toward the surrounding nine doublet MTs. Using cryo-electron tomography coupled with subtomogram averaging, we visualized and compared the 3D structures of the CPC in both the green alga Chlamydomonas and the sea urchin Strongylocentrotus at the highest resolution published to date. Despite the evolutionary distance between these species, their CPCs exhibit remarkable structural conservation. We identified several new projections, including those that form the elusive sheath, and show that the bridge has a more complex architecture than previously thought. Organism-specific differences include the presence of MT inner proteins in Chlamydomonas, but not Strongylocentrotus, and different overall outlines of the highly connected projection network, which forms a round-shaped cylinder in algae, but is more oval in sea urchin. These differences could be adaptations to the mechanical requirements of the rotating CPC in Chlamydomonas, compared to the Strongylocentrotus CPC which has a fixed orientation.
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Affiliation(s)
| | - Thomas Heuser
- Biology Department, Rosenstiel Center, MS029, Brandeis University, 415 South Street, Waltham, MA 02454, USA
| | - Xiaofeng Fu
- Biology Department, Rosenstiel Center, MS029, Brandeis University, 415 South Street, Waltham, MA 02454, USA
- Howard Hughes Medical Institute, Brandeis University, 415 South Street, Waltham, MA 02454, USA
| | - Jianfeng Lin
- Biology Department, Rosenstiel Center, MS029, Brandeis University, 415 South Street, Waltham, MA 02454, USA
| | - Brandon W. Smith
- Department of Cell and Developmental Biology, Upstate Medical University, 750 E. Adams St., Syracuse, NY 13210, USA
| | - David R. Mitchell
- Department of Cell and Developmental Biology, Upstate Medical University, 750 E. Adams St., Syracuse, NY 13210, USA
| | - Daniela Nicastro
- Biology Department, Rosenstiel Center, MS029, Brandeis University, 415 South Street, Waltham, MA 02454, USA
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64
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Bui KH, Ishikawa T. 3D Structural Analysis of Flagella/Cilia by Cryo-Electron Tomography. Methods Enzymol 2013; 524:305-23. [DOI: 10.1016/b978-0-12-397945-2.00017-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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65
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Advances in tomography: probing the molecular architecture of cells. Nat Rev Mol Cell Biol 2012; 13:736-42. [DOI: 10.1038/nrm3453] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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66
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Lin J, Heuser T, Song K, Fu X, Nicastro D. One of the nine doublet microtubules of eukaryotic flagella exhibits unique and partially conserved structures. PLoS One 2012; 7:e46494. [PMID: 23071579 PMCID: PMC3468612 DOI: 10.1371/journal.pone.0046494] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Accepted: 09/05/2012] [Indexed: 12/26/2022] Open
Abstract
The axonemal core of motile cilia and flagella consists of nine doublet microtubules surrounding two central single microtubules. Attached to the doublets are thousands of dynein motors that produce sliding between neighboring doublets, which in turn causes flagellar bending. Although many structural features of the axoneme have been described, structures that are unique to specific doublets remain largely uncharacterized. These doublet-specific structures introduce asymmetry into the axoneme and are likely important for the spatial control of local microtubule sliding. Here, we used cryo-electron tomography and doublet-specific averaging to determine the 3D structures of individual doublets in the flagella of two evolutionarily distant organisms, the protist Chlamydomonas and the sea urchin Strongylocentrotus. We demonstrate that, in both organisms, one of the nine doublets exhibits unique structural features. Some of these features are highly conserved, such as the inter-doublet link i-SUB5-6, which connects this doublet to its neighbor with a periodicity of 96 nm. We also show that the previously described inter-doublet links attached to this doublet, the o-SUB5-6 in Strongylocentrotus and the proximal 1–2 bridge in Chlamydomonas, are likely not homologous features. The presence of inter-doublet links and reduction of dynein arms indicate that inter-doublet sliding of this unique doublet against its neighbor is limited, providing a rigid plane perpendicular to the flagellar bending plane. These doublet-specific features and the non-sliding nature of these connected doublets suggest a structural basis for the asymmetric distribution of dynein activity and inter-doublet sliding, resulting in quasi-planar waveforms typical of 9+2 cilia and flagella.
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Affiliation(s)
- Jianfeng Lin
- Biology Department, Rosenstiel Center, Brandeis University, Waltham, Massachusetts, United States of America
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67
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Mizuno N, Taschner M, Engel BD, Lorentzen E. Structural studies of ciliary components. J Mol Biol 2012; 422:163-80. [PMID: 22683354 PMCID: PMC3426769 DOI: 10.1016/j.jmb.2012.05.040] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Revised: 05/23/2012] [Accepted: 05/24/2012] [Indexed: 11/24/2022]
Abstract
Cilia are organelles found on most eukaryotic cells, where they serve important functions in motility, sensory reception, and signaling. Recent advances in electron tomography have facilitated a number of ultrastructural studies of ciliary components that have significantly improved our knowledge of cilium architecture. These studies have produced nanometer-resolution structures of axonemal dynein complexes, microtubule doublets and triplets, basal bodies, radial spokes, and nexin complexes. In addition to these electron tomography studies, several recently published crystal structures provide insights into the architecture and mechanism of dynein as well as the centriolar protein SAS-6, important for establishing the 9-fold symmetry of centrioles. Ciliary assembly requires intraflagellar transport (IFT), a process that moves macromolecules between the tip of the cilium and the cell body. IFT relies on a large 20-subunit protein complex that is thought to mediate the contacts between ciliary motor and cargo proteins. Structural investigations of IFT complexes are starting to emerge, including the first three-dimensional models of IFT material in situ, revealing how IFT particles organize into larger train-like arrays, and the high-resolution structure of the IFT25/27 subcomplex. In this review, we cover recent advances in the structural and mechanistic understanding of ciliary components and IFT complexes.
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Key Words
- 2d, two‐dimensional
- 3d, three‐dimensional
- dic, differential interference contrast
- drc, dynein regulatory complex
- em, electron microscopy
- et, electron tomography
- ida, inner dynein arm
- ift, intraflagellar transport
- mt, microtubule
- mtbd, microtubule binding domain
- oda, outer dynein arm
- rs, radial spoke
- rsp, radial spoke protein
- cilium
- intraflagellar transport
- electron tomography
- ift complex
- flagellum
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Affiliation(s)
- Naoko Mizuno
- Department of Structural Cell Biology, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany
| | - Michael Taschner
- Department of Structural Cell Biology, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany
| | - Benjamin D. Engel
- Department of Molecular Structural Biology, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany
| | - Esben Lorentzen
- Department of Structural Cell Biology, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany
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68
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Heuser T, Dymek EE, Lin J, Smith EF, Nicastro D. The CSC connects three major axonemal complexes involved in dynein regulation. Mol Biol Cell 2012; 23:3143-55. [PMID: 22740634 PMCID: PMC3418309 DOI: 10.1091/mbc.e12-05-0357] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
This study reveals the 3D structure of the CSC and its connections to three major axonemal complexes involved in dynein regulation, including the distal radial spoke and the nexin-DRC. The findings corroborate radial spoke heterogeneity and suggest a unique role for the distal spoke in calcium-mediated signal transduction and flagellar motility. Motile cilia and flagella are highly conserved organelles that play important roles in human health and development. We recently discovered a calmodulin- and spoke-associated complex (CSC) that is required for wild-type motility and for the stable assembly of a subset of radial spokes. Using cryo–electron tomography, we present the first structure-based localization model of the CSC. Chlamydomonas flagella have two full-length radial spokes, RS1 and RS2, and a shorter RS3 homologue, the RS3 stand-in (RS3S). Using newly developed techniques for analyzing samples with structural heterogeneity, we demonstrate that the CSC connects three major axonemal complexes involved in dynein regulation: RS2, the nexin–dynein regulatory complex (N-DRC), and RS3S. These results provide insights into how signals from the radial spokes may be transmitted to the N-DRC and ultimately to the dynein motors. Our results also indicate that although structurally very similar, RS1 and RS2 likely serve different functions in regulating flagellar motility.
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Affiliation(s)
- Thomas Heuser
- Biology Department, Rosenstiel Center, Brandeis University, Waltham, MA 02454, USA
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