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Bera A, Gupta ML. Microtubules in Microorganisms: How Tubulin Isotypes Contribute to Diverse Cytoskeletal Functions. Front Cell Dev Biol 2022; 10:913809. [PMID: 35865635 PMCID: PMC9294176 DOI: 10.3389/fcell.2022.913809] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Accepted: 06/15/2022] [Indexed: 11/19/2022] Open
Abstract
The cellular functions of the microtubule (MT) cytoskeleton range from relatively simple to amazingly complex. Assembled from tubulin, a heterodimeric protein with α- and β-tubulin subunits, microtubules are long, hollow cylindrical filaments with inherent polarity. They are intrinsically dynamic polymers that utilize GTP binding by tubulin, and subsequent hydrolysis, to drive spontaneous assembly and disassembly. Early studies indicated that cellular MTs are composed of multiple variants, or isotypes, of α- and β-tubulins, and that these multi-isotype polymers are further diversified by a range of posttranslational modifications (PTMs) to tubulin. These findings support the multi-tubulin hypothesis whereby individual, or combinations of tubulin isotypes possess unique properties needed to support diverse MT structures and/or cellular processes. Beginning 40 years ago researchers have sought to address this hypothesis, and the role of tubulin isotypes, by exploiting experimentally accessible, genetically tractable and functionally conserved model systems. Among these systems, important insights have been gained from eukaryotic microbial models. In this review, we illustrate how using microorganisms yielded among the earliest evidence that tubulin isotypes harbor distinct properties, as well as recent insights as to how they facilitate specific cellular processes. Ongoing and future research in microorganisms will likely continue to reveal basic mechanisms for how tubulin isotypes facilitate MT functions, along with valuable perspectives on how they mediate the range of conserved and diverse processes observed across eukaryotic microbes.
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2
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Abstract
The microtubule cytoskeleton is assembled from the α- and β-tubulin subunits of the canonical tubulin heterodimer, which polymerizes into microtubules, and a small number of other family members, such as γ-tubulin, with specialized functions. Overall, microtubule function involves the collective action of multiple α- and β-tubulin isotypes. However, despite 40 years of awareness that most eukaryotes harbor multiple tubulin isotypes, their role in the microtubule cytoskeleton has remained relatively unclear. Various model organisms offer specific advantages for gaining insight into the role of tubulin isotypes. Whereas simple unicellular organisms such as yeast provide experimental tractability that can facilitate deeper access to mechanistic details, more complex organisms, such as the fruit fly, nematode and mouse, can be used to discern potential specialized functions of tissue- and structure-specific isotypes. Here, we review the role of α- and β-tubulin isotypes in microtubule function and in associated tubulinopathies with an emphasis on the advances gained using model organisms. Overall, we argue that studying tubulin isotypes in a range of organisms can reveal the fundamental mechanisms by which they mediate microtubule function. It will also provide valuable perspectives on how these mechanisms underlie the functional and biological diversity of the cytoskeleton.
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Affiliation(s)
- Emmanuel T Nsamba
- Genetics, Development, and Cell Biology, Iowa State University, Ames, IA 50011, USA
| | - Mohan L Gupta
- Genetics, Development, and Cell Biology, Iowa State University, Ames, IA 50011, USA
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3
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Sinclair AN, de Graffenried CL. More than Microtubules: The Structure and Function of the Subpellicular Array in Trypanosomatids. Trends Parasitol 2019; 35:760-777. [PMID: 31471215 PMCID: PMC6783356 DOI: 10.1016/j.pt.2019.07.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 07/25/2019] [Accepted: 07/26/2019] [Indexed: 10/26/2022]
Abstract
The subpellicular microtubule array defines the wide range of cellular morphologies found in parasitic kinetoplastids (trypanosomatids). Morphological studies have characterized array organization, but little progress has been made towards identifying the molecular mechanisms that are responsible for array differentiation during the trypanosomatid life cycle, or the apparent stability and longevity of array microtubules. In this review, we outline what is known about the structure and biogenesis of the array, with emphasis on Trypanosoma brucei, Trypanosoma cruzi, and Leishmania, which cause life-threatening diseases in humans and livestock. We highlight unanswered questions about this remarkable cellular structure that merit new consideration in light of our recently improved understanding of how the 'tubulin code' influences microtubule dynamics to generate complex cellular structures.
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Affiliation(s)
- Amy N Sinclair
- Department of Molecular Microbiology and Immunology, Brown University, Providence, RI 02912, USA
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4
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Vaughan S, Gull K. Basal body structure and cell cycle-dependent biogenesis in Trypanosoma brucei. Cilia 2016; 5:5. [PMID: 26862392 PMCID: PMC4746817 DOI: 10.1186/s13630-016-0023-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2015] [Accepted: 01/19/2016] [Indexed: 11/10/2022] Open
Abstract
Basal bodies are microtubule-based organelles that assemble cilia and flagella, which are critical for motility and sensory functions in all major eukaryotic lineages. The core structure of the basal body is highly conserved, but there is variability in biogenesis and additional functions that are organism and cell type specific. Work carried out in the protozoan parasite Trypanosoma brucei has arguably produced one of the most detailed dissections of basal body structure and biogenesis within the context of the flagellar pocket and associated organelles. In this review, we provide a detailed overview of the basic basal body structure in T. brucei along with the accessory structures and show how basal body movements during the basal body duplication cycle orchestrate cell and organelle morphogenesis. With this in-depth three-dimensional knowledge, identification of many basal body genes coupled with excellent genetic tools makes it an attractive model organism to study basal body biogenesis and maintenance.
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Affiliation(s)
- Sue Vaughan
- Department of Biological and Medical Sciences, Faculty of Health and Life Science, Oxford Brookes University, Oxford, OX3 0BP UK
| | - Keith Gull
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford, OX1 3RE UK
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5
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Turk E, Wills AA, Kwon T, Sedzinski J, Wallingford JB, Stearns T. Zeta-Tubulin Is a Member of a Conserved Tubulin Module and Is a Component of the Centriolar Basal Foot in Multiciliated Cells. Curr Biol 2015; 25:2177-83. [PMID: 26234217 DOI: 10.1016/j.cub.2015.06.063] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Revised: 06/12/2015] [Accepted: 06/24/2015] [Indexed: 10/23/2022]
Abstract
There are six members of the tubulin superfamily in eukaryotes. Alpha- and beta-tubulin form a heterodimer that polymerizes to form microtubules, and gamma-tubulin nucleates microtubules as a component of the gamma-tubulin ring complex. Alpha-, beta-, and gamma-tubulin are conserved in all eukaryotes. In contrast, delta- and epsilon-tubulin are conserved in many, but not all, eukaryotes and are associated with centrioles, although their molecular function is unclear. Zeta-tubulin is the sixth and final member of the tubulin superfamily and is largely uncharacterized. We find that zeta-, epsilon-, and delta-tubulin form an evolutionarily co-conserved module, the ZED module, that has been lost at several junctions in eukaryotic evolution and that zeta- and delta-tubulin are evolutionarily interchangeable. Humans lack zeta-tubulin but have delta-tubulin. In Xenopus multiciliated cells, zeta-tubulin is a component of the basal foot, a centriolar appendage that connects centrioles to the apical cytoskeleton, and co-localizes there with epsilon-tubulin. Depletion of zeta-tubulin results in disorganization of centriole distribution and polarity in multiciliated cells. In contrast with multiciliated cells, zeta-tubulin in cycling cells does not localize to centrioles and is associated with the TRiC/CCT cytoplasmic chaperone complex. We conclude that zeta-tubulin facilitates interactions between the centrioles and the apical cytoskeleton as a component of the basal foot in differentiated cells and propose that the ZED tubulins are important for centriole functionalization and orientation of centrioles with respect to cellular polarity axes.
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Affiliation(s)
- Erin Turk
- Department of Biology, Stanford University, Stanford, CA 94305, USA
| | - Airon A Wills
- Department of Molecular Biosciences and Center for Systems and Synthetic Biology, University of Texas at Austin, Austin, TX 78712, USA
| | - Taejoon Kwon
- Department of Molecular Biosciences and Center for Systems and Synthetic Biology, University of Texas at Austin, Austin, TX 78712, USA
| | - Jakub Sedzinski
- Department of Molecular Biosciences and Center for Systems and Synthetic Biology, University of Texas at Austin, Austin, TX 78712, USA
| | - John B Wallingford
- Department of Molecular Biosciences and Center for Systems and Synthetic Biology, University of Texas at Austin, Austin, TX 78712, USA; Howard Hughes Medical Institute
| | - Tim Stearns
- Department of Biology, Stanford University, Stanford, CA 94305, USA; Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305, USA.
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6
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Selvaa Kumar C, Gadewal N, Mohammed SM. Seminal role of deletion of amino acid residues in H1-S2 and S-loop regions in eukaryotic β-tubulin investigated from docking and dynamics perspective. J Theor Biol 2015; 378:79-88. [PMID: 25956360 DOI: 10.1016/j.jtbi.2015.04.035] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2014] [Revised: 04/20/2015] [Accepted: 04/24/2015] [Indexed: 11/16/2022]
Abstract
Tubulin is the fundamental unit of microtubules. It is reported to effect different functions like cell division, chromosomal segregation, motility and intracellular transportation. α- and β-tubulin associate laterally and longitudinally to form protofilaments. Both the subunits are structurally identical to each other except for the deletions reported in H1-S2 and S loop regions in eukaryotic β-tubulin. These deletions mimic the ancestral tubulin protein named Latest Common FtsZ-Tubulin Ancestor (LCFTA) with a shorter S-loop region resulting in weak dimerization. However, in eukaryotic beta tubulin, the significance of this shorter region remains elusive till date. The main objective of this study was to model variants of beta tubulin (βmut1, βmut2 and βmut3) with inserts that lengthened the loop, and to compare them with the native α- and β-subunits to understand their biological significance. Further, one more mutant was modeled with the intention of understanding the counter effect of additional deletion of amino acid residues from both H1-S2 and S-loop regions; this mutant was designated as βmut4. Our study confirms that the insertion of amino acid residues considerably increases the protein-protein interactions in βmut1-βmut1, βmut2-βmut2 and βmut3-βmut3 compared to their native β-subunit. Similarly, the binding affinity of GTP also increases in βmut2 and βmut3 as compared to the wild type. However, these deletions result in decreased protein-protein and ligand interactions in wild beta tubulin and βmut4, as compared to βmut1, βmut2,and βmut3. Therefore, we conclude here that residual inserts in the H1-S2 and S loop sub segments bring about conformational changes in regions critically involved in lateral interactions and in the nucleotide binding site, thus altering the binding affinities between the dimers and the ligands. Regarding the biological importance of such deletions in wild beta tubulin, these deletions result in flexible M-loop leading to weak protein-protein interaction. This could be an adaptive feature playing a crucial role in protofilament dissociation during GTP hydrolysis, because of weak dimerization.
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Affiliation(s)
- C Selvaa Kumar
- School of Biotechnology and Bioinformatics, D.Y. Patil University, CBD Belapur, Navi Mumbai, India.
| | - Nikhil Gadewal
- Advanced Centre for Treatment, Research and Education in Cancer, Kharghar, Navi Mumbai, India.
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7
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Findeisen P, Mühlhausen S, Dempewolf S, Hertzog J, Zietlow A, Carlomagno T, Kollmar M. Six subgroups and extensive recent duplications characterize the evolution of the eukaryotic tubulin protein family. Genome Biol Evol 2014; 6:2274-88. [PMID: 25169981 PMCID: PMC4202323 DOI: 10.1093/gbe/evu187] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Tubulins belong to the most abundant proteins in eukaryotes providing the backbone for many cellular substructures like the mitotic and meiotic spindles, the intracellular cytoskeletal network, and the axonemes of cilia and flagella. Homologs have even been reported for archaea and bacteria. However, a taxonomically broad and whole-genome-based analysis of the tubulin protein family has never been performed, and thus, the number of subfamilies, their taxonomic distribution, and the exact grouping of the supposed archaeal and bacterial homologs are unknown. Here, we present the analysis of 3,524 tubulins from 504 species. The tubulins formed six major subfamilies, α to ζ. Species of all major kingdoms of the eukaryotes encode members of these subfamilies implying that they must have already been present in the last common eukaryotic ancestor. The proposed archaeal homologs grouped together with the bacterial TubZ proteins as sister clade to the FtsZ proteins indicating that tubulins are unique to eukaryotes. Most species contained α- and/or β-tubulin gene duplicates resulting from recent branch- and species-specific duplication events. This shows that tubulins cannot be used for constructing species phylogenies without resolving their ortholog–paralog relationships. The many gene duplicates and also the independent loss of the δ-, ε-, or ζ-tubulins, which have been shown to be part of the triplet microtubules in basal bodies, suggest that tubulins can functionally substitute each other.
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Affiliation(s)
- Peggy Findeisen
- Group Systems Biology of Motor Proteins, Department of NMR-based Structural Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Stefanie Mühlhausen
- Group Systems Biology of Motor Proteins, Department of NMR-based Structural Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Silke Dempewolf
- Group Systems Biology of Motor Proteins, Department of NMR-based Structural Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Jonny Hertzog
- Group Systems Biology of Motor Proteins, Department of NMR-based Structural Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Alexander Zietlow
- Group Systems Biology of Motor Proteins, Department of NMR-based Structural Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Teresa Carlomagno
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Martin Kollmar
- Group Systems Biology of Motor Proteins, Department of NMR-based Structural Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
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8
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Hayashi S, Mikami T, Murai Y, Takano Y, Imura J. Α-tubulin nuclear overexpression is an indicator of poor prognosis in patients with non-Hodgkin's lymphoma. Int J Mol Med 2014; 34:483-90. [PMID: 24898903 DOI: 10.3892/ijmm.2014.1793] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Accepted: 04/16/2014] [Indexed: 11/05/2022] Open
Abstract
In the present study, the newly established mouse monoclonal antibody, Y-49, binding to a specific epitope of α-tubulin, was used to examine immunohistochemical reactivity in 116 patients with non-Hodgkin's lymphoma (NHL). The protein was detected at elevated levels in the nuclei of human proliferating cells by western blot analysis, flow cytometry and immunohistochemical analysis. The relatively weak binding in the cytoplasm was evident in almost all cases. The investigation of the correlation between immuno-histochemical positivity and clinicopathological variables revealed links with the MIB-1 proliferation index and poor survival. Nuclear positivity with Y-49 was more frequent in older-aged patients, those with nodal NHL and in those who harbored the diffuse large B-cell histological subtype, and was strongly associated with high MIB-1 labeling indices (LIs). Survival analysis by the Kaplan-Meier method revealed statistically significant differences between patients with high and low Y-49 LIs (p=0.0181), even in the group with advanced (stage III/IV) disease (p=0.0327). Multivariate analysis revealed that overexpression of α-tubulin is an independent prognostic factor in NHL with a relative risk of 2.786.
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Affiliation(s)
- Shinichi Hayashi
- Department of Diagnostic Pathology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama 930-0194, Japan
| | - Tetsuo Mikami
- Department of Pathology, Toho University School of Medicine, Ota, Tokyo 143-8540, Japan
| | - Yoshihiro Murai
- Department of Nursing, Toyama College of Welfare Science, Imizu 939-0341, Japan
| | - Yasuo Takano
- Kanagawa Cancer Center Research Institute, Asahi, Yokohama 241-8515, Japan
| | - Johji Imura
- Department of Diagnostic Pathology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama 930-0194, Japan
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9
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Koumandou VL, Wickstead B, Ginger ML, van der Giezen M, Dacks JB, Field MC. Molecular paleontology and complexity in the last eukaryotic common ancestor. Crit Rev Biochem Mol Biol 2014; 48:373-96. [PMID: 23895660 PMCID: PMC3791482 DOI: 10.3109/10409238.2013.821444] [Citation(s) in RCA: 133] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Eukaryogenesis, the origin of the eukaryotic cell, represents one of the fundamental evolutionary transitions in the history of life on earth. This event, which is estimated to have occurred over one billion years ago, remains rather poorly understood. While some well-validated examples of fossil microbial eukaryotes for this time frame have been described, these can provide only basic morphology and the molecular machinery present in these organisms has remained unknown. Complete and partial genomic information has begun to fill this gap, and is being used to trace proteins and cellular traits to their roots and to provide unprecedented levels of resolution of structures, metabolic pathways and capabilities of organisms at these earliest points within the eukaryotic lineage. This is essentially allowing a molecular paleontology. What has emerged from these studies is spectacular cellular complexity prior to expansion of the eukaryotic lineages. Multiple reconstructed cellular systems indicate a very sophisticated biology, which by implication arose following the initial eukaryogenesis event but prior to eukaryotic radiation and provides a challenge in terms of explaining how these early eukaryotes arose and in understanding how they lived. Here, we provide brief overviews of several cellular systems and the major emerging conclusions, together with predictions for subsequent directions in evolution leading to extant taxa. We also consider what these reconstructions suggest about the life styles and capabilities of these earliest eukaryotes and the period of evolution between the radiation of eukaryotes and the eukaryogenesis event itself.
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Affiliation(s)
- V Lila Koumandou
- Biomedical Research Foundation, Academy of Athens, Soranou Efesiou 4, Athens 115 27, Greece
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10
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Ludueña RF. A Hypothesis on the Origin and Evolution of Tubulin. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 302:41-185. [DOI: 10.1016/b978-0-12-407699-0.00002-9] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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11
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Attwood TK, Coletta A, Muirhead G, Pavlopoulou A, Philippou PB, Popov I, Romá-Mateo C, Theodosiou A, Mitchell AL. The PRINTS database: a fine-grained protein sequence annotation and analysis resource--its status in 2012. Database (Oxford) 2012; 2012:bas019. [PMID: 22508994 PMCID: PMC3326521 DOI: 10.1093/database/bas019] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2012] [Accepted: 03/12/2012] [Indexed: 01/07/2023]
Abstract
The PRINTS database, now in its 21st year, houses a collection of diagnostic protein family 'fingerprints'. Fingerprints are groups of conserved motifs, evident in multiple sequence alignments, whose unique inter-relationships provide distinctive signatures for particular protein families and structural/functional domains. As such, they may be used to assign uncharacterized sequences to known families, and hence to infer tentative functional, structural and/or evolutionary relationships. The February 2012 release (version 42.0) includes 2156 fingerprints, encoding 12 444 individual motifs, covering a range of globular and membrane proteins, modular polypeptides and so on. Here, we report the current status of the database, and introduce a number of recent developments that help both to render a variety of our annotation and analysis tools easier to use and to make them more widely available. Database URL: www.bioinf.manchester.ac.uk/dbbrowser/PRINTS/.
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Affiliation(s)
- Teresa K Attwood
- Faculty of Life Sciences, The University of Manchester, Manchester M13 9PT, UK.
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12
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Abstract
The cytoskeleton is a system of intracellular filaments crucial for cell shape, division, and function in all three domains of life. The simple cytoskeletons of prokaryotes show surprising plasticity in composition, with none of the core filament-forming proteins conserved in all lineages. In contrast, eukaryotic cytoskeletal function has been hugely elaborated by the addition of accessory proteins and extensive gene duplication and specialization. Much of this complexity evolved before the last common ancestor of eukaryotes. The distribution of cytoskeletal filaments puts constraints on the likely prokaryotic line that made this leap of eukaryogenesis.
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Affiliation(s)
- Bill Wickstead
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, England, UK.
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13
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Fritz-Laylin LK, Prochnik SE, Ginger ML, Dacks JB, Carpenter ML, Field MC, Kuo A, Paredez A, Chapman J, Pham J, Shu S, Neupane R, Cipriano M, Mancuso J, Tu H, Salamov A, Lindquist E, Shapiro H, Lucas S, Grigoriev IV, Cande WZ, Fulton C, Rokhsar DS, Dawson SC. The genome of Naegleria gruberi illuminates early eukaryotic versatility. Cell 2010; 140:631-42. [PMID: 20211133 DOI: 10.1016/j.cell.2010.01.032] [Citation(s) in RCA: 341] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2009] [Revised: 11/17/2009] [Accepted: 01/15/2010] [Indexed: 12/18/2022]
Abstract
Genome sequences of diverse free-living protists are essential for understanding eukaryotic evolution and molecular and cell biology. The free-living amoeboflagellate Naegleria gruberi belongs to a varied and ubiquitous protist clade (Heterolobosea) that diverged from other eukaryotic lineages over a billion years ago. Analysis of the 15,727 protein-coding genes encoded by Naegleria's 41 Mb nuclear genome indicates a capacity for both aerobic respiration and anaerobic metabolism with concomitant hydrogen production, with fundamental implications for the evolution of organelle metabolism. The Naegleria genome facilitates substantially broader phylogenomic comparisons of free-living eukaryotes than previously possible, allowing us to identify thousands of genes likely present in the pan-eukaryotic ancestor, with 40% likely eukaryotic inventions. Moreover, we construct a comprehensive catalog of amoeboid-motility genes. The Naegleria genome, analyzed in the context of other protists, reveals a remarkably complex ancestral eukaryote with a rich repertoire of cytoskeletal, sexual, signaling, and metabolic modules.
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Affiliation(s)
- Lillian K Fritz-Laylin
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
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14
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Alieva IB, Uzbekov RE. The centrosome is a polyfunctional multiprotein cell complex. BIOCHEMISTRY (MOSCOW) 2008; 73:626-43. [DOI: 10.1134/s0006297908060023] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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15
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Nordle AKL, Rios P, Gaulton A, Pulido R, Attwood TK, Tabernero L. Functional assignment of MAPK phosphatase domains. Proteins 2007; 69:19-31. [PMID: 17596826 DOI: 10.1002/prot.21477] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Mitogen-activated protein kinase (MAPK) pathways are well conserved in most organisms, from yeast to humans. The principal components of these pathways are MAP kinases whose activity is regulated by phosphorylation, implicating various MAPK protein effectors-in particular, protein phosphatases that inactivate MAPKs by dephosphorylation. The molecular basis of binding specificity of such regulatory phosphatases to MAPKs is poorly understood. To try to pinpoint potential functional regions within the sequences and to help identify new family members, we have applied a multimotif pattern-recognition approach to characterize two MAPK phosphatase subfamilies (tyrosine-specific and dual specificity) that are crucial in the regulation of MAPKs. We built "fingerprints" for these two subfamilies that are unique to, and highly discriminatory for, each group of proteins. The fingerprints were used in a genome-wide screen, identifying more than 80 MAPK phosphatase domains, several of which were in partial sequences or unclassified proteins. We confirmed experimentally that one predicted MAPK phosphatase orthologue in Xenopus binds to ERK1/2, suggesting a role in MAPK signaling and thus supporting our functional predictions. Further analysis, mapping the fingerprints on the three-dimensional structure of MAPK phosphatases, revealed that some of the fingerprint motifs reside in the N-terminal noncatalytic regions coinciding with reported MAPK binding sites, while others lie within the catalytic phosphatase domain. These results also suggest the presence of putative allosteric sites in the catalytic region for modulation of protein-protein interactions, and provide a framework for future experimental validation.
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Affiliation(s)
- Anna K L Nordle
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
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16
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De Lima AR, Medina R, Uzcanga GL, Noris Suárez K, Contreras VT, Navarro MC, Arteaga R, Bubis J. Tight binding between a pool of the heterodimeric α/β tubulin and a protein kinase CK2 inTrypanosoma cruziepimastigotes. Parasitology 2005; 132:511-23. [PMID: 16332290 DOI: 10.1017/s0031182005009352] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2005] [Revised: 09/28/2005] [Accepted: 09/28/2005] [Indexed: 01/23/2023]
Abstract
Tubulin is the predominant phosphoprotein inTrypanosoma cruziepimastigotes and is phosphorylated by a protein kinase CK2. Interestingly, the presence or absence of divalent cations affected the solubilization of a pool of the parasite tubulin and the CK2 responsible for its phosphorylation. This fraction of tubulin and its kinase co-eluted using phosphocellulose, DEAE-Sepharose and Sephacryl S-300 chromatographies. Anti-α tubulin antibodies co-immunoprecipitated both tubulin and the CK2 responsible for its phosphorylation, and anti-CK2 α-subunit antibodies immunoprecipitated radioactively labelled α and β tubulin from phosphorylated epimastigote homogenates. Additionally, native polyacrylamide gel electrophoresis of the purified and radioactively labelled fraction containing tubulin and its kinase demonstrated the phosphorylation of a unique band that reacted with both anti-CK2 α-subunit and anti-tubulin antibodies. Together, these results establish a strong interaction between a pool of the heterodimeric α/β tubulin and a CK2 in this parasite. Hydrodynamic measurements indicated that theT. cruzitubulin-CK2 complex is globular with an estimated size of 145·4–147·5 kDa.
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Affiliation(s)
- A R De Lima
- Departamento de Biología Celular, Universidad Simón Bolívar, Apartado 89.000, Valle de Sartenejas, Caracas 1081-A, Venezuela
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17
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Abstract
Eukaryotic cilia and flagella are cytoskeletal organelles that are remarkably conserved from protists to mammals. Their basic unit is the axoneme, a well-defined cylindrical structure composed of microtubules and up to 250 associated proteins. These complex organelles are assembled by a dynamic process called intraflagellar transport. Flagella and cilia perform diverse motility and sensitivity functions in many different organisms. Trypanosomes are flagellated protozoa, responsible for various tropical diseases such as sleeping sickness and Chagas disease. In this review, we first describe general knowledge on the flagellum: its occurrence in the living world, its molecular composition, and its mode of assembly, with special emphasis on the exciting developments that followed the discovery of intraflagellar transport. We then present recent progress regarding the characteristics of the trypanosome flagellum, highlighting the original contributions brought by this organism. The most striking phenomenon is the involvement of the flagellum in several aspects of the trypanosome cell cycle, including cell morphogenesis, basal body migration, and cytokinesis.
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Affiliation(s)
- Linda Kohl
- INSERM U565, CNRS UMR5153, and MNHN USM 0503, Muséum National d'Histoire Naturelle, 75231 Paris, France
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18
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Vayssié L, Vargas M, Weber C, Guillén N. Double-stranded RNA mediates homology-dependant gene silencing of γ-tubulin in the human parasite Entamoeba histolytica. Mol Biochem Parasitol 2004; 138:21-8. [PMID: 15500912 DOI: 10.1016/j.molbiopara.2004.07.005] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2004] [Revised: 07/05/2004] [Accepted: 07/15/2004] [Indexed: 10/26/2022]
Abstract
Approaches that eliminate mRNA are a powerful tool for reverse genetics applications in eukaryotic microbes for which gene replacement techniques have not yet been developed. Here, for the first time, we demonstrate that RNA duplexes efficiently inhibit gene expression when introduced into the human parasite Entamoeba histolytica. Chemically synthesized, small interfering RNA (siRNA) were highly specific and efficient in silencing parasite gamma-tubulin mRNA. Use of specific antibodies revealed that microtubules and gamma-tubulin were intra-nuclear in E. histolytica. The RNAi approach to modulation of gamma-tubulin mRNA resulted in loss of the highly organized microtubule array an observation that correlates with a significant reduction of gamma-tubulin as well as of the specific mRNA. Our results suggest that gamma-tubulin is essential for microtubule nucleation in E. histolytica.
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Affiliation(s)
- Laurence Vayssié
- Unité Biologie Cellulaire du Parasitisme, Institut National de la Santé et de la Recherche Médicale U389, Institut Pasteur, 28 rue du Dr Roux, 75724 Paris Cedex 15, France
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19
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Ruiz F, Dupuis-Williams P, Klotz C, Forquignon F, Bergdoll M, Beisson J, Koll F. Genetic evidence for interaction between eta- and beta-tubulins. EUKARYOTIC CELL 2004; 3:212-20. [PMID: 14871951 PMCID: PMC329518 DOI: 10.1128/ec.3.1.212-220.2004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The thermosensitive allelic mutations sm19-1 and sm19-2 of Paramecium tetraurelia cause defective basal body duplication: growth at the nonpermissive temperature yields smaller and smaller cells with fewer and fewer basal bodies. Complementation cloning of the SM19 gene identified a new tubulin, eta-tubulin, showing low homology with each of the other five tubulins, alpha to epsilon, characterized in P. tetraurelia. In order to analyze eta-tubulin functions, we used a genetic approach to identify interacting molecules. Among a series of extragenic suppressors of the sm19-1 mutation, the su3-1 mutation was characterized as an E288K substitution in the beta-PT2 gene coding for a beta-tubulin, while the mutation nocr1 conferring nocodazole resistance and localized in another beta-tubulin gene, beta-PT3, was shown to enhance the mutant phenotype. The interaction between eta-tubulin and microtubules, revealed by genetic data, is supported by two further types of evidence: first, the mutant phenotype is rescued by taxol, which stabilizes microtubules; second, molecular modeling suggests that eta-tubulin, like gamma- and delta-tubulins, might be a microtubule minus-end capping molecule. The likely function of eta-tubulin as part of a complex specifically involved in basal body biogenesis is discussed.
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Affiliation(s)
- F Ruiz
- Centre de Génétique Moléculaire, CNRS, 91198 Gif-sur-Yvette, France
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20
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Nagasato C, Motomura T. Destruction of maternal centrioles during fertilization of the brown alga, Scytosiphon lomentaria (Scytosiphonales, Phaeophyceae). CELL MOTILITY AND THE CYTOSKELETON 2004; 59:109-18. [PMID: 15362114 DOI: 10.1002/cm.20021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In brown algal fertilization, a pair of centrioles is derived from the male gamete, irrespective of the sexual reproduction pattern, i.e., isogamy, anisogamy, or oogamy. In this study, the manner in which the maternal centriole structure is destroyed in early zygotes of the isogamous brown alga Scytosiphon lomentaria was examined by electron microscopy. At fertilization, the zygote had two pairs of centrioles (flagellar basal bodies) derived from motile male and female gametes, and there was no morphological difference between the two pairs. The flagellar basal plate and the axonemal microtubules were still connected with the distal end of centrioles. Ultrastructural observations showed that the integrity of maternal-derived centrioles began to degenerate even in the 1-h-old zygote. At that time, the cylinder of triplet microtubules of the maternal centrioles became shorter from the distal end, and a section passing through the centrioles indicated that a part of the nine triplets of microtubules changed into doublet or singlet microtubules by degeneration of B and/or C tubules. In 2-h-old zygote, there was no trace of maternal centrioles ultrastructurally, and only the paternal centrioles remained. Further, reduction of centrin accompanying destruction of the maternal centrioles was examined in immunofluorescence microscopy. Centrin localized at the paternal and the maternal centrioles had the same fluorescence intensity in the early zygotes. At 4-6 h after fertilization, two spots indicating centrin localization showed different fluorescence intensity. Later, the weaker spot disappeared completely. These results showed that there is a difference in time between the destruction of the centriolar cylinders and the reduction of centrin molecules around them.
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Affiliation(s)
- Chikako Nagasato
- Muroran Marine Station, Field Science Center for Northern Biosphere, Hokkaido University, Japan.
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21
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22
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Sahasrabuddhe AA, Bajpai VK, Gupta CM. A novel form of actin in Leishmania: molecular characterisation, subcellular localisation and association with subpellicular microtubules. Mol Biochem Parasitol 2004; 134:105-14. [PMID: 14747148 DOI: 10.1016/j.molbiopara.2003.11.008] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
To study the occurrence and subcellular distribution of actin in trypanosomatid parasites, we have cloned and overexpressed Leishmania donovani actin gene in bacteria, purified the protein, and employed the affinity purified rabbit polyclonal anti-recombinant actin antibodies as a probe to study the organisation and subcellular distribution of actin in Leishmania cells. The Leishmania actin did not cross react with antimammalian actin antibodies but was readily recognized by the anti-Leishmania actin antibodies in both the promastigote and amastigote forms of the parasite. About 10(6) copies per cell of this protein (M(r) 42.05 kDa) were present in the Leishmania promastigote. Unlike other eukaryotic actins, the oligomeric forms of Leishmania actin were not stained by phalloidin nor were dissociated by actin filament-disrupting agents, like Latrunculin B and Cytochalasin D. Analysis of the primary structure of this protein revealed that these unusual characteristics may be related to the presence of highly diverged amino acids in the DNase I-binding loop (amino acids 40-50) and the hydrophobic plug (amino acids 262-272) regions of Leishmania actin. The subcellular distribution of actin was studied in the Leishmania promastigotes by employing immunoelectron and immunofluorescence microscopies. This protein was present not only in the flagella, flagellar pocket, nucleus and the kinetoplast but it was also localized on the nuclear, vacuolar and cytoplasmic face of the plasma membranes. Further, the plasma membrane-associated actin was colocalised with subpellicular microtubules, while most of the actin present in the kinetoplast colocalised with the k-DNA network. These results clearly indicate that Leishmania contains a novel form of actin which may structurally and functionally differ from other eukaryotic actins. The functional significance of these observations is discussed.
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Affiliation(s)
- Amogh A Sahasrabuddhe
- Division of Molecular and Structural Biology, Central Drug Research Institute, Lucknow 226 001, India
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23
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Dutcher SK. Long-lost relatives reappear: identification of new members of the tubulin superfamily. Curr Opin Microbiol 2004; 6:634-40. [PMID: 14662361 DOI: 10.1016/j.mib.2003.10.016] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The identification and analysis of new members of the tubulin superfamily has advanced the belief that these tubulins play important roles in the duplication and assembly of centrioles and basal bodies. This idea is supported by their distribution in organisms with centrioles containing triplet microtubules and by recent functional analysis of the new tubulins. delta- and epsilon-tubulin are found in most organisms that assemble triplet microtubules. delta-tubulin is needed for maintaining triplet microtubules in Chlamydomonas and Paramecium. epsilon-tubulin is needed for centriole and basal body duplication and is an essential gene in Chlamydomonas. The distribution of eta-tubulin is more limited and has been found in only four organisms to date. Phylogenetic analysis suggests that it is most closely related to delta-tubulin, which suggests that delta- and eta-tubulin could have overlapping functions.
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Affiliation(s)
- Susan K Dutcher
- Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110, USA.
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24
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Fromherz S, Giddings TH, Gomez-Ospina N, Dutcher SK. Mutations in α-tubulin promote basal body maturation and flagellar assembly in the absence of δ-tubulin. J Cell Sci 2004; 117:303-14. [PMID: 14676280 DOI: 10.1242/jcs.00859] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have isolated suppressors of the deletion allele of δ-tubulin, uni3-1, in the biflagellate green alga Chlamydomonas reinhardtii. The deletion of δ-tubulin produces cells that assemble zero, one or two flagella and have basal bodies composed primarily of doublet rather than triplet microtubules. Flagellar number is completely restored in the suppressed strains. Most of the uni3-1 suppressors map to the TUA2 locus, which encodes α2-tubulin. Twelve independent tua2 mutations were sequenced. Amino acids D205 or A208, which are nearly invariant residues in α-tubulin, were altered. The tua2 mutations on their own have a second phenotype - they make the cells colchicine supersensitive. Colchicine supersensitivity itself is not needed for suppression and colchicine cannot phenocopy the suppression. The suppressors partially restore the assembly of triplet microtubules. These results suggest that the δ-tubulin plays two roles: it is needed for extension or stability of the triplet microtubule and also for early maturation of basal bodies. We suggest that the mutant α-tubulin promotes the early maturation of the basal body in the absence of δ-tubulin, perhaps through interactions with other partners, and this allows assembly of the flagella.
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Affiliation(s)
- Sylvia Fromherz
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Boulder, CO 80309-0347, USA
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25
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Abstract
In eukaryotic cells, basal bodies and their structural equivalents, centrioles, play essential roles. They are needed for the assembly of flagella or cilia as well as for cell division. Chlamydomonas reinhardtii provides an excellent model organism for the study of the basal body and centrioles. Genes for two new members of the tubulin superfamily are needed for basal body/centriole duplication. In addition, other genes that play roles in the duplication and segregation of basal bodies are discussed.
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Affiliation(s)
- Susan K Dutcher
- Department of Genetics, Washington University School of Medicine, 660 S. Euclid Ave, St. Louis, MO 63110, USA.
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26
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Abstract
Protists provide the opportunity to integrate analyses from a low (molecular) to a high (organism) level of complexity within a broad evolutionary framework. The perpectives they offer in the cytoskeletal field are discussed with respect to emerging concepts of cellular biology.
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Affiliation(s)
- Anne Fleury-Aubusson
- Laboratoire de Biologie Cellulaire 4, Bat 444, Faculté d'Orsay, Université Paris XI, 91 405 Orsay Cedex, France.
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27
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Chang P, Giddings TH, Winey M, Stearns T. Epsilon-tubulin is required for centriole duplication and microtubule organization. Nat Cell Biol 2003; 5:71-6. [PMID: 12510196 DOI: 10.1038/ncb900] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2002] [Revised: 10/10/2002] [Accepted: 11/18/2002] [Indexed: 11/08/2022]
Abstract
Centrosomes nucleate microtubules and serve as poles of the mitotic spindle. Centrioles are a core component of centrosomes and duplicate once per cell cycle. We previously identified epsilon-tubulin as a new member of the tubulin superfamily that localizes asymmetrically to the two centrosomes after duplication. We show that recruitment of epsilon-tubulin to the new centrosome can only occur after exit from S phase and that epsilon-tubulin is associated with the sub-distal appendages of mature centrioles. Xenopus laevis epsilon-tubulin was cloned and shown to be similar to human epsilon-tubulin in both sequence and localization. Depletion of epsilon-tubulin from Xenopus egg extracts blocks centriole duplication in S phase and formation of organized centrosome-independent microtubule asters in M phase. We conclude that epsilon-tubulin is a component of the sub-distal appendages of the centriole, explaining its asymmetric localization to old and new centrosomes, and that epsilon-tubulin is required for centriole duplication and organization of the pericentriolar material.
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Affiliation(s)
- Paul Chang
- Department of Biological Sciences, Stanford University, Stanford, CA 94305, USA
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28
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Jenkins C, Samudrala R, Anderson I, Hedlund BP, Petroni G, Michailova N, Pinel N, Overbeek R, Rosati G, Staley JT. Genes for the cytoskeletal protein tubulin in the bacterial genus Prosthecobacter. Proc Natl Acad Sci U S A 2002; 99:17049-54. [PMID: 12486237 PMCID: PMC139267 DOI: 10.1073/pnas.012516899] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Tubulins, the protein constituents of the microtubule cytoskeleton, are present in all known eukaryotes but have never been found in the Bacteria or Archaea. Here we report the presence of two tubulin-like genes [bacterial tubulin a (btuba) and bacterial tubulin b (btubb)] in bacteria of the genus Prosthecobacter (Division Verrucomicrobia). In this study, we investigated the organization and expression of these genes and conducted a comparative analysis of the bacterial and eukaryotic protein sequences, focusing on their phylogeny and 3D structures. The btuba and btubb genes are arranged as adjacent loci within the genome along with a kinesin light chain gene homolog. RT-PCR experiments indicate that these three genes are cotranscribed, and a probable promoter was identified upstream of btuba. On the basis of comparative modeling data, we predict that the Prosthecobacter tubulins are monomeric, unlike eukaryotic alpha and beta tubulins, which form dimers and are therefore unlikely to form microtubule-like structures. Phylogenetic analyses indicate that the Prosthecobacter tubulins are quite divergent and do not support recent horizontal transfer of the genes from a eukaryote. The discovery of genes for tubulin in a bacterial genus may offer new insights into the evolution of the cytoskeleton.
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Affiliation(s)
- Cheryl Jenkins
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
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29
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Dutcher SK, Morrissette NS, Preble AM, Rackley C, Stanga J. Epsilon-tubulin is an essential component of the centriole. Mol Biol Cell 2002; 13:3859-69. [PMID: 12429830 PMCID: PMC133598 DOI: 10.1091/mbc.e02-04-0205] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Centrioles and basal bodies are cylinders composed of nine triplet microtubule blades that play essential roles in the centrosome and in flagellar assembly. Chlamydomonas cells with the bld2-1 mutation fail to assemble doublet and triplet microtubules and have defects in cleavage furrow placement and meiosis. Using positional cloning, we have walked 720 kb and identified a 13.2-kb fragment that contains epsilon-tubulin and rescues the Bld2 defects. The bld2-1 allele has a premature stop codon and intragenic revertants replace the stop codon with glutamine, glutamate, or lysine. Polyclonal antibodies to epsilon-tubulin show peripheral labeling of full-length basal bodies and centrioles. Thus, epsilon-tubulin is encoded by the BLD2 allele and epsilon-tubulin plays a role in basal body/centriole morphogenesis.
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Affiliation(s)
- Susan K Dutcher
- Department of Genetics,Washington University School of Medicine, St Louis, Missouri 63110, USA.
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30
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Dupuis-Williams P, Fleury-Aubusson A, de Loubresse NG, Geoffroy H, Vayssié L, Galvani A, Espigat A, Rossier J. Functional role of epsilon-tubulin in the assembly of the centriolar microtubule scaffold. J Cell Biol 2002; 158:1183-93. [PMID: 12356863 PMCID: PMC2173240 DOI: 10.1083/jcb.200205028] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2002] [Revised: 08/09/2002] [Accepted: 08/20/2002] [Indexed: 11/26/2022] Open
Abstract
Centrioles and basal bodies fascinate by their spectacular architecture, featuring an arrangement of nine microtubule triplets into an axial symmetry, whose biogenesis relies on yet elusive mechanisms. However, the recent discovery of new tubulins, such as delta-, epsilon-, or eta-tubulin, could constitute a breakthrough for deciphering the assembly steps of this unconventional microtubule scaffold. Here, we report the functional analysis in vivo of epsilon-tubulin, based on gene silencing in Paramecium, which demonstrates that this protein, which localizes at the basal bodies, is essential for the assembly and anchorage of the centriolar microtubules.
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Affiliation(s)
- Pascale Dupuis-Williams
- Laboratoire de Neurobiologie, UMR 7637 Centre National de la Recherche Scientifique, 75005 Paris, France.
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31
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Hutchings NR, Donelson JE, Hill KL. Trypanin is a cytoskeletal linker protein and is required for cell motility in African trypanosomes. J Cell Biol 2002; 156:867-77. [PMID: 11864997 PMCID: PMC2173309 DOI: 10.1083/jcb.200201036] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The cytoskeleton of eukaryotic cells is comprised of a complex network of distinct but interconnected filament systems that function in cell division, cell motility, and subcellular trafficking of proteins and organelles. A gap in our understanding of this dynamic network is the identification of proteins that connect subsets of cytoskeletal structures. We previously discovered a family of cytoskeleton-associated proteins that includes GAS11, a candidate human tumor suppressor upregulated in growth-arrested cells, and trypanin, a component of the flagellar cytoskeleton of African trypanosomes. Although these proteins are intimately associated with the cytoskeleton, their function has yet to be determined. Here we use double-stranded RNA interference to block trypanin expression in Trypanosoma brucei, and demonstrate that this protein is required for directional cell motility. Trypanin(minus sign) mutants have an active flagellum, but are unable to coordinate flagellar beat. As a consequence, they spin and tumble uncontrollably, occasionally moving backward. Immunofluorescence experiments demonstrate that trypanin is located along the flagellum/flagellum attachment zone and electron microscopic analysis revealed that cytoskeletal connections between the flagellar apparatus and subpellicular cytoskeleton are destabilized in trypanin(minus sign) mutants. These results indicate that trypanin functions as a cytoskeletal linker protein and offer insights into the mechanisms of flagellum-based cell motility.
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Affiliation(s)
- Nathan R Hutchings
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
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32
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Abstract
Although most eukaryotic cells can express multiple isotypes of αβ-tubulin, the significance of this diversity has not always been apparent. Recent data indicate that particular αβ-tubulin isotypes, both genome encoded and those derived by post-translational modification, can directly influence microtubule structure and function — thus validating ideas originally proposed in the multitubulin hypothesis over 25 years ago.It has also become increasingly evident over the past year that some (but intriguingly not all) eukaryotes encode several other tubulin proteins, and to date five further members of the tubulin superfamily, γ, δ, ϵ, 𝛇 and η, have been identified. Although the role of γ-tubulin in the nucleation of microtubule assembly is now well established, far less is known about the functions of δ-, ϵ-, 𝛇- and η-tubulin. Recent work has expanded our knowledge of the functions and localisation of these newer members of the tubulin superfamily, and the emerging data suggesting a restricted evolutionary distribution of these `new' tubulin proteins, conforms to established knowledge of microtubule cell biology. On the basis of current evidence, we predict that δ-, ϵ-, 𝛇- and η-tubulin all have functions associated with the centriole or basal body of eukaryotic cells and organisms.
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Affiliation(s)
- P G McKean
- School of Biological Sciences, University of Manchester, UK
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33
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Gull K. The biology of kinetoplastid parasites: insights and challenges from genomics and post-genomics. Int J Parasitol 2001; 31:443-52. [PMID: 11334928 DOI: 10.1016/s0020-7519(01)00154-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Kinetoplastid parasites exhibit a rich and diverse biology which mirrors many of the most interesting topics of current interest and study in the broader biological sciences. These evolutionarily ancient organisms possess intriguing mechanisms for control of gene expression, and exhibit complex patterns of cell morphogenesis orchestrated by an internal cytoskeleton. Their cell shapes change during a set of complex cell type differentiations in their life cycles. These differentiations are intimately linked to interactions with mammalian hosts or insect vectors, and often, these differentiations appear central to the successful transfer of the parasite between vector and host, and host and vector. The basics of this rich and complex cell and life cycle biology were described (with often rather forgotten clarity and prescience) in the early period of the last century. The last 30 years have seen major developments in our understanding of this biology. Ultrastructural differences in the various cells of the life cycle stages of Trypanosoma brucei, Trypanosoma cruzi and the various Leishmania species have been documented, and such studies have proven highly informative in defining important aspects of parasite adaptation. They have also proven to be a rich source of information for defining unusual aspects of parasite cell biology, novel organelles and cell architecture. This ultrastructural cell biology has been mirrored in a set of biochemical explanations defining unusual aspects of metabolism, surface molecules, and organelles. Finally, the application of molecular biology to these parasites revealed fascinating layers of complexity in the control of gene expression. These molecular studies have given us particular insights into polycistronic transcription, trans-splicing, RNA editing and gene rearrangements during antigenic variation. In contrast to other microbial systems, these cell biological, biochemical and molecular studies have not been greatly aided by insights gained from genetics--the diploid nature of the genome has discouraged the application of selectional genetics, mutant isolation and analysis. This is an important fact, since in general, it means that we have only recently started to analyse the phenotypes of mutants produced in the context of reverse genetics. In the following, I will argue that this lack of investment in the analysis of mutant phenotype is just one of the challenges that will need to be met if we are to gain the expected added value from the parasite genome projects. In this presentation, I will use some of the current areas of interest in the biology of T. brucei, T. cruzi and the Leishmania species to rehearse some of the insights and challenges that are likely to stem from the application of genomics and post-genomic studies to the kinetoplastid parasites. In some cases, I will exemplify points by illustrations from my laboratory's work, interests and hypotheses. The presentation slants therefore towards T. brucei biology, however, in each case the reader will, no doubt, see the generalities of application to other kinetoplastid parasites.
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Affiliation(s)
- K Gull
- School of Biological Sciences, University of Manchester, 2.205 Stopford Building, Oxford Road, M13 9PT, Manchester, UK.
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34
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Garreau de Loubresse N, Ruiz F, Beisson J, Klotz C. Role of delta-tubulin and the C-tubule in assembly of Paramecium basal bodies. BMC Cell Biol 2001; 2:4. [PMID: 11255590 PMCID: PMC29069 DOI: 10.1186/1471-2121-2-4] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2001] [Accepted: 03/07/2001] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND A breakthrough in the understanding of centriole assembly was provided by the characterization of the UNI3 gene in Chlamydomonas. Deletion of this gene, found to encode a novel member of the tubulin superfamily, delta-tubulin, results in the loss of the C-tubule, in the nine microtubule triplets which are the hallmark of centrioles and basal bodies. Delta-tubulin homologs have been identified in the genomes of mammals and protozoa, but their phylogenetic relationships are unclear and their function is not yet known. RESULTS Using the method of gene-specific silencing, we have inactivated the Paramecium delta-tubulin gene, which was recently identified. This inactivation leads to loss of the C-tubule in all basal bodies, without any effect on ciliogenesis. This deficiency does not directly affect basal body duplication, but perturbs the cortical cytoskeleton, progressively leading to mislocalization and loss of basal bodies and to altered cell size and shape. Furthermore, additional loss of B- and even A-tubules at one or more triplet sites are observed: around these incomplete cylinders, the remaining doublets are nevertheless positioned according to the native ninefold symmetry. CONCLUSIONS The fact that in two distinct phyla, delta-tubulin plays a similar role provides a new basis for interpreting phylogenetic relationships among delta-tubulins. The role of delta-tubulin in C-tubule assembly reveals that tubulins contribute subtle specificities at microtubule nucleation sites. Our observations also demonstrate the existence of a prepattern for the ninefold symmetry of the organelle which is maintained even if less than 9 triplets develop.
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Affiliation(s)
| | - Françoise Ruiz
- Centre de Génétique Moléculaire du C.N.R.S., Allée de la Terrasse, 91190 Gif- sur-Yvette, France
| | - Janine Beisson
- Centre de Génétique Moléculaire du C.N.R.S., Allée de la Terrasse, 91190 Gif- sur-Yvette, France
| | - Catherine Klotz
- Centre de Génétique Moléculaire du C.N.R.S., Allée de la Terrasse, 91190 Gif- sur-Yvette, France
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35
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Abstract
Microtubules perform essential and diverse functions in eukaryotic cells. They are required for spindles during mitosis and meiosis, for axonal transport, for organelle positioning, and for cilia and flagella. gamma-tubulin is necessary to initiate the assembly of alpha-beta tubulin heterodimers into microtubule polymers. Recent genetic analyses and database searches have added four new members of the tubulin superfamily, which now includes alpha-, beta-, gamma-, delta-, epsilon-, zeta-, and eta-tubulin.
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Affiliation(s)
- S K Dutcher
- Department of Genetics, School of Medicine, Washington University, Campus Box 8232, 4566 Scott Avenue, St Louis, Missouri 63110, USA.
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36
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Inclán YF, Nogales E. Structural models for the self-assembly and microtubule interactions of gamma-, delta- and epsilon-tubulin. J Cell Sci 2001; 114:413-22. [PMID: 11148142 DOI: 10.1242/jcs.114.2.413] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
alphabeta-tubulin heterodimers self-assemble to form microtubules nucleated by gamma-tubulin in the cell. Gamma-tubulin is believed to recruit the alphabeta-tubulin dimers that form the minus ends of microtubules, but the molecular mechanism of this action remains a matter of heated controversy. Still less is known about the function and molecular interactions of delta-tubulin and epsilon-tubulin. delta-tubulin may seed the formation of the C triplet tubules in the basal bodies of Chlamydomonas and epsilon-tubulin is known to localize to the centrosome in a cell cycle-dependent manner. Using the structure of alphabeta tubulin as a model, we have analyzed the sequences of gamma-, delta- and epsilon-tubulin in regions corresponding to different polymerization interfaces in the tubulin alphabeta dimer. The sequence comparisons sometimes show clear conservation, pointing to similar types of contacts being functionally important for the new tubulin considered. Conversely, certain surfaces show marked differences that rule out equivalent interactions for non-microtubular tubulins. This sequence/structure analysis has led us to structural models of how these special tubulins may be involved in protein-protein contacts that affect microtubule self-assembly. delta-tubulin most likely interacts longitudinally with alpha-tubulin at the minus ends of microtubules, while epsilon-tubulin most likely binds to the plus end of beta-tubulin. Conservation of key residues in gamma-tubulin suggests that it is capable of longitudinal self-assembly. The implications for the protofilament and template models of nucleation are considered.
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Affiliation(s)
- Y F Inclán
- Howard Hughes Medical Institute, Molecular and Cell Biology Department, University of California at Berkeley, CA 94720-3200, USA
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Bastin P, Pullen TJ, Moreira-Leite FF, Gull K. Inside and outside of the trypanosome flagellum:a multifunctional organelle. Microbes Infect 2000; 2:1865-74. [PMID: 11165931 DOI: 10.1016/s1286-4579(00)01344-7] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Amongst the earliest eukaryotes, trypanosomes have developed conventional organelles but sometimes with extreme features rarely seen in other organisms. This is the case of the flagellum, containing conventional and unique structures whose role in infectivity is still enigmatic.
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Affiliation(s)
- P Bastin
- Department of Biochemistry, School of Biological Sciences, University of Manchester, 2.205 Stopford Building, Oxford Road, M13 9PT, Manchester, UK.
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Abstract
Recent data have revealed that the tubulin superfamily of proteins is much larger than was thought previously. Six distinct families within the tubulin superfamily have been discovered and more might await discovery. alpha-, beta- and gamma-tubulins are ubiquitous in eukaryotes. alpha- and beta-tubulins are the major components of microtubules, and gamma-tubulin plays a major role in the nucleation of microtubule assembly. delta- and epsilon-tubulins are widespread but not ubiquitous, and zeta-tubulin has been found so far only in kinetoplastid protozoa. delta-Tubulin has an important role in flagellar assembly in Chlamydomonas, but its role in other organisms is just beginning to be investigated, as are the functions of the recently discovered epsilon- and zeta-tubulins.
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Affiliation(s)
- B R Oakley
- Dept of Molecular Genetics, The Ohio State University, 484 W. 12th Ave, Columbus, OH 43210, USA.
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Ruiz F, Krzywicka A, Klotz C, Keller A, Cohen J, Koll F, Balavoine G, Beisson J. The SM19 gene, required for duplication of basal bodies in Paramecium, encodes a novel tubulin, eta-tubulin. Curr Biol 2000; 10:1451-4. [PMID: 11102808 DOI: 10.1016/s0960-9822(00)00804-6] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The discovery of delta-tubulin, the fourth member of the tubulin superfamily, in Chlamydomonas [1] has led to the identification in the genomes of vertebrates and protozoa of putative delta homologues and of additional tubulins, epsilon and zeta [2-4]. These discoveries raise questions concerning the functions of these novel tubulins, their interactions with microtubule arrays and microtubule-organising centres, and their evolutionary status. The sm19-1 mutation of Paramecium specifically inhibits basal body duplication [5] and causes delocalisation of gamma-tubulin, which is also required for basal body duplication [6]. We have cloned the SM19 gene by functional complementation and found that it encodes another new member of the tubulin superfamily. SM19p, provisionally called eta-tubulin (eta-tubulin), shows low sequence identity with the tubulins previously identified in Paramecium, namely, alpha [7], beta [8], gamma [6], delta (this work) and epsilon (P. Dupuis-Williams, personal communication). Phylogenetic analysis indicated that SM19p is not consistently grouped with any phylogenetic entity.
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Affiliation(s)
- F Ruiz
- Centre de Génétique Moléculaire du C.N.R.S., Allée de la Terrasse, 91190, Gif-sur-Yvette, France.
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