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Lindemann CB, Lesich KA. The mechanics of cilia and flagella: What we know and what we need to know. Cytoskeleton (Hoboken) 2024. [PMID: 38780123 DOI: 10.1002/cm.21879] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Revised: 05/04/2024] [Accepted: 05/06/2024] [Indexed: 05/25/2024]
Abstract
In this review, we provide a condensed overview of what is currently known about the mechanical functioning of the flagellar/ciliary axoneme. We also present a list of 10 specific areas where our current knowledge is incomplete and explain the benefits of further experimental investigation. Many of the physical parameters of the axoneme and its component parts have not been determined. This limits our ability to understand how the axoneme structure contributes to its functioning in several regards. It restricts our ability to understand how the mechanics of the structure contribute to the regulation of motor function. It also confines our ability to understand the three-dimensional workings of the axoneme and how various beating modes are accomplished. Lastly, it prevents accurate computational modeling of the axoneme in three-dimensions.
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Affiliation(s)
- Charles B Lindemann
- Department of Biological Sciences, Oakland University, Rochester, Michigan, USA
| | - Kathleen A Lesich
- Department of Biological Sciences, Oakland University, Rochester, Michigan, USA
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2
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Gadadhar S, Alvarez Viar G, Hansen JN, Gong A, Kostarev A, Ialy-Radio C, Leboucher S, Whitfield M, Ziyyat A, Touré A, Alvarez L, Pigino G, Janke C. Tubulin glycylation controls axonemal dynein activity, flagellar beat, and male fertility. Science 2021; 371:371/6525/eabd4914. [PMID: 33414192 DOI: 10.1126/science.abd4914] [Citation(s) in RCA: 70] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 10/13/2020] [Accepted: 11/18/2020] [Indexed: 12/30/2022]
Abstract
Posttranslational modifications of the microtubule cytoskeleton have emerged as key regulators of cellular functions, and their perturbations have been linked to a growing number of human pathologies. Tubulin glycylation modifies microtubules specifically in cilia and flagella, but its functional and mechanistic roles remain unclear. In this study, we generated a mouse model entirely lacking tubulin glycylation. Male mice were subfertile owing to aberrant beat patterns of their sperm flagella, which impeded the straight swimming of sperm cells. Using cryo-electron tomography, we showed that lack of glycylation caused abnormal conformations of the dynein arms within sperm axonemes, providing the structural basis for the observed dysfunction. Our findings reveal the importance of microtubule glycylation for controlled flagellar beating, directional sperm swimming, and male fertility.
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Affiliation(s)
- Sudarshan Gadadhar
- Institut Curie, Université PSL, CNRS UMR3348, F-91400 Orsay, France. .,Université Paris-Saclay, CNRS UMR3348, F-91400 Orsay, France
| | - Gonzalo Alvarez Viar
- Max Planck Institute of Molecular Cell Biology and Genetics, D-01307 Dresden, Germany
| | - Jan Niklas Hansen
- Institute of Innate Immunity, Medical Faculty, University of Bonn, D-53127 Bonn, Germany
| | - An Gong
- Center of Advanced European Studies and Research, D-53175 Bonn, Germany
| | - Aleksandr Kostarev
- Max Planck Institute of Molecular Cell Biology and Genetics, D-01307 Dresden, Germany
| | - Côme Ialy-Radio
- Université de Paris, Institut Cochin, INSERM, CNRS, F-75014 Paris, France
| | - Sophie Leboucher
- Institut Curie, Université PSL, CNRS UMR3348, F-91400 Orsay, France.,Université Paris-Saclay, CNRS UMR3348, F-91400 Orsay, France
| | - Marjorie Whitfield
- Université de Paris, Institut Cochin, INSERM, CNRS, F-75014 Paris, France
| | - Ahmed Ziyyat
- Université de Paris, Institut Cochin, INSERM, CNRS, F-75014 Paris, France.,Service d'histologie, d'embryologie, Biologie de la reproduction, Assistance Publique-Hôpitaux de Paris, Hôpital Cochin, F-75014 Paris, France
| | - Aminata Touré
- Université de Paris, Institut Cochin, INSERM, CNRS, F-75014 Paris, France
| | - Luis Alvarez
- Center of Advanced European Studies and Research, D-53175 Bonn, Germany.
| | - Gaia Pigino
- Max Planck Institute of Molecular Cell Biology and Genetics, D-01307 Dresden, Germany. .,Human Technopole, I-20157 Milan, Italy
| | - Carsten Janke
- Institut Curie, Université PSL, CNRS UMR3348, F-91400 Orsay, France. .,Université Paris-Saclay, CNRS UMR3348, F-91400 Orsay, France
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3
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Sarkar D, Thakur S. Spontaneous beating and synchronization of extensile active filament. J Chem Phys 2017; 146:154901. [DOI: 10.1063/1.4979946] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Debarati Sarkar
- Department of Physics, Indian Institute of Science Education and Research Bhopal, Bhopal, India
| | - Snigdha Thakur
- Department of Physics, Indian Institute of Science Education and Research Bhopal, Bhopal, India
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4
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Varner DD, Gibb Z, Aitken RJ. Stallion fertility: a focus on the spermatozoon. Equine Vet J 2014; 47:16-24. [PMID: 24943233 DOI: 10.1111/evj.12308] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Accepted: 06/03/2014] [Indexed: 11/30/2022]
Abstract
Stallion fertility is a vast subject, with a wide array of permutations that can impact reproductive performance in either positive or negative ways. This review is intended to address a mere segment of the male fertility issue, but the very essence of the male contribution to fertilisation, that of the spermatozoon. Spermatozoal ultrastructure and form-to-function are detailed and spermatozoal metabolism is discussed, with specific reference to distinctive characteristics of stallion spermatozoa. Lastly, methods for assessment of spermatozoal function are considered, with emphasis on spermatozoal motility, the acrosome reaction and spermatozoon-oocyte interactions. Closing comments address the need for development and standardisation of molecular-based assays for use with spermatozoa of stallions whose subfertility cannot be explained with conventional tests.
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Affiliation(s)
- D D Varner
- Department of Large Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, USA
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5
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Hydrodynamic instabilities provide a generic route to spontaneous biomimetic oscillations in chemomechanically active filaments. Sci Rep 2013; 3:1964. [PMID: 23752497 PMCID: PMC3678140 DOI: 10.1038/srep01964] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Accepted: 05/22/2013] [Indexed: 02/08/2023] Open
Abstract
Non-equilibrium processes which convert chemical energy into mechanical motion enable the motility of organisms. Bundles of inextensible filaments driven by energy transduction of molecular motors form essential components of micron-scale motility engines like cilia and flagella. The mimicry of cilia-like motion in recent experiments on synthetic active filaments supports the idea that generic physical mechanisms may be sufficient to generate such motion. Here we show, theoretically, that the competition between the destabilising effect of hydrodynamic interactions induced by force-free and torque-free chemomechanically active flows, and the stabilising effect of nonlinear elasticity, provides a generic route to spontaneous oscillations in active filaments. These oscillations, reminiscent of prokaryotic and eukaryotic flagellar motion, are obtained without having to invoke structural complexity or biochemical regulation. This minimality implies that biomimetic oscillations, previously observed only in complex bundles of active filaments, can be replicated in simple chains of generic chemomechanically active beads.
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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: 8.1] [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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Lu X. Fluorescent imaging of Drosophila melanogaster sperm in the reproductive tract: a new model of flagellar motility. Methods Enzymol 2013; 525:131-48. [PMID: 23522468 DOI: 10.1016/b978-0-12-397944-5.00007-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The sperm of Drosophila melanogaster stands out because of its enormous length and perplexing movements that break some norms of flagella. Most flagella with analyzed motility, ranging from flagella of Chlamydomonas to sperm of marine invertebrates and vertebrates, are from a few microns to at most 208 μm in length. Most flagella propagate waves in a constant direction, starting at the base of the flagellum and moving toward the tip (base-to-tip waves). In contrast, the fly sperm is 1.9-mm long and it propagates waves in base-to-tip or tip-to-base direction, generating head-leading or tail-leading movement. Of the two movement orientations, the sperm choose one or the other for a particular movement along the convoluted path leading to fertilization. For example, the sperm enter the seminal receptacle (SR) for storage with a tail-leading movement, but exit it for fertilization with a head-leading movement. Moreover, the sperm move with unusual waveforms. A modified sinusoidal or arc-line waveform generates semistationary movement-moving but staying at a general area-within temporary reservoirs (ejaculatory duct, uterus) and storage organs (SR, spermathecae). In contrast, a corkscrew-like helical waveform is ideal for rapid advancing movement and suspected for traveling through long tubules that interconnect these reservoirs. Here, we describe new methods for capturing these complex sperm movements that naturally occur in the reproductive tract. The imaging methods coupled with large mutant collections and genomic resources make the fly sperm a powerful new model for understanding flagellar motility and its dynamic regulation in vivo. The motility regulatory proteins we have identified in the fly are broadly conserved, thus illustrating a general utility of this model system.
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Affiliation(s)
- Xiangyi Lu
- Institute of Environmental Health Sciences, Department of Biochemistry and Molecular Biology, Wayne State University, Detroit, Michigan, USA.
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Woolley DM. A novel motility pattern in quail spermatozoa with implications for the mechanism of flagellar beating. Biol Cell 2012; 99:663-75. [PMID: 17561807 DOI: 10.1042/bc20070050] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND INFORMATION The spermatozoon of the quail (Coturnix coturnix L., var japonica) has a '9+2' flagellum that is unusually long. When it moves in a viscous medium, near to the coverslip, it develops a meander waveform. Because of the high viscosity, the meander bends are static in relation to the field of view; bend propagation is therefore manifest as the forward movement of the flagellum through the meander shape. At the same time, the origin of the oscillation typically shifts proximally in a stepwise fashion. These movements have been analysed in the hope of contributing to the resolution of problems in flagellar mechanics. RESULTS (1) Meander waves originate from spontaneous sigmoid bend complexes. (2) On a given flagellum, fully developed meander bends are uniform in their large angle, curvature and propagation speed; interbends can vary in length and shape. (3) No intra-axonemal sliding is transmitted through formed bends; sliding related to new bends is accommodated proximally. (4) Sliding reversal is initiated at a threshold shear angle of approx. 1 rad. (5) The arc wavespeed is the product of the arc wavelength and the beat frequency. (6) Physical obstruction to bend development causes a pause in the oscillation. (7) New bend initiation can thus be dissociated from bend propagation on the distal flagellum. (8) The steps in the forward advance of the oscillation site occur during the early phase of bend growth. CONCLUSIONS (1) The main conclusion is that, in meander waves, the mechanical basis of the oscillation appears to be that the propulsive thrust arising from bend propagation acts as a bending stress to trigger sliding reversal, thus perpetuating the rhythmic beating. (2) Oscillations can originate at any position, provided the position is distal to a location where doublet sliding is restrained. (3) Meander waves are an example of new bend development without 'paradoxical' classes of sliding.
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Affiliation(s)
- David M Woolley
- Department of Physiology, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK.
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Mohri H, Inaba K, Ishijima S, Baba SA. Tubulin-dynein system in flagellar and ciliary movement. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2012; 88:397-415. [PMID: 23060230 PMCID: PMC3491082 DOI: 10.2183/pjab.88.397] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Accepted: 08/22/2012] [Indexed: 06/01/2023]
Abstract
Eukaryotic flagella and cilia have attracted the attention of many researchers over the last century, since they are highly arranged organelles and show sophisticated bending movements. Two important cytoskeletal and motor proteins, tubulin and dynein, were first found and described in flagella and cilia. Half a century has passed since the discovery of these two proteins, and much information has been accumulated on their molecular structures and their roles in the mechanism of microtubule sliding, as well as on the architecture, the mechanism of bending movement and the regulation and signal transduction in flagella and cilia. Historical background and the recent advance in this field are described.
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10
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Abstract
Motile cilia and flagella exhibit many waveforms as outputs of dynein activation sequences on the highly conserved axoneme. Motility change of sperm in the reproductive tract is difficult to study and remains an important area of investigation. Sperm typically execute a sinusoidal waveform. Increased viscosity in the medium induces somewhat unusual arc-line and helical waveforms in some sperm. However, whether the latter two waveforms occur in vivo is not known. Using green fluorescence protein imaging, we show that Drosophila sperm in the uterus move in circular foci via arc-line waves, predominantly in a tail-leading orientation. From the uterus, a small fraction of the sperm enters the seminal receptacle (SR) in parallel formations. After sperm storage and coincident with fertilization of the egg, the sperm exit the SR via head-leading helical waves. Consistent with the observed bidirectional movements, the sperm show the ability to propagate both base-to-tip and tip-to-base flagellar waves. Numerous studies have shown that sperm motility is regulated by intraflagellar calcium concentrations; in particular, the Pkd2 calcium channel has been shown to affect sperm storage. Our analyses here suggest that Pkd2 is required for the sperm to adopt the correct waveform and movement orientation during SR entry. A working model for the sperm's SR entry movement is proposed.
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Affiliation(s)
- Yong Yang
- Institute of Environmental Health Sciences and Department of Biochemistry and Molecular Biology, Wayne State University, 259 Mack Avenue, Detroit, MI 48201, USA
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12
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Lindemann CB, Lesich KA. Flagellar and ciliary beating: the proven and the possible. J Cell Sci 2010; 123:519-28. [PMID: 20145000 DOI: 10.1242/jcs.051326] [Citation(s) in RCA: 156] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The working mechanism of the eukaryotic flagellar axoneme remains one of nature's most enduring puzzles. The basic mechanical operation of the axoneme is now a story that is fairly complete; however, the mechanism for coordinating the action of the dynein motor proteins to produce beating is still controversial. Although a full grasp of the dynein switching mechanism remains elusive, recent experimental reports provide new insights that might finally disclose the secrets of the beating mechanism: the special role of the inner dynein arms, especially dynein I1 and the dynein regulatory complex, the importance of the dynein microtubule-binding affinity at the stalk, and the role of bending in the selection of the active dynein group have all been implicated by major new evidence. This Commentary considers this new evidence in the context of various hypotheses of how axonemal dynein coordination might work.
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Affiliation(s)
- Charles B Lindemann
- Department of Biological Sciences, Oakland University, Rochester, MI 48309, USA.
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13
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Abstract
Eukaryotic flagella and cilia have a remarkably uniform internal 'engine' known as the '9+2' axoneme. With few exceptions, the function of cilia and flagella is to beat rhythmically and set up relative motion between themselves and the liquid that surrounds them. The molecular basis of axonemal movement is understood in considerable detail, with the exception of the mechanism that provides its rhythmical or oscillatory quality. Some kind of repetitive 'switching' event is assumed to occur; there are several proposals regarding the nature of the 'switch' and how it might operate. Herein I first summarise all the factors known to influence the rate of the oscillation (the beating frequency). Many of these factors exert their effect through modulating the mean sliding velocity between the nine doublet microtubules of the axoneme, this velocity being the determinant of bend growth rate and bend propagation rate. Then I explain six proposed mechanisms for flagellar oscillation and review the evidence on which they are based. Finally, I attempt to derive an economical synthesis, drawing for preference on experimental research that has been minimally disruptive of the intricate structure of the axoneme. The 'provisional synthesis' is that flagellar oscillation emerges from an effect of passive sliding direction on the dynein arms. Sliding in one direction facilitates force-generating cycles and dynein-to-dynein synchronisation along a doublet; sliding in the other direction is inhibitory. The direction of the initial passive sliding normally oscillates because it is controlled hydrodynamically through the alternating direction of the propulsive thrust. However, in the absence of such regulation, there can be a perpetual, mechanical self-triggering through a reversal of sliding direction due to the recoil of elastic structures that deform as a response to the prior active sliding. This provisional synthesis may be a useful basis for further examination of the problem.
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Affiliation(s)
- David M Woolley
- Department of Physiology and Pharmacology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, U.K.
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Are the local adjustments of the relative spatial frequencies of the dynein arms and the β-tubulin monomers involved in the regulation of the “9+2” axoneme? J Theor Biol 2008; 253:74-89. [DOI: 10.1016/j.jtbi.2008.01.029] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2006] [Revised: 12/17/2007] [Accepted: 01/24/2008] [Indexed: 11/17/2022]
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Woolley DM, Carter DA, Tilly GN. Compliance in the neck structures of the guinea pig spermatozoon, as indicated by rapid freezing and electron microscopy. J Anat 2008; 213:336-41. [PMID: 18537850 DOI: 10.1111/j.1469-7580.2008.00919.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Electron microscopy has been used to investigate whether the transversely striated columns of the connecting piece in the neck region of guinea pig spermatozoa, undergo lengthening and shortening as a result of the forces generated during motility. Motile spermatozoa were subjected to near-instantaneous rapid freezing, followed by freeze-substitution fixation and epoxy embedment. Thin sections passing longitudinally through the striated columns revealed that the periodicity was indeed variable. The repeat period, taken to have an unstressed width of 60 nm, could be found extended to 75 nm in some specimens, and reduced to 54 nm in others. The estimates of the coefficients of variation were 6.6% for the width of the 'dense' band and 33.5% for the 'pale' band. The 'pale' band in the extended state showed longitudinal striae. Such variations in length, which - it is suggested - are physiological, and passively induced, would have functional implications for the flagellum - for both bend initiation and bend growth. Also, hypothetically, any mechanism that could increase the degree of compliance in these columns, such as perhaps phosphorylation of the constituent proteins, could permit the flagellum to develop the exaggerated bend angles and asymmetries of the 'hyperactivated' state.
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Affiliation(s)
- D M Woolley
- Department of Physiology and Pharmacology, University of Bristol, UK.
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16
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Ishikawa R, Shingyoji C. Induction of beating by imposed bending or mechanical pulse in demembranated, motionless sea urchin sperm flagella at very low ATP concentrations. Cell Struct Funct 2007; 32:17-27. [PMID: 17314459 DOI: 10.1247/csf.06035] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A basic feature of the movement of eukaryotic flagella is oscillation. Although flagellar oscillation is thought to be regulated by a self-regulatory feedback system including the mechanical signal of bending itself, the mechanism regulating the dynein motile activity to produce oscillation is not well understood. To elucidate the mechanism, we developed a new experimental system which allowed us to analyze the conditions necessary for the induction of oscillation. When a mechanical signal of bending or a pulse was applied by micromanipulation to a demembranated motionless sea urchin sperm flagellar axoneme at very low ATP concentrations (1-3 microM), a localized pair of bends was induced. The bend formation was often followed by further responses including propagation of the distal bend of paired bends, growth and propagation of the paired bends, and cyclical beating. The beating was induced at 2.0 microM or higher concentrations of ATP, but appeared even at 1.5 microM ATP if a few muM of ADP was also present. When the proximal half of a flagellum was attached to a microneedle, beating could not be induced in the distal free region at 2 microM ATP. These results suggest that mechanical signal is involved in the mechanism regulating the motile activity of dynein to produce oscillation. Our results also showed that the presence of a small amount of ADP and the axial difference along the flagellum are factors essential for the induction of flagellar oscillation.
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Affiliation(s)
- Rina Ishikawa
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Tokyo, Japan
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17
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Lindemann CB. The Geometric Clutch as a Working Hypothesis for Future Research on Cilia and Flagella. Ann N Y Acad Sci 2007; 1101:477-93. [PMID: 17303832 DOI: 10.1196/annals.1389.024] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The Geometric Clutch hypothesis contends that the forces transverse to the flagellar axis (t-forces) act on the axonemal scaffold to regulate flagellar beating. T-forces develop as the product of the curvature and the accumulated tension or compression on the doublet microtubules. In this respect, t-force is a mediator of self-organizing behavior. It arises from the collective action of the assemblage of dynein motors on the structural components of the axoneme and, in turn, imparts order to the sequence of activation and deactivation of the dynein. At the switch point of the flagellar beat, the magnitude of the t-force per micron of flagellum is approximately equal to the sum total of dynein force that can be generated per micron of flagellum. This suggests that the t-force could directly overcome the force-producing dynein bridges and terminate their action. However, many questions remain to be answered concerning the behavior of the axonemal scaffold under stress. Little is known of the force-bearing capacity of the radial spokes and the central pair (cp) projections. The properties of these structures will determine how t-force is distributed within the axoneme. The mechanical and elastic properties of the dynein arms and nexin links need to be better understood to determine how they respond to the application of t-force. In the framework of the Geometric Clutch hypothesis these are the issues that are most important to explore if we are to understand how the flagellum works.
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Affiliation(s)
- Charles B Lindemann
- Department of Biological Sciences, Oakland University, Rochester, Michigan 48309, USA.
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18
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Woolley D, Gadelha C, Gull K. Evidence for a sliding-resistance at the tip of the trypanosome flagellum. ACTA ACUST UNITED AC 2006; 63:741-6. [PMID: 17009329 DOI: 10.1002/cm.20159] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Motility in trypanosomes is achieved through the undulating behaviour of a single "9 + 2" flagellum; normally the flagellar waves begin at the flagellar tip and propagate towards the base. For flagella in general, however, propagation is from base-to-tip and it is believed that bend formation, and sustained regular oscillation, depend upon a localised resistance to inter-doublet sliding - which is normally conferred by structures at the flagellar base, typically the basal body. We therefore predicted that in trypanosomes there must be a resistive structure at the flagellar tip. Electron micrographs of Crithidia deanei, Herpetomonas megaseliae, Trypanosoma brucei and Leishmania major have confirmed that such attachments are present. Thus, it can be assumed that in trypanosomes microtubule sliding at the flagellar tip is resisted sufficiently to permit bend formation.
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Affiliation(s)
- David Woolley
- Department of Physiology, School of Medical Sciences, University of Bristol, Bristol, United Kingdom.
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