DOCSLIB.ORG

The Single Flagellum of Leishmania Has a Fixed Polarisation of Its Asymmetric Beat Ziyin Wang1,‡,*, Tom Beneke1,‡, Eva Gluenz3 and Richard John Wheeler2,§

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Single Flagellum of Leishmania Has a Fixed Polarisation of Its Asymmetric Beat Ziyin Wang1,‡,*, Tom Beneke1,‡, Eva Gluenz3 and Richard John Wheeler2,§ © 2020. Published by The Company of Biologists Ltd | Journal of Cell Science (2020) 133, jcs246637. doi:10.1242/jcs.246637 RESEARCH ARTICLE The single flagellum of Leishmania has a fixed polarisation of its asymmetric beat Ziyin Wang1,‡,*, Tom Beneke1,‡, Eva Gluenz3 and Richard John Wheeler2,§ ABSTRACT undergoing coordinated movement across a tissue. Ultimately, the Eukaryotic flagella undertake different beat types as necessary for correct choice of symmetric or asymmetric waveform, and the correct different functions; for example, the Leishmania parasite flagellum polarisation of the latter, must be used to achieve the necessary undergoes a symmetric tip-to-base beat for forward swimming and an biological function. Defects tend to cause motility defects in asymmetric base-to-tip beat to rotate the cell. In multi-ciliated tissues swimming cells, and ciliopathies, a range of mild to severe genetic or organisms, the asymmetric beats are coordinated, leading to diseases, in humans. movement of the cell, organism or surrounding fluid. This coordination Typical strongly asymmetric beats undergo a power stroke, which involves a polarisation of power stroke direction. Here, we asked drives fluid movement relative to the cell, followed by a recovery whether the asymmetric beat of the single Leishmania flagellum also stroke, returning the cilium/flagellum to its starting configuration. has a fixed polarisation. We developed high frame rate dual-colour A planar asymmetric beat has two possible polarisations, fluorescence microscopy to visualise flagellar-associated structures corresponding to which way the power stroke pushes fluid as the in live swimming cells. This showed that the asymmetric Leishmania flagellum beats. For example, in Fig. 1B the flagellum pushes fluid beat is polarised, with power strokes only occurring in one direction down and rotates the cell anticlockwise while the opposite relative to the asymmetric flagellar machinery. Polarisation of bending polarisation would push the fluid up and rotate the cell clockwise. was retained in deletion mutants whose flagella cannot beat but have The general assumption seems to be that this polarisation is fixed. In a static bend. Furthermore, deletion mutants for proteins required for multi-ciliated systems, the polarisation of the power stroke tends to asymmetric extra-axonemal and rootlet-like flagellum-associated be organised to generate fluid flows [e.g. animal ciliated epithelia, structures also retained normal polarisation. Leishmania beat such as in brain ventricles (Faubel et al., 2016)] or to drive cell Tetrahymena Paramecium polarisation therefore likely arises from either the nine-fold rotational swimming (e.g. and ) (Naitoh and symmetry of the axoneme structure or is due to differences between Kaneko, 1972). There are varied configurations in cells with Chlamydomonas the outer doublet decorations. fewer cilia/flagella; for example, uses asymmetric beating of two flagella with opposite polarisation to achieve forward KEY WORDS: Leishmania, Flagellum, Cilium, Cell motility, swimming (Ringo, 1967), while the unicellular eukaryotic parasite Asymmetry, Trypanosomatid Leishmania uses asymmetric beats of its single flagellum to rotate (Gadelha et al., 2007; Holwill and McGregor, 1975) (Fig. 1A,B). INTRODUCTION Cilia/flagella have asymmetries that contribute to generating the Motile flagella and cilia have essentially indistinguishable correct beat form – firstly those which keep bending in a plane, and ultrastructures but originally received different names based on secondly those which introduce asymmetries in the beat with the their biological function – a combination of where they are present in correct polarisation. Although both structural and functional (e.g. organisms, their structure and the motion they undergo (Takeda and signalling) asymmetries may contribute, far more is known about Narita, 2012). The organelle tends to be called a flagellum when they structural asymmetries. undergo a planar near-symmetric near-sinusoidal beat (Fig. 1A) and Motile flagella/cilia canonically have nine outer microtubule there are few per cell. In contrast, the term cilium tends to be used doublets in a circular arrangement, around a central pair of when they undergo a planar strongly asymmetric wafting beat singlet microtubules (called the 9+2 arrangement). Their beating (Fig. 1B) and there are many cilia per cell or many ciliated cells is driven by coordinated activity of dynein motors bound to the outer doublet microtubules, which drives sliding between adjacent doublets. To generate planar motion, some structural or regulatory 1Sir William Dunn School of Pathology, University of Oxford, Oxford, UK. 2Peter break in this rotational symmetry must exist. Depending on Medawar Building for Pathogen Research, Nuffield Department of Medicine, University of Oxford, Oxford, UK. 3The Wellcome Centre for Integrative Parasitology, the organism, this may involve addition of a fixed orientation Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, central pair complex (Ishijima et al., 1988), which does not have UK. ‡ reflectional or rotational symmetry (Carbajal-González et al., 2013). These authors contributed equally to this work *Present address: Faculty of Medicine, Imperial College, London, UK. Leishmania and related species have a fixed central pair orientation (Gadelha et al., 2006). Alternatively, it may involve the presence § Author for correspondence ([email protected]) of specialised bridges between particular microtubule doublets T.B., 0000-0001-9117-2649; E.G., 0000-0003-4346-8896; R.J.W., 0000-0002- to restrict where dynein-driven sliding occurs (Bui et al., 2009; 4270-8360 Gibbons, 1961), thus removing the nine-fold rotational symmetry of This is an Open Access article distributed under the terms of the Creative Commons Attribution the outer doublets. Flagella with nine-fold rotational symmetry of License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, the outer doublets and no central pair or asymmetric extra-axonemal distribution and reproduction in any medium provided that the original work is properly attributed. structures can undergo three-dimensional rotating or helical Handling Editor: David Stephens movement without a fixed beat plane, such as nodal cilia (Nonaka Received 21 March 2020; Accepted 17 September 2020 et al., 1998). Journal of Cell Science 1 RESEARCH ARTICLE Journal of Cell Science (2020) 133, jcs246637. doi:10.1242/jcs.246637 Fig. 1. Known asymmetries in Leishmania flagellar beating and flagellum ultrastructure. (A,B) Schematic representations of the two types of Leishmania beat. (A) The symmetric beat, where waves propagate from the tip to the base with symmetric curvature (r). (B) The asymmetric beat, where waves propagate from the base to the tip with asymmetric curvature for power and recovery strokes (rp and rr). (C) Schematic representation of key asymmetries in axoneme structure that may contribute to asymmetry of the base-to-tip beat. This includes asymmetries in the central pair and outer doublets of the axoneme, the PFR and (toward the flagellum base) the attachment to the cell body by the FAZ. The nature of structural asymmetries that (1) give rise to includes proteins with Ca2+- and cAMP-associated functions which asymmetric beats and (2) defines their polarisation are less well may regulate beating (Oberholzer et al., 2007; Portman et al., 2009), understood; however, many asymmetries that correlate with while its structure suggests biomechanical effects to convert planar asymmetric beat polarisation are known. Within the 9+2 axoneme, into three dimensional movement (Hughes et al., 2012; Koyfman differences between the outer doublet decoration, particularly the et al., 2011), although we have previously argued against the latter inner dynein arms, are likely important (Bui et al., 2009, 2012). In (Wheeler, 2017). The PFR has a fixed asymmetric position and is addition to the asymmetric 9+2 axoneme, cilium-associated attached to outer microtubule doublets 4–6 (Fuge, 1969; Gadelha structures tend to be asymmetric. This includes the anchoring of et al., 2005). The anchoring of the flagellum base to the cell is also the basal body to the cell by rootlet structures – such as the basal asymmetric, analogous to rootlet structures in other organisms, with body–basal body linkage mediated by the distal striated fibre in lateral attachment to the cell body in the flagellar pocket via the Chlamydomonas (Dutcher and O’Toole, 2016; Ringo, 1967), the flagellum attachment zone (FAZ) only near outer microtubule basal foot structure in ciliated animal epithelia cells (Gibbons, 1961) doublets 9, 1 and 2 (Wheeler et al., 2016). The 9+2 axoneme itself and the basal body-associated structures in Paramecium (Tassin likely also has asymmetries between outer microtubule doublets, et al., 2016). Mutations of rootlet proteins cause a loss of ciliated based on recent cryo-electron tomography of the related species tissue polarity. However, individual cilia rotate randomly while Trypanosoma brucei (Imhof et al., 2019). retaining their normal asymmetric structure (Clare et al., 2014; Analysing polarisation of Leishmania asymmetric beats has a key Kunimoto et al., 2012). Each individual cilium presumably retains challenge – Leishmania cells appear axially symmetric when viewed their asymmetric beat, although this has not been analysed in detail. though transmitted light illumination. To determine
Load more

Recommended publications
  • 하구 및 연안생태학 Estuarine and Coastal Ecology
    하구 및 연안생태학 Estuarine and coastal ecology 2010 년 11월 2 계절적 변동 • 빛과 영양염분의 조건에 따라 • 봄 가을 대발생 계절적 변동 Sverdrup 에 의한 대발생 모델 • Compensation depth (보상심도) • Critical depth (임계수심) Sverdrup 에 의한 대발생 모델 홍재상외, 해양생물학 Sverdrup 에 의한 대발생 모델 봄 여름 가을 겨울 수심 혼합수심 임계수심 (mixed layer depth) (critical depth) Sverdrup 에 의한 대발생 모델 봄 여름 가을 겨울 수심 혼합수심 임계수심 (mixed layer depth) (critical depth) Diatoms (규조류) • Bacillariophyceae (1 fragment of centrics, 19 fragments of pennates in Devonian marble in Poland Kwiecinska & Sieminska 1974) Diatoms (규조류) • Bacillariophyceae • Temperate and high latitude (everywhere) Motility: present in pennate diatoms with a raphe (and male gametes) Resting cells (spores): heavily silicified, often with spines (Î보충설명) Biotopes: marine and freshwater, plankton, benthos, epiphytic, epizooic (e.g., on whales, crustaceans) endozoic, endophytic, discolouration of arctic and Antarctic sea ice Snow Algae (규조류 아님) Snow algae describes cold-tolerant algae and cyanobacteria that grow on snow and ice during alpine and polar summers. Visible algae blooms may be called red snow or watermelon snow. These extremophilic organisms are studied to understand the glacial ecosystem. Snow algae have been described in the Arctic, on Arctic sea ice, and in Greenland, the Antarctic, Alaska, the west coast, east coast, and continental divide of North America, the Himalayas, Japan, New Guinea, Europe (Alps, Scandinavia and Carpathians), China, Patagonia, Chile, and the South Orkney Islands. Diatoms (규조류) • Bacillariophyceae • Temperate and high latitude (everywhere) • 2~1000 um • siliceous frustules • Various patterns in frustule Centric vs Pennate Centric diatom Pennete small discoid plastid large plate plastid Navicula sp.
    [Show full text]
  • Swimming with Protists: Perception, Motility and Flagellum Assembly
    REVIEWS Swimming with protists: perception, motility and flagellum assembly Michael L. Ginger*, Neil Portman‡ and Paul G. McKean* Abstract | In unicellular and multicellular eukaryotes, fast cell motility and rapid movement of material over cell surfaces are often mediated by ciliary or flagellar beating. The conserved defining structure in most motile cilia and flagella is the ‘9+2’ microtubule axoneme. Our general understanding of flagellum assembly and the regulation of flagellar motility has been led by results from seminal studies of flagellate protozoa and algae. Here we review recent work relating to various aspects of protist physiology and cell biology. In particular, we discuss energy metabolism in eukaryotic flagella, modifications to the canonical assembly pathway and flagellum function in parasite virulence. Protists The canonical ‘9+2’ microtubule axoneme is the prin- of inherited pathologies (or ciliopathies), including Eukaryotes that cannot be cipal feature of many motile cilia and flagella and is infertility, chronic respiratory disease, polycystic kid- classified as animals, fungi or one of the most iconic structures in cell biology. The ney disease and syndromes that include Bardet–Biedl, plants. The kingdom Protista origin of the eukaryotic flagellum and cilium is ancient Alstrom and Meckel syndrome6–12. Even illnesses such includes protozoa and algae. and predates the radiation, over 800 million years ago, as cancer, diabetes and obesity have been linked to cili- 1 6 Ciliates of the lineages that gave rise to extant eukaryotes . ary defects . The biological basis for some ciliopathies A ubiquitous group of protists, Therefore the absence of cilia and flagella from yeast, is undoubtedly defective sensing (an essential function members of which can be many fungi, red algae and higher plants are all examples provided by cilia), rather than defects in the assembly found in many wet of secondary loss.
    [Show full text]
  • Ciliary Chemosensitivity Is Enhanced by Cilium Geometry and Motility
    bioRxiv preprint doi: https://doi.org/10.1101/2021.01.13.425992; this version posted January 14, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. Ciliary chemosensitivity is enhanced by cilium geometry and motility David Hickey,1 Andrej Vilfan,1, 2, ∗ and Ramin Golestanian1, 3 1Max Planck Institute for Dynamics and Self-Organization (MPIDS), 37077 G¨ottingen,Germany 2JoˇzefStefan Institute, 1000 Ljubljana, Slovenia 3Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3PU, United Kingdom (Dated: January 13, 2021) Cilia are hairlike organelles involved in both sensory functions and motility. We discuss the question of whether the location of chemical receptors on cilia provides an advantage in terms of sensitivity. Using a simple advection-diffusion model, we compute the capture rates of diffusive molecules on a cilium. Because of its geometry, a non-motile cilium in a quiescent fluid has a capture rate equivalent to a circular absorbing region with ∼ 4× its surface area. When the cilium is exposed to an external shear flow, the equivalent surface area increases to ∼ 10×. Alternatively, if the cilium beats in a non-reciprocal way, its capture rate increases with the beating frequency to the power of 1=3. Altogether, our results show that the protruding geometry of a cilium could be one of the reasons why so many receptors are located on cilia. They also point to the advantage of combining motility with chemical reception.
    [Show full text]
  • Unfolding the Secrets of Coral–Algal Symbiosis
    The ISME Journal (2015) 9, 844–856 & 2015 International Society for Microbial Ecology All rights reserved 1751-7362/15 www.nature.com/ismej ORIGINAL ARTICLE Unfolding the secrets of coral–algal symbiosis Nedeljka Rosic1, Edmund Yew Siang Ling2, Chon-Kit Kenneth Chan3, Hong Ching Lee4, Paulina Kaniewska1,5,DavidEdwards3,6,7,SophieDove1,8 and Ove Hoegh-Guldberg1,8,9 1School of Biological Sciences, The University of Queensland, St Lucia, Queensland, Australia; 2University of Queensland Centre for Clinical Research, The University of Queensland, Herston, Queensland, Australia; 3School of Agriculture and Food Sciences, The University of Queensland, St Lucia, Queensland, Australia; 4The Kinghorn Cancer Centre, Garvan Institute of Medical Research, Sydney, New South Wales, Australia; 5Australian Institute of Marine Science, Townsville, Queensland, Australia; 6School of Plant Biology, University of Western Australia, Perth, Western Australia, Australia; 7Australian Centre for Plant Functional Genomics, The University of Queensland, St Lucia, Queensland, Australia; 8ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, St Lucia, Queensland, Australia and 9Global Change Institute and ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, St Lucia, Queensland, Australia Dinoflagellates from the genus Symbiodinium form a mutualistic symbiotic relationship with reef- building corals. Here we applied massively parallel Illumina sequencing to assess genetic similarity and diversity among four phylogenetically diverse dinoflagellate clades (A, B, C and D) that are commonly associated with corals. We obtained more than 30 000 predicted genes for each Symbiodinium clade, with a majority of the aligned transcripts corresponding to sequence data sets of symbiotic dinoflagellates and o2% of sequences having bacterial or other foreign origin.
    [Show full text]
  • Flagellum Couples Cell Shape to Motility in Trypanosoma Brucei
    Flagellum couples cell shape to motility in Trypanosoma brucei Stella Y. Suna,b,c, Jason T. Kaelberd, Muyuan Chene, Xiaoduo Dongf, Yasaman Nematbakhshg, Jian Shih, Matthew Doughertye, Chwee Teck Limf,g, Michael F. Schmidc, Wah Chiua,b,c,1, and Cynthia Y. Hef,h,1 aDepartment of Bioengineering, James H. Clark Center, Stanford University, Stanford, CA 94305; bDepartment of Microbiology and Immunology, James H. Clark Center, Stanford University, Stanford, CA 94305; cSLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025; dDepartment of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030; eVerna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030; fMechanobiology Institute, National University of Singapore, Singapore 117411; gDepartment of Mechanical Engineering, National University of Singapore, Singapore 117575; and hDepartment of Biological Sciences, Center for BioImaging Sciences, National University of Singapore, Singapore 117543 Contributed by Wah Chiu, May 17, 2018 (sent for review December 29, 2017; reviewed by Phillipe Bastin and Abraham J. Koster) In the unicellular parasite Trypanosoma brucei, the causative Cryo-electron tomography (cryo-ET) allows us to view 3D agent of human African sleeping sickness, complex swimming be- supramolecular details of biological samples preserved in their havior is driven by a flagellum laterally attached to the long and proper cellular context without chemical fixative and/or metal slender cell body. Using microfluidic assays, we demonstrated that stain. However, samples thicker than 1 μm are not accessible to T. brucei can penetrate through an orifice smaller than its maxi- cryo-ET because at typical accelerating voltages (≤300 kV), few mum diameter.
    [Show full text]
  • Construction and Loss of Bacterial Flagellar Filaments
    biomolecules Review Construction and Loss of Bacterial Flagellar Filaments Xiang-Yu Zhuang and Chien-Jung Lo * Department of Physics and Graduate Institute of Biophysics, National Central University, Taoyuan City 32001, Taiwan; [email protected] * Correspondence: [email protected] Received: 31 July 2020; Accepted: 4 November 2020; Published: 9 November 2020 Abstract: The bacterial flagellar filament is an extracellular tubular protein structure that acts as a propeller for bacterial swimming motility. It is connected to the membrane-anchored rotary bacterial flagellar motor through a short hook. The bacterial flagellar filament consists of approximately 20,000 flagellins and can be several micrometers long. In this article, we reviewed the experimental works and models of flagellar filament construction and the recent findings of flagellar filament ejection during the cell cycle. The length-dependent decay of flagellar filament growth data supports the injection-diffusion model. The decay of flagellar growth rate is due to reduced transportation of long-distance diffusion and jamming. However, the filament is not a permeant structure. Several bacterial species actively abandon their flagella under starvation. Flagellum is disassembled when the rod is broken, resulting in an ejection of the filament with a partial rod and hook. The inner membrane component is then diffused on the membrane before further breakdown. These new findings open a new field of bacterial macro-molecule assembly, disassembly, and signal transduction. Keywords: self-assembly; injection-diffusion model; flagellar ejection 1. Introduction Since Antonie van Leeuwenhoek observed animalcules by using his single-lens microscope in the 18th century, we have entered a new era of microbiology.
    [Show full text]
  • Essential Function of the Alveolin Network in the Subpellicular
    RESEARCH ARTICLE Essential function of the alveolin network in the subpellicular microtubules and conoid assembly in Toxoplasma gondii Nicolo` Tosetti1, Nicolas Dos Santos Pacheco1, Eloı¨se Bertiaux2, Bohumil Maco1, Lore` ne Bournonville2, Virginie Hamel2, Paul Guichard2, Dominique Soldati-Favre1* 1Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland; 2Department of Cell Biology, Sciences III, University of Geneva, Geneva, Switzerland Abstract The coccidian subgroup of Apicomplexa possesses an apical complex harboring a conoid, made of unique tubulin polymer fibers. This enigmatic organelle extrudes in extracellular invasive parasites and is associated to the apical polar ring (APR). The APR serves as microtubule- organizing center for the 22 subpellicular microtubules (SPMTs) that are linked to a patchwork of flattened vesicles, via an intricate network composed of alveolins. Here, we capitalize on ultrastructure expansion microscopy (U-ExM) to localize the Toxoplasma gondii Apical Cap protein 9 (AC9) and its partner AC10, identified by BioID, to the alveolin network and intercalated between the SPMTs. Parasites conditionally depleted in AC9 or AC10 replicate normally but are defective in microneme secretion and fail to invade and egress from infected cells. Electron microscopy revealed that the mature parasite mutants are conoidless, while U-ExM highlighted the disorganization of the SPMTs which likely results in the catastrophic loss of APR and conoid. Introduction *For correspondence: Toxoplasma gondii belongs to the phylum of Apicomplexa that groups numerous parasitic protozo- Dominique.Soldati-Favre@unige. ans causing severe diseases in humans and animals. As part of the superphylum of Alveolata, the ch Apicomplexa are characterized by the presence of the alveoli, which consist in small flattened single- membrane sacs, underlying the plasma membrane (PM) to form the inner membrane complex (IMC) Competing interest: See of the parasite.
    [Show full text]
  • Introduction to Bacteriology and Bacterial Structure/Function
    INTRODUCTION TO BACTERIOLOGY AND BACTERIAL STRUCTURE/FUNCTION LEARNING OBJECTIVES To describe historical landmarks of medical microbiology To describe Koch’s Postulates To describe the characteristic structures and chemical nature of cellular constituents that distinguish eukaryotic and prokaryotic cells To describe chemical, structural, and functional components of the bacterial cytoplasmic and outer membranes, cell wall and surface appendages To name the general structures, and polymers that make up bacterial cell walls To explain the differences between gram negative and gram positive cells To describe the chemical composition, function and serological classification as H antigen of bacterial flagella and how they differ from flagella of eucaryotic cells To describe the chemical composition and function of pili To explain the unique chemical composition of bacterial spores To list medically relevant bacteria that form spores To explain the function of spores in terms of chemical and heat resistance To describe characteristics of different types of membrane transport To describe the exact cellular location and serological classification as O antigen of Lipopolysaccharide (LPS) To explain how the structure of LPS confers antigenic specificity and toxicity To describe the exact cellular location of Lipid A To explain the term endotoxin in terms of its chemical composition and location in bacterial cells INTRODUCTION TO BACTERIOLOGY 1. Two main threads in the history of bacteriology: 1) the natural history of bacteria and 2) the contagious nature of infectious diseases, were united in the latter half of the 19th century. During that period many of the bacteria that cause human disease were identified and characterized. 2. Individual bacteria were first observed microscopically by Antony van Leeuwenhoek at the end of the 17th century.
    [Show full text]
  • Can Protozoa Prove the Beginning of the World?
    Southeastern University FireScholars Classical Conversations Spring 2020 Can Protozoa Prove the Beginning of the World? Karina L. Burton Southeastern University - Lakeland, [email protected] Follow this and additional works at: https://firescholars.seu.edu/ccplus Part of the Cell Biology Commons, and the Evolution Commons Recommended Citation Burton, Karina L., "Can Protozoa Prove the Beginning of the World?" (2020). Classical Conversations. 9. https://firescholars.seu.edu/ccplus/9 This Term Paper is brought to you for free and open access by FireScholars. It has been accepted for inclusion in Classical Conversations by an authorized administrator of FireScholars. For more information, please contact [email protected]. 1 Can Protozoa Prove the Beginning of the World? Karina L. Burton Classical Conversations: Challenge 4; Southeastern University ENGL 1233: English Composition II Grace Veach April 16, 2020 2 Abstract Protozoa are magnificent creatures. They exhibit all of the functions intrinsic to living organisms: irritability, metabolism, growth and reproduction. Within these functions, there are numerous examples of mutations that occur in order for organisms to adapt to their given environments. Irritability is demonstrated in protozoa by their use of pseudopodia, flagella, or cilia for motility; it has been shown that such locomotors exhibit diversity while maintaining similar protein and chemical structures that appear to be a result of evolutionary processes. Metabolism in protozoa is similar to that of larger animals, but their diet is unique. They primarily feast upon bacteria, which have begun mutating to evade easy ingestion and digestion by protozoa, therefore increasing their survival rate and making it necessary for protozoa to adapt.
    [Show full text]
  • Protist Phylogeny and the High-Level Classification of Protozoa
    Europ. J. Protistol. 39, 338–348 (2003) © Urban & Fischer Verlag http://www.urbanfischer.de/journals/ejp Protist phylogeny and the high-level classification of Protozoa Thomas Cavalier-Smith Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK; E-mail: [email protected] Received 1 September 2003; 29 September 2003. Accepted: 29 September 2003 Protist large-scale phylogeny is briefly reviewed and a revised higher classification of the kingdom Pro- tozoa into 11 phyla presented. Complementary gene fusions reveal a fundamental bifurcation among eu- karyotes between two major clades: the ancestrally uniciliate (often unicentriolar) unikonts and the an- cestrally biciliate bikonts, which undergo ciliary transformation by converting a younger anterior cilium into a dissimilar older posterior cilium. Unikonts comprise the ancestrally unikont protozoan phylum Amoebozoa and the opisthokonts (kingdom Animalia, phylum Choanozoa, their sisters or ancestors; and kingdom Fungi). They share a derived triple-gene fusion, absent from bikonts. Bikonts contrastingly share a derived gene fusion between dihydrofolate reductase and thymidylate synthase and include plants and all other protists, comprising the protozoan infrakingdoms Rhizaria [phyla Cercozoa and Re- taria (Radiozoa, Foraminifera)] and Excavata (phyla Loukozoa, Metamonada, Euglenozoa, Percolozoa), plus the kingdom Plantae [Viridaeplantae, Rhodophyta (sisters); Glaucophyta], the chromalveolate clade, and the protozoan phylum Apusozoa (Thecomonadea, Diphylleida). Chromalveolates comprise kingdom Chromista (Cryptista, Heterokonta, Haptophyta) and the protozoan infrakingdom Alveolata [phyla Cilio- phora and Miozoa (= Protalveolata, Dinozoa, Apicomplexa)], which diverged from a common ancestor that enslaved a red alga and evolved novel plastid protein-targeting machinery via the host rough ER and the enslaved algal plasma membrane (periplastid membrane).
    [Show full text]
  • Sexual Development in Plasmodium Parasites: Knowing When It’S Time to Commit
    REVIEWS VECTOR-BORNE DISEASES Sexual development in Plasmodium parasites: knowing when it’s time to commit Gabrielle A. Josling1 and Manuel Llinás1–4 Abstract | Malaria is a devastating infectious disease that is caused by blood-borne apicomplexan parasites of the genus Plasmodium. These pathogens have a complex lifecycle, which includes development in the anopheline mosquito vector and in the liver and red blood cells of mammalian hosts, a process which takes days to weeks, depending on the Plasmodium species. Productive transmission between the mammalian host and the mosquito requires transitioning between asexual and sexual forms of the parasite. Blood- stage parasites replicate cyclically and are mostly asexual, although a small fraction of these convert into male and female sexual forms (gametocytes) in each reproductive cycle. Despite many years of investigation, the molecular processes that elicit sexual differentiation have remained largely unknown. In this Review, we highlight several important recent discoveries that have identified epigenetic factors and specific transcriptional regulators of gametocyte commitment and development, providing crucial insights into this obligate cellular differentiation process. Trophozoite Malaria affects almost 200 million people worldwide and viewed under the microscope, it resembles a flat disc. 1 A highly metabolically active and causes 584,000 deaths annually ; thus, developing a After the ring stage, the parasite rounds up as it enters the asexual form of the malaria better understanding of the mechanisms that drive the trophozoite stage, in which it is far more metabolically parasite that forms during development of the transmissible form of the malaria active and expresses surface antigens for cytoadhesion. the intra‑erythrocytic developmental cycle following parasite is a matter of urgency.
    [Show full text]
  • Shrinking Through Cilia-Induced Self-Eating
    RESEARCH HIGHLIGHTS Nature Reviews Molecular Cell Biology | Published online 22 Jun 2016 IN BRIEF SMALL RNAS New microRNA-like molecules Hansen et al. describe a new class of short regulatory RNAs, which associate with Argonaute (AGO) proteins and derive from short introns, hence are termed agotrons. The authors annotated 87 agotrons in human and 18 in mouse, and found that they are conserved across mammalian species. Agotrons are ~80–100 nucleotides long, CG-rich and potentially form strong secondary structures. Vectors encoding three different agotrons (and their flanking exons) were transfected into human cells; the agotrons were expressed but were almost undetectable without co-expression of AGO1 or AGO2, indicating that AGO proteins stabilize spliced agotrons. Similarly to microRNAs, agotrons suppressed the expression of reporter transcripts based on seed-mediated complementarity, but their biogenesis is independent of Dicer: they associate with AGO as spliced but otherwise unprocessed introns. Agotrons potentially have a limited target repertoire compared with microRNAs but are possibly less prone to off-target effects. ORIGINAL ARTICLE Hansen, T. B. et al. Argonaute-associated short introns are a novel class of gene regulators. Nat. Commun. 7, 11538 (2016) AUTOPHAGY Shrinking through cilia-induced self-eating Epithelial cells of the kidney proximal tubules, which reabsorb water and nutrients from the forming urine, shrink in response to fluid flow through mechanisms that involve mechanosensing by primary cilia. Orhon et al. demonstrated that the application of fluid flow induced autophagy in cultured mammalian kidney epithelial cells. This autophagic response to flow depended on the presence of functional cilia and was necessary for cell shrinkage.
    [Show full text]