1
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Moran AL, Louzao-Martinez L, Norris DP, Peters DJM, Blacque OE. Transport and barrier mechanisms that regulate ciliary compartmentalization and ciliopathies. Nat Rev Nephrol 2024; 20:83-100. [PMID: 37872350 DOI: 10.1038/s41581-023-00773-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/19/2023] [Indexed: 10/25/2023]
Abstract
Primary cilia act as cell surface antennae, coordinating cellular responses to sensory inputs and signalling molecules that regulate developmental and homeostatic pathways. Cilia are therefore critical to physiological processes, and defects in ciliary components are associated with a large group of inherited pleiotropic disorders - known collectively as ciliopathies - that have a broad spectrum of phenotypes and affect many or most tissues, including the kidney. A central feature of the cilium is its compartmentalized structure, which imparts its unique molecular composition and signalling environment despite its membrane and cytosol being contiguous with those of the cell. Such compartmentalization is achieved via active transport pathways that bring protein cargoes to and from the cilium, as well as gating pathways at the ciliary base that establish diffusion barriers to protein exchange into and out of the organelle. Many ciliopathy-linked proteins, including those involved in kidney development and homeostasis, are components of the compartmentalizing machinery. New insights into the major compartmentalizing pathways at the cilium, namely, ciliary gating, intraflagellar transport, lipidated protein flagellar transport and ciliary extracellular vesicle release pathways, have improved our understanding of the mechanisms that underpin ciliary disease and associated renal disorders.
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Affiliation(s)
- Ailis L Moran
- School of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
| | - Laura Louzao-Martinez
- Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | | | - Dorien J M Peters
- Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands.
| | - Oliver E Blacque
- School of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland.
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2
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Li L, Ran J. Regulation of ciliary homeostasis by intraflagellar transport-independent kinesins. Cell Death Dis 2024; 15:47. [PMID: 38218748 PMCID: PMC10787775 DOI: 10.1038/s41419-024-06428-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2023] [Revised: 12/20/2023] [Accepted: 01/02/2024] [Indexed: 01/15/2024]
Abstract
Cilia are highly conserved eukaryotic organelles that protrude from the cell surface and are involved in sensory perception, motility, and signaling. Their proper assembly and function rely on the bidirectional intraflagellar transport (IFT) system, which involves motor proteins, including antegrade kinesins and retrograde dynein. Although the role of IFT-mediated transport in cilia has been extensively studied, recent research has highlighted the contribution of IFT-independent kinesins in ciliary processes. The coordinated activities and interplay between IFT kinesins and IFT-independent kinesins are crucial for maintaining ciliary homeostasis. In this comprehensive review, we aim to delve into the specific contributions and mechanisms of action of the IFT-independent kinesins in cilia. By shedding light on their involvement, we hope to gain a more holistic perspective on ciliogenesis and ciliopathies.
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Affiliation(s)
- Lin Li
- Center for Cell Structure and Function, Shandong Provincial Key Laboratory of Animal Resistance Biology, College of Life Sciences, Shandong Normal University, Jinan, 250014, China
| | - Jie Ran
- Center for Cell Structure and Function, Shandong Provincial Key Laboratory of Animal Resistance Biology, College of Life Sciences, Shandong Normal University, Jinan, 250014, China.
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3
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Dougherty LL, Avasthi P. Determinants of cytoplasmic microtubule depolymerization during ciliogenesis in Chlamydomonas. Life Sci Alliance 2024; 7:e202302287. [PMID: 37813489 PMCID: PMC10561824 DOI: 10.26508/lsa.202302287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2023] [Revised: 09/29/2023] [Accepted: 10/03/2023] [Indexed: 10/12/2023] Open
Abstract
At the core of cilia are microtubules which establish length and assist ciliary assembly and disassembly; however, microtubules outside of the cilium can regulate ciliogenesis. The microtubule cytoskeleton polymerizes and depolymerizes rapidly. These processes have been studied across various organisms with chemical and genetic perturbations. However, these have generated conflicting data in terms of the role of cytoplasmic microtubules (CytoMTs) and free tubulin dynamics during ciliogenesis. Here, we look at the relationship between ciliogenesis and CytoMT dynamics in Chlamydomonas reinhardtii using chemical and mechanical perturbations. We find that not only can stabilized CytoMTs allow for normal ciliary assembly, but high calcium concentrations and low pH-induced deciliation cause CytoMTs to depolymerize separately from ciliary shedding. In addition, ciliary shedding through mechanical shearing allows cilia to regenerate earlier despite intact CytoMTs. Our data suggest that CytoMTs are not a sink for a limiting pool of cytoplasmic tubulin in Chlamydomonas, depolymerization after deciliation is a consequence rather than a requirement for ciliogenesis, and intact tubulin in the cytoplasm and proximal cilium support more efficient ciliary assembly.
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Affiliation(s)
- Larissa L Dougherty
- Biochemistry and Cell Biology Department, Geisel School of Medicine at Dartmouth College, Hanover, NH, USA
| | - Prachee Avasthi
- Biochemistry and Cell Biology Department, Geisel School of Medicine at Dartmouth College, Hanover, NH, USA
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4
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Bigge BM, Rosenthal NE, Avasthi P. Initial ciliary assembly in Chlamydomonas requires Arp2/3 complex-dependent endocytosis. Mol Biol Cell 2023; 34:ar24. [PMID: 36753382 PMCID: PMC10092647 DOI: 10.1091/mbc.e22-09-0443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023] Open
Abstract
Ciliary assembly, trafficking, and regulation are dependent on microtubules, but the mechanisms of ciliary assembly also require the actin cytoskeleton. Here, we dissect subcellular roles of actin in ciliogenesis by focusing on actin networks nucleated by the Arp2/3 complex in the powerful ciliary model, Chlamydomonas. We find that the Arp2/3 complex is required for the initial stages of ciliary assembly when protein and membrane are in high demand but cannot yet be supplied from the Golgi complex. We provide evidence for Arp2/3 complex-dependent endocytosis of ciliary proteins, an increase in endocytic activity upon induction of ciliary growth, and relocalization of plasma membrane proteins to newly formed cilia.
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Affiliation(s)
- Brae M Bigge
- Biochemistry and Cell Biology Department, Geisel School of Medicine at Dartmouth College, Hanover, NH 03755; Anatomy and Cell Biology Department, University of Kansas Medical Center, Kansas City, KS 66103
| | - Nicholas E Rosenthal
- Biochemistry and Cell Biology Department, Geisel School of Medicine at Dartmouth College, Hanover, NH 03755; Anatomy and Cell Biology Department, University of Kansas Medical Center, Kansas City, KS 66103
| | - Prachee Avasthi
- Biochemistry and Cell Biology Department, Geisel School of Medicine at Dartmouth College, Hanover, NH 03755; Anatomy and Cell Biology Department, University of Kansas Medical Center, Kansas City, KS 66103
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5
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Abstract
The assembly and maintenance of most cilia and eukaryotic flagella depends on intraflagellar transport (IFT), the bidirectional movement of multi-megadalton IFT trains along the axonemal microtubules. These IFT trains function as carriers, moving ciliary proteins between the cell body and the organelle. Whereas tubulin, the principal protein of cilia, binds directly to IFT particle proteins, the transport of other ciliary proteins and complexes requires adapters that link them to the trains. Large axonemal substructures, such as radial spokes, outer dynein arms and inner dynein arms, assemble in the cell body before attaching to IFT trains, using the adapters ARMC2, ODA16 and IDA3, respectively. Ciliary import of several membrane proteins involves the putative adapter tubby-like protein 3 (TULP3), whereas membrane protein export involves the BBSome, an octameric complex that co-migrates with IFT particles. Thus, cells employ a variety of adapters, each of which is substoichiometric to the core IFT machinery, to expand the cargo range of the IFT trains. This Review summarizes the individual and shared features of the known cargo adapters and discusses their possible role in regulating the transport capacity of the IFT pathway.
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Affiliation(s)
- Karl Lechtreck
- Department of Cellular Biology, University of Georgia, Athens, GA 30602, USA
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6
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Clupper M, Gill R, Elsayyid M, Touroutine D, Caplan JL, Tanis JE. Kinesin-2 motors differentially impact biogenesis of extracellular vesicle subpopulations shed from sensory cilia. iScience 2022; 25:105262. [PMID: 36304122 PMCID: PMC9593189 DOI: 10.1016/j.isci.2022.105262] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2022] [Revised: 07/13/2022] [Accepted: 09/26/2022] [Indexed: 01/21/2023] Open
Abstract
Extracellular vesicles (EVs) are bioactive lipid-bilayer enclosed particles released from nearly all cells. One specialized site for EV shedding is the primary cilium. Here, we discover the conserved ion channel CLHM-1 as a ciliary EV cargo. Imaging of EVs released from sensory neuron cilia of Caenorhabditis elegans expressing fluorescently tagged CLHM-1 and TRP polycystin-2 channel PKD-2 shows enrichment of these cargoes in distinct EV subpopulations that are differentially shed in response to mating partner availability. PKD-2 alone is present in EVs shed from the cilium distal tip, whereas CLHM-1 EVs bud from a secondary site(s), including the ciliary base. Heterotrimeric and homodimeric kinesin-2 motors have discrete impacts on PKD-2 and CLHM-1 colocalization in both cilia and EVs. Total loss of kinesin-2 activity decreases shedding of PKD-2 but not CLHM-1 EVs. Our data demonstrate that anterograde intraflagellar transport is required for selective enrichment of protein cargoes into heterogeneous EVs with different signaling potentials.
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Affiliation(s)
- Michael Clupper
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Rachael Gill
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Malek Elsayyid
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Denis Touroutine
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Jeffrey L. Caplan
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
- Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716, USA
| | - Jessica E. Tanis
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
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7
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Hibbard JVK, Vázquez N, Wallingford JB. Cilia proteins getting to work - how do they commute from the cytoplasm to the base of cilia? J Cell Sci 2022; 135:jcs259444. [PMID: 36073764 PMCID: PMC9482345 DOI: 10.1242/jcs.259444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cilia are multifunctional organelles that originated with the last eukaryotic common ancestor and play central roles in the life cycles of diverse organisms. The motile flagella that move single cells like sperm or unicellular organisms, the motile cilia on animal multiciliated cells that generate fluid flow in organs, and the immotile primary cilia that decorate nearly all cells in animals share many protein components in common, yet each also requires specialized proteins to perform their specialized functions. Despite a now-advanced understanding of how such proteins are transported within cilia, we still know very little about how they are transported from their sites of synthesis through the cytoplasm to the ciliary base. Here, we review the literature concerning this underappreciated topic in ciliary cell biology. We discuss both general mechanisms, as well as specific examples of motor-driven active transport and passive transport via diffusion-and-capture. We then provide deeper discussion of specific, illustrative examples, such as the diverse array of protein subunits that together comprise the intraflagellar transport (IFT) system and the multi-protein axonemal dynein motors that drive beating of motile cilia. We hope this Review will spur further work, shedding light not only on ciliogenesis and ciliary signaling, but also on intracellular transport in general.
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Affiliation(s)
| | | | - John B. Wallingford
- Department of Molecular Biosciences, University of Texas, Austin, TX 78751, USA
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8
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Awasthi M, Ranjan P, Kelterborn S, Hegemann P, Snell WJ. A cytoplasmic protein kinase couples engagement of Chlamydomonas ciliary receptors to cAMP-dependent cellular responses. J Cell Sci 2022; 135:275490. [PMID: 35502650 DOI: 10.1242/jcs.259814] [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: 01/26/2022] [Accepted: 04/25/2022] [Indexed: 11/20/2022] Open
Abstract
The primary cilium is a cellular compartment specialized for receipt of extracellular signals essential for development and homeostasis. Although intraciliary responses to engagement of ciliary receptors are well studied, fundamental questions remain about the mechanisms and molecules that transduce ciliary signals into responses in the cytoplasm. During fertilization in the bi-ciliated alga Chlamydomonas reinhardtii, ciliary adhesion between plus and minus gametes triggers an immediate ∼10-fold increase in cellular cAMP and consequent responses in the cytoplasm required for cell-cell fusion. Here, we identify a new participant in ciliary signaling, Gamete-Specific Protein Kinase (GSPK). GSPK is essential for the adhesion-induced cAMP increase and for rapid gamete fusion. The protein is in the cytoplasm and the entire cellular complement responds to a signal from the cilium by becoming phosphorylated within 1 minute after ciliary receptor engagement. Unlike all other cytoplasmic events in ciliary signaling, GSPK phosphorylation is not responsive to exogenously added cAMP. Thus, during ciliary signaling in Chlamydomonas, a cytoplasmic protein is required to rapidly interpret a still uncharacterized ciliary signal to generate a cytoplasmic response.
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Affiliation(s)
- Mayanka Awasthi
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD, USA
| | - Peeyush Ranjan
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD, USA
| | - Simon Kelterborn
- Experimental Biophysics, Institute for Biology, Humboldt-Universität zu Berlin, Berlin, Germany.,Charité - Universitätsmedizin Berlin, Institute of Translational Physiology, Berlin, Germany
| | - Peter Hegemann
- Experimental Biophysics, Institute for Biology, Humboldt-Universität zu Berlin, Berlin, Germany
| | - William J Snell
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD, USA
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9
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Pinello JF, Liu Y, Snell WJ. MAR1 links membrane adhesion to membrane merger during cell-cell fusion in Chlamydomonas. Dev Cell 2021; 56:3380-3392.e9. [PMID: 34813735 DOI: 10.1016/j.devcel.2021.10.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2021] [Revised: 09/22/2021] [Accepted: 10/28/2021] [Indexed: 01/17/2023]
Abstract
Union of two gametes to form a zygote is a defining event in the life of sexual eukaryotes, yet the mechanisms that underlie cell-cell fusion during fertilization remain poorly characterized. Here, in studies of fertilization in the green alga, Chlamydomonas, we report identification of a membrane protein on minus gametes, Minus Adhesion Receptor 1 (MAR1), that is essential for the membrane attachment with plus gametes that immediately precedes lipid bilayer merger. We show that MAR1 forms a receptor pair with previously identified receptor FUS1 on plus gametes, whose ectodomain architecture we find is identical to a sperm adhesion protein conserved throughout plant lineages. Strikingly, before fusion, MAR1 is biochemically and functionally associated with the ancient, evolutionarily conserved eukaryotic Class II fusion protein HAP2 on minus gametes. Thus, the integral membrane protein MAR1 provides a molecular link between membrane adhesion and bilayer merger during fertilization in Chlamydomonas.
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Affiliation(s)
- Jennifer F Pinello
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA
| | - Yanjie Liu
- Department of Cell Biology, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390-9039, USA
| | - William J Snell
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.
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10
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Establishing and regulating the composition of cilia for signal transduction. Nat Rev Mol Cell Biol 2020; 20:389-405. [PMID: 30948801 DOI: 10.1038/s41580-019-0116-4] [Citation(s) in RCA: 226] [Impact Index Per Article: 56.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The primary cilium is a hair-like surface-exposed organelle of the eukaryotic cell that decodes a variety of signals - such as odorants, light and Hedgehog morphogens - by altering the local concentrations and activities of signalling proteins. Signalling within the cilium is conveyed through a diverse array of second messengers, including conventional signalling molecules (such as cAMP) and some unusual intermediates (such as sterols). Diffusion barriers at the ciliary base establish the unique composition of this signalling compartment, and cilia adapt their proteome to signalling demands through regulated protein trafficking. Much progress has been made on the molecular understanding of regulated ciliary trafficking, which encompasses not only exchanges between the cilium and the rest of the cell but also the shedding of signalling factors into extracellular vesicles.
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11
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Craig EW, Mueller DM, Bigge BM, Schaffer M, Engel BD, Avasthi P. The elusive actin cytoskeleton of a green alga expressing both conventional and divergent actins. Mol Biol Cell 2019; 30:2827-2837. [PMID: 31532705 PMCID: PMC6789165 DOI: 10.1091/mbc.e19-03-0141] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Revised: 09/06/2019] [Accepted: 09/10/2019] [Indexed: 12/13/2022] Open
Abstract
The green alga Chlamydomonas reinhardtii is a leading model system to study photosynthesis, cilia, and the generation of biological products. The cytoskeleton plays important roles in all of these cellular processes, but to date, the filamentous actin network within Chlamydomonas has remained elusive. By optimizing labeling conditions, we can now visualize distinct linear actin filaments at the posterior of the nucleus in both live and fixed vegetative cells. Using in situ cryo-electron tomography, we confirmed this localization by directly imaging actin filaments within the native cellular environment. The fluorescently labeled structures are sensitive to the depolymerizing agent latrunculin B (Lat B), demonstrating the specificity of our optimized labeling method. Interestingly, Lat B treatment resulted in the formation of a transient ring-like filamentous actin structure around the nucleus. The assembly of this perinuclear ring is dependent upon a second actin isoform, NAP1, which is strongly up-regulated upon Lat B treatment and is insensitive to Lat B-induced depolymerization. Our study combines orthogonal strategies to provide the first detailed visual characterization of filamentous actins in Chlamydomonas, allowing insights into the coordinated functions of two actin isoforms expressed within the same cell.
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Affiliation(s)
- Evan W. Craig
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS 66160
| | - David M. Mueller
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS 66160
| | - Brae M. Bigge
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS 66160
| | - Miroslava Schaffer
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Benjamin D. Engel
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Prachee Avasthi
- Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS 66160
- Department of Ophthalmology, University of Kansas Medical Center, Kansas City, KS 66160
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12
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Ranjan P, Awasthi M, Snell WJ. Transient Internalization and Microtubule-Dependent Trafficking of a Ciliary Signaling Receptor from the Plasma Membrane to the Cilium. Curr Biol 2019; 29:2942-2947.e2. [PMID: 31422889 DOI: 10.1016/j.cub.2019.07.022] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Revised: 07/03/2019] [Accepted: 07/09/2019] [Indexed: 12/24/2022]
Abstract
Cilia are ancient organelles used by unicellular and multicellular organisms not only for motility but also to receive and respond to multiple environmental cues, including light, odorants, morphogens, growth factors, and contact with cilia of other cells. Much is known about the cellular mechanisms that deliver membrane proteins to cilia during ciliogenesis. Execution of a ciliary signaling pathway, however, can critically depend on rapid alterations in the receptor composition of the cilium itself, and our understanding of the mechanisms that underlie these rapid, regulated alterations remains limited [1-6]. In the bi-ciliated, unicellular alga Chlamydomonas reinhardtii, interactions between cilia of mating type plus and mating type minus gametes mediated by adhesion receptors SAG1 and SAD1 activate a ciliary signaling pathway [7]. In response, a large, inactive pool of SAG1 on the plasma membrane of plus gametes rapidly becomes enriched in the peri-ciliary membrane and enters the cilia to become active and maintain and enhance ciliary adhesion and signaling [8-14]. Ciliary entry per se of SAG1 is independent of anterograde intraflagellar transport (IFT) [13], but the rapid apical enrichment requires cytoplasmic microtubules and the retrograde IFT motor, dynein 1b [14]. Whether the receptors move laterally within the plasma membrane or transit internally during redistribution is unknown. Here, in coupled immunolocalization/biochemical studies on SAG1, we show that, within minutes after gamete activation is initiated, cell-surface SAG1 is internalized, associates with an apico-basally polarized array of cytoplasmic microtubules, and returns to the cell surface at a peri-ciliary staging area for entry into cilia.
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Affiliation(s)
- Peeyush Ranjan
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA
| | - Mayanka Awasthi
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA
| | - William J Snell
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.
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13
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Pala R, Mohieldin AM, Sherpa RT, Kathem SH, Shamloo K, Luan Z, Zhou J, Zheng JG, Ahsan A, Nauli SM. Ciliotherapy: Remote Control of Primary Cilia Movement and Function by Magnetic Nanoparticles. ACS NANO 2019; 13:3555-3572. [PMID: 30860808 PMCID: PMC7899146 DOI: 10.1021/acsnano.9b00033] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Patients with polycystic kidney disease (PKD) are characterized with uncontrolled hypertension. Hypertension in PKD is a ciliopathy, an abnormal function and/or structure of primary cilia. Primary cilia are cellular organelles with chemo and mechanosensory roles. In the present studies, we designed a cilia-targeted (CT) delivery system to deliver fenoldopam specifically to the primary cilia. We devised the iron oxide nanoparticle (NP)-based technology for ciliotherapy. Live imaging confirmed that the CT-Fe2O3-NPs specifically targeted primary cilia in cultured cells in vitro and vascular endothelia in vivo. Importantly, the CT-Fe2O3-NPs enabled the remote control of the movement and function of a cilium with an external magnetic field, making the nonmotile cilium exhibit passive movement. The ciliopathic hearts displayed hypertrophy with compromised functions in left ventricle pressure, stroke volume, ejection fraction, and overall cardiac output because of prolonged hypertension. The CT-Fe2O3-NPs significantly improved cardiac function in the ciliopathic hypertensive models, in which the hearts also exhibited arrhythmia, which was corrected with the CT-Fe2O3-NPs. Intraciliary and cytosolic Ca2+ were increased when cilia were induced with fluid flow or magnetic field, and this served as a cilia-dependent mechanism of the CT-Fe2O3-NPs. Fenoldopam-alone caused an immediate decrease in blood pressure, followed by reflex tachycardia. Pharmacological delivery profiles confirmed that the CT-Fe2O3-NPs were a superior delivery system for targeting cilia more specifically, efficiently, and effectively than fenoldopam-alone. The CT-Fe2O3-NPs altered the mechanical properties of nonmotile cilia, and these nano-biomaterials had enormous clinical potential for ciliotherapy. Our studies further indicated that ciliotherapy provides a possibility toward personalized medicine in ciliopathy patients.
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Affiliation(s)
- Rajasekharreddy Pala
- Department of Biomedical & Pharmaceutical Sciences, Chapman University School of Pharmacy (CUSP), Harry and Diane Rinker Health Science Campus, Chapman University, Irvine, California 92618, United States
- Department of Medicine, University of California Irvine, Irvine, California 92868, United States
| | - Ashraf M. Mohieldin
- Department of Biomedical & Pharmaceutical Sciences, Chapman University School of Pharmacy (CUSP), Harry and Diane Rinker Health Science Campus, Chapman University, Irvine, California 92618, United States
- Department of Medicine, University of California Irvine, Irvine, California 92868, United States
| | - Rinzhin T. Sherpa
- Department of Biomedical & Pharmaceutical Sciences, Chapman University School of Pharmacy (CUSP), Harry and Diane Rinker Health Science Campus, Chapman University, Irvine, California 92618, United States
- Department of Medicine, University of California Irvine, Irvine, California 92868, United States
| | - Sarmed H. Kathem
- Department of Biomedical & Pharmaceutical Sciences, Chapman University School of Pharmacy (CUSP), Harry and Diane Rinker Health Science Campus, Chapman University, Irvine, California 92618, United States
- Department of Medicine, University of California Irvine, Irvine, California 92868, United States
| | - Kiumars Shamloo
- Department of Biomedical & Pharmaceutical Sciences, Chapman University School of Pharmacy (CUSP), Harry and Diane Rinker Health Science Campus, Chapman University, Irvine, California 92618, United States
- Department of Medicine, University of California Irvine, Irvine, California 92868, United States
| | - Zhongyue Luan
- Chemical Engineering & Material Sciences, University of California Irvine, Irvine, California 92697, United States
| | - Jing Zhou
- Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115, United States
| | - Jian-Guo Zheng
- Irvine Materials Research Institute, University of California Irvine, Irvine, California 92697, United States
| | - Amir Ahsan
- Department of Physics, Computer Science & Engineering, Chapman University, Orange, California 92866, United States
| | - Surya M. Nauli
- Department of Biomedical & Pharmaceutical Sciences, Chapman University School of Pharmacy (CUSP), Harry and Diane Rinker Health Science Campus, Chapman University, Irvine, California 92618, United States
- Department of Medicine, University of California Irvine, Irvine, California 92868, United States
- Corresponding Author: ; . (S.M.N.)
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14
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Bloodgood RA, Tetreault J, Sloboda RD. The flagellar membrane glycoprotein FMG-1B Is necessary for expression of force at the flagellar surface. J Cell Sci 2019; 132:jcs.233429. [DOI: 10.1242/jcs.233429] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Accepted: 07/23/2019] [Indexed: 12/11/2022] Open
Abstract
In addition to bend propagation for swimming, Chlamydomonas cells use their flagella to glide along a surface. When polystyrene microspheres are added to cells, they attach to and move along the flagellar surface, thus serving as a proxy for gliding that can be used to assay for the flagellar components required for gliding motility. Gliding and microsphere movement are dependent on intraflagellar transport (IFT). Circumstantial evidence suggests that mechanical coupling of the IFT force-transducing machinery to a substrate is mediated by the flagellar transmembrane glycoprotein FMG-1B. Cells carrying an insertion in the 5’-UTR of the FMG-1B gene lack FMG-1B protein, yet assemble normal length flagella despite the loss of the major protein component of the flagellar membrane. Transmission electron microscopy shows a complete loss of the glycocalyx normally observed on the flagellar surface, suggesting it is composed of the ectodomains of FMG-1B molecules. Microsphere movements and gliding motility are also greatly reduced in the 5’-UTR mutant. Together, these data provide the first rigorous demonstration that FMG-1B is necessary for the normal expression of force at the flagellar surface in Chlamydomonas.
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Affiliation(s)
- Robert A. Bloodgood
- Department of Cell Biology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Joseph Tetreault
- Department of Biological Sciences, Dartmouth College, Hanover, NH 03750, USA
| | - Roger D. Sloboda
- Department of Biological Sciences, Dartmouth College, Hanover, NH 03750, USA
- The Marine Biological Laboratory, Woods Hole, MA 02543, USA
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15
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Morthorst SK, Christensen ST, Pedersen LB. Regulation of ciliary membrane protein trafficking and signalling by kinesin motor proteins. FEBS J 2018; 285:4535-4564. [PMID: 29894023 DOI: 10.1111/febs.14583] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Revised: 05/09/2018] [Accepted: 06/11/2018] [Indexed: 12/14/2022]
Abstract
Primary cilia are antenna-like sensory organelles that regulate a substantial number of cellular signalling pathways in vertebrates, both during embryonic development as well as in adulthood, and mutations in genes coding for ciliary proteins are causative of an expanding group of pleiotropic diseases known as ciliopathies. Cilia consist of a microtubule-based axoneme core, which is subtended by a basal body and covered by a bilayer lipid membrane of unique protein and lipid composition. Cilia are dynamic organelles, and the ability of cells to regulate ciliary protein and lipid content in response to specific cellular and environmental cues is crucial for balancing ciliary signalling output. Here we discuss mechanisms involved in regulation of ciliary membrane protein trafficking and signalling, with main focus on kinesin-2 and kinesin-3 family members.
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16
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Nachury MV. The molecular machines that traffic signaling receptors into and out of cilia. Curr Opin Cell Biol 2018; 51:124-131. [PMID: 29579578 PMCID: PMC5949257 DOI: 10.1016/j.ceb.2018.03.004] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Revised: 03/06/2018] [Accepted: 03/08/2018] [Indexed: 12/12/2022]
Abstract
Cilia are surface-exposed organelles that dynamically concentrate signaling molecules to organize sensory, developmental and homeostatic pathways. Entry and exit of signaling receptors is germane to the processing of signals and the molecular machines for entry and exit have started to emerge. The IFT-A complex and its membrane recruitment factor Tulp3 complex promotes the entry of signaling receptors into cilia while the BBSome and its membrane recruitment factor Arl6GTP ferry activated signaling receptors out of cilia. Ciliary exit is a surprisingly complex process entailing passage through a first diffusion barrier at the transition zone, diffusion inside an intermediate compartment and crossing of a periciliary diffusion barrier. The two barriers may organize a privileged compartment where activated signaling receptors transiently reside.
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Affiliation(s)
- Maxence V Nachury
- UCSF School of Medicine, Department of Ophthalmology, United States.
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17
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Gong F, Wang J, Li J. Isolation and characterization of peroxiredoxin 1 gene of Dunaliella salina. Gene 2017; 635:39-45. [DOI: 10.1016/j.gene.2017.09.018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 08/05/2017] [Accepted: 09/08/2017] [Indexed: 10/18/2022]
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18
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Mukhopadhyay S, Badgandi HB, Hwang SH, Somatilaka B, Shimada IS, Pal K. Trafficking to the primary cilium membrane. Mol Biol Cell 2017; 28:233-239. [PMID: 28082521 PMCID: PMC5231892 DOI: 10.1091/mbc.e16-07-0505] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 11/14/2016] [Accepted: 11/15/2016] [Indexed: 12/13/2022] Open
Abstract
The primary cilium has been found to be associated with a number of cellular signaling pathways, such as vertebrate hedgehog signaling, and implicated in the pathogenesis of diseases affecting multiple organs, including the neural tube, kidney, and brain. The primary cilium is the site where a subset of the cell's membrane proteins is enriched. However, pathways that target and concentrate membrane proteins in cilia are not well understood. Processes determining the level of proteins in the ciliary membrane include entry into the compartment, removal, and retention by diffusion barriers such as the transition zone. Proteins that are concentrated in the ciliary membrane are also localized to other cellular sites. Thus it is critical to determine the particular role for ciliary compartmentalization in sensory reception and signaling pathways. Here we provide a brief overview of our current understanding of compartmentalization of proteins in the ciliary membrane and the dynamics of trafficking into and out of the cilium. We also discuss major unanswered questions regarding the role that defects in ciliary compartmentalization might play in disease pathogenesis. Understanding the trafficking mechanisms that underlie the role of ciliary compartmentalization in signaling might provide unique approaches for intervention in progressive ciliopathies.
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Affiliation(s)
- Saikat Mukhopadhyay
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, TX 75390
| | - Hemant B Badgandi
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, TX 75390
| | - Sun-Hee Hwang
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, TX 75390
| | | | - Issei S Shimada
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, TX 75390
| | - Kasturi Pal
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, TX 75390
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19
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The Ancient Gamete Fusogen HAP2 Is a Eukaryotic Class II Fusion Protein. Cell 2017; 168:904-915.e10. [PMID: 28235200 PMCID: PMC5332557 DOI: 10.1016/j.cell.2017.01.024] [Citation(s) in RCA: 120] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Revised: 01/03/2017] [Accepted: 01/19/2017] [Indexed: 02/01/2023]
Abstract
Sexual reproduction is almost universal in eukaryotic life and involves the fusion of male and female haploid gametes into a diploid cell. The sperm-restricted single-pass transmembrane protein HAP2-GCS1 has been postulated to function in membrane merger. Its presence in the major eukaryotic taxa—animals, plants, and protists (including important human pathogens like Plasmodium)—suggests that many eukaryotic organisms share a common gamete fusion mechanism. Here, we report combined bioinformatic, biochemical, mutational, and X-ray crystallographic studies on the unicellular alga Chlamydomonas reinhardtii HAP2 that reveal homology to class II viral membrane fusion proteins. We further show that targeting the segment corresponding to the fusion loop by mutagenesis or by antibodies blocks gamete fusion. These results demonstrate that HAP2 is the gamete fusogen and suggest a mechanism of action akin to viral fusion, indicating a way to block Plasmodium transmission and highlighting the impact of virus-cell genetic exchanges on the evolution of eukaryotic life. The primordial gamete fusogen HAP2 exhibits homology to class II viral fusion proteins HAP2 inserts into the target gamete membrane via a hydrophobic fusion loop HAP2 links virus entry into target cells and the origins of sexual reproduction HAP2 is a sex-specific target for blocking fertilization in multiple kingdoms
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20
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Lechtreck KF, Van De Weghe JC, Harris JA, Liu P. Protein transport in growing and steady-state cilia. Traffic 2017; 18:277-286. [PMID: 28248449 DOI: 10.1111/tra.12474] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 02/22/2017] [Accepted: 02/22/2017] [Indexed: 12/18/2022]
Abstract
Cilia and eukaryotic flagella are threadlike cell extensions with motile and sensory functions. Their assembly requires intraflagellar transport (IFT), a bidirectional motor-driven transport of protein carriers along the axonemal microtubules. IFT moves ample amounts of structural proteins including tubulin into growing cilia likely explaining its critical role for assembly. IFT continues in non-growing cilia contributing to a variety of processes ranging from axonemal maintenance and the export of non-ciliary proteins to cell locomotion and ciliary signaling. Here, we discuss recent data on cues regulating the type, amount and timing of cargo transported by IFT. A regulation of IFT-cargo interactions is critical to establish, maintain and adjust ciliary length, protein composition and function.
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Affiliation(s)
- Karl F Lechtreck
- Department of Cellular Biology, University of Georgia, Athens, Georgia
| | | | | | - Peiwei Liu
- Department of Cellular Biology, University of Georgia, Athens, Georgia
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21
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KIF13B establishes a CAV1-enriched microdomain at the ciliary transition zone to promote Sonic hedgehog signalling. Nat Commun 2017; 8:14177. [PMID: 28134340 PMCID: PMC5290278 DOI: 10.1038/ncomms14177] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 12/06/2016] [Indexed: 12/20/2022] Open
Abstract
Ciliary membrane composition is controlled by transition zone (TZ) proteins such as RPGRIP1, RPGRIPL and NPHP4, which are vital for balanced coordination of diverse signalling systems like the Sonic hedgehog (Shh) pathway. Activation of this pathway involves Shh-induced ciliary accumulation of Smoothened (SMO), which is disrupted by disease-causing mutations in TZ components. Here we identify kinesin-3 motor protein KIF13B as a novel member of the RPGRIP1N-C2 domain-containing protein family and show that KIF13B regulates TZ membrane composition and ciliary SMO accumulation. KIF13B is upregulated during ciliogenesis and is recruited to the ciliary base by NPHP4, which binds to two distinct sites in the KIF13B tail region, including an RPGRIP1N-C2 domain. KIF13B and NPHP4 are both essential for establishment of a CAV1 membrane microdomain at the TZ, which in turn is required for Shh-induced ciliary SMO accumulation. Thus KIF13B is a novel regulator of ciliary TZ configuration, membrane composition and Shh signalling.
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22
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Park J, Lee N, Kavoussi A, Seo JT, Kim CH, Moon SJ. Ciliary Phosphoinositide Regulates Ciliary Protein Trafficking in Drosophila. Cell Rep 2016; 13:2808-16. [PMID: 26723017 DOI: 10.1016/j.celrep.2015.12.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Revised: 11/16/2015] [Accepted: 11/25/2015] [Indexed: 10/22/2022] Open
Abstract
Cilia are highly specialized antennae-like cellular organelles. Inositol polyphosphate 5-phosphatase E (INPP5E) converts PI(4,5)P2 into PI4P and is required for proper ciliary function. Although Inpp5e mutations are associated with ciliopathies in humans and mice, the precise molecular role INPP5E plays in cilia remains unclear. Here, we report that Drosophila INPP5E (dINPP5E) regulates ciliary protein trafficking by controlling the phosphoinositide composition of ciliary membranes. Mutations in dInpp5e lead to hearing deficits due to the mislocalization of dTULP and mechanotransduction channels, Inactive and NOMPC, in chordotonal cilia. Both loss of dINPP5E and ectopic expression of the phosphatidylinositol-4-phosphate 5-kinase Skittles increase PI(4,5)P2 levels in the ciliary base. The fact that Skittles expression phenocopies the dInpp5e mutants confirms a central role for PI(4,5)P2 in the regulation of dTULP, Inactive, and NOMPC localization. These data suggest that the spatial localization and levels of PI(4,5)P2 in ciliary membranes are important regulators of ciliary trafficking and function.
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Affiliation(s)
- Jina Park
- Department of Oral Biology, Yonsei University College of Dentistry, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea
| | - Nayoung Lee
- Department of Oral Biology, Yonsei University College of Dentistry, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea
| | - Adriana Kavoussi
- Department of Pharmacology, Brain Research Institute, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea; Severance Biomedical Science Institute, Yonsei University College of Medicine, Seoul 03722, Korea
| | - Jeong Taeg Seo
- Department of Oral Biology, Yonsei University College of Dentistry, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea
| | - Chul Hoon Kim
- Department of Pharmacology, Brain Research Institute, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea; Severance Biomedical Science Institute, Yonsei University College of Medicine, Seoul 03722, Korea.
| | - Seok Jun Moon
- Department of Oral Biology, Yonsei University College of Dentistry, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea.
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23
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Pedersen LB, Mogensen JB, Christensen ST. Endocytic Control of Cellular Signaling at the Primary Cilium. Trends Biochem Sci 2016; 41:784-797. [DOI: 10.1016/j.tibs.2016.06.002] [Citation(s) in RCA: 82] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Revised: 06/03/2016] [Accepted: 06/07/2016] [Indexed: 01/20/2023]
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24
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Mourão A, Christensen ST, Lorentzen E. The intraflagellar transport machinery in ciliary signaling. Curr Opin Struct Biol 2016; 41:98-108. [PMID: 27393972 DOI: 10.1016/j.sbi.2016.06.009] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 06/07/2016] [Indexed: 01/12/2023]
Abstract
Cilia and flagella on eukaryotic cells are slender microtubule-based projections surrounded by a membrane with a unique lipid and protein composition. It is now appreciated that cilia in addition to their established roles in motility also constitute hubs for cellular signaling by sensing external environmental cues necessary for organ development and maintenance of human health. Pathways reported to rely on the cilium organelle include Hedgehog, TGF-β, Wnt, PDGFRα, integrin and DNA damage repair signaling. An emerging theme in ciliary signaling is the requirement for active transport of signaling components into and out of the cilium proper. Here, we review the current state-of-the-art regarding the importance of intraflagellar transport and BBSome multi-subunit complexes in ciliary signaling.
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Affiliation(s)
- André Mourão
- Department of Structural Cell Biology, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany
| | - Søren T Christensen
- Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen, Denmark.
| | - Esben Lorentzen
- Department of Structural Cell Biology, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany.
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25
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Lee J, Chung YD. Ciliary subcompartments: how are they established and what are their functions? BMB Rep 2016; 48:380-7. [PMID: 25936781 PMCID: PMC4577287 DOI: 10.5483/bmbrep.2015.48.7.084] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2015] [Indexed: 12/15/2022] Open
Abstract
Cilia are conserved subcellular organelles with diverse sensory and developmental roles. Recently, they have emerged as crucial organelles whose dysfunction causes a wide spectrum of disorders called ciliopathies. Recent studies on the pathological mechanisms underlying ciliopathies showed that the ciliary compartment is further divided into subdomains with specific roles in the biogenesis, maintenance and function of cilia. Several conserved sets of molecules that play specific roles in each subcompartment have been discovered. Here we review recent progress on our understanding of ciliary subcompartments, especially focusing on the molecules required for their structure and/or function. [BMB Reports 2015; 48(7): 380-387]
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Affiliation(s)
- Jeongmi Lee
- Department of Life Science, University of Seoul, Seoul 130-743, Korea
| | - Yun Doo Chung
- Department of Life Science, University of Seoul, Seoul 130-743, Korea
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26
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Lechtreck KF. IFT-Cargo Interactions and Protein Transport in Cilia. Trends Biochem Sci 2015; 40:765-778. [PMID: 26498262 PMCID: PMC4661101 DOI: 10.1016/j.tibs.2015.09.003] [Citation(s) in RCA: 226] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Revised: 09/07/2015] [Accepted: 09/11/2015] [Indexed: 12/30/2022]
Abstract
The motile and sensory functions of cilia and flagella are indispensable for human health. Cilia assembly requires a dedicated protein shuttle, intraflagellar transport (IFT), a bidirectional motility of multi-megadalton protein arrays along ciliary microtubules. IFT functions as a protein carrier delivering hundreds of distinct proteins into growing cilia. IFT-based protein import and export continue in fully grown cilia and are required for ciliary maintenance and sensing. Large ciliary building blocks might depend on IFT to move through the transition zone, which functions as a ciliary gate. Smaller, freely diffusing proteins, such as tubulin, depend on IFT to be concentrated or removed from cilia. As I discuss here, recent work provides insights into how IFT interacts with its cargoes and how the transport is regulated.
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Affiliation(s)
- Karl F Lechtreck
- Department of Cellular Biology, University of Georgia, 635C Biological Science Building, 1000 Cedar Street, Athens, GA 30602, USA.
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27
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Mori T, Kawai-Toyooka H, Igawa T, Nozaki H. Gamete Dialogs in Green Lineages. MOLECULAR PLANT 2015; 8:1442-54. [PMID: 26145252 DOI: 10.1016/j.molp.2015.06.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Revised: 06/15/2015] [Accepted: 06/28/2015] [Indexed: 05/20/2023]
Abstract
Gamete fusion is a core process of sexual reproduction and, in both plants and animals, different sex gametes fuse within species. Although most of the molecular factors involved in gamete interaction are still unknown in various sex-possessing eukaryotes, reports of such factors in algae and land plants have been increasing in the past decade. In particular, knowledge of gamete interaction in flowering plants and green algae has increased since the identification of the conserved gamete fusion factor generative cell specific 1/hapless 2 (GCS1/HAP2). GCS1 was first identified as a pollen generative cell-specific transmembrane protein in the lily (Lilium longiflorum), and was then shown to function not only in flowering plant gamete fusion but also in various eukaryotes, including unicellular protists and metazoans. In addition, although initially restricted to Chlamydomonas, knowledge of gamete attachment in flowering plants was also acquired. This review focuses on recent progress in the study of gamete interaction in volvocine green algae and flowering plants and discusses conserved mechanisms of gamete recognition, attachment, and fusion leading to zygote formation.
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Affiliation(s)
- Toshiyuki Mori
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
| | - Hiroko Kawai-Toyooka
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Tomoko Igawa
- Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba 271-8510, Japan
| | - Hisayoshi Nozaki
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
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28
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Abstract
Cilia and flagella are closely related centriole-nucleated protrusions of the cell with roles in motility and signal transduction. Two of the best-studied signalling pathways organized by cilia are the transduction cascade for the morphogen Hedgehog in vertebrates and the mating pathway that initiates gamete fusion in the unicellular green alga Chlamydomonas reinhardtii. What is the role of cilia in these signalling transduction cascades? In both Hedgehog and mating pathways, all signalling intermediates have been found to localize to cilia, and, for some signalling factors, ciliary localization is regulated by pathway activation. Given a concentration factor of three orders of magnitude provided by translocating a protein into the cilium, the compartment model proposes that cilia act as miniaturized reaction tubes bringing signalling factors and processing enzymes in close proximity. On the other hand, the scaffolding model views the intraflagellar transport machinery, whose primary function is to build cilia and flagella, as a molecular scaffold for the mating transduction cascade at the flagellar membrane. While these models may coexist, it is hoped that a precise understanding of the mechanisms that govern signalling inside cilia will provide a satisfying answer to the question 'how do cilia organize signalling?'. This review covers the evidence supporting each model of signalling and outlines future directions that may address which model applies in given biological settings.
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Affiliation(s)
- Maxence V Nachury
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, CA 94305, USA
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29
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Cao M, Ning J, Hernandez-Lara CI, Belzile O, Wang Q, Dutcher SK, Liu Y, Snell WJ. Uni-directional ciliary membrane protein trafficking by a cytoplasmic retrograde IFT motor and ciliary ectosome shedding. eLife 2015; 4. [PMID: 25688564 PMCID: PMC4362204 DOI: 10.7554/elife.05242] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2014] [Accepted: 02/14/2015] [Indexed: 12/22/2022] Open
Abstract
The role of the primary cilium in key signaling pathways depends on dynamic regulation of ciliary membrane protein composition, yet we know little about the motors or membrane events that regulate ciliary membrane protein trafficking in existing organelles. Recently, we showed that cilium-generated signaling in Chlamydomonas induced rapid, anterograde IFT-independent, cytoplasmic microtubule-dependent redistribution of the membrane polypeptide, SAG1-C65, from the plasma membrane to the periciliary region and the ciliary membrane. Here, we report that the retrograde IFT motor, cytoplasmic dynein 1b, is required in the cytoplasm for this rapid redistribution. Furthermore, signaling-induced trafficking of SAG1-C65 into cilia is unidirectional and the entire complement of cellular SAG1-C65 is shed during signaling and can be recovered in the form of ciliary ectosomes that retain signal-inducing activity. Thus, during signaling, cells regulate ciliary membrane protein composition through cytoplasmic action of the retrograde IFT motor and shedding of ciliary ectosomes. DOI:http://dx.doi.org/10.7554/eLife.05242.001 Nearly every cell in the human body has slender, hair-like structures known as cilia that project outwards from its surface. These structures can sense and respond to light, chemicals and touch, and they are required for normal development. Failure of cilia to form or function in the correct manner can lead to severe diseases—such as kidney disorders, deafness and loss of vision. A major puzzle for researchers who study cilia has been to understand how cells change the composition of these structures as part of their response to a sensory input. Cilia are ancient structures that were present in early single-celled organisms and researchers interested in cilia have often used a single-celled green alga called Chlamydomonas reinhardtii as a model system for their studies. When these algae reproduce sexually, the two types of sex cells sense the presence of each other when their cilia touch and then stick together. This ciliary touching activates signals that are sent into the cells to get them ready to fuse together, much like sperm and egg cells do in animals. Both ciliary touching and signaling depend on a protein called SAG1, a part of which (known as SAG1-C65) is normally found mostly over the surface membrane of C. reinhardtii. Only very small amounts of SAG1-C65 are normally found on cilia; but, when the sex cells' cilia touch, this protein rapidly moves to the end of the cell nearest the cilia via a previously unknown mechanism. SAG1-C65 then becomes much more enriched in the cilia. Cao, Ning, Hernandez-Lara et al. investigated this process and found that SAG1-C65 movement requires a molecular motor called ‘cytoplasmic dynein’. This motor protein typically walks along the inside of cilia to transport other molecules away from the tip and towards the cell membrane. However, Cao, Ning, Hernandez-Lara et al. found that this dynein also carries SAG1-C65 from the membrane of the cells towards the base of the cilia in preparation for it to enter into these structures. As part of an effort to understand the fate of the protein after it entered cilia, Cao, Ning, Hernandez-Lara et al. discovered that the SAG1-C65 disappeared from the structures without returning to the cell membrane. Instead, SAG1-C65 was packaged within tiny bubble-like structures near the tips of cilia and these packages were then shed from cilia into the external environment. This discovery challenges a widely held view that proteins are only removed from cilia by returning to the cell. Future work will be required to understand more of the molecular details of these processes, which are likely to be present in most cells with cilia. DOI:http://dx.doi.org/10.7554/eLife.05242.002
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Affiliation(s)
- Muqing Cao
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Jue Ning
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Carmen I Hernandez-Lara
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Olivier Belzile
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Qian Wang
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Susan K Dutcher
- Department of Genetics, Washington University, St. Louis, United States
| | - Yanjie Liu
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
| | - William J Snell
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
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30
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Liu Y, Pei J, Grishin N, Snell WJ. The cytoplasmic domain of the gamete membrane fusion protein HAP2 targets the protein to the fusion site in Chlamydomonas and regulates the fusion reaction. Development 2015; 142:962-71. [PMID: 25655701 DOI: 10.1242/dev.118844] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Cell-cell fusion between gametes is a defining step during development of eukaryotes, yet we know little about the cellular and molecular mechanisms of the gamete membrane fusion reaction. HAP2 is the sole gamete-specific protein in any system that is broadly conserved and shown by gene disruption to be essential for gamete fusion. The wide evolutionary distribution of HAP2 (also known as GCS1) indicates it was present in the last eukaryotic common ancestor and, therefore, dissecting its molecular properties should provide new insights into fundamental features of fertilization. HAP2 acts at a step after membrane adhesion, presumably directly in the merger of the lipid bilayers. Here, we use the unicellular alga Chlamydomonas to characterize contributions of key regions of HAP2 to protein location and function. We report that mutation of three strongly conserved residues in the ectodomain has no effect on targeting or fusion, although short deletions that include those residues block surface expression and fusion. Furthermore, HAP2 lacking a 237-residue segment of the cytoplasmic region is expressed at the cell surface, but fails to localize at the apical membrane patch specialized for fusion and fails to rescue fusion. Finally, we provide evidence that the ancient HAP2 contained a juxta-membrane, multi-cysteine motif in its cytoplasmic region, and that mutation of a cysteine dyad in this motif preserves protein localization, but substantially impairs HAP2 fusion activity. Thus, the ectodomain of HAP2 is essential for its surface expression, and the cytoplasmic region targets HAP2 to the site of fusion and regulates the fusion reaction.
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Affiliation(s)
- Yanjie Liu
- Department of Cell Biology, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390-9039, USA
| | - Jimin Pei
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390-9039, USA
| | - Nick Grishin
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390-9039, USA
| | - William J Snell
- Department of Cell Biology, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390-9039, USA
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31
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Craft JM, Harris JA, Hyman S, Kner P, Lechtreck KF. Tubulin transport by IFT is upregulated during ciliary growth by a cilium-autonomous mechanism. ACTA ACUST UNITED AC 2015; 208:223-37. [PMID: 25583998 PMCID: PMC4298693 DOI: 10.1083/jcb.201409036] [Citation(s) in RCA: 137] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
In Chlamydomonas cilia, IFT concentrates soluble tubulin by regulating IFT train occupancy and thereby promotes elongation of axonemal microtubules. The assembly of the axoneme, the structural scaffold of cilia and flagella, requires translocation of a vast quantity of tubulin into the growing cilium, but the mechanisms that regulate the targeting, quantity, and timing of tubulin transport are largely unknown. In Chlamydomonas, GFP-tagged α-tubulin enters cilia as an intraflagellar transport (IFT) cargo and by diffusion. IFT-based transport of GFP-tubulin is elevated in growing cilia and IFT trains carry more tubulin. Cells possessing both nongrowing and growing cilia selectively target GFP-tubulin into the latter. The preferential delivery of tubulin boosts the concentration of soluble tubulin in the matrix of growing versus steady-state cilia. Cilia length mutants show abnormal kinetics of tubulin transport. We propose that cells regulate the extent of occupancy of IFT trains by tubulin cargoes. During ciliary growth, IFT concentrates soluble tubulin in cilia and thereby promotes elongation of the axonemal microtubules.
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Affiliation(s)
- Julie M Craft
- Department of Cellular Biology and College of Engineering, University of Georgia, Athens, GA 30602
| | - J Aaron Harris
- Department of Cellular Biology and College of Engineering, University of Georgia, Athens, GA 30602
| | - Sebastian Hyman
- Department of Cellular Biology and College of Engineering, University of Georgia, Athens, GA 30602
| | - Peter Kner
- Department of Cellular Biology and College of Engineering, University of Georgia, Athens, GA 30602
| | - Karl F Lechtreck
- Department of Cellular Biology and College of Engineering, University of Georgia, Athens, GA 30602
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Takao D, Dishinger JF, Kee HL, Pinskey JM, Allen BL, Verhey KJ. An assay for clogging the ciliary pore complex distinguishes mechanisms of cytosolic and membrane protein entry. Curr Biol 2014; 24:2288-94. [PMID: 25264252 DOI: 10.1016/j.cub.2014.08.012] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Revised: 07/08/2014] [Accepted: 08/07/2014] [Indexed: 01/25/2023]
Abstract
As a cellular organelle, the cilium contains a unique protein composition. Entry of both membrane and cytosolic components is tightly regulated by gating mechanisms at the cilium base; however, the mechanistic details of ciliary gating are largely unknown. We previously proposed that entry of cytosolic components is regulated by mechanisms similar to those of nuclear transport and is dependent on nucleoporins (NUPs), which comprise a ciliary pore complex (CPC). To investigate ciliary gating mechanisms, we developed a system to clog the pore by inhibiting NUP function via forced dimerization. We targeted NUP62, a component of the central channel of the nuclear pore complex (NPC), for forced dimerization by tagging it with the homodimerizing Fv domain. As proof of principle, we show that forced dimerization of NUP62-Fv attenuated (1) active transport of BSA into the nuclear compartment and (2) the kinesin-2 motor KIF17 into the ciliary compartment. Using the pore-clogging technique, we find that forced dimerization of NUP62 attenuated the gated entry of cytosolic proteins but did not affect entry of membrane proteins or diffusional entry of small cytosolic proteins. We propose a model in which active transport of cytosolic proteins into both nuclear and ciliary compartments requires functional NUPs of the central pore, whereas lateral entry of membrane proteins utilizes a different mechanism that is likely specific to each organelle's limiting membrane.
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Affiliation(s)
- Daisuke Takao
- Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - John F Dishinger
- Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - H Lynn Kee
- Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Justine M Pinskey
- Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Ben L Allen
- Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Kristen J Verhey
- Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
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Alford LM, Mattheyses AL, Hunter EL, Lin H, Dutcher SK, Sale WS. The Chlamydomonas mutant pf27 reveals novel features of ciliary radial spoke assembly. Cytoskeleton (Hoboken) 2014; 70:804-18. [PMID: 24124175 DOI: 10.1002/cm.21144] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Revised: 09/10/2013] [Accepted: 09/12/2013] [Indexed: 01/05/2023]
Abstract
To address the mechanisms of ciliary radial spoke assembly, we took advantage of the Chlamydomonas pf27 mutant. The radial spokes that assemble in pf27 are localized to the proximal quarter of the axoneme, but otherwise are fully assembled into 20S radial spoke complexes competent to bind spokeless axonemes in vitro. Thus, pf27 is not defective in radial spoke assembly or docking to the axoneme. Rather, our results suggest that pf27 is defective in the transport of spoke complexes. During ciliary regeneration in pf27, radial spoke assembly occurs asynchronously from other axonemal components. In contrast, during ciliary regeneration in wild-type Chlamydomonas, radial spokes and other axonemal components assemble concurrently as the axoneme grows. Complementation in temporary dikaryons between wild-type and pf27 reveals rescue of radial spoke assembly that begins at the distal tip, allowing further assembly to proceed from tip to base of the axoneme. Notably, rescued assembly of radial spokes occurred independently of the established proximal radial spokes in pf27 axonemes in dikaryons. These results reveal that 20S radial spokes can assemble proximally in the pf27 cilium but as the cilium lengthens, spoke assembly requires transport. We postulate that PF27 encodes an adaptor or modifier protein required for radial spoke–IFT interaction.
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Abstract
Cilia grow by assembling structural precursors delivered to their tips by intraflagellar transport. New work on ciliary length control indicates that, during ciliary growth, cilia send a length signal to the cytoplasm that regulates cargo loading onto the constitutively trafficking intraflagellar transport machinery.
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Affiliation(s)
- Junmin Pan
- MOE Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - William J Snell
- Department of Cell Biology, University of Texas Southwestern Medical School, Dallas, TX 75390, USA.
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35
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Abstract
The primary cilium compartmentalizes a tiny fraction of the cell surface and volume, yet many proteins are highly enriched in this area and so efficient mechanisms are necessary to concentrate them in the ciliary compartment. Here we review mechanisms that are thought to deliver protein cargo to the base of cilia and are likely to interact with ciliary gating mechanisms. Given the immense variety of ciliary cytosolic and transmembrane proteins, it is almost certain that multiple, albeit frequently interconnected, pathways mediate this process. It is also clear that none of these pathways is fully understood at the present time. Mechanisms that are discussed below facilitate ciliary localization of structural and signaling molecules, which include receptors, G-proteins, ion channels, and enzymes. These mechanisms form a basis for every aspect of cilia function in early embryonic patterning, organ morphogenesis, sensory perception and elsewhere.
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Affiliation(s)
- Jarema Malicki
- MRC Centre for Developmental and Biomedical Genetics; Department of Biomedical Science; The University of Sheffield; Sheffield, UK
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Blacque OE, Sanders AAWM. Compartments within a compartment: what C. elegans can tell us about ciliary subdomain composition, biogenesis, function, and disease. Organogenesis 2014; 10:126-37. [PMID: 24732235 DOI: 10.4161/org.28830] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The primary cilium has emerged as a hotbed of sensory and developmental signaling, serving as a privileged domain to concentrate the functions of a wide number of channels, receptors and downstream signal transducers. This realization has provided important insight into the pathophysiological mechanisms underlying the ciliopathies, an ever expanding spectrum of multi-symptomatic disorders affecting the development and maintenance of multiple tissues and organs. One emerging research focus is the subcompartmentalised nature of the organelle, consisting of discrete structural and functional subdomains such as the periciliary membrane/basal body compartment, the transition zone, the Inv compartment and the distal segment/ciliary tip region. Numerous ciliopathy, transport-related and signaling molecules localize at these compartments, indicating specific roles at these subciliary sites. Here, by focusing predominantly on research from the genetically tractable nematode C. elegans, we review ciliary subcompartments in terms of their structure, function, composition, biogenesis and relationship to human disease.
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Affiliation(s)
- Oliver E Blacque
- School of Biomolecular and Biomedical Science; University College Dublin; Dublin, Ireland
| | - Anna A W M Sanders
- School of Biomolecular and Biomedical Science; University College Dublin; Dublin, Ireland
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Sengupta P, Barr MM. New insights into an old organelle: meeting report on biology of cilia and flagella. Traffic 2014; 15:717-26. [PMID: 24612344 DOI: 10.1111/tra.12166] [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: 01/28/2014] [Revised: 02/19/2014] [Accepted: 02/24/2014] [Indexed: 12/20/2022]
Abstract
The rising interest of the scientific community in cilia biology was evident from the fact that registration for the third FASEB conference on 'The Biology of Cilia and Flagella' closed out before the early bird deadline. Cilia and flagella are organelles of profound medical importance; defects in their structure or function result in a plethora of human diseases called ciliopathies. 240 clinicians and basic scientists from around the world gathered from 23 June 2013 to 28 June 2013 at Sheraton at the Falls, Niagara Falls, NY to present and discuss their research on this intensely studied subcellular structure. The meeting was organized by Gregory Pazour (University of Massachusetts Medical School), Bradley Yoder (University of Alabama-Birmingham), and Maureen Barr (Rutgers University) and was sponsored by the Federation of American Societies for Experimental Biology (FASEB). Here, we report highlights, points of discussion, and emerging themes from this exciting meeting.
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Affiliation(s)
- Piali Sengupta
- Department of Biology and National Center for Behavioral Genomics, Brandeis University, 415 South Street, Waltham, MA, 02454, USA
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Dutcher SK. The awesome power of dikaryons for studying flagella and basal bodies in Chlamydomonas reinhardtii. Cytoskeleton (Hoboken) 2013; 71:79-94. [PMID: 24272949 DOI: 10.1002/cm.21157] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Accepted: 11/19/2013] [Indexed: 11/08/2022]
Abstract
Cilia/flagella and basal bodies/centrioles play key roles in human health and homeostasis. Among the organisms used to study these microtubule-based organelles, the green alga Chlamydomonas reinhardtii has several advantages. One is the existence of a temporary phase of the life cycle, termed the dikaryon. These cells are formed during mating when the cells fuse and the behavior of flagella from two genetically distinguishable parents can be observed. During this stage, the cytoplasms mix allowing for a defect in the flagella of one parent to be rescued by proteins from the other parent. This offers the unique advantage of adding back wild-type gene product or labeled protein at endogenous levels that can used to monitor various flagellar and basal body phenotypes. Mutants that show rescue and ones that fail to show rescue are both informative about the nature of the flagella and basal body defects. When rescue occurs, it can be used to determine the mutant gene product and to follow the temporal and spatial patterns of flagellar assembly. This review describes many examples of insights into basal body and flagellar proteins' function and assembly that have been discovered using dikaryons and discusses the potential for further analyses.
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Affiliation(s)
- Susan K Dutcher
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri
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Wren KN, Craft JM, Tritschler D, Schauer A, Patel DK, Smith EF, Porter ME, Kner P, Lechtreck KF. A differential cargo-loading model of ciliary length regulation by IFT. Curr Biol 2013; 23:2463-71. [PMID: 24316207 DOI: 10.1016/j.cub.2013.10.044] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Revised: 09/23/2013] [Accepted: 10/14/2013] [Indexed: 01/07/2023]
Abstract
BACKGROUND During the assembly and maintenance of cilia, precursor proteins need to be transported from the cell body into the organelle. Intraflagellar transport (IFT) is assumed to be the predominant protein transport pathway in cilia, but it remains largely unknown how ciliary proteins use IFT to reach their destination sites in the cilium and whether the amount of cargo transported by IFT is regulated. RESULTS Single-particle imaging showed that DRC4, a structural protein of the axoneme, moves in association with IFT particles inside Chlamydomonas reinhardtii cilia. IFT is required for DRC4 transport both into and within the cilium. DRC4 cargoes dissociate from IFT trains at the tip as well as at various sites along the length of the cilium. Unloaded DRC4 diffuses before docking at its axonemal assembly site. In growing cilia, DRC4 transport by IFT was strongly increased over the steady-state level, and the frequency decreased linearly with the increasing ciliary length. The frequency of DRC4 transport was similarly elevated in short growth-arrested cilia and remained high even when the amount of DRC4 available in the cell body was reduced. CONCLUSIONS DRC4 is a bona fide cargo of IFT. Incompletely assembled cilia trigger an increase in the amount of DRC4 cargo transported by IFT particles, and DRC4 transport is downregulated as cilia approach their steady-state length. We propose a model in which ciliary length is controlled by regulating the amount of cargo transported by IFT particles.
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Affiliation(s)
- Kathryne N Wren
- Department of Cellular Biology, University of Georgia, Athens, GA 30602, USA
| | - Julie M Craft
- Department of Cellular Biology, University of Georgia, Athens, GA 30602, USA
| | - Douglas Tritschler
- Department of Genetics, Cell Biology and Development, University of Minnesota, MN 55455, USA
| | - Alexandria Schauer
- Department of Genetics, Cell Biology and Development, University of Minnesota, MN 55455, USA
| | - Deep K Patel
- Department of Cellular Biology, University of Georgia, Athens, GA 30602, USA
| | - Elizabeth F Smith
- Department of Biological Science, Dartmouth College, Hanover, NH 03755, USA
| | - Mary E Porter
- Department of Genetics, Cell Biology and Development, University of Minnesota, MN 55455, USA
| | - Peter Kner
- College of Engineering, University of Georgia, Athens, GA 30602, USA
| | - Karl F Lechtreck
- Department of Cellular Biology, University of Georgia, Athens, GA 30602, USA.
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Lin H, Miller ML, Granas DM, Dutcher SK. Whole genome sequencing identifies a deletion in protein phosphatase 2A that affects its stability and localization in Chlamydomonas reinhardtii. PLoS Genet 2013; 9:e1003841. [PMID: 24086163 PMCID: PMC3784568 DOI: 10.1371/journal.pgen.1003841] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 08/13/2013] [Indexed: 11/19/2022] Open
Abstract
Whole genome sequencing is a powerful tool in the discovery of single nucleotide polymorphisms (SNPs) and small insertions/deletions (indels) among mutant strains, which simplifies forward genetics approaches. However, identification of the causative mutation among a large number of non-causative SNPs in a mutant strain remains a big challenge. In the unicellular biflagellate green alga Chlamydomonas reinhardtii, we generated a SNP/indel library that contains over 2 million polymorphisms from four wild-type strains, one highly polymorphic strain that is frequently used in meiotic mapping, ten mutant strains that have flagellar assembly or motility defects, and one mutant strain, imp3, which has a mating defect. A comparison of polymorphisms in the imp3 strain and the other 15 strains allowed us to identify a deletion of the last three amino acids, Y313F314L315, in a protein phosphatase 2A catalytic subunit (PP2A3) in the imp3 strain. Introduction of a wild-type HA-tagged PP2A3 rescues the mutant phenotype, but mutant HA-PP2A3 at Y313 or L315 fail to rescue. Our immunoprecipitation results indicate that the Y313, L315, or YFLΔ mutations do not affect the binding of PP2A3 to the scaffold subunit, PP2A-2r. In contrast, the Y313, L315, or YFLΔ mutations affect both the stability and the localization of PP2A3. The PP2A3 protein is less abundant in these mutants and fails to accumulate in the basal body area as observed in transformants with either wild-type HA-PP2A3 or a HA-PP2A3 with a V310T change. The accumulation of HA-PP2A3 in the basal body region disappears in mated dikaryons, which suggests that the localization of PP2A3 may be essential to the mating process. Overall, our results demonstrate that the terminal YFL tail of PP2A3 is important in the regulation on Chlamydomonas mating.
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Affiliation(s)
- Huawen Lin
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Michelle L. Miller
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - David M. Granas
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Center for Genomic Sciences and System Biology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Susan K. Dutcher
- Department of Genetics, Washington University School of Medicine, St. Louis, Missouri, United States of America
- * E-mail:
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