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Wessely O, Obara T. Fish and frogs: models for vertebrate cilia signaling. FRONT BIOSCI-LANDMRK 2008; 13:1866-80. [PMID: 17981674 DOI: 10.2741/2806] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The presence of cilia in many vertebrate cell types and its function has been ignored for many years. Only in the past few years has its importance been rediscovered. In part, this was triggered by the realization that many gene products mutated in polycystic kidney diseases are localized to cilia and dysfunctional cilia result in kidney disease. Another breakthrough was the observation that the establishment of the left-right body axis is dependent on cilia function. Since then, many other developmental paradigms have been shown to rely on cilia-dependent signaling. In addition to mouse and Chlamydomonas, lower vertebrate model systems such as zebrafish, medaka and Xenopus have provided important new insights into cilia signaling and its role during embryonic development. This review will summarize those studies. We will also illustrate how these lower vertebrates are promising model systems for future studies defining the physiological function of cilia during organogenesis and disease pathophysiology.
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Affiliation(s)
- Oliver Wessely
- Department of Cell Biology and Anatomy and Genetics, LSU Health Sciences Center, MEB-6A12, 1901 Perdido Street, New Orleans, LA 70112, USA
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102
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Abstract
Recent studies have revealed unexpected connections between the mammalian Hedgehog (Hh) signal transduction pathway and the primary cilium, a microtubule-based organelle that protrudes from the surface of most vertebrate cells. Intraflagellar transport proteins, which are required for the construction of cilia, are essential for all responses to mammalian Hh proteins, and proteins required for Hh signal transduction are enriched in primary cilia. The phenotypes of different mouse mutants that affect ciliary proteins suggest that cilia may act as processive machines that organize sequential steps in the Hh signal transduction pathway. Cilia on vertebrate cells are likely to be important in additional developmental signaling pathways and are required for PDGF receptor alpha signaling in cultured fibroblasts. Cilia are not essential for either canonical or noncanonical Wnt signaling, although cell-type-specific modulation of cilia components may link cilia and Wnt signaling in some tissues. Because ciliogenesis in invertebrates is limited to a very small number of specialized cell types, the role of cilia in developmental signaling pathways is likely a uniquely vertebrate phenomenon.
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103
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Yeast gain-of-function mutations reveal structure-function relationships conserved among different subfamilies of transient receptor potential channels. Proc Natl Acad Sci U S A 2007; 104:19607-12. [PMID: 18042709 DOI: 10.1073/pnas.0708584104] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Transient receptor potential (TRP) channels found in animals, protists, and fungi are primary chemo-, thermo-, or mechanosensors. Current research emphasizes the characteristics of individual channels in each animal TRP subfamily but not the mechanisms common across subfamilies. A forward genetic screen of the TrpY1, the yeast TRP channel, recovered gain-of-function (GOF) mutations with phenotype in vivo and in vitro. Single-channel patch-clamp analyses of these GOF-mutant channels show prominent aberrations in open probability and channel kinetics. These mutations revealed functionally important aromatic amino acid residues in four locations: at the intracellular end of the fifth transmembrane helix (TM5), at both ends of TM6, and at the immediate extension of TM6. These aromatics have counterparts in most TRP subfamilies. The one in TM5 (F380L) aligns precisely with an exceptional Drosophila mutant allele (F550I) that causes constitutive activity in the canonical TRP channel, resulting in rapid and severe retinal degeneration beyond mere loss of phototaxis. Thus, this phenylalanine maintains the balance of various functional states (conformations) of a channel for insect phototransduction as well as one for fungal mechanotransduction. This residue is among a small cluster of phenylalanines found in all known subfamilies of TRP channels. This unique case illustrates that GOF mutations can reveal structure-function principles that can be generalized across different TRP subfamilies. It appears that the conserved aromatics in the four locations have conserved functions in most TRP channels. The possible mechanistic roles of these aromatics and the further use of yeast genetics to dissect TRP channels are discussed.
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104
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Hovater MB, Olteanu D, Hanson EL, Cheng NL, Siroky B, Fintha A, Komlosi P, Liu W, Satlin LM, Bell PD, Yoder BK, Schwiebert EM. Loss of apical monocilia on collecting duct principal cells impairs ATP secretion across the apical cell surface and ATP-dependent and flow-induced calcium signals. Purinergic Signal 2007; 4:155-70. [PMID: 18368523 PMCID: PMC2377318 DOI: 10.1007/s11302-007-9072-0] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2006] [Revised: 09/25/2006] [Accepted: 11/01/2006] [Indexed: 01/11/2023] Open
Abstract
Renal epithelial cells release ATP constitutively under basal conditions and release higher quantities of purine nucleotide in response to stimuli. ATP filtered at the glomerulus, secreted by epithelial cells along the nephron, and released serosally by macula densa cells for feedback signaling to afferent arterioles within the glomerulus has important physiological signaling roles within kidneys. In autosomal recessive polycystic kidney disease (ARPKD) mice and humans, collecting duct epithelial cells lack an apical central cilium or express dysfunctional proteins within that monocilium. Collecting duct principal cells derived from an Oak Ridge polycystic kidney (orpk ( Tg737 ) ) mouse model of ARPKD lack a well-formed apical central cilium, thought to be a sensory organelle. We compared these cells grown as polarized cell monolayers on permeable supports to the same cells where the apical monocilium was genetically rescued with the wild-type Tg737 gene that encodes Polaris, a protein essential to cilia formation. Constitutive ATP release under basal conditions was low and not different in mutant versus rescued monolayers. However, genetically rescued principal cell monolayers released ATP three- to fivefold more robustly in response to ionomycin. Principal cell monolayers with fully formed apical monocilia responded three- to fivefold greater to hypotonicity than mutant monolayers lacking monocilia. In support of the idea that monocilia are sensory organelles, intentionally harsh pipetting of medium directly onto the center of the monolayer induced ATP release in genetically rescued monolayers that possessed apical monocilia. Mechanical stimulation was much less effective, however, on mutant orpk collecting duct principal cell monolayers that lacked apical central monocilia. Our data also show that an increase in cytosolic free Ca(2+) primes the ATP pool that is released in response to mechanical stimuli. It also appears that hypotonic cell swelling and mechanical pipetting stimuli trigger release of a common ATP pool. Cilium-competent monolayers responded to flow with an increase in cell Ca(2+) derived from both extracellular and intracellular stores. This flow-induced Ca(2+) signal was less robust in cilium-deficient monolayers. Flow-induced Ca(2+) signals in both preparations were attenuated by extracellular gadolinium and by extracellular apyrase, an ATPase/ADPase. Taken together, these data suggest that apical monocilia are sensory organelles and that their presence in the apical membrane facilitates the formation of a mature ATP secretion apparatus responsive to chemical, osmotic, and mechanical stimuli. The cilium and autocrine ATP signaling appear to work in concert to control cell Ca(2+). Loss of a cilium-dedicated autocrine purinergic signaling system may be a critical underlying etiology for ARPKD and may lead to disinhibition and/or upregulation of multiple sodium (Na(+)) absorptive mechanisms and a resultant severe hypertensive phenotype in ARPKD and, possibly, other diseases.
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Affiliation(s)
- Michael B Hovater
- Department of Physiology and Biophysics, University of Alabama at Birmingham, 1918 University Blvd., Birmingham, AL, 35294-0005, USA
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105
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Abstract
Forces are increasingly recognized as major regulators of cell structure and function, and the mechanical properties of cells are essential to the mechanisms by which cells sense forces, transmit them to the cell interior or to other cells, and transduce them into chemical signals that impact a spectrum of cellular responses. Comparison of the mechanical properties of intact cells with those of the purified cytoskeletal biopolymers that are thought to dominate their elasticity reveal the extent to which the studies of purified systems can account for the mechanical properties of the much more heterogeneous and complex cell. This review summarizes selected aspects of current work on cell mechanics with an emphasis on the structures that are activated in cell-cell contacts, that regulate ion flow across the plasma membrane, and that may sense fluid flow that produces low levels of shear stress.
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Affiliation(s)
- Paul A Janmey
- Department of Physiology, Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
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106
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Zhou X, Su Z, Anishkin A, Haynes WJ, Friske EM, Loukin SH, Kung C, Saimi Y. Yeast screens show aromatic residues at the end of the sixth helix anchor transient receptor potential channel gate. Proc Natl Acad Sci U S A 2007; 104:15555-9. [PMID: 17878311 PMCID: PMC2000494 DOI: 10.1073/pnas.0704039104] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Transient receptor potential (TRP) channels are first elements in sensing chemicals, heat, and force and are widespread among protists and fungi as well as animals. Despite their importance, the arrangement and roles of the amino acids that constitute the TRP channel gate are unknown. The yeast TRPY1 is activated in vivo by osmotically induced vacuolar membrane deformation and by cytoplasmic Ca(2+). After a random mutagenesis, we isolated TRPY1 mutants that responded more strongly to mild osmotic upshocks. One such gain-of-function mutant has a Y458H substitution at the C terminus of the predicted sixth transmembrane helix. Direct patch-clamp examination of vacuolar membranes showed that Y458H channels were already active with little stimulus and showed marked flickers between the open and intraburst closed states. They remained responsive to membrane stretch force and to Ca(2+), indicating primary defects in the gate region but not in the sensing of gating principles. None of the other 18 amino acid replacements engineered here showed normal channel kinetics except the two aromatic substitutions, Y458F and Y458W. The Y458 of TRPY1 has its aromatic counterpart in mammalian TRPM. Furthermore, conserved aromatics one alpha-helical turn downstream from this point are also found in animal TRPC, TRPN, TRPP, and TRPML, suggesting that gate anchoring with aromatics may be common among many TRP channels. The possible roles of aromatics at the end of the sixth transmembrane helix are discussed.
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Affiliation(s)
- Xinliang Zhou
- Laboratory of Molecular Biology and Department of Genetics, University of Wisconsin, Madison, WI 53706, USA
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107
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Malchow D, Lusche DF, De Lozanne A, Schlatterer C. A fast Ca2+-induced Ca2+-release mechanism in Dictyostelium discoideum. Cell Calcium 2007; 43:521-30. [PMID: 17854889 DOI: 10.1016/j.ceca.2007.08.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2007] [Revised: 07/16/2007] [Accepted: 08/09/2007] [Indexed: 11/17/2022]
Abstract
In vertebrate cells calcium-induced calcium release (CICR) is thought to be responsible for rapid cytosolic Ca(2+) elevations despite the occurrence of strong Ca(2+) buffering within the cytosol. In Dictyostelium, a CICR mechanism has not been reported. While analyzing Ca(2+) regulation in a vesicular fraction of Dictyostelium rich in Ca(2+)-flux activity, containing contractile vacuoles (CV) as the main component of acidic Ca(2+) stores and ER, we detected a rapid Ca(2+) change upon addition of Ca(2+) (CIC). CIC was three times larger in active stores accumulating Ca(2+) than before Ca(2+) uptake and in inactivated stores. Ca(2+) release was demonstrated with the calmodulin antagonist W7 that inhibits the V-type H(+)ATPase activity and Ca(2+) uptake of acidic Ca(2+) stores. W7 caused a rapid and large increase of extravesicular Ca(2+) ([Ca(2+)](e)), much faster and larger than thapsigargin (Tg), a Ca(2+)-uptake inhibitor of the ER. W7 treatment blocked CIC indicating that a large part of CIC is due to Ca(2+) release. The height of CIC depended on the filling state of the Ca(2+) stores. CIC was virtually unchanged in the iplA(-) strain that lacks a putative IP(3) or ryanodine receptor thought to be located at the endoplasmic reticulum. By contrast, CIC was reduced in two mutants, HGR8 and lvsA(-), that are impaired in acidic Ca(2+)-store function. Purified Ca(2+) stores enriched in CV still displayed CIC, indicating that CV are a source of Ca(2+)-induced Ca(2+) release. CIC-defective mutants were altered in their oscillatory properties. The irregularity of the HGR8 oscillation suggests that the principal oscillator is affected in this mutant.
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Affiliation(s)
- Dieter Malchow
- Department of Biology, University of Konstanz, P.O. Box 5560, D-78457 Konstanz, Germany.
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108
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Tian Y, Kolb R, Hong JH, Carroll J, Li D, You J, Bronson R, Yaffe MB, Zhou J, Benjamin T. TAZ promotes PC2 degradation through a SCFbeta-Trcp E3 ligase complex. Mol Cell Biol 2007; 27:6383-95. [PMID: 17636028 PMCID: PMC2099608 DOI: 10.1128/mcb.00254-07] [Citation(s) in RCA: 151] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Studies of a TAZ knockout mouse reveal a novel function of the transcriptional regulator TAZ, that is, as a binding partner of the F-box protein beta-Trcp. TAZ-/- mice develop polycystic kidney disease (PKD) and emphysema. The calcium-permeable cation channel protein polycystin 2 (PC2) is overexpressed in kidneys of TAZ-/- mice as a result of decreased degradation via an SCF(beta-Trcp) E3 ubiquitin ligase pathway. Replacements of serines in a phosphodegron motif in TAZ prevent beta-Trcp binding and PC2 degradation. Coexpression of a cytoplasmic fragment of polycystin 1 blocks the PC2-TAZ interaction and prevents TAZ-mediated degradation of PC2. Depletion of TAZ in zebrafish also results in a cystic kidney accompanied by overexpression of PC2. These results establish a common role of TAZ across vertebrate species in a protein degradation pathway regulated by phosphorylation and implicate deficiencies in this pathway in the development of PKD.
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Affiliation(s)
- Yu Tian
- Department of Pathology, Harvard Medical School, Boston, MA 02115, USA
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109
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The 10 sea urchin receptor for egg jelly proteins (SpREJ) are members of the polycystic kidney disease-1 (PKD1) family. BMC Genomics 2007; 8:235. [PMID: 17629917 PMCID: PMC1934368 DOI: 10.1186/1471-2164-8-235] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2007] [Accepted: 07/13/2007] [Indexed: 11/10/2022] Open
Abstract
Background Mutations in the human polycystic kidney disease-1 (hPKD1) gene result in ~85% of cases of autosomal dominant polycystic kidney disease, the most frequent human monogenic disease. PKD1 proteins are large multidomain proteins involved in a variety of signal transduction mechanisms. Obtaining more information about members of the PKD1 family will help to clarify their functions. Humans have five hPKD1 proteins, whereas sea urchins have 10. The PKD1 proteins of the sea urchin, Strongylocentrotus purpuratus, are referred to as the Receptor for Egg Jelly, or SpREJ proteins. The SpREJ proteins form a subfamily within the PKD1 family. They frequently contain C-type lectin domains, PKD repeats, a REJ domain, a GPS domain, a PLAT/LH2 domain, 1–11 transmembrane segments and a C-terminal coiled-coil domain. Results The 10 full-length SpREJ cDNA sequences were determined. The secondary structures of their deduced proteins were predicted and compared to the five human hPKD1 proteins. The genomic structures of the 10 SpREJs show low similarity to each other. All 10 SpREJs are transcribed in either embryos or adult tissues. SpREJs show distinct patterns of expression during embryogenesis. Adult tissues show tissue-specific patterns of SpREJ expression. Conclusion Possession of a REJ domain of about 600 residues defines this family. Except for SpREJ1 and 3, that are thought to be associated with the sperm acrosome reaction, the functions of the other SpREJ proteins remain unknown. The sea urchin genome is one-fourth the size of the human genome, but sea urchins have 10 SpREJ proteins, whereas humans have five. Determination of the tissue specific function of each of these proteins will be of interest to those studying echinoderm development. Sea urchins are basal deuterostomes, the line of evolution leading to the vertebrates. The study of individual PKD1 proteins will increase our knowledge of the importance of this gene family.
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110
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Abstract
Cilia are endowed with membrane receptors, channels, and signaling components whose localization and function must be tightly controlled. In primary cilia of mammalian kidney epithelia and sensory cilia of Caenorhabditis elegans neurons, polycystin-1 (PC1) and transient receptor polycystin-2 channel (TRPP2 or PC2), function together as a mechanosensory receptor-channel complex. Despite the importance of the polycystins in sensory transduction, the mechanisms that regulate polycystin activity and localization, or ciliary membrane receptors in general, remain poorly understood. We demonstrate that signal transduction adaptor molecule STAM-1A interacts with C. elegans LOV-1 (PC1), and that STAM functions with hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) on early endosomes to direct the LOV-1-PKD-2 complex for lysosomal degradation. In a stam-1 mutant, both LOV-1 and PKD-2 improperly accumulate at the ciliary base. Conversely, overexpression of STAM or Hrs promotes the removal of PKD-2 from cilia, culminating in sensory behavioral defects. These data reveal that the STAM-Hrs complex, which down-regulates ligand-activated growth factor receptors from the cell surface of yeast and mammalian cells, also regulates the localization and signaling of a ciliary PC1 receptor-TRPP2 complex.
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Affiliation(s)
- Jinghua Hu
- Division of Pharmaceutical Sciences, School of Pharmacy, University of Wisconsin, Madison, WI 53705, USA
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111
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Cantiello HF, Montalbetti N, Li Q, Chen XZ. The Cytoskeletal Connection to Ion Channels as a Potential Mechanosensory Mechanism: Lessons from Polycystin-2 (TRPP2). CURRENT TOPICS IN MEMBRANES 2007; 59:233-96. [PMID: 25168140 DOI: 10.1016/s1063-5823(06)59010-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Mechanosensitivity of ion channels, or the ability to transfer mechanical forces into a gating mechanism of channel regulation, is split into two main working (not mutually exclusive) hypotheses. One is that elastic and/or structural changes in membrane properties act as a transducing mechanism of channel regulation. The other hypothesis involves tertiary elements, such as the cytoskeleton which, itself by dynamic interactions with the ion channel, may convey conformational changes, including those ascribed to mechanical forces. This hypothesis is supported by numerous instances of regulatory changes in channel behavior by alterations in cytoskeletal structures/interactions. However, only recently, the molecular nature of these interactions has slowly emerged. Recently, a surge of evidence has emerged to indicate that transient receptor potential (TRP) channels are key elements in the transduction of a variety of environmental signals. This chapter describes the molecular linkage and regulatory elements of polycystin-2 (PC2), a TRP-type (TRPP2) nonselective cation channel whose mutations cause autosomal dominant polycystic kidney disease (ADPKD). The chapter focuses on the involvement of cytoskeletal structures in the regulation of PC2 and discusses how these connections are the transducing mechanism of environmental signals to its channel function.
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Affiliation(s)
- Horacio F Cantiello
- Renal Unit, Massachusetts General Hospital East, Charlestown, Massachusetts 02129; Department of Medicine, Harvard Medical School, Boston, Massachusetts 02115; Laboratorio de Canales Iónicos, Departamento de Fisicoquímica y Química Analítica, Facultad de Farmacia y Bioquímica, Buenos Aires 1113, Argentina
| | - Nicolás Montalbetti
- Laboratorio de Canales Iónicos, Departamento de Fisicoquímica y Química Analítica, Facultad de Farmacia y Bioquímica, Buenos Aires 1113, Argentina
| | - Qiang Li
- Department of Physiology, University of Alberta, Edmonton T6G 2H7, Canada
| | - Xing-Zhen Chen
- Department of Physiology, University of Alberta, Edmonton T6G 2H7, Canada
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112
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Abstract
This chapter reviews recent evidence indicating that canonical or classical transient receptor potential (TRPC) channels are directly or indirectly mechanosensitive (MS) and can therefore be designated as mechano-operated channels (MOCs). The MS functions of TRPCs may be mechanistically related to their better known functions as store-operated and receptor-operated channels (SOCs and ROCs). Mechanical forces may be conveyed to TRPC channels through the "conformational coupling" mechanism that transmits information regarding the status of internal Ca(2+) stores. All TRPCs are regulated by receptors coupled to phospholipases that are themselves MS and can regulate channels via lipidic second messengers. Accordingly, there may be several nonexclusive mechanisms by which mechanical forces may regulate TRPC channels, including direct sensitivity to bilayer mechanics, physical coupling to internal membranes and/or cytoskeletal proteins, and sensitivity to lipidic second messengers generated by MS enzymes. Various strategies that can be used for separating out different MS-gating mechanisms and their possible role in specific TRPCs are discussed.
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Affiliation(s)
- Owen P Hamill
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, Texas 77555
| | - Rosario Maroto
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, Texas 77555
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113
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Stokely ME, Hwang SY, Hwang JY, Fan B, King MA, Inokuchi K, Koulen P. Polycystin-1 can interact with homer 1/Vesl-1 in postnatal hippocampal neurons. J Neurosci Res 2007; 84:1727-37. [PMID: 17016857 DOI: 10.1002/jnr.21076] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Polycystin-1 (PC-1) has been identified as critical to development of the nervous system, but the significance of PC-1 expression in neurons remains undefined, and little is known of its roles outside the kidney, where mutation results in autosomal dominant polycystic kidney disease (ADPKD). In kidney, PC-1 interacts with cadherins, catenins, and its cognate calcium channel polycystin-2 (PC-2), which in turn interacts with a number of actin-regulatory proteins. Because some of the proteins that interact with PC-1 in kidney also participate in synaptic remodeling and plasticity in the hippocampus, we decided to test PC-1's potential to interact with a recently discovered type of plasticity-associated protein (homer 1a/Vesl-1S) in postnatal mouse hippocampus. Homer 1a/Vesl-1S is an activity-induced protein believed to participate in synaptic remodeling/plasticity responses to temporal lobe seizure and learning. Here we report the following. 1) PC-1 contains a homer-binding motif (PPxxF), which lies within its purported cytoplasmic domain. 2) Immunoreactivity for PC-1 (PC-1-ir) is highly colocalized with homer 1a immunoreactivity (H1a-ir) in primary cultured hippocampal neurons. 3) PC-1-ir and H1a-ir are present and appear to be colocalized in mouse hippocampus but not cortex on postnatal day 2 (P2), when higher frequencies of spontaneous activity are normal for hippocampus compared with cortex. 4) An endogenous PC-1-ir band with the correct size for the reported C-terminal G-protein-sensitive domain cleavage product of PC-1 (approximately 150 kDa) coimmunoprecipitates with endogenous homer 1/Vesl-1 proteins from mouse brain, suggesting that PC-1 can interact with homer 1/Vesl-1 proteins in postnatal hippocampal neurons.
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Affiliation(s)
- Martha E Stokely
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center at Fort Worth, Fort Worth, TX 76107, USA
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114
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Bichet D, Peters D, Patel AJ, Delmas P, Honoré E. Cardiovascular polycystins: insights from autosomal dominant polycystic kidney disease and transgenic animal models. Trends Cardiovasc Med 2007; 16:292-8. [PMID: 17055386 DOI: 10.1016/j.tcm.2006.07.002] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2006] [Revised: 06/28/2006] [Accepted: 07/03/2006] [Indexed: 12/23/2022]
Abstract
Mutations in the PKD1 and PKD2 polycystin genes are responsible for autosomal dominant polycystic kidney disease (ADPKD), one of the most prevalent genetic kidney disorders. ADPKD is a multisystem disease characterized by the formation of numerous fluid-filled cysts in the kidneys, the pancreas, and the liver. Moreover, major cardiovascular manifestations are common complications in ADPKD. Intracranial aneurysms and arterial hypertension are among the leading causes of mortality in this disease. In the present review, we summarize our current understanding of the role of polycystins in the development, maintenance, and function of the cardiovascular system.
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Affiliation(s)
- Delphine Bichet
- Institut de Pharmacologie Moléculaire et Cellulaire, 06560 Valbonne, France
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115
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Wang S, Zhang J, Nauli SM, Li X, Starremans PG, Luo Y, Roberts KA, Zhou J. Fibrocystin/polyductin, found in the same protein complex with polycystin-2, regulates calcium responses in kidney epithelia. Mol Cell Biol 2007; 27:3241-52. [PMID: 17283055 PMCID: PMC1899915 DOI: 10.1128/mcb.00072-07] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Recent evidence suggests that fibrocystin/polyductin (FPC), polycystin-1 (PC1), and polycystin-2 (PC2) are all localized at the plasma membrane and the primary cilium, where PC1 and PC2 contribute to fluid flow sensation and may function in the same mechanotransduction pathways. To further define the exact subcellular localization of FPC, the protein product encoded by the PKHD1 gene responsible for autosomal recessive polycystic kidney disease (PKD) in humans, and whether FPC has direct and/or indirect cross talk with PC2, which, in turn, is pivotal for the pathogenesis of autosomal dominant PKD, we performed double immunostaining and coimmunoprecipitation as well as a microfluorimetry study of kidney tubular epithelial cells. FPC and PC2 are found to completely or partially colocalize at the plasma membrane and the primary cilium and can be reciprocally coimmunoprecipitated. Although incomplete removal of FPC by small interfering RNA and antibody 803 to intracellular epitopes of FPC did not abolish flow-induced intracellular calcium responses, antibody 804 to extracellular epitopes of FPC blocked cellular calcium responses to flow stimulation. These findings suggest that FPC and polycystins share, at least in part, a common mechanotransduction pathway.
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Affiliation(s)
- Shixuan Wang
- Harvard Institutes of Medicine, Room 522, Brigham and Women's Hospital and Harvard Medical School, 4 Blackfan Circle, Boston, MA 02115, USA
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116
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Köttgen M. TRPP2 and autosomal dominant polycystic kidney disease. Biochim Biophys Acta Mol Basis Dis 2007; 1772:836-50. [PMID: 17292589 DOI: 10.1016/j.bbadis.2007.01.003] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2006] [Revised: 01/08/2007] [Accepted: 01/09/2007] [Indexed: 01/26/2023]
Abstract
Mutations in TRPP2 (polycystin-2) cause autosomal dominant polycystic kidney disease (ADPKD), a common genetic disorder characterized by progressive development of fluid-filled cysts in the kidney and other organs. TRPP2 is a Ca(2+)-permeable nonselective cation channel that displays an amazing functional versatility at the cellular level. It has been implicated in the regulation of diverse physiological functions including mechanosensation, cell proliferation, polarity, and apoptosis. TRPP2 localizes to different subcellular compartments, such as the endoplasmic reticulum (ER), the plasma membrane and the primary cilium. The channel appears to have distinct functions in different subcellular compartments. This functional compartmentalization is thought to contribute to the observed versatility and specificity of TRPP2-mediated Ca(2+) signaling. In the primary cilium, TRPP2 has been suggested to function as a mechanosensitive channel that detects fluid flow in the renal tubule lumen, supporting the proposed role of the primary cilium as the unifying pathogenic concept for cystic kidney disease. This review summarizes the known and emerging functions of TRPP2, focusing on the question of how channel function translates into complex morphogenetic programs regulating tubular structure.
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Affiliation(s)
- Michael Köttgen
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, 725 N. Wolfe Street, Baltimore, MD 21205, USA.
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117
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Pedersen SF, Nilius B. Transient Receptor Potential Channels in Mechanosensing and Cell Volume Regulation. Methods Enzymol 2007; 428:183-207. [PMID: 17875418 DOI: 10.1016/s0076-6879(07)28010-3] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Transient receptor potential (TRP) channels are unique cellular sensors responding to a wide variety of extra- and intracellular signals, including mechanical and osmotic stress. In recent years, TRP channels from multiple subfamilies have been added to the list of mechano- and/or osmosensitive channels, and it is becoming increasingly apparent that Ca(2+) influx via TRP channels plays a crucial role in the response to mechanical and osmotic perturbations in a wide range of cell types. Although the events translating mechanical and osmotic stimuli into regulation of TRP channels are still incompletely understood, the specific mechanisms employed vary between different TRP isoforms, and probably include changes in the tension and/or curvature of the lipid bilayer, changes in the cortical cytoskeleton, and signaling events such as lipid metabolism and protein phosphorylation/dephosphorylation. This chapter describes candidate mechanosensitive channels from mammalian TRP subfamilies, discusses inherent and technical issues potentially confounding evaluation of mechano- and/or osmosensitivity, and presents methods relevant to the study of TRP channel regulation by mechanical and osmotic stimuli and involvement in cell volume regulation.
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118
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Abstract
Many human diseases are caused by mutations in ion channels. Dissecting the pathogenesis of these 'channelopathies' has yielded important insights into the regulation of vital biological processes by ions and has become a productive tool of modern ion channel biology. One of the best examples of a synergism between the clinical and basic science aspects of a modern biological topic is cystic fibrosis. Not only did the identification of the ion channel mutated in cystic fibrosis pinpoint the root cause of this disease, but it also has significantly advanced our understanding of basic biological processes as diverse as protein folding and epithelial fluid and electrolyte secretion. The list of confirmed 'channelopathies' is growing and several members of the TRP family of ion channels have been implicated in human diseases such as mucolipidosis type IV (MLIV), autosomal dominant polycystic kidney disease (ADPKD), familial focal segmental glomerulosclerosis (FSG), hypomagnesemia with secondary hypocalcaemia (HSH), and several forms of cancer. Analysing pathogenesis of the diseases linked to TRP dysregulation provides an exciting means of identifying novel functions of TRP channels.
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Affiliation(s)
- Kirill Kiselyov
- Department of Biological Sciences, University of Pittsburgh, 4249 Fifth Avenue, Pittsburgh, PA 15260, USA.
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119
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Schlöndorff JS, Pollak MR. TRPC6 in glomerular health and disease: what we know and what we believe. Semin Cell Dev Biol 2006; 17:667-74. [PMID: 17116414 PMCID: PMC2705932 DOI: 10.1016/j.semcdb.2006.11.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Mutations in TRPC6, a member of the transient receptor potential (TRP) superfamily of non-selective cation channels, have been identified as causing a familial form of focal segmental glomerulosclerosis, a disease characterized by proteinuria and progressive renal failure. Here we review the effect of disease-associated mutations on TRPC6 function and place TRPC6 within the context of other proteins central to glomerular and podocyte function. Finally, the known roles of TRPC6 in the kidney and other organ systems are used as a framework to discuss possible signaling pathways that TRPC6 may modulate during normal glomerular function and in disease states.
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Affiliation(s)
- Johannes S Schlöndorff
- Renal Division, Brigham and Women's Hospital/Harvard Medical School, Boston, MA 02115, USA
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120
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Abstract
This article cannot comprehensively cover the enormous strides made in defining the molecular and cellular basis of renal cystic diseases over the last decade. Therefore, it provides a brief overview and categorization of inherited, developmental, and acquired renal cystic diseases, providing a relevant, up-to-date bibliography as well as a useful list of informative Internet Web sites. Its major focus is the translational biology of polycystic kidney disease. It demonstrates how emerging molecular and cellular knowledge of the pathophysiology of particular diseases such as autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ADPKD) can translate into innovative therapeutic insights.
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Affiliation(s)
- Ellis D Avner
- Children's Research Institute, Children's Hospital & Health System of Wisconsin, and Medical College of Wisconsin, Department of Pediatrics, Division of Pediatrics, 8701 Watertown Plank Road, Milwaukee 53225, USA.
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121
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Nauli SM, Rossetti S, Kolb RJ, Alenghat FJ, Consugar MB, Harris PC, Ingber DE, Loghman-Adham M, Zhou J. Loss of polycystin-1 in human cyst-lining epithelia leads to ciliary dysfunction. J Am Soc Nephrol 2006; 17:1015-25. [PMID: 16565258 DOI: 10.1681/asn.2005080830] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
A "two-hit" hypothesis predicts a second somatic hit, in addition to the germline mutation, as a prerequisite to cystogenesis and has been proposed to explain the focal nature for renal cyst formation in autosomal dominant polycystic kidney disease (ADPKD). It was reported previously that Pkd1(null/null) mouse kidney epithelial cells are unresponsive to flow stimulation. This report shows that Pkd1(+/null) cells are capable of responding to mechanical flow stimulation by changing their intracellular calcium concentration in a manner similar to that of wild-type cells. This paper reports that human renal epithelia require a higher level of shear stress to evoke a cytosolic calcium increase than do mouse renal epithelia. Both immortalized and primary cultured renal epithelial cells that originate from normal and nondilated ADPKD human kidney tubules display normal ciliary expression of the polycystins and respond to fluid-flow shear stress with the typical change in cytosolic calcium. In contrast, immortalized and primary cultured cyst-lining epithelial cells from ADPKD patients with mutations in PKD1 or with abnormal ciliary expression of polycystin-1 or -2 were not responsive to fluid shear stress. These data support a two-hit hypothesis as a mechanism of cystogenesis. This report proposes that calcium response to fluid-flow shear stress can be used as a readout of polycystin function and that loss of mechanosensation in the renal tubular epithelia is a feature of PKD cysts.
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Affiliation(s)
- Surya M Nauli
- Harvard Institutes of Medicine, Suite 520, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
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122
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Torres VE, Harris PC. Mechanisms of Disease: autosomal dominant and recessive polycystic kidney diseases. ACTA ACUST UNITED AC 2006; 2:40-55; quiz 55. [PMID: 16932388 DOI: 10.1038/ncpneph0070] [Citation(s) in RCA: 212] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2005] [Accepted: 09/27/2005] [Indexed: 12/21/2022]
Abstract
Autosomal dominant polycystic kidney disease and autosomal recessive polycystic kidney disease are the best known of a large family of inherited diseases characterized by the development of renal cysts of tubular epithelial cell origin. Autosomal dominant and recessive polycystic kidney diseases have overlapping but distinct pathogeneses. Identification of the causative mutated genes and elucidation of the function of their encoded proteins is shedding new light on the mechanisms that underlie tubular epithelial cell differentiation. This review summarizes recent literature on the role of primary cilia, intracellular calcium homeostasis, and signaling involving Wnt, cyclic AMP and Ras/MAPK, in the pathogenesis of polycystic kidney disease. Improved understanding of pathogenesis and the availability of animal models orthologous to the human diseases provide an excellent opportunity for the development of pathophysiology-based therapies. Some of these have proven effective in preclinical studies, and clinical trials have begun.
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Affiliation(s)
- Vicente E Torres
- Mayo Clinic College of Medicine, Eisenberg S33B, Nephrology, 200 First St SW, Rochester, MN 55905, USA.
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123
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Giamarchi A, Padilla F, Coste B, Raoux M, Crest M, Honoré E, Delmas P. The versatile nature of the calcium-permeable cation channel TRPP2. EMBO Rep 2006; 7:787-93. [PMID: 16880824 PMCID: PMC1525146 DOI: 10.1038/sj.embor.7400745] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2006] [Accepted: 06/02/2006] [Indexed: 12/19/2022] Open
Abstract
TRPP2 is a member of the transient receptor potential (TRP) superfamily of cation channels, which is mutated in autosomal dominant polycystic kidney disease (ADPKD). TRPP2 is thought to function with polycystin 1-a large integral protein-as part of a multiprotein complex involved in transducing Ca(2+)-dependent information. TRPP2 has been implicated in various biological functions including cell proliferation, sperm fertilization, mating behaviour, mechanosensation and asymmetric gene expression. Although its function as a Ca(2+)-permeable cation channel is well established, its precise role in the plasma membrane, the endoplasmic reticulum and the cilium is controversial. Recent studies suggest that TRPP2 function is highly dependent on the subcellular compartment of expression, and is regulated by many interactions with adaptor proteins. This review summarizes the most pertinent evidence about the properties of TRPP2 channels, focusing on the compartment-specific functions of mammalian TRPP2.
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Affiliation(s)
- Aurélie Giamarchi
- Laboratoire de Neurophysiologie Cellulaire, CNRS, UMR 6150, Faculté de Médecine, IFR Jean Roche, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
| | - Françoise Padilla
- Laboratoire de Neurophysiologie Cellulaire, CNRS, UMR 6150, Faculté de Médecine, IFR Jean Roche, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
| | - Bertrand Coste
- Laboratoire de Neurophysiologie Cellulaire, CNRS, UMR 6150, Faculté de Médecine, IFR Jean Roche, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
| | - Matthieu Raoux
- Laboratoire de Neurophysiologie Cellulaire, CNRS, UMR 6150, Faculté de Médecine, IFR Jean Roche, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
| | - Marcel Crest
- Laboratoire de Neurophysiologie Cellulaire, CNRS, UMR 6150, Faculté de Médecine, IFR Jean Roche, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
| | - Eric Honoré
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, 660, Route des Lucioles, Sophia Antipolis, 06560 Valbonne, France
| | - Patrick Delmas
- Laboratoire de Neurophysiologie Cellulaire, CNRS, UMR 6150, Faculté de Médecine, IFR Jean Roche, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
- Tel: +00 33 4 91 69 89 70; Fax: 00 33 4 91 69 89 77
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124
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Masyuk AI, Masyuk TV, Splinter PL, Huang BQ, Stroope AJ, LaRusso NF. Cholangiocyte cilia detect changes in luminal fluid flow and transmit them into intracellular Ca2+ and cAMP signaling. Gastroenterology 2006; 131:911-20. [PMID: 16952559 PMCID: PMC1866168 DOI: 10.1053/j.gastro.2006.07.003] [Citation(s) in RCA: 226] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2005] [Accepted: 06/08/2006] [Indexed: 02/07/2023]
Abstract
BACKGROUND & AIMS Cholangiocytes have primary cilia extending from the apical plasma membrane into the ductal lumen. While the physiologic significance of cholangiocyte cilia is unknown, studies in renal epithelia suggest that primary cilia possess sensory functions. Here, we tested the hypothesis that cholangiocyte cilia are sensory organelles that detect and transmit luminal bile flow stimuli into intracellular Ca2+ ([Ca2+]i) and adenosine 3',5'-cyclic monophosphate (cAMP) signaling. METHODS Scanning electron microscopy, transmission electron microscopy, and immunofluorescent confocal microscopy of rat isolated intrahepatic bile duct units (IBDUs) were used to detect and characterize cholangiocyte cilia. The fluid flow-induced changes in Ca2+ and cAMP levels in cholangiocytes of microperfused IBDUs were detected by epifluorescence microscopy and a fluorescence assay, respectively. RESULTS In microperfused IBDUs, luminal fluid flow induced an increase in [Ca2+]i and caused suppression of the forskolin-stimulated cAMP increase. The fluid flow-induced changes in [Ca2+]i and cAMP levels were significantly reduced or abolished when cilia were removed by chloral hydrate or when ciliary-associated proteins polycystin-1 (a mechanoreceptor), polycystin-2 (a Ca2+ channel), and the Ca2+-inhibitable adenylyl cyclase isoform 6 were individually down-regulated by small interfering RNAs. CONCLUSIONS Cholangiocyte cilia are sensory organelles containing polycystin-1, polycystin-2, and adenylyl cyclase isoform 6 through which luminal fluid flow affects both [Ca2+]i and cAMP signaling in the cell. The data suggest a new model for regulation of ductal bile secretion involving cholangiocyte cilia.
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Affiliation(s)
- Anatoliy I Masyuk
- Miles and Shirley Fiterman Center for Digestive Diseases, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA
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125
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Ishimaru Y, Inada H, Kubota M, Zhuang H, Tominaga M, Matsunami H. Transient receptor potential family members PKD1L3 and PKD2L1 form a candidate sour taste receptor. Proc Natl Acad Sci U S A 2006; 103:12569-74. [PMID: 16891422 PMCID: PMC1531643 DOI: 10.1073/pnas.0602702103] [Citation(s) in RCA: 377] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Animals use their gustatory systems to evaluate the nutritious value, toxicity, sodium content, and acidity of food. Although characterization of molecular identities that receive taste chemicals is essential, molecular receptors underlying sour taste sensation remain unclear. Here, we show that two transient receptor potential (TRP) channel members, PKD1L3 and PKD2L1, are coexpressed in a subset of taste receptor cells in specific taste areas. Cells expressing these molecules are distinct from taste cells having receptors for bitter, sweet, or umami tastants. The PKD2L1 proteins are accumulated at the taste pore region, where taste chemicals are detected. PKD1L3 and PKD2L1 proteins can interact with each other, and coexpression of the PKD1L3 and PKD2L1 is necessary for their functional cell surface expression. Finally, PKD1L3 and PKD2L1 are activated by various acids when coexpressed in heterologous cells but not by other classes of tastants. These results suggest that PKD1L3 and PKD2L1 heteromers may function as sour taste receptors.
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Affiliation(s)
| | - Hitoshi Inada
- Section of Cell Signaling, Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan; and
| | - Momoka Kubota
- Departments of *Molecular Genetics and Microbiology and
| | - Hanyi Zhuang
- Departments of *Molecular Genetics and Microbiology and
| | - Makoto Tominaga
- Section of Cell Signaling, Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Okazaki, Aichi 444-8787, Japan; and
- Department of Physiological Sciences, Graduate University for Advanced Studies, Okazaki 444-8585, Japan
| | - Hiroaki Matsunami
- Departments of *Molecular Genetics and Microbiology and
- Neurobiology, Duke University Medical Center, Research Drive, Durham, NC 27710
- To whom correspondence should be addressed. E-mail:
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126
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Schneider L, Clement CA, Teilmann SC, Pazour GJ, Hoffmann EK, Satir P, Christensen ST. PDGFRalphaalpha signaling is regulated through the primary cilium in fibroblasts. Curr Biol 2006; 15:1861-6. [PMID: 16243034 DOI: 10.1016/j.cub.2005.09.012] [Citation(s) in RCA: 457] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2005] [Revised: 09/01/2005] [Accepted: 09/01/2005] [Indexed: 11/28/2022]
Abstract
Recent findings show that cilia are sensory organelles that display specific receptors and ion channels, which transmit signals from the extracellular environment via the cilium to the cell to control tissue homeostasis and function. Agenesis of primary cilia or mislocation of ciliary signal components affects human pathologies, such as polycystic kidney disease and disorders associated with Bardet-Biedl syndrome. Primary cilia are essential for hedgehog ligand-induced signaling cascade regulating growth and patterning. Here, we show that the primary cilium in fibroblasts plays a critical role in growth control via platelet-derived growth factor receptor alpha (PDGFRalpha), which localizes to the primary cilium during growth arrest in NIH3T3 cells and primary cultures of mouse embryonic fibroblasts. Ligand-dependent activation of PDGFRalphaalpha is followed by activation of Akt and the Mek1/2-Erk1/2 pathways, with Mek1/2 being phosphorylated within the cilium and at the basal body. Fibroblasts derived from Tg737(orpk) mutants fail to form normal cilia and to upregulate the level of PDGFRalpha; PDGF-AA fails to activate PDGFRalphaalpha and the Mek1/2-Erk1/2 pathway. Signaling through PDGFRbeta, which localizes to the plasma membrane, is maintained at comparable levels in wild-type and mutant cells. We propose that ciliary PDGFRalphaalpha signaling is linked to tissue homeostasis and to mitogenic signaling pathways.
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Affiliation(s)
- Linda Schneider
- Department of Biochemistry, Institute for Molecular Biology and Physiology, University of Copenhagen, The August Krogh Building, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark
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127
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Sweeney WE, Avner ED. Molecular and cellular pathophysiology of autosomal recessive polycystic kidney disease (ARPKD). Cell Tissue Res 2006; 326:671-85. [PMID: 16767405 DOI: 10.1007/s00441-006-0226-0] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2006] [Accepted: 04/20/2006] [Indexed: 12/19/2022]
Abstract
Autosomal recessive polycystic kidney disease (ARPKD) belongs to a group of congenital hepatorenal fibrocystic syndromes characterized by dual renal and hepatic involvement of variable severity. Despite the wide clinical spectrum of ARPKD (MIM 263200), genetic linkage studies indicate that mutations at a single locus, PKHD1 (polycystic kidney and hepatic disease 1), located on human chromosome region 6p21.1-p12, are responsible for all phenotypes of ARPKD. Identification of cystic disease genes and their encoded proteins has provided investigators with critical tools to begin to unravel the molecular and cellular mechanisms of PKD. PKD cystic epithelia share common phenotypic abnormalities despite the different genetic mutations that underlie the disease. Recent studies have shown that many cyst-causing proteins are expressed in multimeric complexes at distinct subcellular locations within epithelia. This co-expression of cystoproteins suggests that cyst formation, regardless of the underlying disease gene, results from perturbations in convergent and/or integrated signal transduction pathways. To date, no specific therapies are in clinical use for ameliorating cyst growth in ARPKD. However, studies noted in this review suggest that therapeutic targeting of the cAMP and epidermal growth factor receptor (EGFR)-axis abnormalities in cystic epithelia may translate into effective therapies for ARPKD and, by analogy, autosomal dominant polycystic kidney disease (ADPKD). A particularly promising approach appears to be the targeting of downstream intermediates of both the cAMP and EGFR axis. This review focuses on ARPKD and presents a concise summary of the current understanding of the molecular genetics and cellular pathophysiology of this disease. It also highlights phenotypic and mechanistic similarities between ARPKD and ADPKD.
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Affiliation(s)
- William E Sweeney
- Children's Research Institute, Children's Hospital Health System of Wisconsin, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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128
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Gray MA. Primary cilia and regulation of renal Na+ transport. Focus on "Heightened epithelial Na+ channel-mediated Na+ absorption in a murine polycystic kidney disease model epithelium lacking apical monocilia". Am J Physiol Cell Physiol 2006; 290:C947-9. [PMID: 16531571 DOI: 10.1152/ajpcell.00640.2005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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129
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Abstract
The past decade or so has seen rapid progress in our understanding of how left-right (LR) asymmetry is generated in vertebrate embryos. However, many important questions about this process remain unanswered. Although a leftward flow of extra-embryonic fluid in the node cavity (nodal flow) is likely to be the symmetry-breaking event, at least in the mouse embryo, it is not yet known how this flow functions or how the asymmetric signal generated in the node is transferred to the lateral plate. The final step in left-right patterning - translation of the asymmetric signal into morphology - is also little understood.
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Affiliation(s)
- Hidetaka Shiratori
- Developmental Genetics Group, Graduate School for Frontier Biosciences, Osaka University, Japan Science and Technology Corporation
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130
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Wang Q, Pan J, Snell WJ. Intraflagellar Transport Particles Participate Directly in Cilium-Generated Signaling in Chlamydomonas. Cell 2006; 125:549-62. [PMID: 16678098 DOI: 10.1016/j.cell.2006.02.044] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2005] [Revised: 11/18/2005] [Accepted: 02/07/2006] [Indexed: 12/27/2022]
Abstract
Primary cilia are widely used for signal transduction during development and in homeostasis and are assembled and maintained by intraflagellar transport (IFT). Here, we have dissected the role of IFT in signaling within the flagella (structural and functional counterparts of cilia) of the biflagellated green alga Chlamydomonas. Using a conditional IFT mutant enables us to deplete the IFT machinery from intact, existing flagella. We identify a cGMP-dependent protein kinase (CrPKG) within flagella as the substrate of a protein tyrosine kinase activated by flagellar adhesion during fertilization. We demonstrate that flagellar adhesion stimulates association of CrPKG with a new flagellar compartment. Moreover, formation of the compartment requires IFT, and IFT particles themselves are part of the compartment. Our results lead to a model in which the IFT machinery is required not only for assembling cilia and flagella but also for organizing a signaling pathway within the organelles during cilium-generated signaling.
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Affiliation(s)
- Qian Wang
- Department of Cell Biology, University of Texas Southwestern Medical School, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA
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131
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Abstract
The establishment of left-right asymmetry in mammals is a good example of how multiple cell biological processes coordinate in the formation of a basic body plan. The leftward movement of fluid at the ventral node, called nodal flow, is the central process in symmetry breaking on the left-right axis. Nodal flow is autonomously generated by the rotation of cilia that are tilted toward the posterior on cells of the ventral node. These cilia are built by transport via the KIF3 motor complex. How nodal flow is interpreted to create left-right asymmetry has been a matter of debate. Recent evidence suggests that the leftward movement of membrane-sheathed particles, called nodal vesicular parcels (NVPs), may result in the activation of the non-canonical Hedgehog signaling pathway, an asymmetric elevation in intracellular Ca(2+) and changes in gene expression.
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Affiliation(s)
- Nobutaka Hirokawa
- Department of Cell Biology & Anatomy, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan.
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132
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Low SH, Vasanth S, Larson CH, Mukherjee S, Sharma N, Kinter MT, Kane ME, Obara T, Weimbs T. Polycystin-1, STAT6, and P100 function in a pathway that transduces ciliary mechanosensation and is activated in polycystic kidney disease. Dev Cell 2006; 10:57-69. [PMID: 16399078 DOI: 10.1016/j.devcel.2005.12.005] [Citation(s) in RCA: 262] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2005] [Revised: 06/15/2005] [Accepted: 12/08/2005] [Indexed: 11/22/2022]
Abstract
Primary cilia are implicated in the pathogenesis of autosomal-dominant polycystic kidney disease (ADPKD), which results from defects in polycystin-1 (PC1), but the function of PC1 remains poorly understood. Here, we show that PC1 undergoes proteolytic cleavage that results in nuclear translocation of its cytoplasmic tail. The PC1 tail interacts with the transcription factor STAT6 and the coactivator P100, and it stimulates STAT6-dependent gene expression. Under normal conditions, STAT6 localizes to primary cilia of renal epithelial cells. Cessation of apical fluid flow results in nuclear translocation of STAT6. Cyst-lining cells in ADPKD exhibit elevated levels of nuclear STAT6, P100, and the PC1 tail. Exogenous expression of the human PC1 tail results in renal cyst formation in zebrafish embryos. These results identify a novel mechanism of cilia function in the transduction of a mechanical signal to changes of gene expression involving PC1 and show that this pathway is inappropriately activated in ADPKD.
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MESH Headings
- Amino Acid Sequence
- Animals
- Blotting, Northern/methods
- Blotting, Western/methods
- Cell Line
- Cilia/drug effects
- Cilia/metabolism
- Dose-Response Relationship, Drug
- Embryo, Mammalian
- Embryo, Nonmammalian
- Endonucleases
- Enzyme Activation/physiology
- Epithelium/drug effects
- Epithelium/metabolism
- Fluorescent Antibody Technique/methods
- Gene Expression/physiology
- Gene Expression Regulation/drug effects
- Gene Expression Regulation/physiology
- Humans
- Immunoprecipitation/methods
- Interleukin-4/pharmacology
- Kidney/metabolism
- Kidney/pathology
- Kidney/ultrastructure
- Luciferases/metabolism
- Mechanotransduction, Cellular/physiology
- Models, Biological
- Molecular Biology/methods
- Mutagenesis/physiology
- Nuclear Proteins/metabolism
- Polycystic Kidney, Autosomal Dominant/metabolism
- Polycystic Kidney, Autosomal Dominant/pathology
- Protein Binding
- Protein Structure, Tertiary
- Proteins/physiology
- STAT6 Transcription Factor/metabolism
- TRPP Cation Channels
- Trans-Activators/physiology
- Transfection/methods
- Translocation, Genetic
- Zebrafish
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Affiliation(s)
- Seng Hui Low
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California 93106, USA
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133
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Abstract
Transient receptor potential (TRP) receptors are, typically, calcium-permeant cation channels that transduce environmental stimuli. Both kidney epithelial and inner ear sensory cells express TRPV1, are mechanosensors and accumulate the aminoglycoside antibiotic gentamicin. Recently, we showed that Texas Red-conjugated gentamicin (GTTR) enters kidney cells via an endosome-independent pathway. Here, we used GTTR to investigate this non-endocytotic mechanism of gentamicin uptake. In serum-free buffers, GTTR penetrated MDCK cells within 30 s and uptake was modulated by extracellular, multivalent cations (Ca2+, La3+, Gd3+) or protons. We verified the La3+ modulation of GTTR uptake using immunocytochemical detection of unconjugated gentamicin. Membrane depolarization, induced by high extracellular K+ or valinomycin, also reduced GTTR uptake, suggesting electrophoretic permeation through ion channels. GTTR uptake was enhanced by the TRPV1 agonists, resiniferatoxin and anandamide, in Ca2+-free media. Competitive antagonists of the TRPV1 cation current, iodo-resiniferatoxin and SB366791, also enhanced GTTR uptake independently of Ca2+, reinforcing these antagonists' potential as latent agonists in specific situations. Ruthenium Red blocked GTTR uptake in the presence or absence of these TRPV1-agonists and antagonists. In addition, GTTR uptake was blocked by RTX in the presence of more physiological levels (2 mM) of Ca2+. Thus gentamicin enters cells via cation channels, and gentamicin uptake can be modulated by regulators of the TRPV1 channel.
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Affiliation(s)
- Sigrid E Myrdal
- Oregon Hearing Research Center, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA
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134
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Myrdal SE, Johnson KC, Steyger PS. Cytoplasmic and intra-nuclear binding of gentamicin does not require endocytosis. Hear Res 2006; 204:156-69. [PMID: 15925201 PMCID: PMC2736065 DOI: 10.1016/j.heares.2005.02.002] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/10/2004] [Accepted: 02/02/2005] [Indexed: 11/16/2022]
Abstract
Understanding the cellular mechanism(s) by which the oto- and nephrotoxic aminoglycoside antibiotics penetrate cells, and the precise intracellular distribution of these molecules, will enable identification of aminoglycoside-sensitive targets, and potential uptake blockers. Clones of two kidney cell lines, OK and MDCK, were treated with the aminoglycoside gentamicin linked to the fluorophore Texas Red (GTTR). As in earlier reports, endosomal accumulation was observed in live cells, or cells fixed with formaldehyde only. However, delipidation of fixed cells revealed GTTR fluorescence in cytoplasmic and nuclear compartments. Immunolabeling of both GTTR and unconjugated gentamicin corresponded to the cytoplasmic distribution of GTTR fluorescence. Intra-nuclear GTTR binding co-localized with labeled RNA in the nucleoli and trans-nuclear tubules. Cytoplasmic and nuclear distribution of GTTR was quenched by phosphatidylinositol-bisphosphate (PIP2), a known ligand for gentamicin. Cytoplasmic and nuclear GTTR binding increased over time (at 37 degrees C, or on ice to inhibit endocytosis), and was serially competed off by increasing concentrations of unconjugated gentamicin, i.e., GTTR binding is saturable. In contrast, little or no reduction of endocytotic GTTR uptake was observed when cells were co-incubated with up to 4 mg/mL unconjugated gentamicin. Thus, cytoplasmic and nuclear GTTR uptake is time-dependent, weakly temperature-dependent and saturable, suggesting that it occurs via an endosome-independent mechanism, implicating ion channels, transporters or pores in the plasma membrane as bioregulatory routes for gentamicin entry into cells.
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MESH Headings
- Animals
- Anti-Bacterial Agents/adverse effects
- Anti-Bacterial Agents/metabolism
- Binding Sites/drug effects
- Cell Line
- Dogs
- Dose-Response Relationship, Drug
- Endocytosis/physiology
- Fluorescent Dyes
- Gentamicins/adverse effects
- Gentamicins/metabolism
- Immunohistochemistry
- Kidney Tubules, Distal/cytology
- Kidney Tubules, Distal/drug effects
- Kidney Tubules, Distal/metabolism
- Kidney Tubules, Proximal/cytology
- Kidney Tubules, Proximal/drug effects
- Kidney Tubules, Proximal/metabolism
- Microscopy, Confocal
- Neurons/drug effects
- Opossums
- Phosphatidylinositol 4,5-Diphosphate/metabolism
- Phosphatidylinositol 4,5-Diphosphate/pharmacology
- Xanthenes
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Affiliation(s)
- Sigrid E Myrdal
- Oregon Hearing Research Center, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA
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135
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Siroky BJ, Ferguson WB, Fuson AL, Xie Y, Fintha A, Komlosi P, Yoder BK, Schwiebert EM, Guay-Woodford LM, Bell PD. Loss of primary cilia results in deregulated and unabated apical calcium entry in ARPKD collecting duct cells. Am J Physiol Renal Physiol 2006; 290:F1320-8. [PMID: 16396941 DOI: 10.1152/ajprenal.00463.2005] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Recent genetic analysis has identified a pivotal role of primary cilia in the pathogenesis of polycystic kidney disease (PKD). However, little is known regarding how cilia loss/dysfunction contributes to cyst development. In epithelial cells, changes in apical fluid flow induce cilia-mediated Ca2+ entry via polycystin-2 (PC2), a cation channel. The Oak Ridge Polycystic Kidney (orpk) mouse contains a mutated Tg737 gene that disrupts expression of polaris, a protein required for ciliogenesis. These studies examine the effect of cilia malformation on Ca2+ entry in orpk cilia(-) collecting duct principal cells, and in orpk cells in which wild-type Tg737 was reintroduced, orpk cilia(+). [Ca2+]i was monitored in confluent cell monolayers using fluorescence microscopy. Intrinsic apical Ca2+ entry was measured by Mn2+ quenching and Ca2+ depletion/readdition under flow conditions below the threshold for stimulation. We found that unstimulated apical Ca2+ entry was markedly increased in cilia(-) cells and was sensitive to Gd3+, an inhibitor of PC2. Electrophysiological measurements demonstrate increased abundance of an apical channel, consistent with PC2, in cilia(-) cells. Immunofluorescence studies revealed that PC2, normally expressed on and at the base of cilia in orpk cilia(+) cells, was observed throughout the apical membrane in cilia(-) cells. Furthermore, cilia(-) cells displayed elevated subapical Ca2+ levels measured with the near-membrane Ca2+ indicator FFP-18. We propose that cilia exert a tonic regulatory influence on apical Ca2+ entry, and absence of cilia results in loss of spatial organization of PC2, causing unregulated Ca2+ entry and elevations in subapical [Ca2+], a factor which may contribute to cyst formation.
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Affiliation(s)
- Brian J Siroky
- Department of Physiology, Univ. of Alabama at Birmingham, Birmingham, AL, USA
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136
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Wood JN. Chapter 5 Molecular mechanisms of nociception and pain. HANDBOOK OF CLINICAL NEUROLOGY 2006; 81:49-59. [PMID: 18808827 DOI: 10.1016/s0072-9752(06)80009-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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137
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Hughes P, Robati M, Lu W, Zhou J, Strasser A, Bouillet P. Loss of PKD1 and loss of Bcl-2 elicit polycystic kidney disease through distinct mechanisms. Cell Death Differ 2005; 13:1123-7. [PMID: 16282979 PMCID: PMC2795698 DOI: 10.1038/sj.cdd.4401815] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
We have recently demonstrated that ablation of one or both alleles of the proapoptotic gene Bim prevents the polycystic kidney disease (PKD) that develops in mice deficient for the prosurvival protein Bcl-2. The aim of the present study was to investigate whether loss of Bim or Bcl-2 could influence the disease in the PKD1del34/del34 mutant mice, a model of autosomal dominant PKD. PKD1del34/del34 mice were intercrossed with Bim-deficient mice and Bcl-2+/- mice to generate double mutants. Loss of Bim does not prevent the development of PKD in PKD1del34/del34 mice. On the C57BL/6 genetic background, most older PKD1del34/+ mice do not develop PKD, but present with liver cysts. Surprisingly, loss of Bim completely prevented liver cysts formation in PKD1del34/+ mice. Loss of one Bcl-2 allele did not influence the PKD1del34 phenotype significantly. We conclude that loss of PKD1 and loss of Bcl-2 elicit PKD through distinct mechanisms.
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Affiliation(s)
- P Hughes
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria 3050, Australia
- Department of Medical Biology, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - M Robati
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria 3050, Australia
| | - W Lu
- Renal Division, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, USA
| | - J Zhou
- Renal Division, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, USA
| | - A Strasser
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria 3050, Australia
| | - P Bouillet
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria 3050, Australia
- Corresponding author: P Bouillet, The Walter and Eliza Hall Institute of Medical Research, P.O. The Royal Melbourne Hospital, Parkville, Vic, 3050. Australia. Tel: +61-3-9345-2334; Fax: +61-3-9347-0852;
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138
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Abstract
The past decade has seen remarkable advances in defining the molecular mechanisms underlying formation of the embryonic left right (LR) axis. This information is slowly transforming our understanding of human birth defects that are caused by disturbed LR axis patterning. Reversals, isomerisms, or segmental discordances of thoraco-abdominal organ position, that is, classic heterotaxy, clearly indicate embryonic disruption of normal LR patterning. Other isolated birth defects, particularly cardiovascular malformations, may be caused by deficiencies in the same pathways. Here, we review the distinctive clinical features of human heterotaxias and try to summarize the known connections between them and the corresponding developmental pathways.
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Affiliation(s)
- Lirong Zhu
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
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139
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Brown JH, Bihoreau MT, Hoffmann S, Kränzlin B, Tychinskaya I, Obermüller N, Podlich D, Boehn SN, Kaisaki PJ, Megel N, Danoy P, Copley RR, Broxholme J, Witzgall R, Lathrop M, Gretz N, Gauguier D. Missense mutation in sterile alpha motif of novel protein SamCystin is associated with polycystic kidney disease in (cy/+) rat. J Am Soc Nephrol 2005; 16:3517-26. [PMID: 16207829 DOI: 10.1681/asn.2005060601] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Autosomal dominant polycystic kidney disease (PKD) is the most common genetic disease that leads to kidney failure in humans. In addition to the known causative genes PKD1 and PKD2, there are mutations that result in cystic changes in the kidney, such as nephronophthisis, autosomal recessive polycystic kidney disease, or medullary cystic kidney disease. Recent efforts to improve the understanding of renal cystogenesis have been greatly enhanced by studies in rodent models of PKD. Genetic studies in the (cy/+) rat showed that PKD spontaneously develops as a consequence of a mutation in a gene different from the rat orthologs of PKD1 and PKD2 or other genes that are known to be involved in human cystic kidney diseases. This article reports the positional cloning and mutation analysis of the rat PKD gene, which revealed a C to T transition that replaces an arginine by a tryptophan at amino acid 823 in the protein sequence. It was determined that Pkdr1 is specifically expressed in renal proximal tubules and encodes a novel protein, SamCystin, that contains ankyrin repeats and a sterile alpha motif. The characterization of this protein, which does not share structural homologies with known polycystins, may give new insights into the pathophysiology of renal cyst development in patients.
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Affiliation(s)
- Joanna H Brown
- The Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK
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140
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Abstract
A current challenge in neuroscience is to bridge the gaps between genes, proteins, neurons, neural circuits, and behavior in a single animal model. The nematode Caenorhabditis elegans has unique features that facilitate this synthesis. Its nervous system includes exactly 302 neurons, and their pattern of synaptic connectivity is known. With only five olfactory neurons, C. elegans can dynamically respond to dozens of attractive and repellent odors. Thermosensory neurons enable the nematode to remember its cultivation temperature and to track narrow isotherms. Polymodal sensory neurons detect a wide range of nociceptive cues and signal robust escape responses. Pairing of sensory stimuli leads to long-lived changes in behavior consistent with associative learning. Worms exhibit social behaviors and complex ultradian rhythms driven by Ca(2+) oscillators with clock-like properties. Genetic analysis has identified gene products required for nervous system function and elucidated the molecular and neural bases of behaviors.
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Affiliation(s)
- Mario de Bono
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom.
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141
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Wilczynska Z, Happle K, Müller-Taubenberger A, Schlatterer C, Malchow D, Fisher PR. Release of Ca2+ from the endoplasmic reticulum contributes to Ca2+ signaling in Dictyostelium discoideum. EUKARYOTIC CELL 2005; 4:1513-25. [PMID: 16151245 PMCID: PMC1214202 DOI: 10.1128/ec.4.9.1513-1525.2005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2005] [Accepted: 06/17/2005] [Indexed: 11/20/2022]
Abstract
Ca2+ responses to two chemoattractants, folate and cyclic AMP (cAMP), were assayed in Dictyostelium D. discoideum mutants deficient in one or both of two abundant Ca2+-binding proteins of the endoplasmic reticulum (ER), calreticulin and calnexin. Mutants deficient in either or both proteins exhibited enhanced cytosolic Ca2+ responses to both attractants. Not only were the mutant responses greater in amplitude, but they also exhibited earlier onsets, faster rise rates, earlier peaks, and faster fall rates. Correlations among these kinetic parameters and the response amplitudes suggested that key events in the Ca2+ response are autoregulated by the magnitude of the response itself, i.e., by cytosolic Ca2+ levels. This autoregulation was sufficient to explain the altered kinetics of the mutant responses: larger responses are faster in both mutant and wild-type cells in response to both folate (vegetative cells) and cAMP (differentiated cells). Searches of the predicted D. discoideum proteome revealed three putative Ca2+ pumps and four putative Ca2+ channels. All but one contained sequence motifs for Ca2+- or calmodulin-binding sites, consistent with Ca2+ signals being autoregulatory. Although cytosolic Ca2+ responses in the calnexin and calreticulin mutants are enhanced, the influx of Ca2+ from the extracellular medium into the mutant cells was smaller. Compared to wild-type cells, Ca2+ release from the ER in the mutants thus contributes more to the total cytosolic Ca2+ response while influx from the extracellular medium contributes less. These results provide the first molecular genetic evidence that release of Ca2+ from the ER contributes to cytosolic Ca2+ responses in D. discoideum.
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Affiliation(s)
- Zofia Wilczynska
- Department of Microbiology, La Trobe University, Victoria 3086, Australia
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142
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Abstract
The mammalian TRP (transient receptor potential) family consists of six main subfamilies termed the TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), and TRPA (ankyrin) groups. These subfamilies encompass 28 ion channels that function as diverse cellular sensors. All of the channels are permeable to monovalent cations, and most are also permeable to Ca(2+). There are strong indications that TRP channels are involved in many diseases. At this point, four channelopathies have been identified in which a defect in a TRP channel-encoding gene is the direct cause of disease. TRPs are also involved in some systemic diseases because of their role as receptors for irritants, inflammation products, and xenobiotic toxins. Other indications of the involvement of TRPs in several diseases come from correlations between the levels of channel expression and disease symptoms or from the mapping of TRP-encoding genes to susceptible chromosome regions. Finally, the phenotypes of TRP knockout mice and other transgenic models allow a degree of extrapolation to human diseases. We present an overview of current knowledge about the role of TRP channels in human disease and highlight some TRP "suspects" for which a role in disease can be anticipated. An understanding of the genetics of disease may lead to the development of targeted new therapies.
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Affiliation(s)
- Bernd Nilius
- Department of Physiology, Campus Gasthuisberg Katholieke Universiteit, Leuven, Belgium.
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143
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Montalbetti N, Li Q, González-Perrett S, Semprine J, Chen XZ, Cantiello HF. Effect of hydro-osmotic pressure on polycystin-2 channel function in the human syncytiotrophoblast. Pflugers Arch 2005; 451:294-303. [PMID: 16025301 DOI: 10.1007/s00424-005-1458-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2005] [Accepted: 04/25/2005] [Indexed: 12/23/2022]
Abstract
Polycystin-2 (PC2), one of the gene products whose mutations cause autosomal dominant polycystic kidney disease is a transient receptor potential (TRP)-type (TRPP2) Ca(2+)-permeable, non-selective cation channel. PC2 is localized in the plasma membrane, the primary cilium, and other cellular organelles of renal epithelial and other cells. Recent studies indicate that PC2 is involved in signal transduction events associated with the transient increase in cytosolic Ca(2+). Proof of evidence now hinges on involvement of the PC2 channel in the transduction of environmental signals. PC2 is abundantly expressed in the apical membrane of human syncytiotrophoblast (hST), a highly intricate epithelial tissue, which is essential for the maternal-fetal transfer of solutes, including ions. Physical forces such as hydrostatic (H) and osmotic (Pi) pressure play important roles in placenta homeostasis. In this study, we provide new information on PC2 channel regulation in the hST by these environmental factors, and propose a model as to how they may trigger the activation of PC2. Using apical hST vesicles reconstituted in a lipid bilayer system, we found that a change in either H or Pi modified PC2 channel activity. This stimulatory effect was no longer observed in hST vesicles pre-treated with the actin cytoskeleton disrupter cytochalasin D. As shown by immunofluorescence analysis PC2 co-localized with actin filaments in the vicinity of the plasma membrane. This co-localization was disrupted by cytochalasin D. Taken together, our findings indicate that physical forces exerted on cells regulate PC2 channel activity by a sensory mechanism involving the actin cytoskeleton.
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Affiliation(s)
- Nicolás Montalbetti
- Laboratorio de Canales Iónicos, Departamento de Fisicoquímica y Química Analítica, Facultad de Farmacia y Bioquímica, Buenos Aires, Argentina
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144
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Kramer-Zucker AG, Olale F, Haycraft CJ, Yoder BK, Schier AF, Drummond IA. Cilia-driven fluid flow in the zebrafish pronephros, brain and Kupffer's vesicle is required for normal organogenesis. Development 2005; 132:1907-21. [PMID: 15790966 DOI: 10.1242/dev.01772] [Citation(s) in RCA: 523] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cilia, as motile and sensory organelles, have been implicated in normal development, as well as diseases including cystic kidney disease, hydrocephalus and situs inversus. In kidney epithelia, cilia are proposed to be non-motile sensory organelles, while in the mouse node, two cilia populations, motile and non-motile have been proposed to regulate situs. We show that cilia in the zebrafish larval kidney, the spinal cord and Kupffer's vesicle are motile, suggesting that fluid flow is a common feature of each of these organs. Disruption of cilia structure or motility resulted in pronephric cyst formation, hydrocephalus and left-right asymmetry defects. The data show that loss of fluid flow leads to fluid accumulation, which can account for organ distension pathologies in the kidney and brain. In Kupffer's vesicle, loss of flow is associated with loss of left-right patterning, indicating that the 'nodal flow' mechanism of generating situs is conserved in non-mammalian vertebrates.
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145
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Koulen P, Duncan RS, Liu J, Cohen NE, Yannazzo JAS, McClung N, Lockhart CL, Branden M, Buechner M. Polycystin-2 accelerates Ca2+ release from intracellular stores in Caenorhabditis elegans. Cell Calcium 2005; 37:593-601. [PMID: 15862350 DOI: 10.1016/j.ceca.2005.03.003] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2004] [Revised: 03/07/2005] [Accepted: 03/10/2005] [Indexed: 11/15/2022]
Abstract
Polycystin-2, a member of the TRP family of calcium channels, is encoded by the human PKD2 gene. Mutations in that gene can lead to swelling of nephrons into the fluid-filled cysts of polycystic kidney disease. In addition to expression in tubular epithelial cells, human polycystin-2 is found in muscle and neuronal cells, but its cell biological function has been unclear. A homologue in Caenorhabditis elegans is necessary for male mating behavior. We compared the behavior, calcium signaling mechanisms, and electrophysiology of wild-type and pkd-2 knockout C. elegans. In addition to characterizing PKD-2-mediated aggregation and mating behaviors, we found that polycystin-2 is an intracellular Ca(2+) release channel that is required for the normal pattern of Ca(2+) responses involving IP(3) and ryanodine receptor-mediated Ca(2+) release from intracellular stores. Activity of polycystin-2 creates brief cytosolic Ca(2+) transients with increased amplitude and decreased duration. Polycystin-2, along with the IP(3) and ryanodine receptors, acts as a major calcium-release channel in the endoplasmic reticulum in cells where rapid calcium signaling is required, and polycystin-2 activity is essential in those excitable cells for rapid responses to stimuli.
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Affiliation(s)
- Peter Koulen
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center at Fort Worth, 76107-2699, USA.
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146
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O'Neil RG, Heller S. The mechanosensitive nature of TRPV channels. Pflugers Arch 2005; 451:193-203. [PMID: 15909178 DOI: 10.1007/s00424-005-1424-4] [Citation(s) in RCA: 237] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2005] [Accepted: 03/28/2005] [Indexed: 01/26/2023]
Abstract
Transient receptor potential vanilloid (TRPV) channels are widely expressed in both sensory and nonsensory cells. Whereas the channels display a broad diversity to activation by chemical and physical stimuli, activation by mechanical stimuli is common to many members of this group in both lower and higher organisms. Genetic screening in Caenorhabditis elegans has demonstrated an essential role for two TRPV channels in sensory neurons. OSM-9 and OCR-2, for example, are essential for both osmosensory and mechanosensory (nose-touch) behaviors. Likewise, two Drosophila TRPV channels, NAN and IAV, have been shown to be critical for hearing by the mechanosensitive chordotonal organs located in the fly's antennae. The mechanosensitive nature of the channels appears to be conserved in higher organisms for some TRPV channels. Two vertebrate channels, TRPV2 and TRPV4, are sensitive to hypotonic cell swelling, shear stress/fluid flow (TRPV4), and membrane stretch (TRPV2). In the osmosensing neurons of the hypothalamus (circumventricular organs), TRPV4 appears to function as an osmoreceptor, or part of an osmoreceptor complex, in control of vasopressin release, whereas in inner ear hair cells and vascular baroreceptors a mechanosensory role is suggestive, but not demonstrated. Finally, in many nonsensory cells expressing TRPV4, such as vascular endothelial cells and renal tubular epithelial cells, the channel exhibits well-developed local mechanosensory transduction processes where both cell swelling and shear stress/fluid flow lead to channel activation. Hence, many TRPV channels, or combinations of TRPV channels, display a mechanosensitive nature that underlies multiple mechanosensitive processes from worms to mammals.
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Affiliation(s)
- Roger G O'Neil
- Department of Integrative Biology and Pharmacology, Medical School, The University of Texas Health Science Center at Houston, 6431 Fannin Street, Houston, TX 77030, USA.
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147
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Abstract
The primary cilium, an organelle largely ignored by physiologists, functions both as a mechano-sensor and a chemo-sensor in renal tubular epithelia. This forgotten structure is critically involved in the determination of left-right sidedness during development and is a key factor in the development of polycystic kidney disease, as well as a number of other abnormalities. This review provides an update of our current understanding about the function of primary cilia. Much new information obtained in the past five years has been stimulated, in part, by discoveries of the primary cilium's key role in the genesis of polycystic kidney disease as well as its involvement in determination of left-right axis asymmetry. Here we focus on the various functions of the primary cilium rather than on its role in pathology.
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Affiliation(s)
- Helle A Praetorius
- The Water and Salt Research Center, Clinical Institute, University of Aarhus, 8200 Aarhus N, Denmark.
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148
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Ishikawa H, Kubo A, Tsukita S, Tsukita S. Odf2-deficient mother centrioles lack distal/subdistal appendages and the ability to generate primary cilia. Nat Cell Biol 2005; 7:517-24. [PMID: 15852003 DOI: 10.1038/ncb1251] [Citation(s) in RCA: 232] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2005] [Accepted: 03/21/2005] [Indexed: 11/09/2022]
Abstract
Outer dense fibre 2 (Odf2; also known as cenexin) was initially identified as a main component of the sperm tail cytoskeleton, but was later shown to be a general scaffold protein that is specifically localized at the distal/subdistal appendages of mother centrioles. Here we show that Odf2 expression is suppressed in mouse F9 cells when both alleles of Odf2 genes are deleted. Unexpectedly, the cell cycle of Odf2(-/-) cells does not seem to be affected. Immunofluorescence and ultrathin-section electron microscopy reveals that in Odf2(-/-) cells, distal/subdistal appendages disappear from mother centrioles, making it difficult to distinguish mother from daughter centrioles. In Odf2(-/-) cells, however, the formation of primary cilia is completely suppressed, although approximately 25% of wild-type F9 cells are ciliated under the steady-state cell cycle. The loss of primary cilia in Odf2(-/-) F9 cells can be rescued by exogenous Odf2 expression. These findings indicate that Odf2 is indispensable for the formation of distal/subdistal appendages and the generation of primary cilia, but not for other cell-cycle-related centriolar functions.
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Affiliation(s)
- Hiroaki Ishikawa
- Department of Cell Biology, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
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149
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O'Hagan R, Chalfie M. Mechanosensation in Caenorhabditis elegans. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2005; 69:169-203. [PMID: 16492465 DOI: 10.1016/s0074-7742(05)69006-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Robert O'Hagan
- Department of Biological Sciences, Columbia University, New York, New York, USA
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