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Tremp AZ, Khater EI, Dessens JT. IMC1b is a putative membrane skeleton protein involved in cell shape, mechanical strength, motility, and infectivity of malaria ookinetes. J Biol Chem 2008; 283:27604-27611. [PMID: 18650444 PMCID: PMC2562075 DOI: 10.1074/jbc.m801302200] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Membrane skeletons are cytoskeletal elements that have important roles in
cell development, shape, and structural integrity. Malaria parasites encode a
conserved family of putative membrane skeleton proteins related to articulins.
One member, IMC1a, is expressed in sporozoites and localizes to the pellicle,
a unique membrane complex believed to form a scaffold onto which the ligands
and glideosome are arranged to mediate parasite motility and invasion. IMC1b
is a closely related structural paralogue of IMC1a, fostering speculation that
it could be functionally homologous but in a different invasive life stage.
Here we have generated genetically modified parasites that express IMC1b
tagged with green fluorescent protein, and we show that it is targeted
exclusively to the pellicle of ookinetes. We also show that IMC1b-deficient
ookinetes display abnormal cell shape, reduced gliding motility, decreased
mechanical strength, and reduced infectivity. These findings are consistent
with a membrane skeletal role of IMC1b and provide strong experimental support
for the view that membrane skeletons form an integral part of the pellicle of
apicomplexan zoites and function to provide rigidity to the pellicular
membrane complex. The similarities observed between the loss-of-function
phenotypes of IMC1a and IMC1b show that membrane skeletons of ookinetes and
sporozoites function in an overall similar way. However, the fact that
ookinetes and sporozoites do not use the same IMC1 protein implies that
different mechanical properties are required of their respective membrane
skeletons, likely reflecting the distinct environments in which these life
stages must operate.
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Affiliation(s)
- Annie Z Tremp
- Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, United Kingdom
| | - Emad I Khater
- Department of Entomology, Ain Shams University, Abbassia 11566, Cairo, Egypt
| | - Johannes T Dessens
- Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, United Kingdom.
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2
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Khater EI, Sinden RE, Dessens JT. A malaria membrane skeletal protein is essential for normal morphogenesis, motility, and infectivity of sporozoites. ACTA ACUST UNITED AC 2004; 167:425-32. [PMID: 15533999 PMCID: PMC2172497 DOI: 10.1083/jcb.200406068] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Membrane skeletons are structural elements that provide mechanical support to the plasma membrane and define cell shape. Here, we identify and characterize a putative protein component of the membrane skeleton of the malaria parasite. The protein, named PbIMC1a, is the structural orthologue of the Toxoplasma gondii inner membrane complex protein 1 (TgIMC1), a component of the membrane skeleton in tachyzoites. Using targeted gene disruption in the rodent malaria species Plasmodium berghei, we show that PbIMC1a is involved in sporozoite development, is necessary for providing normal sporozoite cell shape and mechanical stability, and is essential for sporozoite infectivity in insect and vertebrate hosts. Knockout of PbIMC1a protein expression reduces, but does not abolish, sporozoite gliding locomotion. We identify a family of proteins related to PbIMC1a in Plasmodium and other apicomplexan parasites. These results provide new functional insight in the role of membrane skeletons in apicomplexan parasite biology.
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Affiliation(s)
- Emad I Khater
- Department of Biological Sciences, Imperail College London, London SW7 2AZ, England, UK
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3
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Knyihár-Csillik E, Tajti J, Chadaide Z, Csillik B, Vécsei L. Functional immunohistochemistry of neuropeptides and nitric oxide synthase in the nerve fibers of the supratentorial dura mater in an experimental migraine model. Microsc Res Tech 2001; 53:193-211. [PMID: 11301495 DOI: 10.1002/jemt.1084] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The supratentorial cerebral dura of the albino rat is equipped with a rich sensory innervation both in the connective tissue and around blood vessels, which includes nociceptive axons and their terminals; these display intense calcitonin gene-related peptide (CGRP) immunoreactivity. Stereotactic electrical stimulation of the trigeminal (Gasserian) ganglion, regarded as an experimental migraine model, caused marked increase and disintegration of club-like perivascular CGRP-immunopositive nerve endings in the dura mater and induced an apparent increase in the lengths of CGRP-immunoreactive axons. Intravenous administration of sumatriptan or eletriptan, prior to electrical stimulation, prevented disintegration of perivascular terminals and induced accumulation of CGRP in terminal and preterminal portions of peripheral sensory axons. Consequently, immunopositive terminals and varicosities increased in size; accumulation of axoplasmic organelles resulted in the "hollow" appearence of numerous varicosities. Since triptans exert their anti-migraine effect by virtue of agonist action on 5-HT(1D/B) receptors, we suggest that these drugs prevent the release of CGRP from perivascular nerve terminals in the dura mater by an action at 5-HT(1D/B) receptors. Nitroglycerine (NitroPOHL), given subcutaneously to rats, induces increased beading of nitric oxide synthase (NOS)-immunoreactive nerve fibers in the supratentorial cerebral dura mater, and an apparent increase in the number of NOS-immunoreactive nerve fibers in the dural areas supplied by the anterior and middle meningeal arteries, and the sinus sagittalis superior. Structural alterations of nitroxidergic axons innervating blood vessels of the dura mater support the idea that nitric oxide (NO) is involved in the induction of headache, a well-known side effect of coronary dilator agents.
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Affiliation(s)
- E Knyihár-Csillik
- Department of Neurology, Albert Szent-Györgyi Medical and Pharmaceutical Center, University of Szeged, H-6701 Szeged, Hungary.
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4
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Woo MK, Lee A, Fischer RS, Moyer J, Fowler VM. The lens membrane skeleton contains structures preferentially enriched in spectrin-actin or tropomodulin-actin complexes. CELL MOTILITY AND THE CYTOSKELETON 2000; 46:257-68. [PMID: 10962480 DOI: 10.1002/1097-0169(200008)46:4<257::aid-cm3>3.0.co;2-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The spectrin-based membrane skeleton plays an important role in determining the distributions and densities of receptors, ion channels, and pumps, thus influencing cell shape and deformability, cell polarity, and adhesion. In the paradigmatic human erythrocyte, short tropomodulin-capped actin filaments are cross-linked by spectrin into a hexagonal network, yet the extent to which this type of actin filament organization is utilized in the membrane skeletons of nonerythroid cells is not known. Here, we show that associations of tropomodulin and spectrin with actin in bovine lens fiber cells are distinct from that of the erythrocyte and imply a very different molecular organization. Mechanical disruption of the lens fiber cell membrane skeleton releases tropomodulin and actin-containing oligomeric complexes that can be isolated by gel filtration column chromatography, sucrose gradient centrifugation and immunoadsorption. These tropomodulin-actin complexes do not contain spectrin. Instead, spectrin is associated with actin in different complexes that do not contain tropomodulin. Immunofluorescence staining of isolated fiber cells further demonstrates that tropomodulin does not precisely colocalize with spectrin along the lateral membranes of lens fiber cells. Taken together, our data suggest that tropomodulin-capped actin filaments and spectrin-cross-linked actin filaments are assembled in distinct structures in the lens fiber cell membrane skeleton, indicating that it is organized quite differently from that of the erythrocyte membrane skeleton.
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Affiliation(s)
- M K Woo
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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5
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Porter GA, Scher MG, Resneck WG, Porter NC, Fowler VM, Bloch RJ. Two populations of beta-spectrin in rat skeletal muscle. CELL MOTILITY AND THE CYTOSKELETON 2000; 37:7-19. [PMID: 9142435 DOI: 10.1002/(sici)1097-0169(1997)37:1<7::aid-cm2>3.0.co;2-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We use immunoblotting, immunoprecipitation, and centrifugation in sucrose density gradients to show that the product of the erythrocyte beta-spectrin gene in rat skeletal muscle (muscle beta-spectrin) is present in two states, one associated with fodrin, and another that is not associated with any identifiable spectrin or fodrin subunit. Immunofluorescence studies indicate that a significant amount of beta-spectrin without alpha-fodrin is present in the myoplasm of some muscle fibers, and, more strikingly, at distinct regions of the sarcolemma. These results suggest that alpha-fodrin and muscle beta-spectrin associate in muscle in situ, but that some muscle beta-spectrin without a paired alpha-subunit forms distinct domains at the sarcolemma.
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Affiliation(s)
- G A Porter
- Department of Physiology, University of Maryland School of Medicine, Baltimore, USA
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6
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Li Y, Hua F, Carraway KL, Carraway CA. The p185(neu)-containing glycoprotein complex of a microfilament-associated signal transduction particle. Purification, reconstitution, and molecular associations with p58(gag) and actin. J Biol Chem 1999; 274:25651-8. [PMID: 10464301 DOI: 10.1074/jbc.274.36.25651] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Microfilaments associate with the microvillar membrane of 13762 ascites mammary adenocarcinoma cells via a large transmembrane complex (TMC) comprising the major glycoproteins TMC-gp120, -110, -80, -65, and -55, the receptor kinase p185(neu), and the cytoplasmic proteins actin and p58(gag), linking the receptor with microfilaments in a signal transduction particle. Immunoblot screening with polyclonal antisera to TMC glycoproteins showed selective epithelial expression in normal rat tissues and epithelially derived tumor cells. The TMC glycoproteins were isolated by solubilization of microfilament core preparations in SDS, dilution, and separation on a concanavalin A-agarose affinity column. The large p185(neu)-containing complex was reconstituted from the column eluate after displacement of SDS with nonionic detergent, demonstrated by gel filtration and co-immunoprecipitation of the glycoproteins with anti-gp55 or anti-p185(neu). Exhaustive biotinylation of the glycoproteins gave a stoichiometry of gp120:gp110:gp80:gp65:gp55 of approximately 1:1:1:0.5:1. Overlay blots with biotinylated actin and in vitro translated, [(35)S]methionine-labeled p58(gag), respectively, showed specific interactions of actin with gp55 and gp120 and of p58(gag) with gp65 and gp55. These results provide evidence for a specific complex of microfilament-associated glycoproteins containing p185(neu) and p58(gag) and suggest a role for the complex in signal transduction scaffolding.
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Affiliation(s)
- Y Li
- Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Miami, Florida 33101, USA
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7
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Wilk T, Gowen B, Fuller SD. Actin associates with the nucleocapsid domain of the human immunodeficiency virus Gag polyprotein. J Virol 1999; 73:1931-40. [PMID: 9971772 PMCID: PMC104434 DOI: 10.1128/jvi.73.3.1931-1940.1999] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/1998] [Accepted: 12/07/1998] [Indexed: 11/20/2022] Open
Abstract
Recently, it was shown that actin molecules are present in human immunodeficiency virus type 1 (HIV-1) particles. We have examined the basis for incorporation and the location of actin molecules within HIV-1 and murine retrovirus particles. Our results show that the retroviral Gag polyprotein is sufficient for actin uptake. Immunolabeling studies demonstrate that actin molecules localize to a specific radial position within the immature particle, clearly displaced from the matrix domain underneath the viral membrane but in proximity to the nucleocapsid (NC) domain of the Gag polyprotein. When virus or subviral Gag particles were disrupted with nonionic detergent, actin molecules remained associated with the disrupted particles. Actin molecules remained in a stable complex with the NC cleavage product (or an NC-RNA complex) after treatment of the disrupted HIV-1 particles with recombinant HIV-1 protease. In contrast, matrix and capsid molecules were released. The same result was obtained when mature HIV-1 particles were disrupted with detergent. Taken together, these results indicate that actin molecules are associated with the NC domain of the viral polyprotein.
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Affiliation(s)
- T Wilk
- Structural Biology Programme, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
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8
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Knyihár-Csillik E, Vécsei L. Effect of a nitric oxide donor on nitroxergic nerve fibers in the rat dura mater. Neurosci Lett 1999; 260:97-100. [PMID: 10025708 DOI: 10.1016/s0304-3940(98)00949-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Nitroglycerine, given subcutaneously to rats (10 mg/kg body weight) induces increased beading of nitric oxide synthase immunoreactive (NOS-IR) nerve fibers in the supratentorial cerebral dura mater, and an apparent increase in the number of NOS-IR nerve fibers in the dural areas supplied by the anterior and middle meningeal arteries, and the sinus sagittalis superior. Structural alterations of nitroxergic axons innervating blood vessels of the dura mater support the idea that nitric oxide is involved in the induction of headache also by a primary peripheral action, a well-known side effect of coronary dilator agents.
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Affiliation(s)
- E Knyihár-Csillik
- Department of Neurology, Albert Szent-Györgyi University Medical School, Szeged, Hungary.
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9
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Tomishige M, Sako Y, Kusumi A. Regulation mechanism of the lateral diffusion of band 3 in erythrocyte membranes by the membrane skeleton. J Cell Biol 1998; 142:989-1000. [PMID: 9722611 PMCID: PMC2132872 DOI: 10.1083/jcb.142.4.989] [Citation(s) in RCA: 141] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/1998] [Revised: 07/10/1998] [Indexed: 02/08/2023] Open
Abstract
Mechanisms that regulate the movement of a membrane spanning protein band 3 in erythrocyte ghosts were investigated at the level of a single or small groups of molecules using single particle tracking with an enhanced time resolution (0.22 ms). Two-thirds of band 3 undergo macroscopic diffusion: a band 3 molecule is temporarily corralled in a mesh of 110 nm in diameter, and hops to an adjacent mesh an average of every 350 ms. The rest (one-third) of band 3 exhibited oscillatory motion similar to that of spectrin, suggesting that these band 3 molecules are bound to spectrin. When the membrane skeletal network was dragged and deformed/translated using optical tweezers, band 3 molecules that were undergoing hop diffusion were displaced toward the same direction as the skeleton. Mild trypsin treatment of ghosts, which cleaves off the cytoplasmic portion of band 3 without affecting spectrin, actin, and protein 4.1, increased the intercompartmental hop rate of band 3 by a factor of 6, whereas it did not change the corral size and the microscopic diffusion rate within a corral. These results indicate that the cytoplasmic portion of band 3 collides with the membrane skeleton, which causes temporal confinement of band 3 inside a mesh of the membrane skeleton.
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Affiliation(s)
- M Tomishige
- Department of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
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10
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Bezakova G, Bloch RJ. The zinc finger domain of the 43-kDa receptor-associated protein, rapsyn: role in acetylcholine receptor clustering. Mol Cell Neurosci 1998; 11:274-88. [PMID: 9698394 DOI: 10.1006/mcne.1998.0688] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We injected rat myotubes with proteins and antibodies to assess the importance of the zinc finger (ZnF) domain of the 43-kDa receptor-associated protein, rapsyn, in clustering acetylcholine receptors (AChR). Injection of rat myotubes with a fusion protein containing the ZnF domain of rapsyn disrupted AChR clusters. Clusters were unaffected by a fusion protein containing a double mutant that does not bind zinc. Similar results were obtained with the purified wild type and mutant ZnF domains. The ZnF of HIV-1 nucleocapsid protein had no effect. AChR clusters were also disrupted in myotubes injected with antibodies to the ZnF domain, followed by injection of anti-antibodies. Injection of antibodies directed against a different rapsyn epitope or against the cytoplasmic domain of the AChR had no effect. In transfection experiments with HEK 293 cells, the ZnF domain failed to associate with membrane aggregates containing full-length rapsyn, AChR, or rapsyn and AChR together. We conclude that the ZnF domain of rapsyn provides a binding site essential for AChR clustering, but that this site is unlikely to be involved in high affinity binding of rapsyn to itself or to AChR.
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Affiliation(s)
- G Bezakova
- Department of Physiology, University of Maryland School of Medicine, 660 West Redwood Street, Baltimore, Maryland, 21201, USA
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11
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Elliott G, O'Hare P. Herpes simplex virus type 1 tegument protein VP22 induces the stabilization and hyperacetylation of microtubules. J Virol 1998; 72:6448-55. [PMID: 9658087 PMCID: PMC109805 DOI: 10.1128/jvi.72.8.6448-6455.1998] [Citation(s) in RCA: 131] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The role of the herpes simplex virus type 1 tegument protein VP22 during infection is as yet undefined. We have previously shown that VP22 has the unusual property of efficient intercellular transport, such that the protein spreads from single expressing cells into large numbers of surrounding cells. We also noted that in cells expressing VP22 by transient transfection, the protein localizes in a distinctive cytoplasmic filamentous pattern. Here we show that this pattern represents a colocalization between VP22 and cellular microtubules. Moreover, we show that VP22 reorganizes microtubules into thick bundles which are easily distinguishable from nonbundled microtubules. These bundles are highly resistant to microtubule-depolymerizing agents such as nocodazole and incubation at 4 degreesC, suggesting that VP22 has the capacity to stabilize the microtubule network. In addition, we show that the microtubules contained in these bundles are modified by acetylation, a marker for microtubule stability. Analysis of infected cells by both immunofluorescence and measurement of microtubule acetylation further showed that colocalization between VP22 and microtubules, and induction of microtubule acetylation, also occurs during infection. Taken together, these results suggest that VP22 exhibits the properties of a classical microtubule-associated protein (MAP) during both transfection and infection. This is the first demonstration of a MAP encoded by an animal virus.
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Affiliation(s)
- G Elliott
- Marie Curie Research Institute, Oxted, Surrey RH8 OTL, United Kingdom.
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12
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Ochs S, Pourmand R, Jersild RA, Friedman RN. The origin and nature of beading: a reversible transformation of the shape of nerve fibers. Prog Neurobiol 1997; 52:391-426. [PMID: 9304699 DOI: 10.1016/s0301-0082(97)00022-1] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Nerve fibers which appear beaded (varicose, spindle-shaped, etc.) are often considered the result of pathology, or a preparation artifact. However, beading can be promptly elicited in fresh normal nerve by a mild stretch and revealed by fast-freezing and freeze-substitution, or by aldehyde fixating at a temperature near 0 degree C (cold-fixation). The key change in beading are the constrictions, wherein the axon is much reduced in diameter. Axoplasmic fluid and soluble components are shifted from the constrictions into the expansions leaving behind compacted microtubules and neurofilaments. Labeled cytoskeletal proteins carried down by slow axonal transport are seen to move with the soluble components and not to have been incorporated into and remain with, the cytoskeletal organelles on beading the fibers. Lipids and other components of the myelin sheath are also shifted from the constrictions into the expansions, with preservation of its fine structure and thickness. Additionally, myelin intrusions into the axons are produced and a localized bulging into the axon termed "leafing". The beading constrictions do not arise from the myelin sheath: beading occurs in the axons of unmyelinated fibers. It does not depend on the axonal cytoskeleton: exposure of nerves in vitro to beta, beta'-iminodipropionitrile (IDPN) disaggregates the cytoskeletal organelles and even augments beading. The hypothesis advanced was that the beading constrictions are due to the membrane skeleton; the subaxolemmal network comprised of spectrin/fodrin, actin, ankyrin, integrins and other transmembrane proteins. The mechanism can be activated directly by neurotoxins, metabolic changes, and by an interruption of axoplasmic transport producing Wallerian degeneration.
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Affiliation(s)
- S Ochs
- Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46202, USA
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13
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Topf PM, Stockem W. Protein and lipid composition of the cell surface complex from Amoeba proteus (Rhizopoda: Amoebida). Eur J Protistol 1996. [DOI: 10.1016/s0932-4739(96)80017-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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14
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Ochs S, Pourmand R, Jersild RA. Origin of beading constrictions at the axolemma: presence in unmyelinated axons and after beta,beta'-iminodipropionitrile degradation of the cytoskeleton. Neuroscience 1996; 70:1081-96. [PMID: 8848169 DOI: 10.1016/0306-4522(95)00390-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Myelinated nerve fibres become beaded when nerves are subjected to a mild stretch; the beading is seen as varicosities, a series of alternating constrictions and enlargements, when using freeze-substitution or cold-fixation to hold this labile form change in place during fixation. One possibility for how this form change comes about is that the myelin sheath or its Schwann cell initiates beading. We now report, however, that a similar beading is seen in the axons of unmyelinated fibres. In electron micrographs, longitudinal sections of axons show the series of constrictions and expansions typical of beading. In cross-sections, axons with unusually small diameter, corresponding to the constrictions, are seen to contain closely packed microtubules and neurofilaments while neighbouring swollen axons with widely dispersed microtubules correspond to the beading expansions. Another possibility for the form change is that the cytoskeleton is responsible for beading. We discovered that direct exposure of nerves to beta, beta'-iminodipropionitrile in vitro for 1-6 h causes both axonal microtubules and neurofilaments to become degraded and replaced by an amorphous residue. Nevertheless, beta,beta'-iminodipropionitrile-treated nerves show constrictions in myelinated fibres when stretched. An even greater degree of beading with narrower and longer constrictions appears in some fibres, with the expanded regions having oblate ends giving the appearance of a string of sausages. In cross-sections taken through the constrictions, a greater than usual reduction of axonal area was seen, this was due to the loss of cytoskeletal organelles which would act to limit the degree of constriction. With longer exposure to beta, beta'-iminodipropinitrile more fibres show complete degeneration of the cytoskeleton and form ovoids typical of Wallerian degeneration. Unmyelinated axons of beta, beta'-iminodipropionitrile-treated nerves which showed degeneration of their cytoskeleton with its replacement by amorphous material still demonstrated beading. As neither the myelin sheath nor the intact cytoskeleton within the axon is necessary for beading, by exclusion, we consider beading constrictions to be initiated at the level of the axolemma. In our hypothesis the membrane skeleton is responsible; namely, the spectrin, actin and other molecular species lining the inside of the axolemma and binding to transmembrane proteins. The membrane skeleton may be activated by stretch via transmembrane proteins (e.g. beta 1-integrins). The membrane skeleton mechanism may also be directly engaged in the production of Wallerian degeneration or be induced by neurotoxic agents.
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Affiliation(s)
- S Ochs
- Department of Physiology/Biophysics, Indiana University School of Medicine, Indianapolis 46202, USA
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15
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Affiliation(s)
- W R Jeffery
- Section of Molecular and Cellular Biology, University of California, Davis 95616, USA
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16
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Kräusslich HG, Welker R. Intracellular transport of retroviral capsid components. Curr Top Microbiol Immunol 1996; 214:25-63. [PMID: 8791724 DOI: 10.1007/978-3-642-80145-7_2] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- H G Kräusslich
- Department of Cell Biology and Virology, Heinrich Pette Institute of Experimental Virology and Immunology, Hamburg, Germany
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17
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Abstract
Hyphal tip growth is an exquisitely controlled process that forms developmentally regulated, species-specific, even-diameter tubes at rates of up to about 50 μm/min. The traditional view is that this process results from the balance between the expansive force of turgor pressure and the controlled extensibility of the apical cell wall. While these elements are involved, the model places regulation into either the global domain (turgor pressure) or the extracellular environment (the cell wall), neither of which seem well suited to the level of control evinced. Recent evidence suggests that F-actin-rich elements of the cytoskeleton are important in tip morphogenesis. Our current models propose that tip expansion is regulated (restrained under normal turgor pressure and protruded under low turgor) by a peripheral network of F-actin that is attached to the plasmalemma and the cell wall by integrin-containing linkages, thus placing control in the cytoplasm where it is accessible to normal intracellular regulatory systems. The F-actin system also functions in cytoplasmic and organelle motility; control of plasmalemma-located, stretch-activated, Ca2+-transporting, ion channel distribution; vectoral vesicle transport; and exocytosis. Regulation of the system may involve Ca2+, the concentration of which is influenced by the tip-high gradient of the stretch-activated channels, thus suggesting a possible feedback regulation mechanism. Key words: tip growth, fungi, stretch-activated channels, F-actin, Ca2+, hyphae.
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18
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Shaw MK, Tilney LG. The entry of Theileria parva merozoites into bovine erythrocytes occurs by a process similar to sporozoite invasion of lymphocytes. Parasitology 1995; 111 ( Pt 4):455-61. [PMID: 11023409 DOI: 10.1017/s0031182000065951] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The entry of Theileria parva merozoites into bovine erythrocytes in vivo is described and compared to sporozoite invasion of lymphocytes. Merozoites make initial contact with erythrocytes with any part of their surface and invasion of the host cell does not require the re-orientation of the apical end of the merozoite towards the surface of the erythrocyte. After the initial attachment the merozoite and host cell membranes form a continual close junction with the two apposed membranes separated by a 6-8 nm gap containing moderately dense material. The progressive circumferential 'zippering' of these closely apposed membranes leads to the movement of the parasite into the erythrocyte. The newly internalized merozoite which is completely surrounded by the erythrocyte plasma membrane escapes from this enclosing membrane by a process involving the discharge of at least the rhoptries; whether the merozoite also contain other types of secretory organelles (e.g. micronemes, microspheres or dense bodies) remains to be determined. Morphologically, the events involved in merozoite invasion of erythrocytes are almost identical to the process of sporozoite invasion of lymphocytes but differ significantly from the entry process of the invasive stages of other Apicomplexan parasites.
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Affiliation(s)
- M K Shaw
- International Laboratory for Research on Animal Diseases, Nairobi, Kenya
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Apel ED, Roberds SL, Campbell KP, Merlie JP. Rapsyn may function as a link between the acetylcholine receptor and the agrin-binding dystrophin-associated glycoprotein complex. Neuron 1995; 15:115-26. [PMID: 7619516 DOI: 10.1016/0896-6273(95)90069-1] [Citation(s) in RCA: 173] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The 43 kDa AChR-associated protein rapsyn is required for the clustering of nicotinic acetylcholine receptors (AChRs) at the developing neuromuscular junction, but the functions of other postsynaptic proteins colocalized with the AChR are less clear. Here we use a fibroblast expression system to investigate the role of the dystrophin-glycoprotein complex (DGC) in AChR clustering. The agrin-binding component of the DGC, dystroglycan, is found evenly distributed across the cell surface when expressed in fibroblasts. However, dystroglycan colocalizes with AChR-rapsyn clusters when these proteins are coexpressed. Furthermore, dystroglycan colocalizes with rapsyn clusters even in the absence of AChR, indicating that rapsyn can cluster dystroglycan and AChR independently. Immunofluorescence staining using a polyclonal antibody to utrophin reveals a lack of staining of clusters, suggesting that the immunoreactive species, like the AChR, does not mediate the observed rapsyndystroglycan interaction. Rapsyn may therefore be a molecular link connecting the AChR to the DGC. At the neuromuscular synapse, rapsyn-mediated linkage of the AChR to the cytoskeleton-anchored DGC may underlie AChR cluster stabilization.
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Affiliation(s)
- E D Apel
- Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Abstract
alpha-Dystroglycan has been suggested to be the receptor for agrin, an extracellular glycoprotein that signals postsynaptic differentiation at the neuromuscular junction, but it may not have the necessary specificity.
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Tasaka K, Mio M, Miyake K. Lateral movement of mast cell surface protein detected by gold-labeled anti-IgE and its relation with fodrin. AGENTS AND ACTIONS 1994; 41 Spec No:C53-5. [PMID: 7526659 DOI: 10.1007/bf02007764] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Rat mast cells were incubated with gold-conjugated concanavalin A and the movement of gold particles was observed using a polarization microscope. In resting cells, the movement of gold particles was very slow. When cells were stimulated with compound 48/80, the gold particles rapidly moved laterally, unrelated to granule extrusion. When sensitized mast cells were stimulated with gold-conjugated anti-IgE (anti-IgE-gold), patching of anti-IgE-gold was also observed. Immunofluorescence microscopy of rat mast cells stained with anti-fodrin antibody and rhodamine-phalloidin revealed that both fodrin and actin exist beneath the cell membrane forming a complicated network. After stimulation of the cells with anti-IgE-gold, the fodrin network was disrupted and thin fluorescence was observed homogeneously on the cell surface. By means of Western blotting, alpha-fodrin was detected in the membrane fraction of mast cells at the 240 kDa protein band. From the present study, it is suggested that disruption of the fodrin network may occur in association with the process leading to mast cell degranulation.
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Affiliation(s)
- K Tasaka
- Department of Pharmacology, Faculty of Pharmaceutical Sciences, Okayama University, Japan
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Analysis of Microfilament Organization and Contractile Activities in Physarum. ACTA ACUST UNITED AC 1994. [DOI: 10.1016/s0074-7696(08)62088-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
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Affiliation(s)
- A Ishihara
- Department of Cell Biology and Anatomy, University North Carolina at Chapel Hill 27599
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Jeffery WR, Swalla BJ. An ankryin-like protein in ascidian eggs and its role in the evolution of direct development. ZYGOTE 1993; 1:197-208. [PMID: 8081816 DOI: 10.1017/s0967199400001477] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
An erythrocyte anti-ankryin antibody was used to investigate the presence and distribution of ankryin in eggs and embryos of ascidian species with different modes of development. In eggs of the indirect developer Ascidia ceratodes, anti-ankryin reacted with a 210 kDa polypeptide which has an electrophoretic mobility similar to the vertebrate ankryins. Immunofluorescence microscopy showed that the ankryin-like protein is co-distributed with the myoplasm throughout development. It is restricted to a thin layer under the plasma membrane in unfertilised eggs, undergoes ooplasmic segregation to the posterior pole of the zygote after fertilisation, and is distributed to the tail muscle cells during cleavage and embryogenesis. After gastrulation and neurulation, lower levels of the ankryin-like protein, presumably of zygotic origin, were observed in brain cells and in the apical margin of epidermal cells. The ankryin-like protein was also localised in the myoplasm in eggs and embryos of another indirect developing species, Halocynthia roretzi. The ankryin-like protein may link the cytoskeleton with the plasma membrane in ascidian eggs, as it does in vertebrate erythrocytes. In contrast to A. ceratodes and H. roretzi, which are members of the families Ascidiidae and Pyuridae respectively, the pattern of ankryin-like protein expression was changed in five species in the family Molgulidae. These molgulid ascidians exhibit either indirect or direct development, and eggs of the direct developing species have lost or modified the myoplasm. The ankryin-like protein was present in young oocytes but failed to persist during oogenesis and disappeared in mature eggs and embryos of these molgulid species. The change in ankryin-like protein expression may be a preadaptation for loss of the myoplasm and the evolution of direct development.
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Affiliation(s)
- W R Jeffery
- Section of Molecular and Cellular Biology, University of California, Davis 94923
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