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Antoine AF, Faure JE, Dumas C, Feijó JA. Differential contribution of cytoplasmic Ca2+ and Ca2+ influx to gamete fusion and egg activation in maize. Nat Cell Biol 2001; 3:1120-3. [PMID: 11781574 DOI: 10.1038/ncb1201-1120] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
In multicellular organisms, gamete fusion triggers a set of events, collectively known as egg activation, that leads to the development of a new individual. Every species that has been studied shows at least one rise in cytoplasmic Ca2+ concentration ([Ca2+]Cyt) after gamete fusion which is believed to be involved in activation. Yet the source and regulation of this Ca2+ signal and the way it is transduced inside the zygote are controversial. In higher plants, in vitro fertilization (IVF) has enabled the description of a rise in [Ca2+]Cyt (ref. 4) that is sufficient for activation, and of a Ca2+ influx that spreads as a wavefront from the fusion site The relationship between these two responses is unknown. Using a new combination of methods that simultaneously monitor the extracellular flux with a Ca2+-vibrating probe, and [Ca2+]Cyt by widefield imaging, we directly determined that the Ca2+ influx precedes the [Ca2+]Cyt elevation by 40-120 s. In addition, results from experiments using the Ca2+-channel inhibitor gadolinium (Gd3+) suggest that the Ca2+ influx may be necessary for sperm incorporation. We also present evidence for a putative sperm-dependent Gd3+-insensitive localized Ca2+ influx confined to the fusion point.
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Affiliation(s)
- A F Antoine
- Laboratoire Reproduction et Développement des Plantes, UMR 5667 CNRS/INRA/ENS/Université Lyon I, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, F-69364 Lyon, France.
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2
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Wolfe SE, Howard DE, Schetz JA, Cheng CJ, Webber R, Beatty DM, Chronwall BM, Morris SJ. Dopamine D2-receptor isoforms expressed in AtT20 cells inhibit Q-type high-voltage-activated Ca2+ channels via a membrane-delimited pathway. J Neurochem 1999; 72:479-90. [PMID: 9930719 DOI: 10.1046/j.1471-4159.1999.0720479.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Dopamine D2 receptors both acutely and chronically inhibit high-voltage-activated Ca2+ channels (HVA-CCs). Two alternatively spliced isoforms, D2L (long) and D2S (short), are expressed at high levels in rat pituitary intermediate lobe melanotropes but are lacking in anterior lobe corticotropes. We stably transfected D2L and D2S into corticotrope-derived AtT20 cells. Both isoforms coupled to inhibition of Q-type calcium channels through pertussis toxin-sensitive G proteins. Thus, we have created a model system in which to study the kinetics of D2-receptor regulation of Ca2+ channels. Rapid inhibition of HVA-CCs was characterized using a novel fluorescence video imaging technique for the measurement of millisecond kinetic events. We measured the time elapsed (lag time) between the arrival of depolarizing isotonic 66 mM K+, sensed by fluorescence from included carboxy-X-rhodamine (CXR), and the beginning of increased intracellular Ca2+ levels (sensed by changes in indo 1 fluorescence ratio). The lag time averaged 350-550 ms, with no significant differences among cell types. Addition of the D2-agonist quinpirole (250 microM) to the K+/CXR solution significantly increased the lag times for D2-expressing cells but did not alter the lag time for AtT20 controls. The increased lag times for D2L- and D2S-transfected cells suggest that at least a fraction of the Ca2+ channels was inhibited within the initial 350-550 ms. As this inhibition time is too fast for a multistep second messenger pathway, we conclude that inhibition occurs via a membrane-delimited diffusion mechanism.
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MESH Headings
- Animals
- Binding, Competitive/physiology
- Calcium/metabolism
- Calcium Channel Blockers/pharmacology
- Calcium Channels/genetics
- Calcium Channels/metabolism
- Calcium Channels, N-Type
- Dopamine Antagonists/pharmacology
- Dose-Response Relationship, Drug
- Electric Conductivity
- Gene Expression/physiology
- Ion Channel Gating/physiology
- Isomerism
- Male
- Melanocytes/chemistry
- Melanocytes/physiology
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Microscopy, Fluorescence
- Microscopy, Video/instrumentation
- Microscopy, Video/methods
- Nifedipine/pharmacology
- Pituitary Gland/cytology
- Potassium/pharmacology
- Rats
- Rats, Sprague-Dawley
- Reaction Time/physiology
- Receptors, Dopamine D2/chemistry
- Receptors, Dopamine D2/genetics
- Receptors, Dopamine D2/metabolism
- Signal Transduction/physiology
- Spiperone/pharmacology
- Transfection
- Tritium
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Affiliation(s)
- S E Wolfe
- Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, 64110-2499, USA
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3
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Blumenthal R, Morris SJ. The influenza haemagglutinin-induced fusion cascade: effects of target membrane permeability changes. Mol Membr Biol 1999; 16:43-7. [PMID: 10332736 DOI: 10.1080/096876899294742] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
To define the stages in influenza haemagglutinin (HA)-mediated fusion the kinetics of fusion between cell pairs consisting of single influenza HA-expressing cells and single erythrocytes (RBC) which had been labelled with both a fluorescent lipid (Dil) in the membrane and a fluorescent solute (calcein) in the aqueous space have been monitored. It is shown that release of solute from the target cell occurs, following the formation of the hemi-fusion diaphragm. These results are discussed in terms of a model in which fusion peptide insertion into the target membrane induces lipid stalks, which results in the formation of a hemifusion diaphragm and a fusion pore. Bilayer expansion due to overproduction of these stalks can give rise to collateral damage of target membranes.
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Affiliation(s)
- R Blumenthal
- Laboratory of Experimental and Computational Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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4
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Chernomordik LV, Frolov VA, Leikina E, Bronk P, Zimmerberg J. The pathway of membrane fusion catalyzed by influenza hemagglutinin: restriction of lipids, hemifusion, and lipidic fusion pore formation. J Cell Biol 1998; 140:1369-82. [PMID: 9508770 PMCID: PMC2132678 DOI: 10.1083/jcb.140.6.1369] [Citation(s) in RCA: 318] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The mechanism of bilayer unification in biological fusion is unclear. We reversibly arrested hemagglutinin (HA)-mediated cell-cell fusion right before fusion pore opening. A low-pH conformation of HA was required to form this intermediate and to ensure fusion beyond it. We present evidence indicating that outer monolayers of the fusing membranes were merged and continuous in this intermediate, but HA restricted lipid mixing. Depending on the surface density of HA and the membrane lipid composition, this restricted hemifusion intermediate either transformed into a fusion pore or expanded into an unrestricted hemifusion, without pores but with unrestricted lipid mixing. Our results suggest that restriction of lipid flux by a ring of activated HA is necessary for successful fusion, during which a lipidic fusion pore develops in a local and transient hemifusion diaphragm.
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Affiliation(s)
- L V Chernomordik
- Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-1855, USA.
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Schroth-Diez B, Ponimaskin E, Reverey H, Schmidt MF, Herrmann A. Fusion activity of transmembrane and cytoplasmic domain chimeras of the influenza virus glycoprotein hemagglutinin. J Virol 1998; 72:133-41. [PMID: 9420208 PMCID: PMC109357 DOI: 10.1128/jvi.72.1.133-141.1998] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The role of the sequence of transmembrane and cytoplasmic/intraviral domains of influenza virus hemagglutinin (HA, subtype H7) for HA-mediated membrane fusion was explored. To analyze the influence of the two domains on the fusogenic properties of HA, we designed HA-chimeras in which the cytoplasmic tail and/or transmembrane domain of HA was replaced with the corresponding domains of the fusogenic glycoprotein F of Sendai virus. These chimeras, as well as constructs of HA in which the cytoplasmic tail was replaced by peptides of human neurofibromin type 1 (NF1) or c-Raf-1, NF78 (residues 1441 to 1518), and Raf81 (residues 51 to 131), respectively, were expressed in CV-1 cells by using the vaccinia virus-T7 polymerase transient-expression system. Wild-type and chimeric HA were cleaved properly into two subunits and expressed as trimers. Membrane fusion between CV-1 cells and bound human erythrocytes (RBCs) mediated by parental or chimeric HA proteins was studied by a lipid-mixing assay with the lipid-like fluorophore octadecyl rhodamine B chloride (R18). No profound differences in either extent or kinetics could be observed. After the pH was lowered, the above proteins also induced a flow of the aqueous fluorophore calcein from preloaded RBCs into the cytoplasm of the protein-expressing CV-1 cells, indicating that membrane fusion involves both leaflets of the lipid bilayers and leads to formation of an aqueous fusion pore. We conclude that neither HA-specific sequences in the transmembrane and cytoplasmic domains nor their length is crucial for HA-induced membrane fusion activity.
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Affiliation(s)
- B Schroth-Diez
- Institut für Biologie/Biophysik, Mathematisch-Naturwissenschaftliche Fakultät I, Humboldt-Universität zu Berlin, Germany
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Chernomordik LV, Leikina E, Frolov V, Bronk P, Zimmerberg J. An early stage of membrane fusion mediated by the low pH conformation of influenza hemagglutinin depends upon membrane lipids. J Cell Biol 1997; 136:81-93. [PMID: 9008705 PMCID: PMC2132452 DOI: 10.1083/jcb.136.1.81] [Citation(s) in RCA: 175] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/1996] [Revised: 11/07/1996] [Indexed: 02/03/2023] Open
Abstract
While the specificity and timing of membrane fusion in diverse physiological reactions, including virus-cell fusion, is determined by proteins, fusion always involves the merger of membrane lipid bilayers. We have isolated a lipid-dependent stage of cell-cell fusion mediated by influenza hemagglutinin and triggered by cell exposure to mildly acidic pH. This stage preceded actual membrane merger and fusion pore formation but was subsequent to a low pH-induced change in hemagglutinin conformation that is required for fusion. A low pH conformation of hemagglutinin was required to achieve this lipid-dependent stage and also, downstream of it, to drive fusion to completion. The lower the pH of the medium applied to trigger fusion and, thus, the more hemagglutinin molecules activated, the less profound was the dependence of fusion on lipids. Membrane-incorporated lipids affected fusion in a manner that correlated with their dynamic molecular shape, a characteristic that determines a lipid monolayer's propensity to bend in different directions. The lipid sensitivity of this stage, i.e., inhibition of fusion by inverted cone-shaped lysophosphatidylcholine and promotion by cone-shaped oleic acid, was consistent with the stalk hypothesis of fusion, suggesting that fusion proteins begin membrane merger by promoting the formation of a bent, lipid-involving, stalk intermediate.
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Affiliation(s)
- L V Chernomordik
- Laboratary of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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Blumenthal R, Sarkar DP, Durell S, Howard DE, Morris SJ. Dilation of the influenza hemagglutinin fusion pore revealed by the kinetics of individual cell-cell fusion events. J Biophys Biochem Cytol 1996; 135:63-71. [PMID: 8858163 PMCID: PMC2121025 DOI: 10.1083/jcb.135.1.63] [Citation(s) in RCA: 181] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
We have monitored kinetics of fusion between cell pairs consisting of a single influenza hemaglutinin (HA)-expressing cell and a single erythrocyte (RBC) that had been labeled with both a fluorescent lipid (Dil) in the membrane and a fluorescent solute (calcein) in the aqueous space. Initial fusion pore opening between the RBC and HA-expressing cell produced a change in RBC membrane potential (delta psi) that was monitored by a decrease in Dil fluorescence. This event was followed by two distinct stages of fusion pore dilation: the flux of fluorescent lipid (phi L) and the flux of a large aqueous fluorescent dye (phi s). We have analyzed the kinetics of events that occur as a result of transitions between a fusion pore (FP) and a solute permissive fusion pore (FPs). Our data are consistent with a fusion pore comprising six HA trimers.
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Affiliation(s)
- R Blumenthal
- Section on Membrane Structure and Function, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
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Blumenthal R, Pak CC, Raviv Y, Krumbiegel M, Bergelson LD, Morris SJ, Lowy RJ. Transient domains induced by influenza haemagglutinin during membrane fusion. Mol Membr Biol 1995; 12:135-42. [PMID: 7767373 DOI: 10.3109/09687689509038509] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
During low pH-induced fusion of influenza virus with erythrocytes we have observed differential dispersion of viral lipid and haemagglutinin (HA) into the erythrocyte membrane, and viral RNA into the erythrocyte using fluorescence video microscopy. The movement of both viral lipid and HA from virus to cell was restricted during the initial stages of fusion relative to free diffusion. This indicates the existence of relatively long-lived barriers to diffusion subsequent to fusion pore formation. Fluorescence anisotropy of phospholipid analogues incorporated into the viral membrane decreased when the pH was lowered to levels required for optimum fusion. This indicates that the restricted motion of viral membrane components was not due to rigidification of membrane lipids. The movement of HA from the fusion site was also assessed by photosensitized labelling by means of a fluorescent substrate (NBD-taurine) passing through the band 3 sialoglycoprotein (the erythrocyte anion transporter). We also examined the flow of lipid and aqueous markers during fusion of HA-expressing cells with labelled erythrocytes. During this cell-cell fusion, movement of lipid between fusing membranes begins before the fusion pore is wide enough to allow diffusion of aqueous molecules (M(r) > 500). The data indicate that HA is capable of creating domains in the membrane and controlling continuity of aqueous compartments which are bounded by such domains.
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Zimmerberg J, Blumenthal R, Sarkar DP, Curran M, Morris SJ. Restricted movement of lipid and aqueous dyes through pores formed by influenza hemagglutinin during cell fusion. J Cell Biol 1994; 127:1885-94. [PMID: 7806567 PMCID: PMC2120276 DOI: 10.1083/jcb.127.6.1885] [Citation(s) in RCA: 138] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The fusion of cells by influenza hemagglutinin (HA) is the best characterized example of protein-mediated membrane fusion. In simultaneous measurements of pairs of assays for fusion, we determined the order of detectable events during fusion. Fusion pore formation in HA-triggered cell-cell fusion was first detected by changes in cell membrane capacitance, next by a flux of fluorescent lipid, and finally by flux of aqueous fluorescent dye. Fusion pore conductance increased by small steps. A retardation of lipid and aqueous dyes occurred during fusion pore fluctuations. The flux of aqueous dye depended on the size of the molecule. The lack of movement of aqueous dyes while total fusion pore conductance increased suggests that initial HA-triggered fusion events are characterized by the opening of multiple small pores: the formation of a "sieve".
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Affiliation(s)
- J Zimmerberg
- Laboratory of Theoretical and Physical Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892
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Bagai S, Sarkar DP. Effect of substitution of hemagglutinin-neuraminidase with influenza hemagglutinin on Sendai virus F protein mediated membrane fusion. FEBS Lett 1994; 353:332-6. [PMID: 7957887 DOI: 10.1016/0014-5793(94)01076-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Recombinant virosomes containing fusion protein (F) of Sendai virus and the envelope glycoproteins hemagglutinin (HA) and neuraminidase (NA) of influenza virus within the same membrane were prepared. Such hybrid vesicles were found to hemolyse red blood cells both at pH 7.4 and pH 5.0. Hemolysis induced by hybrid vesicles was much higher than seen with F-virosomes in the presence of WGA, but was about two-fold less than the hemolysis caused by F,HN-virosomes. Reconstituted influenza virus envelopes and F-virosomes failed to induce hemolysis at pH 7.4. Using a fluorescence probe-based lipid mixing fusion assay, hybrid virosomes were found to fuse with cultured HeLa cells both at pH 7.4 as well as pH 5.0. The data indicate that the presence of Sendai virus HN protein in the virosomal membrane is not absolutely essential for the virosome cell fusion process.
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Affiliation(s)
- S Bagai
- Department of Biochemistry, University of Delhi South Campus, India
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Morris SJ, Wiegmann TB, Welling LW, Chronwall BM. Rapid simultaneous estimation of intracellular calcium and pH. Methods Cell Biol 1994; 40:183-220. [PMID: 8201976 DOI: 10.1016/s0091-679x(08)61115-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- S J Morris
- Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri at Kansas City 64110
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