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Torrezan-Nitao E, Figueiredo RCBQ, Marques-Santos LF. Mitochondrial permeability transition pore in sea urchin female gametes. Mech Dev 2018; 154:208-218. [DOI: 10.1016/j.mod.2018.07.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2018] [Revised: 07/21/2018] [Accepted: 07/24/2018] [Indexed: 12/20/2022]
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2
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Abstract
Compared with the animal kingdom, fertilization is particularly complex in flowering plants (angiosperms). Sperm cells of angiosperms have lost their motility and require transportation as a passive cargo by the pollen tube cell to the egg apparatus (egg cell and accessory synergid cells). Sperm cell release from the pollen tube occurs after intensive communication between the pollen tube cell and the receptive synergid, culminating in the lysis of both interaction partners. Following release of the two sperm cells, they interact and fuse with two dimorphic female gametes (the egg and the central cell) forming the major seed components embryo and endosperm, respectively. This process is known as double fertilization. Here, we review the current understanding of the processes of sperm cell reception, gamete interaction, their pre-fertilization activation and fusion, as well as the mechanisms plants use to prevent the fusion of egg cells with multiple sperm cells. The role of Ca(2+) is highlighted in these various processes and comparisons are drawn between fertilization mechanisms in flowering plants and other eukaryotes, including mammals.
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Affiliation(s)
- Thomas Dresselhaus
- Cell Biology and Plant Biochemistry, Biochemie-Zentrum Regensburg, University of Regensburg, 93040 Regensburg, Germany.
| | - Stefanie Sprunck
- Cell Biology and Plant Biochemistry, Biochemie-Zentrum Regensburg, University of Regensburg, 93040 Regensburg, Germany
| | - Gary M Wessel
- Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, Rhode Island 02912, USA
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3
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Mahadeo M, Furber KL, Lam S, Coorssen JR, Prenner EJ. Secretory vesicle cholesterol: Correlating lipid domain organization and Ca2+ triggered fusion. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:1165-74. [DOI: 10.1016/j.bbamem.2015.02.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2014] [Revised: 01/02/2015] [Accepted: 02/07/2015] [Indexed: 12/13/2022]
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4
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Abbineni PS, Hibbert JE, Coorssen JR. Critical role of cortical vesicles in dissecting regulated exocytosis: overview of insights into fundamental molecular mechanisms. THE BIOLOGICAL BULLETIN 2013; 224:200-217. [PMID: 23995744 DOI: 10.1086/bblv224n3p200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Regulated exocytosis is one of the defining features of eukaryotic cells, underlying many conserved and essential functions. Definitively assigning specific roles to proteins and lipids in this fundamental mechanism is most effectively accomplished using a model system in which distinct stages of exocytosis can be effectively separated. Here we discuss the establishment of sea urchin cortical vesicle fusion as a model to study regulated exocytosis-a system in which the docked, release-ready, and late Ca(2+)-triggered steps of exocytosis are isolated and can be quantitatively assessed using the rigorous coupling of functional and molecular assays. We provide an overview of the insights this has provided into conserved molecular mechanisms and how these have led to and integrate with findings from other regulated exocytotic cells.
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Affiliation(s)
- Prabhodh S Abbineni
- Department of Molecular Physiology, School of Medicine, University of Western Sydney, NSW, Australia
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5
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de Araújo Leite JC, Marques-Santos LF. Extracellular Ca2+influx is crucial for the early embryonic development of the sea urchinEchinometra lucunter. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2012; 318:123-33. [DOI: 10.1002/jezb.21450] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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6
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Rogasevskaia TP, Coorssen JR. A new approach to the molecular analysis of docking, priming, and regulated membrane fusion. J Chem Biol 2011; 4:117-36. [PMID: 22315653 DOI: 10.1007/s12154-011-0056-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2010] [Accepted: 12/23/2010] [Indexed: 12/12/2022] Open
Abstract
Studies using isolated sea urchin cortical vesicles have proven invaluable in dissecting mechanisms of Ca(2+)-triggered membrane fusion. However, only acute molecular manipulations are possible in vitro. Here, using selective pharmacological manipulations of sea urchin eggs ex vivo, we test the hypothesis that specific lipidic components of the membrane matrix selectively affect defined late stages of exocytosis, particularly the Ca(2+)-triggered steps of fast membrane fusion. Egg treatments with cholesterol-lowering drugs resulted in the inhibition of vesicle fusion. Exogenous cholesterol recovered fusion extent and efficiency in cholesterol-depleted membranes; α-tocopherol, a structurally dissimilar curvature analogue, selectively restored fusion extent. Inhibition of phospholipase C reduced vesicle phosphatidylethanolamine and suppressed both the extent and kinetics of fusion. Although phosphatidylinositol-3-kinase inhibition altered levels of polyphosphoinositide species and reduced all fusion parameters, sequestering polyphosphoinositides selectively inhibited fusion kinetics. Thus, cholesterol and phosphatidylethanolamine play direct roles in the fusion pathway, contributing negative curvature. Cholesterol also organizes the physiological fusion site, defining fusion efficiency. A selective influence of phosphatidylethanolamine on fusion kinetics sheds light on the local microdomain structure at the site of docking/fusion. Polyphosphoinositides have modulatory upstream roles in priming: alterations in specific polyphosphoinositides likely represent the terminal priming steps defining fully docked, release-ready vesicles. Thus, this pharmacological approach has the potential to be a robust high-throughput platform to identify molecular components of the physiological fusion machine critical to docking, priming, and triggered fusion.
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7
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Furber KL, Churchward MA, Rogasevskaia TP, Coorssen JR. Identifying critical components of native Ca2+-triggered membrane fusion. Integrating studies of proteins and lipids. Ann N Y Acad Sci 2009; 1152:121-34. [PMID: 19161383 DOI: 10.1111/j.1749-6632.2008.03993.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Ca(2+)-triggered membrane fusion is the defining step of exocytosis. Despite realization that the fusion machinery must include lipids and proteins working in concert, only of late has work in the field focused more equally on both these components. Here we use isolated sea urchin egg cortical vesicles (CV), a stage-specific preparation of Ca(2+)-sensitive release-ready vesicles that enables the tight coupling of molecular and functional analyses necessary to dissect molecular mechanisms. The stalk-pore hypothesis proposes that bilayer merger proceeds rapidly via transient, high-negative curvature, intermediate membrane structures. Consistent with this, cholesterol, a major component of the CV membrane, contributes to a critical local negative curvature that supports formation of lipidic fusion intermediates. Following cholesterol depletion, structurally dissimilar lipids having intrinsic negative curvature greater than or equal to cholesterol recover the ability of CV to fuse but do not recover fusion efficiency (Ca(2+) sensitivity and kinetics). Conversely, cholesterol- and sphingomyelin-enriched microdomains regulate the efficiency of the fusion mechanism, presumably by contributing spatial and functional organization of other critical lipids and proteins at the fusion site. Critical proteins are thought to participate in Ca(2+) sensing, initiating membrane deformations, and facilitating fusion pore expansion. Capitalizing on a novel effect of the thiol-reactive reagent iodoacetamide (IA), potentiation of the Ca(2+) sensitivity and kinetics, a fluorescently tagged IA has been used to enhance fusion efficiency and simultaneously label the proteins involved. Isolation of cholesterol-enriched CV membrane fractions, using density gradient centrifugation, is being used to narrow the list of protein candidates potentially critical to the mechanism of fast Ca(2+)-triggered membrane fusion.
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Affiliation(s)
- Kendra L Furber
- Department of Physiology and Biophysics, University of Calgary, Faculty of Medicine, Calgary, Canada
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8
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Copper (II) sulfate charring for high sensitivity on-plate fluorescent detection of lipids and sterols: quantitative analyses of the composition of functional secretory vesicles. J Chem Biol 2008; 1:79-87. [PMID: 19568800 DOI: 10.1007/s12154-008-0007-1] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2008] [Revised: 05/20/2008] [Accepted: 05/23/2008] [Indexed: 10/21/2022] Open
Abstract
A wide range of methods exist for the on-plate detection of lipids resolved by thin layer chromatography. Fluorescence generally offers improvements in sensitivity over methods that use colorimetric or simple densitometric detection. In this paper, we report that a classic cupric sulfate charring protocol produces a fluorescent signal that sensitively and quantitatively detects a wide range of phospholipids, neutral lipids, and sterols after automated, multi-development high performance thin layer chromatography. The measured lower limits of detection and quantification, respectively, were, on average, 80 and 210 pmol for phospholipids and 43 fmol and 8.7 pmol for sterols. The simple, inexpensive, and highly sensitive approach described here was used to quantitatively analyze the lipid and sterol composition of sea urchin cortical vesicles, a stage-specific model system used to study the mechanism of regulated membrane fusion.
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9
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Roux MM, Radeke MJ, Goel M, Mushegian A, Foltz KR. 2DE identification of proteins exhibiting turnover and phosphorylation dynamics during sea urchin egg activation. Dev Biol 2008; 313:630-47. [DOI: 10.1016/j.ydbio.2007.10.053] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2007] [Revised: 10/29/2007] [Accepted: 10/31/2007] [Indexed: 10/22/2022]
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10
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Hibbert JE, Butt RH, Coorssen JR. Actin is not an essential component in the mechanism of calcium-triggered vesicle fusion. Int J Biochem Cell Biol 2005; 38:461-71. [PMID: 16309945 DOI: 10.1016/j.biocel.2005.10.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2005] [Accepted: 10/17/2005] [Indexed: 10/25/2022]
Abstract
Actin has been suggested as an essential component in the membrane fusion stage of exocytosis. In some model systems disruption of the actin filament network associated with exocytotic membranes results in a decrease in secretion. Here we analyze the fast Ca2+-triggered membrane fusion steps of regulated exocytosis using a stage-specific preparation of native secretory vesicles (SV) to directly test whether actin plays an essential role in this mechanism. Although present on secretory vesicles, selective pharmacological inhibition of actin did not affect the Ca2+-sensitivity, extent, or kinetics of membrane fusion, nor did the addition of exogenous actin or an anti-actin antibody. There was also no discernable affect on inter-vesicle contact (docking). Overall, the results do not support a direct role for actin in the fast, Ca2+-triggered steps of regulated membrane fusion. It would appear that actin acts elsewhere within the exocytotic cycle.
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Affiliation(s)
- Julie E Hibbert
- Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, Calgary, Alta., Canada T2N 4N1
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11
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Churchward MA, Rogasevskaia T, Höfgen J, Bau J, Coorssen JR. Cholesterol facilitates the native mechanism of Ca2+-triggered membrane fusion. J Cell Sci 2005; 118:4833-48. [PMID: 16219690 DOI: 10.1242/jcs.02601] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The process of regulated exocytosis is defined by the Ca2+-triggered fusion of two apposed membranes, enabling the release of vesicular contents. This fusion step involves a number of energetically complex steps and requires both protein and lipid membrane components. The role of cholesterol has been investigated using isolated release-ready native cortical secretory vesicles to analyze the Ca2+-triggered fusion step of exocytosis. Cholesterol is a major component of vesicle membranes and we show here that selective removal from membranes, selective sequestering within membranes, or enzymatic modification causes a significant inhibition of the extent, Ca2+ sensitivity and kinetics of fusion. Depending upon the amount incorporated, addition of exogenous cholesterol to cholesterol-depleted membranes consistently recovers the extent, but not the Ca2+ sensitivity or kinetics of fusion. Membrane components of comparable negative curvature selectively recover the ability to fuse, but are unable to recover the kinetics and Ca2+ sensitivity of vesicle fusion. This indicates at least two specific positive roles for cholesterol in the process of membrane fusion: as a local membrane organizer contributing to the efficiency of fusion, and, by virtue of its intrinsic negative curvature, as a specific molecule working in concert with protein factors to facilitate the minimal molecular machinery for fast Ca2+-triggered fusion.
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Affiliation(s)
- Matthew A Churchward
- Department of Physiology and Biophysics, Hotchkiss Brain Institute, University of Calgary, Health Sciences Centre, Faculty of Medicine, Calgary, Alberta, T2N 4N1, Canada
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12
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Wessel GM, Brooks JM, Green E, Haley S, Voronina E, Wong J, Zaydfudim V, Conner S. The biology of cortical granules. INTERNATIONAL REVIEW OF CYTOLOGY 2002; 209:117-206. [PMID: 11580200 DOI: 10.1016/s0074-7696(01)09012-x] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
An egg-that took weeks to months to make in the adult-can be extraordinarily transformed within minutes during its fertilization. This review will focus on the molecular biology of the specialized secretory vesicles of fertilization, the cortical granules. We will discuss their role in the fertilization process, their contents, how they are made, and the molecular mechanisms that regulate their secretion at fertilization. This population of secretory vesicles has inherent interest for our understanding of the fertilization process. In addition, they have import because they enhance our understanding of the basic processes of secretory vesicle construction and regulation, since oocytes across species utilize this vesicle type. Here, we examine diverse animals in a comparative approach to help us understand how these vesicles function throughout phylogeny and to establish conserved themes of function.
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Affiliation(s)
- G M Wessel
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, Rhode Island 02912 , USA
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13
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Ikebuchi Y, Baibakov B, Smith RM, Vogel SS. Plasma membrane resident 'fusion complexes' mediate reconstituted exocytosis. Traffic 2001; 2:654-67. [PMID: 11555419 DOI: 10.1034/j.1600-0854.2001.20908.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Calcium-triggered exocytosis is thought to be mediated by membrane-associated protein complexes. In sea urchin eggs, high concentrations of calcium activate multiple 'fusion complexes' per cortical vesicle-plasma membrane docking site. Some of these fusion complexes are known to reside in the vesicle membrane. It is not known if fusion complexes also reside in the plasma membrane, or if plasma membrane-resident fusion complexes require cognate partners in the vesicle membrane. Using reconstitution, we show that N-ethylmaleimide treatment of either vesicles or plasma membrane fragments prior to reconstitution does not completely inhibit exocytosis. Treatment of both components did result in complete inhibition. Upon reconstitution, cortical vesicles and the early endosomes formed by compensatory endocytosis both contributed, on average, two fusion complexes per reconstituted docking site. The plasma membrane contributed, on average, two fusion complexes per docking site when assembled with cortical vesicles, but only one complex when reconstituted with endosomes. We conclude that there are at least two types of plasma membrane-resident fusion complexes that participate in reconstituted cortical vesicle-plasma membrane fusion. The activity of one of these fusion complexes is target-specific for cortical vesicles, while the second type also supports fusion with endosomes.
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Affiliation(s)
- Y Ikebuchi
- Institute of Molecular Medicine and Genetics, Department of Medicine, Medical College of Georgia, 1120 15th Street CB 2803. Augusta, GA 30912-2630, USA
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14
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Abstract
Drosophila melanogaster mature oocytes in ovaries are arrested at metaphase I of meiosis. Eggs that have reached the uterus have released this arrest. It was not known where in the female reproductive tract egg activation occurs and what triggers it. We investigated when and where the egg is activated in Drosophila in vivo and at what meiotic stage the egg is fertilized. We found that changes in the egg's envelope's permeability, one feature of activation, initiate during ovulation, even while most of the egg is still within the ovary. The egg becomes impermeable as it proceeds down the oviducts; the process is complete by the time the egg is in the uterus. Cross-linking of vitelline membrane protein sV23 also increases progressively as the egg moves through the oviducts and the uterus. Activation also triggers meiosis to resume before the egg reaches the uterus, such that the earliest eggs that reach the uterus are in anaphase I. We discuss models for Drosophila egg activation in vivo.
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Affiliation(s)
- Y Heifetz
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703, USA
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15
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McNeil PL, Vogel SS, Miyake K, Terasaki M. Patching plasma membrane disruptions with cytoplasmic membrane. J Cell Sci 2000; 113 ( Pt 11):1891-902. [PMID: 10806100 DOI: 10.1242/jcs.113.11.1891] [Citation(s) in RCA: 150] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Vesicle-vesicle fusion initiated in cell cytoplasm by high Ca(2+) can rapidly erect large membrane boundaries. These might be used as a ‘patch’ for resealing plasma membrane disruptions. Three central predictions of this ‘patch’ hypothesis are here established in sea urchin eggs. First, we show that surface markers for plasma membrane protein and lipid are initially absent over disruption sites after resealing is complete. Second, we demonstrate that resealing capacity is strongly dependent upon local availability of fusion competent cytoplasmic organelles, specifically the reserve or yolk granule. Lastly, we demonstrate that the reserve granule is capable of rapid (t(1/2) <1 second), Ca(2+)-regulated (high threshold) fusion capable of erecting large (>1000 μm(2)), continuous membrane boundaries. Production of patch vesicles for resealing may proceed by an ‘emergency’ fusion mechanism distinct from that utilized for the much slower, highly regulated, cytosol-requiring organelle-organelle fusion events typical of constitutive membrane trafficking pathways.
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Affiliation(s)
- P L McNeil
- Department of Cellular Biology and Anatomy, and Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, GA, USA.
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16
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Zimmerberg J, Coorssen JR, Vogel SS, Blank PS. Sea urchin egg preparations as systems for the study of calcium-triggered exocytosis. J Physiol 1999; 520 Pt 1:15-21. [PMID: 10517796 PMCID: PMC2269559 DOI: 10.1111/j.1469-7793.1999.00015.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/1999] [Accepted: 08/20/1999] [Indexed: 12/01/2022] Open
Abstract
This paper reviews recent work in our laboratory on the mechanism of calcium-triggered exocytosis. Upon echinoderm egg fertilization, cortical secretory vesicle exocytosis is massive and synchronous. By combining physiological and molecular analyses with a variety of purified membrane isolates containing secretory vesicles that fuse to the plasma membrane or each other, we have characterized the final steps of this calcium-triggered exocytosis. Our kinetic analysis led to a functional definition of the fusion complex whose activation by calcium follows Poisson statistics. The properties of this complex are compared with the properties of the heterotrimeric SNARE protein complex that is present in the cortical vesicle system. Our data do not support the hypothesis that this particular heterotrimeric complex is by itself the biological fusogen.
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Affiliation(s)
- J Zimmerberg
- Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-1855, USA.
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17
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Abstract
Although catalyzed by different proteins, the energy barriers for lipid bilayer fusion in exocytosis, viral fusion, and trafficking seem to be the same as those for the fusion of protein-free phospholipid membranes. To minimize this energy, fusion will proceed through a minimal number of lipid molecules, probably localized in bent non-bilayer intermediates. Experiments on phospholipid bilayer membrane fusion show the pathway of contact, hemifusion, flickering fusion pore formation, and fusion pore enlargement caused by swelling of the vesicle. Lipid curvature determines the barriers to hemifusion and fusion pore formation, while swelling-induced membrane tension drives fusion pore enlargement. Experiments on viral protein-induced cell-cell fusion and exocytosis show the same pathway with the same fundamental effects of lipid curvature and membrane tension. Thus while proteins control these reactions, lipid energetics determine the basic reaction scheme for membrane fusion.
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Affiliation(s)
- J Zimmerberg
- Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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18
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Blank PS, Cho MS, Vogel SS, Kaplan D, Kang A, Malley J, Zimmerberg J. Submaximal responses in calcium-triggered exocytosis are explained by differences in the calcium sensitivity of individual secretory vesicles. J Gen Physiol 1998; 112:559-67. [PMID: 9806965 PMCID: PMC2229435 DOI: 10.1085/jgp.112.5.559] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A graded response to calcium is the defining feature of calcium-regulated exocytosis. That is, there exist calcium concentrations that elicit submaximal exocytotic responses in which only a fraction of the available population of secretory vesicles fuse. The role of calcium-dependent inactivation in defining the calcium sensitivity of sea urchin egg secretory vesicle exocytosis in vitro was examined. The cessation of fusion in the continued presence of calcium was not due to calcium-dependent inactivation. Rather, the calcium sensitivity of individual vesicles within a population of exocytotic vesicles is heterogeneous. Any specific calcium concentration above threshold triggered subpopulations of vesicles to fuse and the size of the subpopulations was dependent upon the magnitude of the calcium stimulus. The existence of multiple, stable subpopulations of vesicles is consistent with a fusion process that requires the action of an even greater number of calcium ions than the numbers suggested by models based on the assumption of a homogeneous vesicle population.
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Affiliation(s)
- P S Blank
- Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
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Vogel SS, Blank PS, Zimmerberg J. Poisson-distributed active fusion complexes underlie the control of the rate and extent of exocytosis by calcium. J Cell Biol 1996; 134:329-38. [PMID: 8707819 PMCID: PMC2120878 DOI: 10.1083/jcb.134.2.329] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
We have investigated the consequences of having multiple fusion complexes on exocytotic granules, and have identified a new principle for interpreting the calcium dependence of calcium-triggered exocytosis. Strikingly different physiological responses to calcium are expected when active fusion complexes are distributed between granules in a deterministic or probabilistic manner. We have modeled these differences, and compared them with the calcium dependence of sea urchin egg cortical granule exocytosis. From the calcium dependence of cortical granule exocytosis, and from the exposure time and concentration dependence of N-ethylmaleimide inhibition, we determined that cortical granules do have spare active fusion complexes that are randomly distributed as a Poisson process among the population of granules. At high calcium concentrations, docking sites have on average nine active fusion complexes.
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Affiliation(s)
- S S Vogel
- Laboratory of Theoretical and Physical Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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20
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Bi GQ, Alderton JM, Steinhardt RA. Calcium-regulated exocytosis is required for cell membrane resealing. J Biophys Biochem Cytol 1995; 131:1747-58. [PMID: 8557742 PMCID: PMC2120667 DOI: 10.1083/jcb.131.6.1747] [Citation(s) in RCA: 242] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Using confocal microscopy, we visualized exocytosis during membrane resealing in sea urchin eggs and embryos. Upon wounding by a laser beam, both eggs and embryos showed a rapid burst of localized Ca(2+)-regulated exocytosis. The rate of exocytosis was correlated quantitatively with successfully resealing. In embryos, whose activated surfaces must first dock vesicles before fusion, exocytosis and membrane resealing were inhibited by neurotoxins that selectively cleave the SNARE complex proteins, synaptobrevin, SNAP-25, and syntaxin. In eggs, whose cortical vesicles are already docked, vesicles could be reversibly undocked with externally applied stachyose. If cortical vesicles were undocked both exocytosis and plasma membrane resealing were completely inhibited. When cortical vesicles were transiently undocked, exposure to tetanus toxin and botulinum neurotoxin type C1 rendered them no longer competent for resealing, although botulinum neurotoxin type A was still ineffective. Cortical vesicles transiently undocked in the presence of tetanus toxin were subsequently fusion incompetent although to a large extent they retained their ability to redock when stachyose was diluted. We conclude that addition of internal membranes by exocytosis is required and that a SNARE-like complex plays differential roles in vesicle docking and fusion for the repair of disrupted plasma membrane.
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Affiliation(s)
- G Q Bi
- Group in Biophysics, University of California, Berkeley 94720-3200, USA
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21
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Whalley T, Terasaki M, Cho MS, Vogel SS. Direct membrane retrieval into large vesicles after exocytosis in sea urchin eggs. J Cell Biol 1995; 131:1183-92. [PMID: 8522582 PMCID: PMC2120644 DOI: 10.1083/jcb.131.5.1183] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
At fertilization in sea urchin eggs, elevated cytosolic Ca2+ leads to the exocytosis of 15,000-18,000 1.3-microns-diam cortical secretory granules to form the fertilization envelope. Cortical granule exocytosis more than doubles the surface area of the egg. It is thought that much of the added membrane is retrieved by subsequent endocytosis. We have investigated how this is achieved by activating eggs in the presence of aqueous- and lipid-phase fluorescent dyes. We find rapid endocytosis of membrane into 1.5-microns-diam vesicles starting immediately after cortical granule exocytosis and persisting over the following 15 min. The magnitude of this membrane retrieval can compensate for the changes in the plasma membrane of the egg caused by exocytosis. This membrane retrieval is not stimulated by PMA treatment which activates the endocytosis of clathrin-coated vesicles. When eggs are treated with short wave-length ultraviolet light, cortical granule exocytosis still occurs, but granule cores fail to disperse. After egg activation, large vesicles containing semi-intact cortical granule protein cores are observed. These data together with experiments using sequential pulses of fluid-phase markers support the hypothesis that the bulk of membrane retrieval immediately after cortical granule exocytosis is achieved through direct retrieval into large endocytotic structures.
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Affiliation(s)
- T Whalley
- Laboratory of Theoretical and Physical Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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22
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Terasaki M. Visualization of exocytosis during sea urchin egg fertilization using confocal microscopy. J Cell Sci 1995; 108 ( Pt 6):2293-300. [PMID: 7673349 DOI: 10.1242/jcs.108.6.2293] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A Ca2+ wave at fertilization triggers cortical granule exocytosis in sea urchin eggs. New methods for visualizing exocytosis of individual cortical granules were developed using fluorescent probes and confocal microscopy. Electron microscopy previously provided evidence that cortical granule exocytosis results in the formation of long-lived depressions in the cell surface. Fluorescent dextran or ovalbumin in the sea water seemed to label these depressions and appeared by confocal microscopy as disks. FM 1–43, a water-soluble fluorescent dye which labels membranes in contact with the sea water, seemed to label the membrane of these depressions and appeared as rings. In double-labeling experiments, the disk and ring labeling by the two types of fluorescent dyes were coincident to within 0.5 second. The fluorescent labeling is coincident with the disappearance of cortical granules by transmitted light microscopy, demonstrating that the labeling corresponds to cortical granule exocytosis. Fluorescent labeling was simultaneous with an expansion of the space occupied by the cortical granule, and labeling by the fluorescent dextran was found to take 0.1-0.2 second. These results are consistent with, and reinforce the previous electron microscopic evidence for, long-lived depressions formed by exocytosis; in addition, the new methods provide new ways to investigate cortical granule exocytosis in living eggs. The fluorescence labeling methods were used with the Ca2+ indicator Ca Green-dextran to test if Ca2+ and cortical granule exocytosis are closely related spatially and temporally. In any given region of the cortex, Ca2+ increased relatively slowly.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Terasaki
- Laboratory of Neurobiology, NINDS, NIH, Bethesda, MD 20892, USA
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Lysophosphatidylcholine reversibly arrests exocytosis and viral fusion at a stage between triggering and membrane merger. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(19)74455-x] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Chernomordik LV, Vogel SS, Sokoloff A, Onaran HO, Leikina EA, Zimmerberg J. Lysolipids reversibly inhibit Ca(2+)-, GTP- and pH-dependent fusion of biological membranes. FEBS Lett 1993; 318:71-6. [PMID: 8436229 DOI: 10.1016/0014-5793(93)81330-3] [Citation(s) in RCA: 160] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Membrane fusion in exocytosis, intracellular trafficking, and enveloped viral infection is thought to be mediated by specialized proteins acting to merge membrane lipid bilayers. We now show that one class of naturally-occurring phospholipids, lysolipids, inhibits fusion between cell membranes, organelles, and between organelles and plasma membrane. Inhibition was reversible, did not correlate with lysis, and could be attributed to the molecular shape of lysolipids rather than to any specific chemical moiety. Fusion was arrested at a stage preceding fusion pore formation. Our results are consistent with the hypothesis that biological fusion, irrespective of trigger, involves the formation of a highly bent intermediate between membranes, the fusion stalk.
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Affiliation(s)
- L V Chernomordik
- Laboratory of Theoretical and Physical Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
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