Membrane Fusion in a Model System

Satir, Birgit H.; Schooley, Caroline; Satir, Peter

doi:10.1083/jcb.56.1.153

Cited by 331 publications

(46 citation statements)

References 22 publications

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“…Similar images have been observed previously in other secretory systems, such as the neuromuscular junction (16,22), the adrenal medulla (45), and the pancreatic beta cells (34), and interpreted as an early event in the release process, i.e., as points of fusion between the plasmalemma and the membrane of the secretory granules. Rosettes, annuli, or localized modifications of particle distribution, which have been reported to characterize the points of membrane adhesion in some protozoa (38,39,40) as well as endothelial cells (41) and macrophages (44), were never observed around these areas. Analogous observations had been made previously in other glandular cells (34,45).…”

Section: Stimulated Cellsmentioning

confidence: 99%

Dynamic changes of the luminal plasmalemma in stimulated parotid acinar cells. A freeze-fracture study.

Camilli¹,

Peluchetti²,

Meldolesi³

1976

The Journal of Cell Biology

112

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In the acinar cells of the rat parotid gland the two membranes participating in exocytosis, i.e., the luminal plasmalemma and the secretory granule membrane, are clearly distinguishable in freeze-fracture because of their different densities in particles. In order to obtain point-specific information about the fusion-fission of these two membranes that occurs during the secretory cycle, glands were studied at various times (5 min to 6 h) after stimulation with isoproterenol. We observed that, in the course of the release of secretion products and shortly afterwards, the enlarged luminal plasmalemma exhibits a mosaic organization consisting of an alternation of membrane patches of high (original plasmalemma) and low (fused granule membrane) particle density. The transition between these two patterns is usually sharp. Later, concomitant with the reformation of acinar canaliculi, the low particle density membrane is found at the cell surface but only bounding vacuolar infoldings, and then it finally disappears.These results suggest that (a) fusion of these membranes does not result in a random intermixing of the molecular components of the participating membranes, which retain their structural identity; and (b) the enlarged luminal plasmalemma reverts to its original size by a progressive, specific removal of the regions of low particle density from the cell surface.In secretory cells the exportable proteins are known to be vectorially transported from the site of synthesis to the extracellular space through a pathway which includes a number of distinct membrane-bounded organelles (8,9,23,24): in sequence, the rough endoplasmic reticulum, the Golgi complex, and the secretion granules. The content of the latter is then discharged by exocytosis, i.e., by fusion of the granule limiting membrane with the plasmalemma followed by an opening at the point of fusion (36). Since the transport of the secretion products between adjacent cell compartments occurs in bulk, by means of membrane-bounded vesicles, a concomitant transfer of membranes must be postulated.The fate of the transferred membrane is still debated. Biochemical studies carried out on various secretory systems have clearly shown that the turnover rate of the molecular components of all the membranes involved is much slower than that of the secretory products (28,29,46,47); thus, it is most likely that these molecular components are reutilized in several secretory cycles (28,29). However, the mechanisms of this reutilization are still unclear, since it is not known whether membrane patches, after fusing with a membrane of a

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Section: Stimulated Cellsmentioning

confidence: 99%

Dynamic changes of the luminal plasmalemma in stimulated parotid acinar cells. A freeze-fracture study.

Camilli¹,

Peluchetti²,

Meldolesi³

1976

The Journal of Cell Biology

112

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“…THE MUCOCYSTS (Figure I c) are cortical organelles; they are shown in the intact and extruding form. Mucocysts have been studied extensively both structurally (140,3,143,144,122,123,120,92) and chemically (1, 50); however, the biogenesis of the organelles has not been revealed in detail. Tetrahymena contains about 1000 mucocysts; the extruded mucocyst material binds the cationic dye, alcian blue (90,92,100,138), and the possible role of this material in nutrient uptake has been discussed (92,97).…”

Section: The Cell Organellesmentioning

confidence: 99%

On cell organelles in Tetrahymena. With special reference to mitochondria and peroxisomes

Nilsson

1981

Carlsberg Res. Commun.

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In the ciliate, Tetrahymena pyriformis, the population of cell organelles shows variation during the culture cycle and when the cells are subjected to various treatments. New cell constituents may appear and the fine structure of mitochondria and peroxisomes may change. Such dynamic structural changes are described and reviewed in relation to physiological and biochemical studies on Tetrahymena. The cell organelles discussed are about I tam in diameter or smaller~ reference is also made to the nuc[eotar organization which is the most sensitive indicator of the physiologica~ state of the ceils. The presumed distribution of the various cell organelles in subcellular fractions of Tetrahymena is mentioned, since dependent on the pretreatment of the cells, especially the mitochondrial and peroxisomal fractions may be contaminated to varying degrees with other cell organelles~The purpose of the review is to demonstrate that a correlation exists between the structure and function of cell organelles, especially mitochondria and peroxisomes, and that the overall fine structure of a cell reflects its physiological state.

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“…Using these techniques, Satir and co-workers (33,34) observed membrane fusion during mucocyst secretion in Tetrahymena and proposed a model for membrane reorganization during fusion which is qualitatively different from that of Palade and Bruns. Briefly, a rosette of membrane particles (thought to represent protein-containing intramembrane structures) was formed before fusion.…”

mentioning

confidence: 99%

“…The formation of bilayer membrane diaphragms during fusion can be found in micrographs included in the freeze-fracture study of membrane fusion during mucocyst secretion (33,34)? Here, a rosette of particles (diameter -60 nm) appears on the region of the plasma membrane which is fusing with the secretory vesicle.…”

mentioning

confidence: 99%

Membrane fusion during secretion. A hypothesis based on electron microscope observation of Phytophthora Palmivora zoospores during encystment.

Silva¹,

Nogueira²

1977

The Journal of Cell Biology

151

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Interpretation of freeze-fracture and thin-section results shows that fusion of the peripheral vesicle with the plasmalemma of a Phytophthora palmivora zoospore occurs at several discrete sites and results in the formation and expansion of a particle-free bilayer membrane diaphragm and in the appearance of a polymorphic network of membrane-bounded tunnels, the lumina of which are continuous with the cytoplasm. The outer half of the bilayer membrane diaphragm appears continuous with the outer half of the plasma membrane; the inner half of the bilayer membrane diaphragm with the inner half of the peripheral vesicle membrane; and the inner half of the plasmalemma with the outer half of the peripheral vesicle membrane.Interpretation of our results leads us to formulate a hypothesis for a sequence of several intermediate stages involved in membrane fusion. The initial fusion event is viewed as a local catastrophe (Thorn, R. 1972. Stabilit6 Structurelle et Morphogen~se. W. A. Benjamin Inc., Reading, Mass.) involving the sudden reorganization of apposed elements of the inner half of the plasmalemma and the outer half of the peripheral vesicle membrane. Fusion of apposed components at the rim of the perimeter of fusion results in the formation of a toroid hemi-micelle which provides continuity between the inner half of the plasmalemma and the outer half of the peripheral vesicle membrane. Simultaneously, apposed components at the site of fusion may reorganize into an inverted membrane micelle. A bilayer membrane diaphragm is then formed by apposition and flowing of components form the outer half of the plasmalemma and the inner (exoplasmic) half of the peripheral vesicle membrane. The existence of large areas of membrane contact before fusion may lead to several fusion events and the formation of a polymorphic network of membrane-bound tunnels.Membrane fusion is a frequent and important event in the life of most eukaryotic cells (17,23,29,30). Among other cellular processes, merebrane fusion mediates secretion as a necessary step to the transfer of macromolecules contained within cytoplasmic vesicles to the cell periphery or

show abstract

Membrane Fusion in a Model System

Cited by 331 publications

References 22 publications

Dynamic changes of the luminal plasmalemma in stimulated parotid acinar cells. A freeze-fracture study.

Dynamic changes of the luminal plasmalemma in stimulated parotid acinar cells. A freeze-fracture study.

On cell organelles in Tetrahymena. With special reference to mitochondria and peroxisomes

Membrane fusion during secretion. A hypothesis based on electron microscope observation of Phytophthora Palmivora zoospores during encystment.

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