Scinderin and cortical F-actin are components of the secretory machinery

1999 ◽  
Vol 77 (9) ◽  
pp. 660-671 ◽  
Author(s):  
J -M Trifaró
Keyword(s):  
Chromaffin Cell ◽  
Secretory Vesicle ◽  
Secretory Vesicles ◽  
Actin Network ◽  
Filamentous Actin ◽  
Actin Networks ◽  
Reserve Pool ◽  
Vesicle Exocytosis

Secretory vesicle exocytosis is the mechanism of release of neurotransmitters and neuropeptides. Secretory vesicles are localized in at least two morphologically and functionally distinct compartments: the reserve pool and the release-ready pool. Filamentous actin networks play an important role in this compartmentalization and in the trafficking of vesicles between these compartments. The cortical F-actin network constitutes a barrier (negative clamp) to the movement of secretory vesicles to release sites, and it must be locally disassembled to allow translocation of secretory vesicles in preparation for exocytosis. The disassembly of the cortical F-actin network is controlled by scinderin (a Ca2+-dependent F-actin severing protein) upon activation by Ca2+ entering the cells during stimulation. There are several factors that regulate scinderin activation (i.e., Ca2+ levels, phosphatidylinositol 4,5-bisphosphate (PIP2), etc.). The results suggest that scinderin and the cortical F-actin network are components of the secretory machinery.Key words: F-actin, scinderin, exocytosis, cytoskeleton, chromaffin cell.

Molecular mechanism of secretory vesicle docking

2010 ◽  
Vol 38 (1) ◽  
pp. 192-198 ◽  
Author(s):  
Heidi de Wit
Keyword(s):  
Plasma Membrane ◽  
Cell Model ◽  
Secretory Vesicle ◽  
Model Systems ◽  
Secretory Vesicles ◽  
Filamentous Actin ◽  
Embryonic Mouse ◽  
Vesicle Docking ◽  
Bovine Chromaffin Cell ◽  
Stable Association

Docking, the stable association of secretory vesicles with the plasma membrane, is considered to be the necessary first step before vesicles gain fusion-competence, but it is unclear how vesicles dock. In adrenal medullary chromaffin cells, access of secretory vesicles to docking sites is controlled by dense F-actin (filamentous actin) beneath the plasma membrane. Recently, we found that, in the absence of Munc18-1, the number of docked vesicles and the thickness of cortical F-actin are affected. In the present paper, I discuss the possible mechanism by which Munc18-1 modulates cortical F-actin and how it orchestrates the docking machinery via an interaction with syntaxin-1. Finally, a comparison of Munc18's role in embryonic mouse and adult bovine chromaffin cell model systems will be made to clarify observed differences in cortical F-actin as well as docking phenotypes.

scholarly journals Rab27b regulates exocytosis of secretory vesicles in acinar epithelial cells from the lacrimal gland

2011 ◽  
Vol 301 (2) ◽  
pp. C507-C521 ◽  
Author(s):  
Lilian Chiang ◽  
Julie Ngo ◽  
Joel E. Schechter ◽  
Serhan Karvar ◽  
Tanya Tolmachova ◽  
...  
Keyword(s):  
Lacrimal Gland ◽  
Morphological Changes ◽  
Acinar Cells ◽  
Secretory Vesicle ◽  
Dominant Negative ◽  
Secretory Vesicles ◽  
Apical Surface ◽  
Tear Proteins ◽  
Vesicle Exocytosis ◽  
Constitutively Active

Tear proteins are supplied by the regulated fusion of secretory vesicles at the apical surface of lacrimal gland acinar cells, utilizing trafficking mechanisms largely yet uncharacterized. We investigated the role of Rab27b in the terminal release of these secretory vesicles. Confocal fluorescence microscopy analysis of primary cultured rabbit lacrimal gland acinar cells revealed that Rab27b was enriched on the membrane of large subapical vesicles that were significantly colocalized with Rab3D and Myosin 5C. Stimulation of cultured acinar cells with the secretagogue carbachol resulted in apical fusion of these secretory vesicles with the plasma membrane. Evaluation of morphological changes by transmission electron microscopy of lacrimal glands from Rab27b −/− and Rab27 ash/ash /Rab27b −/− mice, but not ashen mice deficient in Rab27a, showed changes in abundance and organization of secretory vesicles, further confirming a role for this protein in secretory vesicle exocytosis. Glands lacking Rab27b also showed increased lysosomes, damaged mitochondria, and autophagosome-like organelles. In vitro, expression of constitutively active Rab27b increased the average size but retained the subapical distribution of Rab27b-enriched secretory vesicles, whereas dominant-negative Rab27b redistributed this protein from membrane to the cytoplasm. Functional studies measuring release of a cotransduced secretory protein, syncollin-GFP, showed that constitutively active Rab27b enhanced, whereas dominant-negative Rab27b suppressed, stimulated release. Disruption of actin filaments inhibited vesicle fusion to the apical membrane but did not disrupt homotypic fusion. These data show that Rab27b participates in aspects of lacrimal gland acinar cell secretory vesicle formation and release.

scholarly journals Submaximal Responses in Calcium-triggered Exocytosis Are Explained by Differences in the Calcium Sensitivity of Individual Secretory Vesicles

1998 ◽  
Vol 112 (5) ◽  
pp. 559-567 ◽  
Author(s):  
Paul S. Blank ◽  
Myoung-Soon Cho ◽  
Steven S. Vogel ◽  
Doron Kaplan ◽  
Albert Kang ◽  
...  
Keyword(s):  
Calcium Sensitivity ◽  
Secretory Vesicle ◽  
Secretory Vesicles ◽  
Calcium Dependent ◽  
Sea Urchin Egg ◽  
Dependent Inactivation ◽  
Graded Response ◽  
Vesicle Exocytosis

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.

Reptation of Microtubules in F-Actin Networks : Effects of Filament Stiffness and Network Topology on Reptation Dynamics

1997 ◽  
Vol 489 ◽  
Author(s):  
Jagesh V. Shah ◽  
Lisa A. Flanagan ◽  
David Bahk ◽  
Paul A. Janmey
Keyword(s):  
Network Topology ◽  
Actin Filaments ◽  
Diffusion Constant ◽  
Actin Network ◽  
Filamentous Actin ◽  
Actin Networks ◽  
Apparent Diffusion ◽  
Thermally Driven

AbstractThe thermally driven motions of fluorescently labeled microtubules embedded in a network of filamentous actin polymers are analysed as the diffusion of a rod-like polymer within a virtual tube formed by the surrounding semiflexible actin filaments. The apparent diffusion constant parallel to the tube scales with the inverse of the microtubule length and the magnitude is consistant with diffusion through a medium with a viscosity of approximately 10 centipoise. Introduction of crosslinks between the actin filaments does not alter the diffusion of the microtubules in the actin network.

scholarly journals The contributions of the actin machinery to endocytic membrane bending and vesicle formation

2018 ◽  
Vol 29 (11) ◽  
pp. 1346-1358 ◽  
Author(s):  
Andrea Picco ◽  
Wanda Kukulski ◽  
Hetty E. Manenschijn ◽  
Tanja Specht ◽  
John A. G. Briggs ◽  
...  
Keyword(s):  
Cross Linking ◽  
Actin Network ◽  
Filamentous Actin ◽  
Actin Networks ◽  
Cellular Processes ◽  
Membrane Invagination ◽  
Imaging Approach ◽  
Proportional Increase ◽  
Membrane Bending ◽  
Membrane Changes

Branched and cross-linked actin networks mediate cellular processes that move and shape membranes. To understand how actin contributes during the different stages of endocytic membrane reshaping, we analyzed deletion mutants of yeast actin network components using a hybrid imaging approach that combines live imaging with correlative microscopy. We could thus temporally dissect the effects of different actin network perturbations, revealing distinct stages of actin-based membrane reshaping. Our data show that initiation of membrane bending requires the actin network to be physically linked to the plasma membrane and to be optimally cross-linked. Once initiated, the membrane invagination process is driven by nucleation and polymerization of new actin filaments, independent of the degree of cross-linking and unaffected by a surplus of actin network components. A key transition occurs 2 s before scission, when the filament nucleation rate drops. From that time point on, invagination growth and vesicle scission are driven by an expansion of the actin network without a proportional increase of net actin amounts. The expansion is sensitive to the amount of filamentous actin and its cross-linking. Our results suggest that the mechanism by which actin reshapes the membrane changes during the progress of endocytosis, possibly adapting to varying force requirements.

scholarly journals Calcium Dependencies of Regulated Exocytosis in Different Endocrine Cells

2011 ◽  
pp. S29-S38
Author(s):  
J. DOLENŠEK ◽  
M. SKELIN ◽  
M. S. RUPNIK
Keyword(s):  
Pancreatic Beta Cells ◽  
Endocrine Cells ◽  
Secretory Vesicle ◽  
Pituitary Cells ◽  
Secretory Vesicles ◽  
Regulated Exocytosis ◽  
Vesicle Exocytosis ◽  
Adrenal Chromaffin ◽  
Endocrine Tissues

Exocytotic machinery in neuronal and endocrine tissues is sensitive to changes in intracellular Ca2+ concentration. Endocrine cell models, that are most frequently used to study the mechanisms of regulated exocytosis, are pancreatic beta cells, adrenal chromaffin cells and pituitary cells. To reliably study the Ca2+ sensitivity in endocrine cells, accurate and fast determination of Ca2+ dependence in each tested cell is required. With slow photo-release it is possible to induce ramp-like increase in intracellular Ca2+ concentration ([Ca2+]i) that leads to a robust exocytotic activity. Slow increases in the [Ca2+]i revealed exocytotic phases with different Ca2+ sensitivities that have been largely masked in step-like flash photo-release experiments. Strikingly, in the cells of the three described model endocrine tissues (beta, chromaffin and melanotroph cells), distinct Ca2+ sensitivity ‘classes’ of secretory vesicles have been observed: a highly Ca2+-sensitive, a medium Ca2+-sensitive and a low Ca2+-sensitive kinetic phase of secretory vesicle exocytosis. We discuss that a physiological modulation of a cellular activity, e.g. by activating cAMP/PKA transduction pathway, can switch the secretory vesicles between Ca2+ sensitivity classes. This significantly alters late steps in the secretory release of hormones even without utilization of an additional Ca2+ sensor protein.

scholarly journals The contributions of the actin machinery to endocytic membrane bending and vesicle formation

2017 ◽  
Author(s):  
Andrea Picco ◽  
Wanda Kukulski ◽  
Hetty E. Manenschijn ◽  
Tanja Specht ◽  
John A. G. Briggs ◽  
...  
Keyword(s):  
Hybrid Imaging ◽  
Correlative Microscopy ◽  
Actin Network ◽  
Filamentous Actin ◽  
Actin Networks ◽  
Cellular Processes ◽  
Membrane Invagination ◽  
Imaging Approach ◽  
Membrane Bending ◽  
Time Point

AbstractBranched and crosslinked actin networks mediate cellular processes that move and shape membranes. To understand how actin contributes during the different stages of endocytic membrane reshaping, we analysed deletion mutants of yeast actin network components using a hybrid imaging approach that combines live imaging with correlative microscopy. We could thereby temporally dissect the effects of different actin network perturbations, revealing distinct stages of actin-based membrane reshaping. Our data show that initiation of membrane bending requires the actin network to be physically linked to the plasma membrane and to be optimally crosslinked. Once initiated, the membrane invagination process is driven by nucleation and polymerization of new actin filaments, independently of the degree of cross-linking and unaffected by a surplus of actin network components. A key transition occurs 2 seconds before scission when the filament nucleation rate drops. From that time point on, invagination growth and vesicle scission are driven by an expansion of the assembled actin network. The expansion is sensitive to the amount of filamentous actin and its crosslinking. Our results suggest that the mechanism by which actin reshapes the membrane adapts to force requirements that vary during the progress of endocytosis.

scholarly journals Cortical filamentous actin disassembly and scinderin redistribution during chromaffin cell stimulation precede exocytosis, a phenomenon not exhibited by gelsolin.

1991 ◽  
Vol 113 (5) ◽  
pp. 1057-1067 ◽  
Author(s):  
M L Vitale ◽  
A Rodríguez Del Castillo ◽  
L Tchakarov ◽  
J M Trifaró
Keyword(s):  
Actin Filament ◽  
Chromaffin Cells ◽  
Chromaffin Cell ◽  
Catecholamine Secretion ◽  
Cortical Region ◽  
Cortical Surface ◽  
Filamentous Actin ◽  
Cell Stimulation ◽  
Rhodamine Phalloidin ◽  
Filament Networks

Immunofluorescence and cytochemical studies have demonstrated that filamentous actin is mainly localized in the cortical surface of the chromaffin cell. It has been suggested that these actin filament networks act as a barrier to the secretory granules, impeding their contact with the plasma membrane. Stimulation of chromaffin cells produces a disassembly of actin filament networks, implying the removal of the barrier. The presence of gelsolin and scinderin, two Ca(2+)-dependent actin filament severing proteins, in the cortical surface of the chromaffin cells, suggests the possibility that cell stimulation brings about activation of one or more actin filament severing proteins with the consequent disruption of actin networks. Therefore, biochemical studies and fluorescence microscopy experiments with scinderin and gelsolin antibodies and rhodamine-phalloidin, a probe for filamentous actin, were performed in cultured chromaffin cells to study the distribution of scinderin, gelsolin, and filamentous actin during cell stimulation and to correlate the possible changes with catecholamine secretion. Here we report that during nicotinic stimulation or K(+)-evoked depolarization, subcortical scinderin but not gelsolin is redistributed and that this redistribution precedes catecholamine secretion. The rearrangement of scinderin in patches is mediated by nicotinic receptors. Cell stimulation produces similar patterns of distribution of scinderin and filamentous actin. However, after the removal of the stimulus, the recovery of scinderin cortical pattern of distribution is faster than F-actin reassembly, suggesting that scinderin is bound in the cortical region of the cell to a component other than F-actin. We also demonstrate that peripheral actin filament disassembly and subplasmalemmal scinderin redistribution are calcium-dependent events. Moreover, experiments with an antibody against dopamine-beta-hydroxylase suggest that exocytosis sites are preferentially localized to areas of F-actin disassembly.

Synaptotagmin-1: A Multi-Functional Protein that Mediates Vesicle Docking, Priming, and Fusion

2021 ◽  
Vol 22 ◽  
Author(s):  
Najeeb Ullah ◽  
Ezzouhra El Maaiden ◽  
Md. Sahab Uddin ◽  
Ghulam Md Ashraf
Keyword(s):  
Plasma Membrane ◽  
Secretory Granules ◽  
Secretory Vesicle ◽  
Neuroendocrine Cells ◽  
Snare Complex ◽  
Secretory Vesicles ◽  
Functional Protein ◽  
Vesicle Docking ◽  
Synaptotagmin 1

: The fusion of secretory vesicles with the plasma membrane depends on the assembly of v-SNAREs (VAMP2/synaptobrevin2) and t-SNAREs (SNAP25/syntaxin1) into the SNARE complex. Vesicles go through several upstream steps, referred to as docking and priming, to gain fusion competence. The vesicular protein synaptotagmin-1 (Syt-1) is the principal Ca2+ sensor for fusion in several central nervous system neurons and neuroendocrine cells and part of the docking complex for secretory granules. Syt-1 binds to the acceptor complex such as synaxin1, SNAP-25 on the plasma membrane to facilitate secretory vesicle docking, and upon Ca2+-influx promotes vesicle fusion. This review assesses the role of the Syt-1 protein involved in the secretory vesicle docking, priming, and fusion.

scholarly journals The Cooh-Terminal Domain of Myo2p, a Yeast Myosin V, Has a Direct Role in Secretory Vesicle Targeting

1999 ◽  
Vol 147 (4) ◽  
pp. 791-808 ◽  
Author(s):  
Daniel Schott ◽  
Jackson Ho ◽  
David Pruyne ◽  
Anthony Bretscher
Keyword(s):  
Secretory Vesicle ◽  
Restrictive Temperature ◽  
Secretory Vesicles ◽  
Tail Domain ◽  
Myosin V ◽  
Direct Role ◽  
Rab Protein ◽  
Polarized Delivery ◽  
Actin Cables ◽  
Type V

MYO2 encodes a type V myosin heavy chain needed for the targeting of vacuoles and secretory vesicles to the growing bud of yeast. Here we describe new myo2 alleles containing conditional lethal mutations in the COOH-terminal tail domain. Within 5 min of shifting to the restrictive temperature, the polarized distribution of secretory vesicles is abolished without affecting the distribution of actin or the mutant Myo2p, showing that the tail has a direct role in vesicle targeting. We also show that the actin cable–dependent translocation of Myo2p to growth sites does not require secretory vesicle cargo. Although a fusion protein containing the Myo2p tail also concentrates at growth sites, this accumulation depends on the polarized delivery of secretory vesicles, implying that the Myo2p tail binds to secretory vesicles. Most of the new mutations alter a region of the Myo2p tail conserved with vertebrate myosin Vs but divergent from Myo4p, the myosin V involved in mRNA transport, and genetic data suggest that the tail interacts with Smy1p, a kinesin homologue, and Sec4p, a vesicle-associated Rab protein. The data support a model in which the Myo2p tail tethers secretory vesicles, and the motor transports them down polarized actin cables to the site of exocytosis.

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