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Antioxidants & Redox Signaling Jun 2009Vesicle formation provides a means of cellular entry for extracellular substances and for recycling of membrane constituents. Mechanisms governing the two primary... (Review)
Review
Vesicle formation provides a means of cellular entry for extracellular substances and for recycling of membrane constituents. Mechanisms governing the two primary endocytic pathways (i.e., caveolae- and clathrin-mediated endocytosis, as well as newly emerging vesicular pathways) have become the focus of intense investigation to improve our understanding of nutrient, hormone, and drug delivery, as well as opportunistic invasion of pathogens. In this review of endocytosis, we broadly discuss the structural and signaling proteins that compose the molecular machinery governing endocytic vesicle formation (budding, invagination, and fission from the membrane), with some regard for the specificity observed in certain cell types and species. Important biochemical functions of endocytosis and diseases caused by their disruption also are discussed, along with the structures of key components of endocytic pathways and their known mechanistic contributions. The mechanisms by which principal components of the endocytic machinery are recruited to the plasma membrane, where they interact to induce vesicle formation, are discussed, together with computational approaches used to simulate simplified versions of endocytosis with the hope of clarifying aspects of vesicle formation that may be difficult to determine experimentally. Finally, we pose several unanswered questions intended to stimulate further research interest in the cell biology and modeling of endocytosis.
Topics: Animals; Caveolae; Cell Membrane; Clathrin; Endocytosis; Humans; Models, Biological; Signal Transduction; Transport Vesicles
PubMed: 19113823
DOI: 10.1089/ars.2008.2397 -
Molecular Neurobiology Feb 2008The hypothesis that release of classical neurotransmitters and neuropeptides is facilitated by increasing the mobility of small synaptic vesicles (SSVs) and dense core... (Review)
Review
The hypothesis that release of classical neurotransmitters and neuropeptides is facilitated by increasing the mobility of small synaptic vesicles (SSVs) and dense core vesicles (DCVs) could not be tested until the advent of methods for visualizing these secretory vesicles in living nerve terminals. In fact, fluorescence imaging studies have only since 2005 established that activity increases secretory vesicle mobility in motoneuron terminals and chromaffin cells. Mobilization of DCVs and SSVs appears to be due to liberation of hindered vesicles to promote quicker diffusion. However, F-actin and synapsin, which have been featured in mobilization models, are not required for activity-dependent increases in the mobility of DCVs or SSVs. Most recently, the signaling required for sustained mobilization has been identified for Drosophila motoneuron DCVs and shown to increase synaptic transmission. Specifically, presynaptic endoplasmic reticulum ryanodine receptor-mediated Ca2+ release activates Ca2+/calmodulin-dependent kinase II to mobilize DCVs and induce post-tetanic potentiation (PTP) of neuropeptide release in the Drosophila neuromuscular junction. The shared signaling for increasing vesicle mobility and PTP links vesicle mobilization and synaptic plasticity.
Topics: Animals; Axonal Transport; Calcium Signaling; Exocytosis; Humans; Neuronal Plasticity; Presynaptic Terminals; Ryanodine Receptor Calcium Release Channel; Secretory Vesicles; Synaptic Transmission; Synaptic Vesicles
PubMed: 18446451
DOI: 10.1007/s12035-008-8014-3 -
Comparative Biochemistry and... Jun 2022For amphibian species that display external fertilization in an aquatic environment, hypoosmotic shock to sperm cells can quickly result in damage to cellular structure...
For amphibian species that display external fertilization in an aquatic environment, hypoosmotic shock to sperm cells can quickly result in damage to cellular structure and function. This study sought to determine how fertilization media osmolality, temperature, and time impact the stability of the mitochondrial vesicle's association with the sperm head and thus motility and quality of forward progression. The presence of the mitochondrial vesicle and its relationship with sperm motility and quality of forward progression were analyzed in sperm samples from the Fowler's toad (Anaxyrus fowleri) (n = 10) when held for six hours under two temperatures and four osmolalities. Results indicated that the presence of the mitochondrial vesicle is needed for sperm motility over time (p < 0.001), where higher osmolalities (p < 0.001) and lower temperatures (p < 0.001) correlated with maintaining the vesicle attachment to the spermatozoa. The higher osmolality of spermic urine was the most important factor for maintaining higher quality of forward progressive motility (p < 0.01) of spermatozoa. Sperm samples held at 4 °C and 40 mOsm/kg had the longest half-life for motility (540 min) and quality of forward progression (276 min), whereas sperm held at 22 °C and 2.5 mOsm/kg had the shortest half-life for motility (7 min) and quality of forward progression (18 min). Special attention should be given to the osmolality and temperature of fertilization solutions, or breeding tank water, when developing cold storage protocols for toad sperm or reproducing animals to ensure the retention of the mitochondrial vesicle for maximum fertilization capability.
Topics: Animals; Bufonidae; Cryopreservation; Male; Osmolar Concentration; Sperm Motility; Spermatozoa
PubMed: 35321851
DOI: 10.1016/j.cbpa.2022.111191 -
Traffic (Copenhagen, Denmark) Apr 2015Neuronal communication relies on chemical synaptic transmission for information transfer and processing. Chemical neurotransmission is initiated by synaptic vesicle... (Review)
Review
Neuronal communication relies on chemical synaptic transmission for information transfer and processing. Chemical neurotransmission is initiated by synaptic vesicle fusion with the presynaptic active zone resulting in release of neurotransmitters. Classical models have assumed that all synaptic vesicles within a synapse have the same potential to fuse under different functional contexts. In this model, functional differences among synaptic vesicle populations are ascribed to their spatial distribution in the synapse with respect to the active zone. Emerging evidence suggests, however, that synaptic vesicles are not a homogenous population of organelles, and they possess intrinsic molecular differences and differential interaction partners. Recent studies have reported a diverse array of synaptic molecules that selectively regulate synaptic vesicles' ability to fuse synchronously and asynchronously in response to action potentials or spontaneously irrespective of action potentials. Here we discuss these molecular mediators of vesicle pool heterogeneity that are found on the synaptic vesicle membrane, on the presynaptic plasma membrane, or within the cytosol and consider some of the functional consequences of this diversity. This emerging molecular framework presents novel avenues to probe synaptic function and uncover how synaptic vesicle pools impact neuronal signaling.
Topics: Action Potentials; Animals; Humans; Neurotransmitter Agents; Synaptic Membranes; Synaptic Transmission; Synaptic Vesicles
PubMed: 25620674
DOI: 10.1111/tra.12262 -
The Journal of Neuroscience : the... Aug 2020Retrieval of synaptic vesicles via endocytosis is essential for maintaining sustained synaptic transmission, especially for neurons that fire action potentials at high...
Retrieval of synaptic vesicles via endocytosis is essential for maintaining sustained synaptic transmission, especially for neurons that fire action potentials at high frequencies. However, how neuronal activity regulates synaptic vesicle recycling is largely unknown. Here we report that Na substantially accumulated in the mouse calyx of Held terminals of either sex during repetitive high-frequency spiking. Elevated presynaptic Na accelerated both slow and rapid forms of endocytosis and facilitated endocytosis overshoot, but did not affect the readily releasable pool size, Ca influx, or exocytosis. To examine whether this facilitation of endocytosis is related to the Na-dependent vesicular content change, we dialyzed glutamate into the presynaptic cytosol or blocked the vesicular glutamate uptake with bafilomycin and found that the rate of endocytosis was not affected by regulating the vesicular glutamate content. Endocytosis is critically dependent on intracellular Ca, and the activity of Na/Ca exchanger (NCX) may be altered when the Na gradient is changed. However, neither NCX inhibitor nor change of extracellular Na concentration affected the endocytosis rate. Moreover, two-photon Ca imaging showed that presynaptic Na did not affect the action potential-evoked intracellular Ca transient and decay. Therefore, we revealed a novel mechanism of cytosolic Na in accelerating vesicle endocytosis. During high-frequency synaptic transmission, when large numbers of synaptic vesicles were fused, the rapid buildup of presynaptic cytosolic Na promoted vesicle recycling and sustained synaptic transmission. High-frequency firing neurons are widely distributed in the CNS. A large number of synaptic vesicles are released during high-frequency synaptic transmission; accordingly, synaptic vesicles need to be recycled rapidly to replenish the vesicle pool. Synaptic vesicle exocytosis and endocytosis are tightly coupled, and their coupling is essential for synaptic function and structural stability. We showed here that intracellular Na concentration at the calyx of Held terminal increased rapidly during spike activity and the increased Na accelerated endocytosis. Thus, when large numbers of synaptic vesicles are released during high-frequency synaptic transmission, Na accumulated in terminals and facilitated vesicle recycling. These findings represent a novel cellular mechanism that supports reliable synaptic transmission at high frequency in the CNS.
Topics: Animals; Calcium; Calcium Signaling; Cytoplasm; Endocytosis; Female; Glutamic Acid; Male; Mice; Mice, Inbred C57BL; Sodium; Sodium-Calcium Exchanger; Synaptic Transmission; Synaptic Vesicles
PubMed: 32605936
DOI: 10.1523/JNEUROSCI.0119-20.2020 -
Frontiers in Bioengineering and... 2022Lipid vesicles are valuable mesoscale molecular confinement vessels for studying membrane mechanics and lipid-protein interactions, and they have found utility among...
Lipid vesicles are valuable mesoscale molecular confinement vessels for studying membrane mechanics and lipid-protein interactions, and they have found utility among bio-inspired technologies, including drug delivery vehicles. While vesicle morphology can be modified by changing the lipid composition and introducing fusion or pore-forming proteins and detergents, the influence of extramembrane crowding on vesicle morphology has remained under-explored owing to a lack of experimental tools capable of capturing morphological changes on the nanoscale. Here, we use biocompatible polymers to simulate molecular crowding , and through combinations of FRET spectroscopy, lifetime analysis, dynamic light scattering, and single-vesicle imaging, we characterize how crowding regulates vesicle morphology. We show that both freely diffusing and surface-tethered vesicles fluorescently tagged with the DiI and DiD FRET pair undergo compaction in response to modest concentrations of sorbitol, polyethylene glycol, and Ficoll. A striking observation is that sorbitol results in irreversible compaction, whereas the influence of high molecular weight PEG-based crowders was found to be reversible. Regulation of molecular crowding allows for precise control of the vesicle architecture , with vast implications for drug delivery and vesicle trafficking systems. Furthermore, our observations of vesicle compaction may also serve to act as a mechanosensitive readout of extramembrane crowding.
PubMed: 36394015
DOI: 10.3389/fbioe.2022.958026 -
ACS Measurement Science Au Dec 2021In this work, we introduce a novel method for visualization and quantitative measurement of the vesicle opening process by correlation of vesicle impact electrochemical...
In this work, we introduce a novel method for visualization and quantitative measurement of the vesicle opening process by correlation of vesicle impact electrochemical cytometry (VIEC) with confocal microscopy. We have used a fluorophore conjugated to lipids to label the vesicle membrane and manipulate the membrane properties, which appears to make the membrane more susceptible to electroporation. The neurotransmitters inside the vesicles were visualized by use of a fluorescence false neurotransmitter 511 (FFN 511) through accumulation inside the vesicle via the neuronal vesicular monoamine transporter 2 (VMAT 2). Optical and electrochemical measurements of single vesicle electroporation were carried out using an in-house, disk-shaped, gold-modified ITO (Au/ITO) microelectrode device (5 nm thick, 33 μm diameter), which simultaneously acted as an electrode surface for VIEC and an optically transparent surface for confocal microscopy. As a result, the processes of adsorption, electroporation, and opening of single vesicles followed by neurotransmitter release on the Au/ITO surface have been simultaneously visualized and measured. Three opening patterns of single isolated vesicles were frequently observed. Comparing the vesicle opening patterns with their corresponding VIEC spikes, we propose that the behavior of the vesicular membrane on the electrode surface, including the adsorption time, residence time before vesicle opening, and the retention time after vesicle opening, are closely related to the vesicle content and size. Large vesicles with high content tend to adsorb to the electrode faster with higher frequency, followed by a shorter residence time before releasing their content, and their membrane remains on the electrode surface longer compared to the small vesicles with low content. With this approach, we start to unravel the vesicle opening process and to examine the fundamentals of exocytosis, supporting the proposed mechanism of partial or subquantal release in exocytosis.
PubMed: 34939075
DOI: 10.1021/acsmeasuresciau.1c00021 -
Journal of Neurochemistry Aug 2009The fusion of synaptic vesicles with the pre-synaptic plasma membrane mediates the secretion of neurotransmitters at nerve terminals. This pathway is regulated by an... (Review)
Review
The fusion of synaptic vesicles with the pre-synaptic plasma membrane mediates the secretion of neurotransmitters at nerve terminals. This pathway is regulated by an array of protein-protein interactions. Of central importance are the soluble NSF (N-ethylmaleimide-sensitive factor) attachment protein receptor (SNARE) proteins syntaxin 1 and SNAP25, which are associated with the pre-synaptic plasma membrane and vesicle-associated membrane protein (VAMP2), a synaptic vesicle SNARE. Syntaxin 1, SNAP25 and VAMP2 interact to form a tight complex bridging the vesicle and plasma membranes, which has been suggested to represent the minimal membrane fusion machinery. Synaptic vesicle fusion is stimulated by a rise in intraterminal Ca2+ levels, and a major Ca2+ sensor for vesicle fusion is synaptotagmin I. Synaptotagmin is likely to couple Ca2+ entry to vesicle fusion via Ca2+-dependent and independent interactions with membrane phospholipids and the SNARE proteins. Intriguingly, syntaxin 1, SNAP25, VAMP2 and synaptotagmin I have all been reported to be modified by palmitoylation in neurons. In this review, we discuss the mechanisms and dynamics of palmitoylation of these proteins and speculate on how palmitoylation might contribute to the regulation of synaptic vesicle fusion.
Topics: Animals; Calcium Signaling; Humans; Lipoylation; Membrane Fusion; Membrane Proteins; Presynaptic Terminals; SNARE Proteins; Synaptic Membranes; Synaptic Transmission; Synaptic Vesicles; Synaptotagmins
PubMed: 19508429
DOI: 10.1111/j.1471-4159.2009.06205.x -
FEBS Letters Nov 2018Vesicles in neurons and neuroendocrine cells store neurotransmitters and peptide hormones, which are released by vesicle fusion in response to Ca -evoking stimuli.... (Review)
Review
Vesicles in neurons and neuroendocrine cells store neurotransmitters and peptide hormones, which are released by vesicle fusion in response to Ca -evoking stimuli. Synaptotagmin-1 (Syt1), a Ca sensor, mediates ultrafast exocytosis in neurons and neuroendocrine cells. After vesicle docking, Syt1 has two main groups of binding partners: anionic phospholipids and the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) complex. The molecular mechanisms by which Syt1 triggers vesicle fusion remain controversial. This Review introduces and summarizes six molecular models of Syt1: (a) Syt1 triggers SNARE unclamping by displacing complexin, (b) Syt1 clamps SNARE zippering, (c) Syt1 causes membrane curvature, (d) membrane bridging by Syt1, (e) Syt1 is a vesicle-plasma membrane distance regulator, and (f) Syt1 undergoes circular oligomerization. We discuss important conditions to test Syt1 activity in vitro and attempt to illustrate the possible roles of Syt1.
Topics: Animals; Calcium; Exocytosis; Humans; Membrane Fusion; Models, Neurological; Protein Binding; SNARE Proteins; Synaptic Vesicles; Synaptotagmin I
PubMed: 30004579
DOI: 10.1002/1873-3468.13193 -
Biochimica Et Biophysica Acta Aug 1998One of the main functions of the Golgi complex is to generate transport vesicles for the post-Golgi trafficking of proteins in secretory pathways. Many different... (Review)
Review
One of the main functions of the Golgi complex is to generate transport vesicles for the post-Golgi trafficking of proteins in secretory pathways. Many different populations of vesicles are distinguished by unique sets of structural and regulatory proteins which participate in vesicle budding and fusion. Monomeric and heterotrimeric G proteins regulate vesicle budding and secretory traffic into and out of the Golgi complex. An inventory of G protein alpha subunits associated with Golgi membranes highlights their diverse involvement and potential for coupling Golgi trafficking, through various signal transduction pathways, to cell growth or other more specialized cell functions. Cytoskeletal proteins are now also known to associate specifically with the Golgi complex and Golgi-derived vesicles. Amongst these, conventional and unconventional myosins are recruited to vesicle membranes. Several roles in vesicle budding and vesicle trafficking can be proposed for these actin-based motors.
Topics: Animals; Forecasting; GTP-Binding Proteins; Golgi Apparatus; Humans; Intracellular Membranes; Myosins
PubMed: 9714787
DOI: 10.1016/s0167-4889(98)00055-x