The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Samara L Reckpeterson - One of the best experts on this subject based on the ideXlab platform.
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peroxisomes move by hitchhiking on early endosomes using the novel linker protein pxda
Journal of Cell Biology, 2016Co-Authors: John Salogiannis, Martin J Egan, Samara L ReckpetersonAbstract:Eukaryotic cells use microtubule-based intracellular transport for the delivery of many subcellular cargos, including Organelles. The canonical view of organelle transport is that Organelles directly recruit molecular motors via cargo-specific adaptors. In contrast with this view, we show here that peroxisomes move by hitchhiking on early endosomes, an organelle that directly recruits the transport machinery. Using the filamentous fungus Aspergillus nidulans we found that hitchhiking is mediated by a novel endosome-associated linker protein, PxdA. PxdA is required for normal distribution and long-range movement of peroxisomes, but not early endosomes or nuclei. Using simultaneous time-lapse imaging, we find that early endosome-associated PxdA localizes to the leading edge of moving peroxisomes. We identify a coiled-coil region within PxdA that is necessary and sufficient for early endosome localization and peroxisome distribution and motility. These results present a new mechanism of microtubule-based organelle transport in which peroxisomes hitchhike on early endosomes and identify PxdA as the novel linker protein required for this coupling.
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peroxisomes move by hitchhiking on early endosomes using the novel linker protein pxda
bioRxiv, 2015Co-Authors: John Salogiannis, Martin J Egan, Samara L ReckpetersonAbstract:Eukaryotic cells use microtubule-based intracellular transport for the delivery of many subcellular cargos, including Organelles. The canonical view of organelle transport is that Organelles directly recruit molecular motors via cargo-specific adaptors. In contrast to this view, we show here that peroxisomes move by hitchhiking on early endosomes, an organelle that directly recruits the transport machinery. Using the filamentous fungus Aspergillus nidulans we find that hitchhiking is mediated by a novel endosome-associated linker protein, PxdA. PxdA is required for normal distribution and long-range movement of peroxisomes, but not early endosomes or nuclei. Using simultaneous time-lapse imaging we find that early endosome-associated PxdA localizes to the leading edge of moving peroxisomes. We identify a coiled-coil region within PxdA that is necessary and sufficient for early endosome localization and peroxisome distribution and motility. These results present a new mechanism of microtubule-based organelle transport where peroxisomes hitchhike on early endosomes and identify PxdA as the novel linker protein required for this coupling.
Sean Munro - One of the best experts on this subject based on the ideXlab platform.
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untangling the evolution of rab g proteins implications of a comprehensive genomic analysis
BMC Biology, 2012Co-Authors: Tobias H Klopper, Nickias Kienle, Dirk Fasshauer, Sean MunroAbstract:Background Membrane-bound Organelles are a defining feature of eukaryotic cells, and play a central role in most of their fundamental processes. The Rab G proteins are the single largest family of proteins that participate in the traffic between Organelles, with 66 Rabs encoded in the human genome. Rabs direct the organelle-specific recruitment of vesicle tethering factors, motor proteins, and regulators of membrane traffic. Each organelle or vesicle class is typically associated with one or more Rab, with the Rabs present in a particular cell reflecting that cell's complement of Organelles and trafficking routes.
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a comprehensive comparison of transmembrane domains reveals organelle specific properties
Cell, 2010Co-Authors: Hayley J Sharpe, Tim J Stevens, Sean MunroAbstract:The various membranes of eukaryotic cells differ in composition, but it is at present unclear if this results in differences in physical properties. The sequences of transmembrane domains (TMDs) of integral membrane proteins should reflect the physical properties of the bilayers in which they reside. We used large datasets from both fungi and vertebrates to perform a comprehensive comparison of the TMDs of proteins from different Organelles. We find that TMDs are not generic but have organelle-specific properties with a dichotomy in TMD length between the early and late parts of the secretory pathway. In addition, TMDs from post-ER Organelles show striking asymmetries in amino acid compositions across the bilayer that is linked to residue size and varies between Organelles. The pervasive presence of organelle-specific features among the TMDs of a particular organelle has implications for TMD prediction, regulation of protein activity by location, and sorting of proteins and lipids in the secretory pathway.
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organelle identity and the signposts for membrane traffic
Nature, 2005Co-Authors: Rudy Behnia, Sean MunroAbstract:Eukaryotic cells have systems of internal Organelles to synthesize lipids and membrane proteins, to release secreted proteins, to take up nutrients and to degrade membrane-bound and internalized molecules. Proteins and lipids move from organelle to organelle using transport vesicles. The accuracy of this traffic depends upon Organelles being correctly recognized. In general, Organelles are identified by the activated GTPases and specific lipid species that they display. These short-lived determinants provide Organelles with an identity that is both unique and flexible. Recent studies have helped to establish how cells maintain and restrict these determinants and explain how this system is exploited by invading pathogens.
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organelle identity and the targeting of peripheral membrane proteins
Current Opinion in Cell Biology, 2002Co-Authors: Sean MunroAbstract:Within the secretory pathway, most proteins involved in vesicle formation, motor recruitment and vesicle tethering are not integral membrane proteins but, rather, peripheral membrane proteins recruited to the relevant Organelles from the cytosol. From recent studies on diverse Organelles, it appears that such recruitment is usually mediated by binding to a labile determinant, such as an activated G protein or a short-lived lipid species, whose distribution is restricted to a single organelle. This suggests that these determinants are what specify organelle identity, and raises interesting questions about how they are generated in an organelle-specific fashion.
A. V. Kuznetsov - One of the best experts on this subject based on the ideXlab platform.
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a coupled model of fast axonal transport of Organelles and slow axonal transport of tau protein
Computer Methods in Biomechanics and Biomedical Engineering, 2015Co-Authors: I. A. Kuznetsov, A. V. KuznetsovAbstract:We have developed a model that accounts for the effect of a non-uniform distribution of tau protein along the axon length on fast axonal transport of intracellular Organelles. The tau distribution is simulated by using a slow axonal transport model; the numerically predicted tau distributions along the axon length were validated by comparing them with experimentally measured tau distributions reported in the literature. We then developed a fast axonal transport model for Organelles that accounts for the reduction of kinesin attachment rate to microtubules by tau. We investigated organelle transport for two situations: (1) a uniform tau distribution and (2) a non-uniform tau distribution predicted by the slow axonal transport model. We found that non-uniform tau distributions observed in healthy axons (an increase in tau concentration towards the axon tip) result in a significant enhancement of organelle transport towards the synapse compared with the uniform tau distribution with the same average amount of tau. This suggests that tau may play the role of being an enhancer of organelle transport.
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modeling bidirectional transport of new and used Organelles in fast axonal transport in neurons
Journal of Heat Transfer-transactions of The Asme, 2011Co-Authors: A. V. KuznetsovAbstract:This paper develops a model for simulating transport of newly synthesized material from the neuron body toward the synapse of the axon as well as transport of misfolded and aggregated proteins back to the neuron body for recycling. The model demonstrates that motor-assisted transport, much similar to diffusion, can occur due to a simple concentration difference between the cell body and the synapse; Organelles heading to the synapse do not need to attach preferably to plus-end-directed molecular motors, same as Organelles heading to the neuron body for recycling do not need to attach preferably to minus-end-directed molecular motors. The underlying mechanics of molecular-motor-assisted transport is such that Organelles would be transported to the right place even if new and used Organelles had the same probability of attachment to plus-end-directed (and minus-end-directed) motors. It is also demonstrated that the axon with organelle traps and a region with a reversed microtubule polarity would support much smaller organelle fluxes of both new and used Organelles than a healthy axon. The flux of Organelles is shown to decrease as the width of organelle traps increases.
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effect of diffusion on slowing the velocity of a bell shaped wave in slow axonal transport
International Communications in Heat and Mass Transfer, 2010Co-Authors: A. V. Kuznetsov, Andriy A. Avramenko, Dmitry G. BlinovAbstract:Abstract This paper models transport of Organelles by slow axonal transport utilizing the stop-and-go hypothesis, which postulates that in slow axonal transport the motion of Organelles does not occur continuously; instead, Organelles move along microtubules (MTs) alternating between short periods of rapid movement, short on-track pauses, and prolonged off-track pauses, when they temporarily disengage from MTs. The model considers six kinetic states of Organelles: anterogradely moving state, retrogradely moving state, anterogradely pausing state, retrogradely pausing state, off-track anterograde state, and off-track retrograde state. The paper extends the existing model of slow axonal transport by accounting for the diffusivity of off-track Organelles and investigates how the diffusivity of these Organelles affects the amplitude, velocity, and rate of change of the variance of the bell-shaped wave which describes the probability density function (PDF) corresponding to the ratio of the chance of finding an organelle within an infinitesimal interval in the axon to the length of this interval. The velocity of this wave characterizes the average effective velocity (calculated including pauses) of an organelle in slow axonal transport while the rate of change of the variance characterizes the rate of spread of the initial packet of Organelles transported in the axon. The goal of this research is not only to develop a more accurate transport model, but also to understand fundamentally the effects of diffusion on slow axonal transport. It is demonstrated that diffusion decreases the amplitude of the wave and increases the rate of its spread but does not affect wave's velocity.
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effect of vesicle traps on traffic jam formation in fast axonal transport
Bellman Prize in Mathematical Biosciences, 2010Co-Authors: A. V. KuznetsovAbstract:The purpose of this paper is to develop a model for simulation of the formation of organelle traps in fast axonal transport. Such traps may form in the regions of microtubule polar mismatching. Depending on the orientation of microtubules pointing toward the trap region, these traps can accumulate either plus-end or minus-end oriented vesicles. The model predicts that the maximum concentrations of Organelles occur at the boundaries of the trap regions; the overall concentration of Organelles in the axon with traps is greatly increased compared to that in a healthy axon, which is expected to contribute to mechanical damages of the axon. The organelle traps induce hindrance to organelle transport down the axon; the total organelle flux down the axon with traps is found to be significantly reduced compared to that in a healthy axon.
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effect of the degree of polar mismatching on traffic jam formation in fast axonal transport
Computer Methods in Biomechanics and Biomedical Engineering, 2010Co-Authors: A. V. KuznetsovAbstract:This paper simulates an axon with a region of reversed microtubule (MT) polarity, and investigates how the degree of polar mismatching in this region affects the formation of organelle traps in the axon. The model is based on modified Smith–Simmons equations governing molecular-motor-assisted transport in neurons. It is established that the structure that develops as a result of a region with disoriented MTs consists of two organelle traps, the trap to the left of this region accumulates plus-end-oriented Organelles and the trap to the right of this region accumulates minus-end-oriented Organelles. The presence of such a structure is shown to inhibit the transport of Organelles down the axon. The degree by which the transport of Organelles is inhibited depends on the degree of polar mismatching of MTs in the region between MT traps. Four cases with a different degree of polar mismatching are investigated.
Jennifer Lippincottschwartz - One of the best experts on this subject based on the ideXlab platform.
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er membranes exhibit phase behavior at sites of organelle contact
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Christopher L King, Prabuddha Sengupta, Jennifer LippincottschwartzAbstract:The endoplasmic reticulum (ER) is the site of synthesis of secretory and membrane proteins and contacts every organelle of the cell, exchanging lipids and metabolites in a highly regulated manner. How the ER spatially segregates its numerous and diverse functions, including positioning nanoscopic contact sites with other Organelles, is unclear. We demonstrate that hypotonic swelling of cells converts the ER and other membrane-bound Organelles into micrometer-scale large intracellular vesicles (LICVs) that retain luminal protein content and maintain contact sites with each other through localized organelle tethers. Upon cooling, ER-derived LICVs phase-partition into microscopic domains having different lipid-ordering characteristics, which is reversible upon warming. Ordered ER lipid domains mark contact sites with ER and mitochondria, lipid droplets, endosomes, or plasma membrane, whereas disordered ER lipid domains mark contact sites with lysosomes or peroxisomes. Tethering proteins concentrate at ER–organelle contact sites, allowing time-dependent behavior of lipids and proteins to be studied at these sites. These findings demonstrate that LICVs provide a useful model system for studying the phase behavior and interactive properties of Organelles in intact cells.
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applying systems level spectral imaging and analysis to reveal the organelle interactome
Nature, 2017Co-Authors: Alex M. Valm, Justin Melunis, Andrew R Cohen, Sarah S Cohen, Michael W Davidson, Uri Hershberg, Wesley R Legant, Eric Betzig, Eric Wait, Jennifer LippincottschwartzAbstract:Using confocal and lattice light sheet microscopy, the authors perform systems-level analysis of the organelle interactome in live cells, allowing them to visualize the frequency and locality of up to five-way interactions between different Organelles. Various cell components, or Organelles, make contacts that are not mediated by trafficking vesicles, and which result in changes to their physical behaviour, biochemical composition and functionality. Imaging is a powerful tool for studying inter-organelle contact sites, but work by Jennifer Lippincott-Schwartz and colleagues take such analysis to a new level. Using confocal and lattice light sheet microscopy, as well as a multispectral image acquisition and analysis method, they perform systems-level analysis of the organelle interactome in live cells. The approach allows them to visualize the frequency and locality of up to five-way interactions among six different Organelles (endoplasmic reticulum, Golgi, lysosome, peroxisome, mitochondria and lipid droplet), providing unexpected insights into the dynamics of these interactions. The method could prove a useful tool for further analysis of non-vesicular communication within the cell. The organization of the eukaryotic cell into discrete membrane-bound Organelles allows for the separation of incompatible biochemical processes, but the activities of these Organelles must be coordinated. For example, lipid metabolism is distributed between the endoplasmic reticulum for lipid synthesis, lipid droplets for storage and transport, mitochondria and peroxisomes for β-oxidation, and lysosomes for lipid hydrolysis and recycling1,2,3,4,5. It is increasingly recognized that organelle contacts have a vital role in diverse cellular functions5,6,7,8. However, the spatial and temporal organization of Organelles within the cell remains poorly characterized, as fluorescence imaging approaches are limited in the number of different labels that can be distinguished in a single image9. Here we present a systems-level analysis of the organelle interactome using a multispectral image acquisition method that overcomes the challenge of spectral overlap in the fluorescent protein palette. We used confocal and lattice light sheet10 instrumentation and an imaging informatics pipeline of five steps to achieve mapping of organelle numbers, volumes, speeds, positions and dynamic inter-organelle contacts in live cells from a monkey fibroblast cell line. We describe the frequency and locality of two-, three-, four- and five-way interactions among six different membrane-bound Organelles (endoplasmic reticulum, Golgi, lysosome, peroxisome, mitochondria and lipid droplet) and show how these relationships change over time. We demonstrate that each organelle has a characteristic distribution and dispersion pattern in three-dimensional space and that there is a reproducible pattern of contacts among the six Organelles, that is affected by microtubule and cell nutrient status. These live-cell confocal and lattice light sheet spectral imaging approaches are applicable to any cell system expressing multiple fluorescent probes, whether in normal conditions or when cells are exposed to disturbances such as drugs, pathogens or stress. This methodology thus offers a powerful descriptive tool and can be used to develop hypotheses about cellular organization and dynamics.
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brefeldin a insights into the control of membrane traffic and organelle structure
Journal of Cell Biology, 1992Co-Authors: Richard D. Klausner, Julie G. Donaldson, Jennifer LippincottschwartzAbstract:THE definition of cellular Organelles has evolved over the last hundred years largely driven by morphologic observations, but more recently has been supplemented and complemented by functional and biochemical studies (Palade, 1975) . Thus, Organelles are now identified both by their morphology and by the set ofcomponents that comprise them . Determining how organelle identity is established and maintained and how newly synthesized protein and membrane are sorted to different Organelles are the central issues of organellogenesis . Essential to the many cellular functions that take place within the central vacuolar system (which consists ofthe ER, Golgi apparatus, secretory vesicles, endosomes, and lysosomes) is membrane traffic which mediates the exchange of components between different Organelles . There are two critical characteristics of membrane traffic . First, only certain sets ofOrganelles exchange membrane and the patterns of this exchange define what are called membrane pathways . Second, multiple pathways intersect at specific points within the central vacuolar system . For specific components to "choose" the correct pathway at such points of crossing, mechanisms exist to impose choices on specific molecules . This process is called sorting . The characteristicsofeachorganelle within the central vacuolar system are likely to be intimately tied to the properties ofmembrane traffic . An imbalance in the magnitude ofmembrane input into and egress from an organelle would have profound effects on the size ofthat compartment . In addition, failures in sorting or aberrations in targeting pathways would be expected to profoundly affect the identity of individual Organelles . Recently, the relationship between the control of membrane traffic and the maintenance of organelle structure has been investigated with the use ofa remarkable drug, brefeldin A (BFA).' In this review we will summarize recent findings with BFA and propose some speculative models concerning the mechanism and regulation ofmembrane traffic within the central vacuolar system .
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brefeldin a insights into the control of membrane traffic and organelle structure
Journal of Cell Biology, 1992Co-Authors: Richard D. Klausner, Julie G. Donaldson, Jennifer LippincottschwartzAbstract:THE definition of cellular Organelles has evolved over the last hundred years largely driven by morphologic observations, but more recently has been supplemented and complemented by functional and biochemical studies (Palade, 1975) . Thus, Organelles are now identified both by their morphology and by the set ofcomponents that comprise them . Determining how organelle identity is established and maintained and how newly synthesized protein and membrane are sorted to different Organelles are the central issues of organellogenesis . Essential to the many cellular functions that take place within the central vacuolar system (which consists ofthe ER, Golgi apparatus, secretory vesicles, endosomes, and lysosomes) is membrane traffic which mediates the exchange of components between different Organelles . There are two critical characteristics of membrane traffic . First, only certain sets ofOrganelles exchange membrane and the patterns of this exchange define what are called membrane pathways . Second, multiple pathways intersect at specific points within the central vacuolar system . For specific components to "choose" the correct pathway at such points of crossing, mechanisms exist to impose choices on specific molecules . This process is called sorting . The characteristicsofeachorganelle within the central vacuolar system are likely to be intimately tied to the properties ofmembrane traffic . An imbalance in the magnitude ofmembrane input into and egress from an organelle would have profound effects on the size ofthat compartment . In addition, failures in sorting or aberrations in targeting pathways would be expected to profoundly affect the identity of individual Organelles . Recently, the relationship between the control of membrane traffic and the maintenance of organelle structure has been investigated with the use ofa remarkable drug, brefeldin A (BFA).' In this review we will summarize recent findings with BFA and propose some speculative models concerning the mechanism and regulation ofmembrane traffic within the central vacuolar system .
Duncan C Krause - One of the best experts on this subject based on the ideXlab platform.
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cytoskeletal protein p41 is required to anchor the terminal organelle of the wall less prokaryote mycoplasma pneumoniae
Molecular Microbiology, 2007Co-Authors: Benjamin M Hasselbring, Duncan C KrauseAbstract:The cell wall-less prokaryote Mycoplasma pneumoniae approaches the minimal requirements for a cell yet produces a complex terminal organelle that mediates cytadherence and gliding motility. Here we explored the molecular nature of the M. pneumoniae gliding machinery, utilizing fluorescent protein fusions and digital microcinematography to characterize gliding-altered mutants having transposon insertions in MPN311, encoding the cytoskeletal protein P41. Disruption of MPN311 resulted in loss of P41 and P24, the downstream gene product. Gliding ceases in wild-type M. pneumoniae during terminal organelle development, which occurs at the cell poles adjacent to an existing structure. In contrast, terminal organelle development in MPN311 mutants did not necessarily coincide with gliding cessation, and new terminal Organelles frequently formed at lateral sites. Furthermore, new terminal Organelles exhibited gliding capacity quickly, unlike wild-type M. pneumoniae. P41 and P24 localize at the base of the terminal organelle; in their absence this structure detached from the cell body of motile and dividing cells but retained gliding capacity and thus constitutes the gliding apparatus. Recombinant wild-type P41 restored cell integrity, establishing a role for this protein in anchoring the terminal organelle to the cell body.
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terminal organelle development in the cell wall less bacterium mycoplasma pneumoniae
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: Benjamin M Hasselbring, Jarrat L Jordan, Robert W Krause, Duncan C KrauseAbstract:Mycoplasmas are cell wall-less bacteria considered among the smallest and simplest prokaryotes known, and yet several species including Mycoplasma pneumoniae have a remarkably complex cellular organization highlighted by the presence of a differentiated terminal organelle, a membrane-bound cell extension distinguished by an electron-dense core. Adhesin proteins localize specifically to the terminal organelle, which is also the leading end in gliding motility. Duplication of the terminal organelle is thought to precede cell division, but neither the mechanism of its duplication nor its role in this process is understood. Here we used fluorescent protein fusions and time-lapse digital imaging to study terminal organelle formation in detail in growing cultures of M. pneumoniae. Individual cells ceased gliding as a new terminal organelle formed adjacent to an existing structure, which then migrated away from the transiently stationary nascent structure. Multiple terminal Organelles often formed before cytokinesis was observed. The separation of terminal Organelles was impaired in a nonmotile mutant, indicating a requirement for gliding in normal cell division. Examination of cells expressing two different fluorescent protein fusions concurrently established their relative order of appearance, and changes in the fluorescence pattern over time suggested that nascent terminal Organelles originated de novo rather than from an existing structure. In summary, spatial and temporal analysis of terminal organelle formation has yielded insights into the nature of M. pneumoniae cell division and the role of gliding motility in that process.