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Marcel Mettlen

Bio: Marcel Mettlen is an academic researcher from University of Texas Southwestern Medical Center. The author has contributed to research in topics: Endocytosis & Dynamin. The author has an hindex of 27, co-authored 45 publications receiving 4395 citations. Previous affiliations of Marcel Mettlen include Scripps Research Institute & Scripps Health.

Papers
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Journal ArticleDOI
TL;DR: This approach shows that the GTPase dynamin differentially affects the kinetics of long- and short-lived endocytic structures and that the motion of CD36 receptors along cytoskeleton-mediated linear tracks increases their aggregation probability.
Abstract: Single-particle tracking (SPT) is often the rate-limiting step in live-cell imaging studies of subcellular dynamics. Here we present a tracking algorithm that addresses the principal challenges of SPT, namely high particle density, particle motion heterogeneity, temporary particle disappearance, and particle merging and splitting. The algorithm first links particles between consecutive frames and then links the resulting track segments into complete trajectories. Both steps are formulated as global combinatorial optimization problems whose solution identifies the overall most likely set of particle trajectories throughout a movie. Using this approach, we show that the GTPase dynamin differentially affects the kinetics of long- and short-lived endocytic structures and that the motion of CD36 receptors along cytoskeleton-mediated linear tracks increases their aggregation probability. Both applications indicate the requirement for robust and complete tracking of dense particle fields to dissect the mechanisms of receptor organization at the level of the plasma membrane.

1,753 citations

Journal ArticleDOI
TL;DR: From data, the existence of an endocytic restriction or checkpoint, responsive to cargo and regulated by dynamin is inferred, which significantly enhances the maturation efficiency of productive CCPs, but has only minor effects on their lifetimes.
Abstract: Total internal reflection fluorescence microscopy (TIR-FM) has become a powerful tool for studying clathrin-mediated endocytosis. However, due to difficulties in tracking and quantifying their heterogeneous dynamic behavior, detailed analyses have been restricted to a limited number of selected clathrin-coated pits (CCPs). To identify intermediates in the formation of clathrin-coated vesicles and factors that regulate progression through these stages, we used particle-tracking software and statistical methods to establish an unbiased and complete inventory of all visible CCP trajectories. We identified three dynamically distinct CCP subpopulations: two short-lived subpopulations corresponding to aborted intermediates, and one longer-lived productive subpopulation. In a manner dependent on AP2 adaptor complexes, increasing cargo concentration significantly enhances the maturation efficiency of productive CCPs, but has only minor effects on their lifetimes. In contrast, small interfering RNA (siRNA) depletion of dynamin-2 GTPase and reintroduction of wild-type or mutant dynamin-1 revealed dynamin's role in controlling the turnover of abortive intermediates and the rate of CCP maturation. From these data, we infer the existence of an endocytic restriction or checkpoint, responsive to cargo and regulated by dynamin.

386 citations

Journal ArticleDOI
TL;DR: A framework for unbiased measurement of EAP recruitment to CCPs and their direct effects on CCP dynamics is presented and dynamin and the EAP-binding α-adaptin appendage domain of the AP2 adaptor are identified as switches in a regulated, multistep maturation process and provide direct evidence for a molecular checkpoint in CME.

325 citations

Journal ArticleDOI
TL;DR: This review summarizes recent findings on the regulation of CME and the evolution of this complex process and describes the role of the GTPase dynamin in this process.
Abstract: Clathrin-mediated endocytosis (CME) is the major endocytic pathway in mammalian cells. It is responsible for the uptake of transmembrane receptors and transporters, for remodeling plasma membrane composition in response to environmental changes, and for regulating cell surface signaling. CME occurs via the assembly and maturation of clathrin-coated pits that concentrate cargo as they invaginate and pinch off to form clathrin-coated vesicles. In addition to the major coat proteins, clathrin triskelia and adaptor protein complexes, CME requires a myriad of endocytic accessory proteins and phosphatidylinositol lipids. CME is regulated at multiple steps-initiation, cargo selection, maturation, and fission-and is monitored by an endocytic checkpoint that induces disassembly of defective pits. Regulation occurs via posttranslational modifications, allosteric conformational changes, and isoform and splice-variant differences among components of the CME machinery, including the GTPase dynamin. This review summarizes recent findings on the regulation of CME and the evolution of this complex process.

323 citations

Journal ArticleDOI
11 Jul 2013-Nature
TL;DR: Septin filaments and phosphatidylinositol-4,5-bisphosphate rearrange locally at endoplasmic reticulum–plasma membrane junctions before and during formation ofSTIM1–ORAI1 clusters, facilitating STIM1 targeting to these junctions and promoting the stable recruitment of ORAI1.
Abstract: A genome-wide RNA interference analysis identifies the septin family of cytoskeletal filaments as important regulators of store-operated Ca2+ entry into the cell; septins are shown to organize plasma membrane microdomains important in STIM1 and ORAI1 signalling, and may also be relevant in membrane microdomains underlying other signalling processes. Cellular Ca2+ signalling is regulated by STIM (stromal interaction molecule) proteins, which are Ca2+ sensors in the endoplasmic reticulum that connect Ca2+ store depletion to the opening of the Ca2+ release-activated Ca2+ (CRAC) channels in the plasma membrane. ORAI proteins are the pore subunits of the CRAC channel and control the opening of this channel. Here Sharma et al. present a genome-wide RNA interference analysis designed to identify essential regulators of store-operated Ca2+ entry. They find that the septin family of cytoskeletal filaments are important regulators of this process, acting via the association between ORAI1 and STIM1. The STIM1–ORAI1 pathway of store-operated Ca2+ entry is an essential component of cellular Ca2+ signalling1. STIM1 senses depletion of intracellular Ca2+ stores in response to physiological stimuli, and relocalizes within the endoplasmic reticulum to plasma-membrane-apposed junctions, where it recruits and gates open plasma membrane ORAI1 Ca2+ channels. Here we use a genome-wide RNA interference screen in HeLa cells to identify filamentous septin proteins as crucial regulators of store-operated Ca2+ entry. Septin filaments and phosphatidylinositol-4,5-bisphosphate (also known as PtdIns(4,5)P2) rearrange locally at endoplasmic reticulum–plasma membrane junctions before and during formation of STIM1–ORAI1 clusters, facilitating STIM1 targeting to these junctions and promoting the stable recruitment of ORAI1. Septin rearrangement at junctions is required for PtdIns(4,5)P2 reorganization and efficient STIM1–ORAI1 communication. Septins are known to demarcate specialized membrane regions such as dendritic spines, the yeast bud and the primary cilium, and to serve as membrane diffusion barriers and/or signalling hubs in cellular processes such as vesicle trafficking, cell polarity and cytokinesis2,3,4. Our data show that septins also organize the highly localized plasma membrane domains that are important in STIM1–ORAI1 signalling, and indicate that septins may organize membrane microdomains relevant to other signalling processes.

198 citations


Cited by
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Journal ArticleDOI
15 Feb 2017-Methods
TL;DR: TrackMate is an extensible platform where developers can easily write their own detection, particle linking, visualization or analysis algorithms within the TrackMate environment and is validated for quantitative lifetime analysis of clathrin-mediated endocytosis in plant cells.

2,356 citations

01 Jan 2016
TL;DR: In this paper, the authors present the principles of optics electromagnetic theory of propagation interference and diffraction of light, which can be used to find a good book with a cup of coffee in the afternoon, instead of facing with some infectious bugs inside their computer.
Abstract: Thank you for reading principles of optics electromagnetic theory of propagation interference and diffraction of light. As you may know, people have search hundreds times for their favorite novels like this principles of optics electromagnetic theory of propagation interference and diffraction of light, but end up in harmful downloads. Rather than enjoying a good book with a cup of coffee in the afternoon, instead they are facing with some infectious bugs inside their computer.

2,213 citations

Journal ArticleDOI
TL;DR: Clathrin-mediated endocytosis is the endocytic portal into cells through which cargo is packaged into vesicles with the aid of a clathrin coat and is fundamental to neurotransmission, signal transduction and the regulation of many plasma membrane activities and is thus essential to higher eukaryotic life.
Abstract: Clathrin-mediated endocytosis is the endocytic portal into cells through which cargo is packaged into vesicles with the aid of a clathrin coat. It is fundamental to neurotransmission, signal transduction and the regulation of many plasma membrane activities and is thus essential to higher eukaryotic life. Morphological stages of vesicle formation are mirrored by progression through various protein modules (complexes). The process involves the formation of a putative FCH domain only (FCHO) initiation complex, which matures through adaptor protein 2 (AP2)-dependent cargo selection, and subsequent coat building, dynamin-mediated scission and finally auxilin- and heat shock cognate 70 (HSC70)-dependent uncoating. Some modules can be used in other pathways, and additions or substitutions confer cell specificity and adaptability.

1,974 citations

Journal ArticleDOI
TL;DR: It is time for the diverse functional roles of glycans to be fully incorporated into the mainstream of biological sciences, as they are no different from other major macromolecular building blocks of life, simply more rapidly evolving and complex.
Abstract: Simple and complex carbohydrates (glycans) have long been known to play major metabolic, structural and physical roles in biological systems. Targeted microbial binding to host glycans has also been studied for decades. But such biological roles can only explain some of the remarkable complexity and organismal diversity of glycans in nature. Reviewing the subject about two decades ago, one could find very few clear-cut instances of glycan-recognition-specific biological roles of glycans that were of intrinsic value to the organism expressing them. In striking contrast there is now a profusion of examples, such that this updated review cannot be comprehensive. Instead, a historical overview is presented, broad principles outlined and a few examples cited, representing diverse types of roles, mediated by various glycan classes, in different evolutionary lineages. What remains unchanged is the fact that while all theories regarding biological roles of glycans are supported by compelling evidence, exceptions to each can be found. In retrospect, this is not surprising. Complex and diverse glycans appear to be ubiquitous to all cells in nature, and essential to all life forms. Thus, >3 billion years of evolution consistently generated organisms that use these molecules for many key biological roles, even while sometimes coopting them for minor functions. In this respect, glycans are no different from other major macromolecular building blocks of life (nucleic acids, proteins and lipids), simply more rapidly evolving and complex. It is time for the diverse functional roles of glycans to be fully incorporated into the mainstream of biological sciences.

1,588 citations

Book ChapterDOI
TL;DR: The latest developments in computerized image analysis are surveyed and the various computational approaches, software tools, and quantitative measures for tracking and motion analysis of cells and particles in time-lapse microscopy images are discussed.
Abstract: Achieving complete understanding of any living thing inevitably requires thorough analysis of both its anatomic and dynamic properties. Live-cell imaging experiments carried out to this end often produce massive amounts of time-lapse image data containing far more information than can be digested by a human observer. Computerized image analysis offers the potential to take full advantage of available data in an efficient and reproducible manner. A recurring task in many experiments is the tracking of large numbers of cells or particles and the analysis of their (morpho)dynamic behavior. In the past decade, many methods have been developed for this purpose, and software tools based on these are increasingly becoming available. Here, we survey the latest developments in this area and discuss the various computational approaches, software tools, and quantitative measures for tracking and motion analysis of cells and particles in time-lapse microscopy images.

1,361 citations