Eukaryotic Cell Physical Compartments Membrane cartoon Cell Membranes and Compartments From CellBiology Introduction A major difference between eukayotes and prokaryotes is the presence of physical compartments (membrane bound) within the cell. These compartments allow the separation/specialization of processes within the cell. There also exist within each of these physical compartments, functional compartments where specific processes may occur or are restricted too. This lecture is an introduction to compartments within the cell and membranes. The key components are: cell compartments, membrane structure, membrane models, membrane specializations. 2017 Lecture PDF Lecture Archive: 2016 (https://cellbiology.med.unsw.edu.au/cellbiology/index.php? title=Cell_Membranes_and_Compartments&oldid=58465) | 2015 (http://php.med.unsw.edu.au/cellbiology/index.php? title=Cell_Membranes_and_Compartments&printable=yes) | 2014 (http://php.med.unsw.edu.au/cellbiology/index.php? title=Cell_Membranes_and_Compartments&oldid=48070) | 2013 (http://php.med.unsw.edu.au/cellbiology/index.php? title=Cell_Membranes_and_Compartments&oldid=42439) 2012 (http://php.med.unsw.edu.au/cellbiology/index.php? title=Cell_Membranes_and_Compartments&oldid=32154) | 2010 | 2009 | 2008 (http://cellbiology.med.unsw.edu.au/units/science/lecture0803.htm) | 1/page 2007 (viewing only) 43 pages, 1.4 Mb (http://cellbiology.med.unsw.edu.au/units/pdf/ANAT3231L2s1.pdf) Objectives Understand the concept of separate intracellular spaces Understand the structure of membranes Brief understanding of history of membrane models Understand the difference between physical and functional compartments Brief understanding of membrane specializations History Robert Hooke (1635-1703) used early microscopes to view cork tree bark was the first to use the term CELL Robert Brown 1825 identified nuclei in plant cells Theodor Schwann (1810 - 1882) together with Matthias Schleiden (plants) developed the cell theory in 1839 Cell Theory All organisms consist of one or more cells
Transcript
Eukaryotic Cell Physical Compartments
Membrane cartoon
Cell Membranes and CompartmentsFrom CellBiology
IntroductionA major difference between eukayotes and prokaryotes isthe presence of physical compartments (membrane bound)within the cell. These compartments allow theseparation/specialization of processes within the cell.There also exist within each of these physicalcompartments, functional compartments where specificprocesses may occur or are restricted too. This lecture isan introduction to compartments within the cell andmembranes. The key components are: cell compartments,membrane structure, membrane models, membranespecializations.
ObjectivesUnderstand the concept of separate intracellular spacesUnderstand the structure of membranesBrief understanding of history of membrane modelsUnderstand the difference between physical and functional compartmentsBrief understanding of membrane specializations
HistoryRobert Hooke (1635-1703)
used early microscopes to view cork tree barkwas the first to use the term CELL
Robert Brown 1825identified nuclei in plant cells
Theodor Schwann (1810 - 1882)together with Matthias Schleiden (plants) developed the cell theory in 1839
The cell is the basic unit of structure for all cellsAll cells arise only from preexisting cells
Plasma Membrane Images
The cell membrane (plasma membrane or plasmalemma) encloses or covers all cell types and is 7 nanometers (7 x 109 M)thick. Begin by some different ways of looking microscopically at membranes.
R T Watson, S Shigematsu, S H Chiang, S Mora, M Kanzaki, I G Macara, AR Saltiel, J E Pessin Lipid raft microdomain compartmentalization ofTC10 is required for insulin signaling and GLUT4 translocation. J. CellBiol.: 2001, 154(4);829-40 PubMed 11502760
Membrane - Scanning Electron Micrograph
thickness 3.5 nm
Membrane - Transmission Electron Micrograph
Links: Block-Face Scanning Electron Microscopy to Reconstruct Three-Dimensional Tissue Nanostructure(http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0020329%7CSerial) Denk W,Horstmann H (2004) Serial Block-Face Scanning Electron Microscopy to Reconstruct Three-Dimensional TissueNanostructure. PLoS Biol 2(11): e329
Table 12-1. Relative Volumes Occupied by the Major Intracellular Compartments in a Liver Cell (Hepatocyte)(http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=hepatocyte&rid=mboc4.table.2135)
Table 12-2. Relative Amounts of Membrane Types in Two Kinds of Eucaryotic Cells(http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=hepatocyte&rid=mboc4.table.2136)
Compartments are DynamicMovies showing flexibility of membranes and their changing shape and size.
Fluidity of the Lipid Bilayer (http://www.garlandscience.com/garlandscience_resources/resource_detail.jsf?landing=student&resource_id=9780815341291_CH11_QTM01)
Nuclear CompartmentNuclear matrix - consisting of Intermediate filaments (lamins)Nucleoli (functional compartment - localised transcription DNA of RNA genes)Chromosomes (DNA and associated proteins)
(MH - you will not see chromosomes in interphase nuclei only during mitosis, more in the Nucleus Lecture)
Functional compartmentsoccur in nucleus, cytoplasm, in organelles and outside organellessignaling, metabolic reactions, processing genetic information, cytoskeleton dynamics, vesicle dynamics
Membrane FunctionsForm compartmentsAllow “specialization”Metabolic and biochemicalLocalization of functionRegulation of transportDetection of signalsCell-cell communicationCell Identity
Plasma Membrane ImageCell (Plasma) encloses or covers or cell types.
phospholipids, proteins and cholesterolfirst compartment formedprokaryotes (bacteria) just this 1 compartmenteukaryotic cells many different compartments
Amphipathic - having both hydrophilic and hydrophobic properties. (phospholipids, cholesterol, glycolipids).
Links: Three views of a cell membrane (http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mboc4.figgrp.1862) |MCB Schematic diagram of typical membrane proteins in a biological membrane(http://www.ncbi.nlm.nih.gov/books/NBK21570/figure/A609)
Phospholipid OrientationFigure 2-22. Phospholipid structure and the orientation of phospholipids in membranes(http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mboc4%2Efiggrp%2E211)
A liposome (lipid vesicle) is a small aqueous compartmentsurrounded by a lipid bilayer.A micelle is a small compartment surrounded by a single lipidlayer.
Membranes History1890 Charles Overton
selective permeation of membranesnon-polar pass through (lipid soluble)polar refractorylipids present as a coat
1905 Irving Langmuirlipids faced with heads towards water away from organic solvents
monolayer of lipid isolated from rbctwice (2x) surface area of cell (bilayer)
1930-40 Danielle-DavsonProteins coat a bilayer with polar “pores”
1960s RobertsonModification with glycoprotein on one side, thereforeasymmetric
1972 Singer and Nicholsonproteins “floating” within lipid bilayer like a “liquid”surface
1975 Unwin and Hendersonintegral membrane proteinsboth hydrophobic and hydrophilicalternating -phobic and -philic represent trans-membraneloopsglycoprotein carbohydrate groups on outer surface
Links: MCB - Freeze fracturing can separate the twophospholipid leaflets that form every cellular membrane
(http://www.ncbi.nlm.nih.gov/books/NBK21583/figure/A1166/) | MCB - Solubilization of integral membrane proteinsby nonionic detergents (http://www.ncbi.nlm.nih.gov/books/NBK21589/figure/A631/)
Membranes Recent History1997 Simons - cholesterol to form rafts that move within the fluidbilayer“Membrane Rafts” “A new aspect of cell membrane structure ispresented, based on the dynamic clustering of sphingolipids andcholesterol to form rafts that move within the fluid bilayer. It isproposed that these rafts function as platforms for the attachment ofproteins when membranes are moved around inside the cell andduring signal transduction.”saturated lipids and cholesterol form liquid-ordered domains
Cartoon of different raft roles (http://jcs.biologists.org/content/118/6/1099/F1.large.jpg)
Links: PMID20044567 (http://www.ncbi.nlm.nih.gov/pubmed/20044567) | Fig. 1 Evolution of the raft concept forsubcompartmentalization in cell membranes (http://www.sciencemag.org/content/327/5961/46/F1.large.jpg)
Membrane Proteins
Protein Layer-Lipid-Protein Island Model
Outside Inside
Links: Protein Layer-Lipid-Protein Island Model | Membrane size | Outside | Inside | PMID 24806512
20-30% of the genome encodes membrane proteins PMID 9568909Proteins can be embedded in the inner phospholipid layer, outer phospholipid layer or span both layersSome proteins are folded such that they span the membrane in a series of “loops”
Two major protein transmembrane structures
1. α-helical - ubiquitously distributed2. β-barrel - outer membranes of Gram-negative bacteria, chloroplasts, and mitochondria
Membrane Protein Functions
transport channelsenzyme reactionscytoskeleton linkcell adhesioncell identity
Links: MCB Topologies of some integral membrane proteins synthesized on the rough ER(http://www.ncbi.nlm.nih.gov/books/NBK21731/figure/A4776/)
Membrane GlycoproteinsGlycoproteins are proteins which have carbohydrate groups (sugars) attachedto produce these proteins go through a very specific cellular pathway of organelles (secretory pathway)to reach the cell surface where they are either secreted (form part of the extracellular matrix)or are embedded in the membrane with the carbohydrate grouped on the outside surface (integral membrane protein)distribution of glycoproteins have functional effects (motility, migration, channel distribution, signalling) PMID24040379
Membrane CholesterolSmall molecule embedded between the phospholipid molecules and regulates lipid mobility (MH - see rafts)
Cholesterol can be at different concentrations in different regions of plasmamembranelateral organization of membranes and free volume distributionmay control membrane protein activity and "raft” formationfine tuning of membrane lipid composition, organization/dynamics, functionbacterial membranes (except for Mycoplasma and some methylotrophic bacteria)have no sterols, they lack the enzymes required for sterol biosynthesis.
Links: MBoC Figure 10-9. Cholesterol in a lipid bilayer(http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=cholesterol&rid=cell.figgrp.2458)
Bacterial Membranes(MH - covered this in previous Lecture)
Bacteria with double membranes (Example: E. coli)inner membrane is the cell's plasma membraneGram Negative do not retain dark blue dye used in gram staining
Bacteria with single membranes (Example: staphylo-cocci and streptococci)thicker cell wallsGram Positive because they do retain blue dyesingle membrane comparable to inner (plasma) membrane of gram negative bacteria
Membrane Fluidityfusion of 2 cellsFRAPmembrane domains (polarized cells)
epithelia - apical, basal and lateral domains
Tubular Bridges
(cytonemes and tunneling nanotubes, TNTs) - New membrane structuresidentified that can facilitate transfer of cellular signals and componentsover large distances (hundreds of microns) representing the longest directconnections between cells in vitro and in vivo.
File:Bronchial epithelial bridge.mov
Tubular Bridges for Bronchial Epithelial Cell Migration andCommunication
J F Presley, N B Cole, T A Schroer, KHirschberg, K J Zaal, J Lippincott-SchwartzER-to-Golgi transport visualized in livingcells. Nature: 1997, 389(6646);81-5 PubMed9288971
Links: FRAP (http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=FRAP&rid=mcb.figgrp.1162) | MBC - MembraneFluidity (http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=Membrane%20Proteins&rid=mcb.figgrp.1161)
Liver sinusoidal endothelial cells (LSECs)[2] act as a filter between blood and the hepatocytes andare highly fenestrated cells (contain transcellular pores with diameters between 50 to 200 nm). Thesmall sizes of the fenestrae have so far prohibited any functional analysis with standard andadvanced light microscopy techniques.
labeled LSEC movie
Adhesion SpecializationsA series of different types of proteins and cytoskeleton associations forming different classes of adhesion junctions (MH -covered in detail in a lecture 8)
Membrane TransportThree major forms of transport across the membrane
Passive - Simple diffusionFacilitated - transport proteinsActive - transport proteins for nutrient uptake, secretion, ion balance
Links: Figure 17-13The secretory pathway of protein synthesis and sorting(http://www.ncbi.nlm.nih.gov/books/NBK21471/figure/A4740/)
Ion Channelsphospholipid impermeable to ions in aqueous solutionprotein channels permit rapid ion flux1960’s structure and function, ionophores (simple ion channels)common structural motif alpha helix75 + different ion channelsAllosteric proteins - conformation regulated by different stimuliopening/closing, “gating” of ions
Ion Channel Types
3 rapid + 1 slow gate (gap junction)Voltage-gated - propogation of electrical signals along nerve,muscleLigand-gated - opened by non-covalent, reversible binding ofligand between nerve cells, nerve-muscle, gland cellsMechanical-gated - regulated by mechanical deformationGap junction - allow ions to flow between adjacent cellsopen/close in response to Ca2+ and protons
Apoptosis and Membranesprogrammed cell deathmembrane "blebbing" encloses cellular component fragments
Link: Time-lapse movie of human HeLa cells undergoing apoptosis(http://www.nature.com/nrm/journal/v9/n3/extref/nrm2312-s1.mov) PMID: 18073771(http://www.ncbi.nlm.nih.gov/pubmed/18073771?) | Example of early apoptotic blebbing(http://jcs.biologists.org/content/vol118/issue17/images/data/4059/DC1/JCS14488Video1.mov) PMID:16129889(http://www.ncbi.nlm.nih.gov/pubmed/16129889?)
Membrane Transport DiseaseCystic Fibrosis
1989 Collins (US), Tsui and Riordan (Canada)Chloride channel protein mutationpoint mutant, folded improperly, trapped and degraded in ER
Historic PapersBelow are some example historical research finding related to cell membranes from the JCB Archive and other sources.
1957 The invention of freeze fracture EM and the determination of membrane structure(http://jcb.rupress.org/cgi/content/full/168/2/174-a) Russell Steere introduces his home-made contraption for freeze fractureelectron microscopy (EM), and Daniel Branton uses it to conclude that membranes are bilayers.
1971 Spectrin is peripheral (http://www.jcb.org/cgi/doi/10.1083/jcb1701fta1) S. Jonathan Singer, Garth Nicolson, and VincentMarchesi use red cell ghosts to provide strong evidence for the existence of peripheral membrane proteins.
1992 Lipid raft idea is floated (http://jcb.rupress.org/cgi/content/full/172/2/166) Gerrit van Meer and Kai Simons get the firsthints of lipid rafts based on lipid sorting experiments.
1. Viola Mönkemöller, Cristina Øie, Wolfgang Hübner, Thomas Huser, Peter McCourt Multimodal super-resolutionoptical microscopy visualizes the close connection between membrane and the cytoskeleton in liver sinusoidalendothelial cell fenestrations. Sci Rep: 2015, 5;16279 PubMed 26549018
2. Viola Mönkemöller, Cristina Øie, Wolfgang Hübner, Thomas Huser, Peter McCourt Multimodal super-resolutionoptical microscopy visualizes the close connection between membrane and the cytoskeleton in liver sinusoidalendothelial cell fenestrations. Sci Rep: 2015, 5;16279 PubMed 26549018
ReferencesTextbooks
Molecular Biology of the CellChapter 10 - Membrane Structure (http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=cell&part=A2443)Three views of a cell membrane (http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mboc4.figgrp.1862)The evolution of higher animals and plants (Figure 1-38) (http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=cell.figgrp.83)From Procaryotes to Eucaryotes (http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=cell.section.25#60)From Single Cells to Multicellular Organisms (http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=cell.section.61#82)Some of the different types of cells present in the vertebrate body(http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=cell.box.79)
Molecular Cell BiologyThe Dynamic Cell (http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mcb.chapter.145)The Architecture of Cells (http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=&rid=mcb.section.203)Microscopy and Cell Architecture (http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=mcb.section.1084)
The Cell- A Molecular ApproachAn Overview of Cells and Cell Research (http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=cooper.chapter.89)Tools of Cell Biology (http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?db=Books&rid=cooper.section.128)
Search Online Textbooks
"cell compartments" Molecular Biology of the Cell (http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?db=Books&cmd=search&doptcmdl=DocSum&term=cell+compartments+AND+mboc4%5Bbook%5D) | MolecularCell Biology (http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?db=Books&cmd=search&doptcmdl=DocSum&term=cell+compartments+AND+mcb%5Bbook%5D) | The Cell- Amolecular Approach (http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?db=Books&cmd=search&doptcmdl=DocSum&term=cell+compartments+AND+cooper%5Bbook%5D)
"cell membrane" Molecular Biology of the Cell (http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?db=Books&cmd=search&doptcmdl=DocSum&term=cell+membrane+AND+mboc4%5Bbook%5D) | Molecular CellBiology (http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?db=Books&cmd=search&doptcmdl=DocSum&term=cell+membrane+AND+mcb%5Bbook%5D) | The Cell- Amolecular Approach (http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?db=Books&cmd=search&doptcmdl=DocSum&term=cell+membrane+AND+cooper%5Bbook%5D)
Books
The Cytoskeleton - cellular architecture and choreography (http://books.google.com/books?id=JNHuxHzTm7IC)
Reviews
Vertebrate membrane proteins: structure, function, and insights from biophysical approaches. Müller DJ, Wu N, PalczewskiK. Pharmacol Rev. 2008 Mar;60(1):43-78. Epub 2008 Mar 5. Review. PMID: 18321962
Articles
Studying the Nucleated Mammalian Cell Membrane by Single Molecule Approaches (http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0091595)
Images
Protein Layer-Lipid-Protein Island (PLLPI)model of the cellmembrane
Protein Layer-Lipid-Protein Island (PLLPI)model of the cellmembrane
Protein Layer-Lipid-Protein Island (PLLPI)model of the cellmembrane
Protein Layer-Lipid-Protein Island (PLLPI)model of the cellmembrane
Model of Exocytosismechanisms alsoshowing new membraneturnover.
Caveolae EM as part ofmembrane turnover
Membrane Termsadhesion junction membrane specialization allowing either cell-cell or cell-extracellular matrix adhesion generally inmulticellular organisms.
bilayer having two layers, refers to the 2 lipid layers of a single membrane.
blebbing a plasma membrane change often associated with apoptosis. The underlying cell cytoskeleton is disruptedleading to a the bubbling of the plasma membrane, which will enclose cytoplasmic and nuclear components.
cholesterol small steroid metabolite that decreases membrane motility involved in many membrane functions(endocytosis, membrane rafts). Bacterial membranes (except for Mycoplasma and some methylotrophic bacteria) haveno sterols, they lack the enzymes required for sterol biosynthesis.
cytonemes thin, actin-based extensions that project from cells and allow cell-cell communication.
electron microscopy a microscope technique that uses beams of electrons instead of light to generate high resolutionimages of cellular components. This technique historically gave the first images of the membrane bilayer structure.
electron tomography an electron microscopic technique to generate a three dimensional (3-D) image from any electronmicroscopy specimen.
exosomes small vesicles that bud from the endosome membrane into its lumen. Following endosome fusion with theplasma membrane, the exosomes are released into the extracellular space.http://jcb.rupress.org/cgi/content/full/172/6/785?
flippases enzymes that catalyze rapid translocation of phospholipids across the endoplasmic reticulum membrane.Required for balanced growth of both halves of the bilayer.
flotillin (flotillin-1 and -2) protein that is ubiquitously enriched in detergent resistant membranes (membrane rafts).
functional compartment a specialized region formed within a cell which is not limited by a membrane, compared to a"structural compartment".
Gram negative term used to describe bacteria which do not retain the Gram dye when stained. These are bacteria withdouble membranes, the inner membrane is the cell's plasma membrane (Example: E. coli).
Gram positive term used to describe bacteria which do retain the Gram dye when stained. These are bacteria withsingle membranes and thicker cell wall (Example: staphylo-cocci and streptococci).
lipids the basic molecules forming the lipid bilayer as phospholipids, glycolipids, and steroids. The main lipidcomponents include phosphatidylcholine (~50%), phosphatidylethanolamine (~10%), phosphatidylserine (~15%),sphingolipids (~10%), cholesterol (~10%), and phosphatidylinositol (1%). Medical Microbiology - Plasma(Cytoplasmic) Membranes (http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=plasma%20membrane&rid=mmed.section.305#306)
liposome (lipid vesicle) is a small aqueous compartment surrounded by a lipid bilayer.
membrane cytoskeleton the components of the cell cytoskeleton that directly underly either the cell (plasma) andnuclear membranes.
micelle is a small compartment surrounded by a single lipid layer.
phospholipid the basic molecule forming the lipid bilayer of a typical membrane (see also lipid).
raft (lipid rafts, membrane raft) term used to describe stabilized regions that form within membranes. These rafts"float" within the lipid membrane and are formed by cholesterol altering (stabilizing) the fluidity of the local membrane.
structural compartment a specialized region formed within a cell which is limited by a membrane, compared to a"functional compartment".
trogocytosis process of T and B cells capture antigens via membrane fragments of antigen presenting cells (APC).
vesicle general term given to any membrane enclosing material within the cytoplasm.
protein-to-lipid ratio the analysis of membranes by separating the 2 main components. For example, bacterial plasmamembranes are approximately 3:1, close to those for mitochondrial membranes.
External LinksExternal Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function.If the link no longer works search the web with the link text or name.
American Society Cell Biology (http://www.ascb.org/)American Society Cell Biology - Booklet Exploring the Cell (http://www.ascb.org/files/exploring.pdf)
The Nobel Prize in Physiology or Medicine - Laureates (http://www.nobel.se/medicine/laureates/)
PeopleBerkeley History - Robert Hooke (1635-1703) (http://www.ucmp.berkeley.edu/history/hooke.html)Berkeley History - Antony van Leeuwenhoek (http://www.ucmp.berkeley.edu/history/leeuwenhoek.html)Robert Brown (http://www.whonamedit.com/doctor.cfm/2539.html)Theodor Schwann (http://home.tiscalinet.ch/biografien/biografien/schwann.htm)Matthias Schleiden (1804-1881)
Museum of Microscopy (http://microscopy.fsu.edu/primer/museum/)The WWW Virtual Library of Cell Biology- General Cell Biology(http://vlib.org/Science/Cell_Biology/general_cell_biology.shtm)The Biology Project- Studying Cells (http://www.biology.arizona.edu/cell_bio/tutorials/cells/cells2.html)2003 Double Helix Celebrations (http://www.dna50.org/main.htm)Genome Timeline (http://www.genomenewsnetwork.org/timeline/timeline_overview.shtml)
Movies
JCB
A marker for sequential exocytosis The SNARE protein SNAP25, say Takahashi et al.(http://jcb.rupress.org/cgi/content/abstract/165/2/255), marks the plasma membrane after an initial exocytic event toallow rapid sequential exocytic events (http://jcb.rupress.org/cgi/content/full/jcb.200312033/DC1/1).
A myosin V moves yeast secretory vesicles Secretory vesicles actively move(http://jcb.rupress.org/cgi/content/full/jcb.200110086/DC1/1) to the site of exocytosis in yeast. Schott et al.(http://jcb.rupress.org/cgi/content/abstract/156/1/35) find that multiple secretory vesicles often follow the same lineartrack (http://jcb.rupress.org/cgi/content/full/jcb.200110086/DC1/2) and frequently enter and cross the bud. Thismovement requires (http://jcb.rupress.org/cgi/content/full/jcb.200110086/DC1/3) the activity of the myosin-V heavychain encoded by the MYO2 gene. When the predicted lever arm of this motor is progressively shortened (with the mostextreme example being the 0IQ mutant), the vesicle movements are progressively slowed(http://jcb.rupress.org/cgi/content/full/jcb.200110086/DC1/4).
Rapid cycling of lipid rafts to and from the Golgi Nichols et al. (http://jcb.rupress.org/cgi/content/abstract/153/3/529)detect rapid cycling of lipid raft markers between the plasma membrane and the Golgi. Through selectivephotobleaching, they are able to study transport either out from the Golgi
(http://jcb.rupress.org/cgi/content/full/153/3/529/F3/DC2) to the plasma membrane, or in from the plasma membrane(http://jcb.rupress.org/cgi/content/full/153/3/529/F5/DC1) to the Golgi.
Membrane docking at the immunological synapse requires Rab27a Stinchcombe et al(http://jcb.rupress.org/cgi/content/abstract/152/4/825). find that normal membrane docking(http://jcb.rupress.org/cgi/content/full/152/4/825/F6/DC2) of lytic granules at the immunological synapse is defective incells lacking Rab27a. In cells lacking other Rab proteins, polarization of the secretory granules is incomplete(http://jcb.rupress.org/cgi/content/full/152/4/825/F6/DC4).
Visualizing the location and dynamics of exocytosis Schmoranzer et al.(http://jcb.rupress.org/cgi/content/abstract/149/1/23) use total internal reflection (TIR) fluorescence microscopy tovisualize exocytosis (http://jcb.rupress.org/cgi/content/full/149/1/23/F2/DC1) in mammalian cells (e.g., see event on leftside of video). The analysis reveals that there are no preferred sites for constitutive exocytosis in this system.Visualizing the location and dynamics of exocytosis Toomre et al.(http://jcb.rupress.org/cgi/content/abstract/149/1/33) use a combination of TIR microscopy (green, labeling moleculesclose to or at the membrane) and standard fluorescence microscopy (red, for molecules further from the membrane) tovisualize trafficking to and fusion with(http://jcb.rupress.org/cgi/content/vol149/issue1/images/data/33/DC1/Fig_1b.mov) the plasma membrane duringexocytosis. Red dots turn yellow then green as they approach the membrane, and then explode in a burst of light as theyfuse with the plasma membrane during exocytosis. The transport containers appear to be partially anchored at themembrane before fusion, and can undergo either partial or complete fusion events.
PLoS Movies
File:Membrane label and endosomes.movDynamic Changes in the Spatiotemporal Localization of Rab21 in Live RAW264 Cells during Macropinocytosis(http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0006689)Ordered Patterns of Cell Shape and Orientational Correlation during Spontaneous Cell Migration(http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0003734)From Dynamic Live Cell Imaging to 3D Ultrastructure: Novel Integrated Methods for High Pressure Freezing andCorrelative Light-Electron Microscopy(http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0009014)
Online Movies
SoftSimu Movie Gallery (http://www.apmaths.uwo.ca/~mkarttu/gallery-movie.shtml)Structure of Fluid Lipid Bilayers (http://blanco.biomol.uci.edu/Bilayer_Struc.html)Changes in cholesterol levels in the plasma membrane modulate cell signaling and regulate cell adhesion and migrationon fibronectin (http://www3.interscience.wiley.com/journal/114068500/suppinfo)Neuronal growth cones (http://jcs.biologists.org/cgi/content/full/121/22/3757/DC1)
