L1 Introduction to the Cytoskeleton PDF

The dynamic cytoskeleton BS31004 Cell Shape and Movement L1 : Introduction to the Cytoskeleton Alan Prescott [email protected]  Recommended text book for BS31004 : Cell shape and movement. Cell adhesion and signalling Alberts et al. Molecular Biology of the Cell, Ch...

The dynamic cytoskeleton BS31004 Cell Shape and Movement L1 : Introduction to the Cytoskeleton Alan Prescott [email protected]  Recommended text book for BS31004 : Cell shape and movement. Cell adhesion and signalling Alberts et al. Molecular Biology of the Cell, Chapter 16 & Chapter 19 2  Cytoskeleton Lectures L1 Intoduction-general principles and specialised cells L2 Intermediate Filaments L3 Actin microfilaments L4 Microtubules  Cells: Cytosol and the Cytoskeleton CYTOSOL – soluble components – 4 x more viscous than water – movement by diffusion? CYTOSKELETON – Pellet produced on cell lysis – Systems of filaments through cytoplasm – Transport, directionality and compartmentalisation Fibroblast cytoskeleton  All cells must be able to respond to extracellular signals (physical and chemical) in order to undergo mitosis migrate (wound healing, embryogenesis) adopt a specific cell shape when differentiating maintain this specialised shape in a multicellular tissue and in doing so, they must resist being pulled apart or ruptured maintain their orientation Figure 16-2 Molecular Biology of the Cell (© Garland Science 2008)  Components determining cell form and function - properties required of a cytoskeleton Determining shape and form – Strong - physical stresses on cells – Rigidity versus flexibility – Permissive of cell functions Capacity for remodelling – Dynamic response to growth signals Reliability – Excess capacity, genetic redundancy  Cytoskeleton ? A framework for cell form and function The Major Cytoskeleton Systems Actin microfilaments Tubulin microtubules Intermediate filaments Overview of the cytoskeletons of an epithelial cell and a migrating cell. Three cytoskeleton components in a polarised epithelium actin tubulin intermediate filaments  The components of the cytoskeleton. Immunofluorescence microscopy  Immunofluorescence microscopy Actin-microfilaments Tubulin-microtubules Figure 16-1 Molecular Biology of the Cell (© Garland Science 2008) Electron micrograph intermediate filaments actin filaments microtubules Figure 16-5 Molecular Biology of the Cell (© Garland Science 2008)  Actin Tubulin Intermediate Filaments seen in cultured epithelial cells using immunofluorescence Regulation of cytoskeleton function by cell signaling.  Signals: Growth factors Cytokines Matrix components Figure 16-7 Molecular Biology of the Cell (© Garland Science 2008)  Single protofilaments are prone to mechanical stress -single bonds Figure 16-8 (part 1 of 2) Molecular Biology of the Cell (© Garland Science 2008)  Multiple protofilaments are resistant to mechanical stress -multiple bonds Figure 16-8 (part 2 of 2) Molecular Biology of the Cell (© Garland Science 2008)  Strong cross-links make intermediate filaments very stable Figure 16-9 Molecular Biology of the Cell (© Garland Science 2008) A dynamic cytoskeleton allows for the rapid changes in cell shape necessary for cell motility Neutrophil chasing bacteria Comparison of actin, tubulin and intermediate filaments ACTIN TUBULIN INTERMEDIATE FILAMENTS microfilaments microtubules intermediate filaments 4-6 nm 25nm 10nm very dynamic extremely dynamic rather stable; flux within filaments POLAR POLAR APOLAR form bundles and Single microtubules bundles or single meshworks remodelled by remodelled by remodelled by ATP/ADP GTP/GDP phosphorylation Specialised cells and role of cytoskeleton Muscle cells – Contraction machinery; supporting shape changes Epithelia – Polarisation; barrier formation Neurones – Polarisation; supporting extreme shapes Glial cells – Maintaining directed cell extensions Sensory cells – Polarity; cell shapes  villus brush border cells (absorptive) Epithelial cells of the small goblet cells intestine in situ (mucus) crypt (stem cells here)  The Cytoskeleton is required for cell polarity Apical and baso-lateral membranes are functionally different  The “brush border” of intestinal epithelial cells Figure 16-50b Molecular Biology of the Cell (© Garland Science 2008)  Brush border microvillus tip Note linking proteins between cytoskeleton and plasma membrane Specialised cells: (i) the photoreceptor Specialised cells: (ii) the cochlear hair cells Specialised cells: (iii) skeletal muscle cells Structure of the skeletal muscle sarcomere. Wound healing In Epithelial Cells The leading edge of a crawling cell: lamellipodia and filopodia Actin distribution in moving cells-polarised Phagocytosis and actin dynamics. Cell shape is determined by the cytoskeleton The membrane cytoskeleton of the red blood cell Cell shape and anchorage - prerequisites for division and survival  The challenge of intracellular transport Figure 16-106 Molecular Biology of the Cell (© Garland Science 2008)  Molecular motors transport vesicles along the cytoskeletal filaments-actin and microtubules Figure 16-104 Molecular Biology of the Cell (© Garland Science 2008) Organelle transport by microtubule motors.  Neuronal growth cone-lamellipodia and filopodia Figure 16-105 Molecular Biology of the Cell (© Garland Science 2008)  Actin-dependent dendritic spines-memory Figure 16-107 Molecular Biology of the Cell (© Garland Science 2008) Co-ordinated cell movements Cytoskeleton attachment points  Cell junctions: overview Junction Transmembran Extracellular Intracellular Some e linker protein ligand cytoskeletal intracellular attachment attachment proteins Adherens (cell-cell) Cadherin (E- Cadherin in Actin filaments Catenins, cadherin) neighbouring cell vinculin, a- actinin, plakoglobin Desmosome Cadherin Cadherin in Intermediate Desmoplakin, (desmogleins neighbouring cell filaments plakoglobin and desmocollins) Adherens (cell – integrin Extracellular Actin filaments Talin, vinculin, matrix) matrix proteins a-actinin Hemidesmosome Integrin (a6ß4 ) Extracellular Intermediate BPAG matrix filaments  The cytoskeleton and disease Cytoskeleton “oncogenes” involved in cancer Adhesion molecules (e.g. cadherins) Signalling molecules (e.g. ras) Mutations in cytoskeleton genes cause hereditary disorders Haemolytic anaemia (spectrin) Skin fragility disorders (keratins) Motorneurone disease (neurofilaments) Cardio- and skeletal myopathies (desmin) Progeria (lamin) Male sterility (tubulin) Deafness, blindness (myosin and kinesin-type motors) Table 16-2 Molecular Biology of the Cell (© Garland Science 2008) Figure 16-23a Molecular Biology of the Cell (© Garland Science 2008)  Pacific yew (Taxus brevifolia) Natural source of Taxol Paclitaxel- used to treat breast and lung cancer Figure 16-23d Molecular Biology of the Cell (© Garland Science 2008)  Liver epithelial cell microtubules + Taxol Figure 16-23b,c Molecular Biology of the Cell (© Garland Science 2008) The cytoskeleton components Filaments – Intermediate filaments – Microfilaments (made of actin) – Microtubules (made of tubulin) Associated proteins – Motor proteins – Linkers – Modifying proteins Membrane binding sites – Attachment proteins