molecular cell biology intermediate filaments cooper
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Molecular Cell Biology
Intermediate FilamentsCooper
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Introduction
Filaments 10 nm wide => “intermediate”
Present in Metazoa / Animals• i.e. not Plants or Unicellular Organisms
Complex Gene Superfamily• 70 in Human Genome
Specific Expression at Different Times and Places
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Intermediate Filament Biochemical Properties In Vitro
Very stable. Little subunit exchange.
Very strong. Filaments do not break.• MT’s strong but brittle
• Actin weak
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Intermediate FilamentPotential Functions In Vivo
Mechanical Strength of Cytoplasm
Help a Layer of Epithelial Cells Resist Shear Stress - Filaments Connect to Cell-cell Junctions
Hold Nucleus in Center of Cell
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IntermediateFilamentStructure &Assembly
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Intermediate Filaments by EM:Filament Unraveling
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Classes of Intermediate FilamentsClass Name Cells
Number ofIsoforms
Size(kD) Polymers
I Acidic Keratin Epithelia ~15 40-60 Obligate HeteropolymersII Basic Keratin Epithelia ~15 50-70 One acidic + one basic
III Vimentin Mesenchymal 1 53III Desmin Muscle 1 52 Homopolymers (singleIII Glial Fibrillary Glia 1 51 type of subunit) or
Acidic Protein (GFAP) co-polymers w/ eachIII Peripherin Neurons >1 58 other at varied ratios
IV Neurofilament H Neurons 1 135-150IV Neurofilament M Neurons 1 105-110 H & M each requireIV Neurofilament L Neurons 1 60-70 L for polymerIV Nestin Glial scars, Early
neurons & muscle1 240
V Lamin A All 1 60-75 Homopolymers orV Lamin B All 1 60-75 Heteropolymer
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Regulation of IF Assembly
Notoriously Stable• No Nucleotide
Filaments Move Little• Precursors Move More
Disassemble Somewhat during Mitosis• Phosphorylation by Cyclin-depen Kinase
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Vimentin Filaments in a Cultured Cell
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Vimentin
All Cells in Early Development Cage Around Nucleus Interacts with Mt’s Vimentin Knockout Mouse
• Initially normal at gross inspection• Cultured cells have altered properties of
uncertain significance
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FRAP of Vimentin vs. Keratin in One Cell
Left: Vimentin (Green)Right: Keratin (Red)
10 min time intervals
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Dynamics of Keratin Particles in Periphery
QuickTime™ and aPhoto - JPEG decompressorare needed to see this picture.QuickTime™ and aPhoto - JPEG decompressorare needed to see this picture.
11 micrometersover 10 minutes
18 micrometersover 10 minutes
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Desmin
Expressed in Muscle Elastic Elements to Prevent Over-stretching Connects / Aligns Z lines Knockout Mouse - Deranged Myofibril
Architecture
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Keratins Expressed in Epithelia Keratin Filaments Connect to Desmosome and
Hemidesmosomes Differentiation of Epidermis includes Production of
Massive Amounts of Keratin Provides Outer Protection of Skin Composes Hair, Nails, Feathers, etc.
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Density of Keratin Filaments in Outer Epidermis Layers
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Keratin Mutations are Basis forHuman Epidermal Diseases
Structure/Function Analysis of Keratin Assembly
Point Mutation in Terminal Domain Fails to Assemble
Mutant is Dominant, even in Low Amounts, in Cultured Cells and Mice
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Epidermolysis Bullosa Simplex
Wild-type Mutant
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Keratins and EBS
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Neurons
Neurofilament H, M, L Copolymer
Prevent Axon Breakage
Diseases with Clumps of Neurofilaments• Superoxide dismutase model for ALS• Clumps are secondary, not causative
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Neurofilament Transport in Axons
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
Photobleached Zone in the Middle
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Neurofilament Transport in Axons
Photobleached Zone in the Middle
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
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Lamins Square Lattice on Inner Surface of Nuclear Membrane
Present in Metazoans (Animals, not Plants or unicellular organisms)
Mitosis Breakdown• Phosphorylation of A & C by Cyclin-depen Kinase
• B remains with Membrane
Mutations Cause Accelerated Aging Diseases• Progerias - Dominant Mutations
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EM of Nuclear LaminaNuclear Pores
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End