Last Class 1. GPCR signaling: 2. Enzyme-linked Receptor signaling: PKA and Calcium 2. Enzyme-linked Receptor signaling: RTK->Ras and PI3K 3. Proteolysis-mediated signaling pathways NF-KB pathway
The Cytoskeleton
Cytoskeletal Filaments Microtubules: intracellular traffic Actin Filaments: cell shape and locomotion Intermediate Filaments: mechanical strength
Cytoskeleton and changes in cell shape
Multi-filament formation of cytoskeletal filaments
Actin Monomers and Filaments
The Time Courses of Actin Polymerization
The treadmilling of an actin filament
Microtubules
Microtubules: Plus end and Minus end Dynamic Instability
Microtubules: Plus end and Minus end Experimental Recording
Microtubules: Dynamic Instability
Microtubules: GDP-bound and bending
Microtubules: GDP-bound and bending
Intermediate Filaments
Intermediate Filaments Coiled coil formation
Intermediate Filaments Difficult to break
Mutation of Keratin (one kind of intermediate filament) gene causes skin blistering
Cytoskeletal Regulation
Microtubules
g-tubulin nucleation for microtubule polymerization
Centrosome and Microtubule Network (movie)
Centrosome and its center-seeking function (movie: MT-red and ER-green)
Microtubules can find its center
Stathmin on Microtubule depolymerization (sequestering)
Katanin on Microtubule depolymerization cleavage
Protein binding and the effects on microtubule stability (movie, MT binding proteins and dynamics)
Organization of Microtubule bundles MAP: microtubule associated protein
Actin Filaments
Actin Filament Regulation occurs at plasma membrane Green: Phalloidin staining of existing actin fibers Red: new actin filaments incorporating rhodamine actin
ARP proteins and actin nucleation
ARP proteins and actin nucleation
Profilin and Thymosin on Actin polymerization
Profilin and Thymosin on Actin polymerization
Cofilin on Actin Depolymerization
Gelsolin severs actin filaments
Platelet Activation
Capping and Stability
Different Actin Arrays in a cell Bundles and gel-like networks
Actin Cross-Linking Proteins Bundles: Fimbrin: filopodia; a-actinin: stress fibers Gel-like network: spectrin and filamin
Different Bundles with different cross-linking Proteins
ERM Linking Actin to Plasma Membrane (ezrin, radixin, moesin)
Actin Filaments and Cellular functions Focal Adhesions
Actin Filaments Regulations
Molecular Motors
Myosins (movie: heart contraction)
Motor Activity of Myosin Heads
Myosin Structural Changes walking along an actin filament
Movie: summarize actomyosin contraction cycle
Skeletal Muscle Cell, myoblasts
Skeletal Muscle Myofibrils
Sliding Acto-Myosin filaments
Protein Structures of Sarcomere Tropomodulin/troponin: minus end Z-disc/a-actinin: plus end
T-tubules and sarcoplasmic reticulum
Calcium/Troponin and skeletal muscle contraction T, I, C subunits of troponin: tropomyosin binding, inhibitory, calcium binding
Regulation of Myosin
Kinesin and dynein bind to microtubules Kinesin and Myosin Kinesin and dynein bind to microtubules
Kinesin: - to +; Dynein: + to – Both on microtubules (movie, MT transportation)
Cell Behaviors and Cytoskeleton
Cell Migration Model
Migratory Keratocytes
Lamellipodial Fragments Blue: Actin Pink: myosin II
ARP protein and Lamellipodia: Actin: Red ARP: Green
Lamellipodial Fragments Actin: Red Cofilin: Green
Traction forces on the substratum
Chemotaxis and Polarization External signals can control cell behavior
Summary 1. Cytoskeleton components: Microtubules Actin Filaments Intermediate Filaments 2. The regulation of microtubules and Actin filaments 3. Molecular Motors 4. Cell behaviors related to cytoskeleton