L03 Cytoskeleton PDF

The Cytoskeleton Mrs Cassy Ross Week 3 – Cell Biology SCI1023-N-GJ1-2022 2022 Learning Outcomes • Define the cytoskeleton and its location in the cell • Composition of the cytoskeleton • • • Microtubules Microfilaments (or Actin filaments) Intermediate filaments • Specific functions of each comp...

The Cytoskeleton Mrs Cassy Ross Week 3 – Cell Biology SCI1023-N-GJ1-2022 2022 Learning Outcomes • Define the cytoskeleton and its location in the cell • Composition of the cytoskeleton • • • Microtubules Microfilaments (or Actin filaments) Intermediate filaments • Specific functions of each component Do you remember the cell? Eukaryotic cell When you think in eukaryotic cells… • Lots of ‘empty’ cytoplasm? • There’s actually a lot more going on in there! So, what is the cytoskeleton? A support framework with 3 broad functions: • Enable the cell to move and change shape • Organises the contents of the cell • Connects the cell physically and biochemically to the external environment Actin Microtubules Cytoskeleton, not so rigid • The cytoskeleton is not a fixed structure • Dynamic and adaptive • Polymers and regulatory proteins in a constant state of flux It is the contrary…really dynamic! Leading edge of human cell showing dynamic microtubules (blue) and focal adhesions (pink) Human cell showing dynamic microtubule plus tip protein (EB1, in red) Juanes et al., JCB 2017,2019: CB 2020 Cytoskeleton Composition – Think of Lego! • Similarities between LEGO and the proteins that form the cytoskeleton • Multiple copies of key pieces • Fit together to form larger structures • Assembled into a wide range of structures • Disassembled and reassembled into different shapes Parts of the Cytoskeleton • The cytoskeleton consists of • Microtubules • Microfilaments • Intermediate filaments Parts of the Cytoskeleton • The cytoskeleton consists of • Microtubules • Microfilaments • Intermediate filaments Microtubules • Form a dense network across the cell • Act as support beams to stop the cell collapsing Microtubules • Largest and strongest of the cytoskeleton structures • Dimers of α- and β-Tubulin • Form polymer sheets • Rolled into a tube • Hollow, but able to withstand some compression 25 nm Microtubule assembly - cytoskeleton Microtubules Assembly Mechanism I Cytoskeleton - YouTube 15 • Microtubules can switch between two states Rapidly Growingshrinking steadily 16 MTOC Dynamic end – dimers added or removed very quickly (this is essential for their functions!) Microtubule Organising Centre 17 Cytoskeleton – Microtubules – MTOC • Microtubule organising centres bypass the need for a ‘seed’ γ-tubulin Accessory proteins 18 Cytoskeleton – Microtubules – MTOC • Microtubule organising centre or centrosome Before cell division begins, the interphase MTOC replicates to form two distinct MTOCs (now typically referred to as centrosomes). During cell division, these centrosomes move to opposite ends of the cell and nucleate microtubules to help form the mitotic/meiotic spindle All animal cells use centrosomes as MTOCs during mitosis 19 • Centrosome = organelle form of two centrioles • Centriole = structure made of microtubules 2 3 4 1 9 ‘9+0’ 5 6 8 7 Microtubules - Mitosis • Three main types of microtubules • Aster/Astral • Interpolar • Kinetochore Microtubules – extensive highways • Also serves as a transport network • Moving organelles within the cell Motor protein moving vesicle from the Golgi apparatus to the cell membrane Microtubules – critical in neurons • Neuronal cells have to transport mitochondria, vesicles and other materials from one side to the other • Neurons use microtubules as highways along the vast length of their axon. Microtubules – critical for neuronal survival 24 Cystoskeleton – Microtubules – Degenerative disease • Reduced microtubule stability has been observed in neurodegenerative diseases • Alzheimer's disease • Parkinson's disease • Motor neurone disease 25 Cytoskeleton – Microtubules are critical in a variety of cells Questions 1. What is a cytoskeleton? 2. How would you describe a microtubule? 3. Microtubules are made up of which type of proteins? 4. What do microtubules bind to as a result of polymerisation? 5. How many triplets form a centriole? 6. The main functions of microtubules are? 27 Which of these three cytoskeleton structures extends into a 9+0 ratio? Can you remember the three different types of microtubules during mitosis? 29 So, what are the different parts of the cytoskeleton? The cytoskeleton consists of: • Microtubules • Microfilaments • Intermediate filaments 30 So, what are the different parts of the cytoskeleton? The cytoskeleton consists of: • Microtubules • Microfilaments • Intermediate filaments 31 • Microfilaments are also known as actin filaments • Actin subunits bind together to form polymer • Polymer twists around to form filament Double helix Actin 32 • Much less rigid than microtubules • Smaller than microtubules -7 nm • Primarily involved in the movement of the cell • Highly dynamic (assemble and disassemble) 33 • Much less rigid than microtubules • Smaller than microtubules -7 nm • Primarily involved in the movement of the cell • Highly Dynamic àActin polymerisation 34 • Much less rigid than microtubules • Smaller than microtubules -7 nm • Primarily involved in the movement of the cell • Highly Dynamic àActin depolymerisation 35 • Treadmilling is the default state of a microfilament • This is when the actin monomers are added as quickly as they are removed • The rate of addition or removal can be altered by accessory proteins In addition, there are actin nucleator factors that help to assemble actin filaments…. …indeed, you can be updated! Rather than text books, let’s share some recent research The tumour suppressor Adenomatous polyposis coli nucleates actin filaments, alone or in collaboration with formin mDia1 and this activity is inhibited by the microtubule end-binding protein EB1 Juanes et al., Current Biology 2020 Formins also form actin filaments in budding yeast cells 39 Are Actin filaments important in some biological process? Yes! Cell transport Cell migration Cell division … 41 Cytoskeleton – Microfilaments – Endocytosis Cytoskeleton – Actin filaments - Endocytosis • In response to signals downstream of cell surface receptors actin-filament networks protrude 42 Cytoskeleton – Microfilaments – Endocytosis Cytoskeleton – Actin filaments – Cell division • Actin filaments form a contractile ring around the ‘waist’ of the cell • The contraction of the ring aids the splitting of the daughter cells Cytoskeleton – Microfilaments – Endocytosis Cytoskeleton – Actin filaments – Cell migration Pirta Hotulainen and Pekka Lappalainen 2006 Vignjevic et al 2006 Edwards et al 2014 Nat Rev Actin filaments coordinate with microtubules to regulate biological functions! Focal adhesions Microtubules Actin 45 So, what are the different parts of the cytoskeleton? • The cytoskeleton consists of • Microtubules • Microfilaments • Intermediate filaments 46 So, what are the different parts of the cytoskeleton? • The cytoskeleton consists of • Microtubules • Microfilaments • Intermediate filaments 47 • Most flexible of the cytoskeleton polymers • Can cross-link to each other, microtubules and microfilaments • Not as dynamic as microtubules or microfilaments 48 • Often formed in response to mechanical stresses • Epithelial cells of the airway form keratin intermediate fibres to resist shear stress • More common in cells that undergo mechanical stress 49 • Unlike microtubules and microfilaments • Cannot support directional movement of molecular motors • Intermediate filaments are highly divergent in sequence and molecular weight 50 • Intermediate filaments are classified into six types based on sequence similarity • The largest group is type I and type II keratins • Nails and hair • Epithelial cells 51 Let’s revise intermediate filaments https://www.youtube.com/watch?v=ezIJjoQVa-8 52 Cytoskeleton – Micro and intermediate filaments – Review! 3.30min 53 How pathogens can alter the cytoskeleton • Most pathogens manipulate the host cytoskeleton • Cytoskeleton modulation can occur at several points of contact between the pathogen and host • Involves extracellular receptors, intracellular signal transduction and cytoskeleton proteins themselves 54 How pathogens can alter the cytoskeleton 2-minute videos on cytoskeletal dynamics: Innovative Techniques https://www.youtube.com/watch?v=CHknjzglRdg Force generation for cell membrane deformation Force Generation through Polymerization - YouTube Now, time to test yourself: Multiple choice questions on the cytoskeleton! https://forms.office.com/Pages/ResponsePage.aspx?id=W xHSQ16ltkad97AziOz8YHPKVJ7iwLlEi3zi7EZn_8pUN0Yy NDBHVkVWRUhKNDFYQUpNSTJIUVhRTy4u Any questions? [email protected] Thank you!