1. Cell Motility Lecture 24 BSCI 420/421Nov 21, 2002 “ A university is a group of faculty and student entrepreneurs, united by a common opposition to parking policies.” - C. Kerr 1.Microfilament-based motility 2.Microtubule-based motility

2. 1.Microfilament-based motility a.Contractility (mainly Myosin II and actin) 1) Skeletal and cardiac muscle (last lecture) 2) Smooth muscle 3) Cytokinesis (after mitosis) 4) Phagocytosis 5) Non-muscle cell contraction b.Cell migration along surfaces c.Cytoplasmic streaming in plants and protist All except muscle are inhib by cytochalasin and phalloidin.

3. 2) Smooth muscle Involves formation of myosin filaments from ind myosin II mols. MLCK is activated by Calmodulin, activated By Ca2+ release.

4. 5) Non-muscle cell contraction E.g., contraction of terminal web of neural tube cells: (attached by adherens jxs)

5. b) Cell migration along surfaces, e.g. fibroblasts & growth cones of axons (Fig 99).

6. 2.Microtubule-based motility Three different mechanisms: a)Assembly and disassembly b)Transport along MTs by motor proteins c)Sliding of MTs

7. a)Assembly and disassembly (including DI) E.g., formation of neurites, the projections from neurons. formation of cilia and flagella, formation of axopodia of protists. Movement of poles and chromosomes during mitosis. MT inhibitors colchicine & nocodazole inhibit these processes.

8. b) Transport along MTs by motor proteins Kinesin (+) toward the cell surface. (Anterograde) e.g. Secr. Ves, ER Dynein (-) toward the cell center. (Retrograde) e.g. Golgi ves

9. How do we know which direction motors move in axons? When axons are cooled locally, MTs break down and transport stops at the ends of Mts. Kinesin and Kinesin- transported cargo stops at the near edge of the gap, and dynein and dynein transported cargo stops at the far edge of the gap. dynein multivesicular bodies kinesin neurotrans ves mitochondria small amt of dynein

10. c) Sliding of MTs 1) Sliding apart of mitotic spindle polar MTs by bipolar KLP (Bim C), discovered as a mutation in Drosophila. 2) Beating of cilia & flagella

12. Sliding of Flagellar axoneme Mts w & w/o digestion of linker proteins.