3. The cytoskeleton Actin cytoskeleton: polymerisation of G-actin Microtubuli: Polymerisation of tubulin Intermediate filaments: Coiled-coiled structure of e.g. keratins Keratin filaments

4. Green: F-actin Red: VE-cadherin (junction protein) F-actin can be stained specifically with phalloidin G-actin: monomers F-actin: filamentous

5. Actin polymerisation at leading edge of cell: All F-actin Only newly polymerized F-actin Regulation in time and space!!

6. Profilin recruits actin monomers: nucleation of actin

7. Actin related protein (Arp) 2/3 complex: nucleation of actin

8. Actin: Red Arp2/3: Green Arp 2/3 complex: branching of actin

9. Actin treadmilling: cycle of polymerisation/depolymerisation

10. Crosslinking proteins form networks

11. Rho family members (Rac, Rho, CDC42) regulate localized actin polymerisation Effector GAP Rac GDP GEF Rac GTP Stimulus (e.g. chemotatic factor)

12. Rho family members (Rac, Rho, CDC42) regulate localized actin polymerisation: Specificity !

13. Figure 16-98a Molecular Biology of the Cell (© Garland Science 2008)

14. Figure 16-98b Molecular Biology of the Cell (© Garland Science 2008)

15. Polymerised actin is anchored to the plasma membrane: A regulated process

16. Microtubuli are also highly dynamic GFP-EB1 (EB1 is a cap protein)

17. Taxol stabilizes microtubuli: cytostatic agent

18. Cell junctions

19. Tight junctions : Functions: 1. Seal apical lumen from basal lumen: Regulated permeability 2. Barrier between apical and basolateral membrane Cell polarity Glucose transport in the gut: one direction only

20. Claudins and Occludins are major component of TJ

21. Adherence junctions Function Cell cell adhesion Connected to actin bundels: adhesion belt

22. Adhesion belts involved in - keeping the integrity of the epithelial sheet - morphogenesis

23. Cadherins are major component of AJ: Homotypic binding E-cadherin N-cadherin P-cadherin VE-cadherin

24. Cadherins are connected to the actin cytoskeleton through catenines  -catenin Note:  -catenin functions independently in Wnt signalling pathway

25. Cadherins involved in cell sorting Different cadherins Different expression levels

26. Cell junctions are dynamic GFP-ZO-1 Ovcar3 cells Movie: Johan de Rooij

27. Adhesion is regulated by recycling of cadherins Cell division Growth factors Oncogenes Vesicle transport Adherence junctions