Regulation of Actin Dynamics in Animal Cells: the Role of ADF/cofilin and Twinfilin

....................................................................................................8 INTRODUCTION .............................................................................................9 1. THE CYTOSKELETON ..................................................................................9 2. ACTIN........................................................................................................9 3. THE ROLE OF ACTIN IN VARIOUS CELL BIOLOGICAL PROCESSES....................11 3.1 Actin filament structures in cells.........................................................11 3.2 Cell movements rely on the actin cytoskeleton .................................12 4. ACTIN-BINDING PROTEINS .........................................................................13 4.1 The role of actin-binding proteins in actin filament dynamics.............15 4.2 Actin monomer-binding proteins .......................................................16 4.2.1 Profilin ..........................................................................................16 4.2.2 Thymosin β4 ................................................................................17 4.2.3 ADF-H domain proteins................................................................18 4.2.4 ADF/Cofilin...................................................................................19 4.2.4.1 Interactions with actin.............................................................19 4.2.4.2 Cell biological properties ........................................................20 4.2.4.3 Regulation by pH, phosphoinositides and phosphorylation...21 4.2.4.4 ADF/cofilin isoforms ..............................................................21 4.2.5 Twinfilin .......................................................................................22 4.2.5.1 Twinfilin is composed of two ADF-H domains ........................22 4.2.5.2 Biochemical and cell biological activities of yeast twinfilin......23 5. SIGNALING TO THE ACTIN CYTOSKELETON ..................................................23 5.1. Rho family GTPases ........................................................................24 5.1.1. Rho regulates actomyosin-based structures ...............................24 5.1.2. Rac and Cdc42 regulate the formation of lamellipodia and filopodia ................................................................................................25 5.2. PI(4,5)P2 ...........................................................................................26 AIMS OF THE STUDY...................................................................................28 MATERIALS AND METHODS ......................................................................29 RESULTS ......................................................................................................30 6. THE THREE MOUSE ADF/COFILINS HAVE DISTINCT EXPRESSION PATTERNS AS WELL AS DIFFERENT BIOCHEMICAL PROPERTIES (Ι) ..........................................30 7. THE ROLE OF TWINFILIN IN DROSOPHILA DEVELOPMENT (ΙΙ).........................31 8. THE ROLE OF TWINFILIN IN MAMMALS (ΙΙΙ) .................................................31 9. THE TWO MAMMALIAN TWINFILIN ISOFORMS HAVE SIMILAR BIOCHEMICAL PROPERTIES BUT DISTINCT EXPRESSION PATTERNS (UNPUBLISHED) ..................32