II. F-actin network-specific sorting of actin binding proteins

Cells simultaneously assemble diverse F-actin networks from a common pool of monomers at the right time and place. Actin filaments in different networks are organized into complex architectures with proper dynamics that facilitate specific functions such as motility, cytokinesis, endocytosis and polarization. Actin filament organization is driven by the coordinated actions of complementary actin binding proteins that assemble, crosslink, cap and/or sever filaments. Specific sets of actin binding proteins are therefore required to make different F-actin networks, such as branched motile networks or unbranched contractile networks (Figure A). Therefore it is critical to understand how particular actin binding proteins sort to specific F-actin networks, rather than generally associating with all actin filaments (Figure B; Skau and Kovar, Current Biology 2010). Important questions remain concerning the mechanisms by which actin binding protein sorting occurs to allow the formation of different F-actin networks within a common cytoplasm:

  • Why and how do different actin binding proteins associate with one F-actin network over another?
  • What particular properties of actin binding proteins are important for their sorting?
  • What role (if any) does the assembly factor play in setting up actin binding protein sorting?

These types of questions are ideally studied in fission yeast, which has three distinct F-actin networks that are each generated by a unique assembly factor (Figure A). We use both in vivo (Figure B: yeast genetics, live cell imaging) and in vitro (single molecule multi-color TIRF microscopy) methods to determine the mechanisms by which actin binding proteins sort to distinct F-actin networks in cells.