Forming And Destroying Actin Networks

Every cell has to adapt to a multiplicity of different situations. Cell growth, cell division or adaption to different environments each necessitate a high degree of flexibility. To adjust to the various mechanical requirements, actin in conjunction with a whole bunch of actin-binding proteins (e.g. filamin, fascin, formin, cofilin, ...) forms a highly dynamic network.

This project aims to understand the principles underlying the dynamics of the actin network. We address the following questions:

 

 

How are actin networks formed?

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Movie 1: TIRF-micrograph of a growing actin filament.

The elongation of an actin filament attached to the surface is shown in movie 1. The high resolution of TIRF-microscopy allows directly visualizing the elongation kinetics of single filaments. 

Using this techniqe we try to answer several questions:

  • How is the elongation kinetic of actin influenced by the presence of various actin binding proteins?
  • How do actin bundles form?  
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Movie 2: Formation of an actin/fascin bundle.

TIRF-experiments show, that actin/fascin bundles are formed by reorientation of actin filaments in a "zipper"-like manner (movie 2). 

How is depolymerization affected by crosslinking proteins?

Cross-linking molecules are ubiquitous is living cells. Nevertheless, their effect on the dynamics of actin filaments in rather unknown. Utilizing multiple depolymerization assays we aim to reveal how actin kinetics are modified by the presence of cross-linkers.

How can actin networks be destroyed?

Cross-linking molecules such as filamin or a-actinin arrange actin filaments into extremely stable bundle networks. Similar structures can also be observed in living cells (e.g. stress fibers or the contractile ring). Therefore, cells need concepts to disintegrate these bundles in a controlled way.