Complex actin networks

Fig. 1: Confocal image of a kinetically trapped actin/filamin bundle network

Actin is a major component of the cytoskeleton accounting for the cellís mechanical stability as well as motility. To facilitate its numerous tasks, a huge variety of actin binding proteins (ABPs) accomplishes a precisely tailored arrangement of actin filaments into locally differing microstructures. Well-defined in vitro systems with a manageable number of different proteins have been proven essential for a profound understanding of structural and mechanical properties of cytoskeletal networks. Considerable progress has been made in the quantitative investigation of model systems with comparably simple, thermally equilibrated network structures.

Recently, we have started to study more complex networks such as non-equilibrated heterogeneous bundle networks or networks with more than one type of cross-linking protein present. It turned out that the non-equilibrium character of actin bundle networks allows to build stable networks with drastically different structural and mechanical properties using the identical material - just by changing the way of network formation. On the other hand, mixing of cross-linking molecules gives access to a huge variety of different networks, whose architecture and mechanical properties can be finely tuned by varying the cross-linker concentrations.

A combination of various imaging techniques and rheological methods allows a correlation of network structure with the resulting mechanics. Thereby we search for answers to the open questions which might lead to a deep understanding of the physics underlying cytoskeletal actin structures:

Which mechanisms determine the aggregation of out-of-equilibrium actin bundle networks and thereby the network architecture?

What is the effect on the mechanical properties?

Can we use our our knowledge about "simple" actin networks, which are cross-linked by a single type of cross-linking molecules to understand the networks resulting from mixtures?

How do these networks evolve on long time scales?