Non-equilibrium dynamics in the actin cortex*

The actin cortex of cells is a mechanically resilient but also highly active material that provides a protective shell for cells and, at the same time, drives many crucial dynamic processes. Myosin motors locally exert contractile force on the actin network which is kept in a dynamic steady state with the help of a multitude of regulatory proteins. It is not well understood how the cortex self-organizes to form complex structures and perform collective dynamic functions.
We use advanced light microscopy and statistical analysis methods to characterize the mechanical properties of and the motion and stress patterns in reconstituted and cellular cortices. Model cortices were constructed in emulsion droplets from Xenopus egg extract. Cellular cortical activity was monitored by studying the fluctuations of primary cilia of kidney epithelial cells. We developed a method to diagnose thermodynamic non-equilibrium using the principle of detailed balance.