Head: PhD students: MSc student: Technician:

Ewa Paluch, PhD Jakub Sedzinski, MSc Mate Biro, MSc Alba Diz Munoz, MSc Ulrike Schulze, BSc Annelie Oswald, BSc Julia Roensch, BSc

RESEARCH

The cell cortex is a network of actin, myosin and associated proteins that underlies the plasma membrane and determines the shape of the cell body. The cortex enables the cell to resist externally applied stresses and to exert mechanical work. As such, it plays a role in normal physiology during events involving cell deformation such as mitosis, cytokinesis, and cell locomotion, and in the pathophysiology of diseases such as cancer where cortical contractility is upregulated. Despite its importance, little is known about how the cortex is assembled and regulated. As the cortex is an intrinsically mechanical structure (its biological activity results from its ability to contract and to exert forces), its biological properties cannot be understood in isolation from its mechanics. The main focus of the group is to understand how these mechanical properties are determined by the molecular components of the cortex and how these properties are regulated, locally and globally, to allow the cell to undergo deformations such as the ingression of the cleavage furrow during cytokinesis. To this aim, the staff composed of biologists and physicists combine biophysical and molecular approaches. Our main lines of research are:
1. Role of cortical proteins in cortex mechanics
We aim to characterize the role of the various cortical components in cortex mechanics. A long-term project will be to pin down the minimal ingredients necessary for cortex activity.

2. Blebs as a probe of cortex mechanics
We have shown that laser ablation of the cell cortex with a UV pulsed laser leads to the formation of a bleb, a spherical membrane protrusion initially devoid of an actin cortex. After about 30 seconds, a cortex reassembles and the bleb retracts. Similar blebs are known to spontaneously form in cells during cytokinesis, migration and spreading. Bleb formation has been proposed to correlate with elevated levels of cortical tension. We have taken advantage of the laser ablation-induced blebs to thoroughly study the relation between blebbing and tension. We have shown that bleb size and growth dynamics are indeed governed by the tension of the actomyosin cortex and have proposed a theoretical model that accounts for our observations (collaboration with the group of J.-F. Joanny, Paris). Our findings support the view that bleb growth is driven by hydrostatic pressure of the cytoplasm against the cell membrane, and that this pressure is generated by the contractile cortex.

3. Cortex mechanics in cytokinesis and migration
We are also studying how the cortex mechanical properties are controlled during cell migration and division. We particularly focus on the role of blebs in these processes.