Berlin 2018 – scientific programme

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BP: Fachverband Biologische Physik

BP 33: Cytoskeletal Filaments II

BP 33.4: Invited Talk

Thursday, March 15, 2018, 15:45–16:15, H 1028

Dynamics and instabilities of contractile actin networks in artificial cells — •Kinneret Keren — Physics Department, Technion- Israel Institute of Technology, Haifa 32000, Israel

Contractile actin network have an essential role in many cellular processes including cell division, intracellular transport and cell motility. While the molecular components involved are largely known, we still do not understand what controls the large scale properties of these networks. We generate bulk actin networks by introducing cytoplasmic Xenopus egg extracts, which contain all the components of the actin machinery, into cell-sized water-in-oil droplets. Importantly, the presence of turnover in our system allows these networks to attain a dynamic steady state characterized by contractile actin flows which persist for hours. We find that under a broad range of conditions, the network undergoes homogenous contraction despite large spatial variations in network density, and that this contraction rate is inversely proportional to the actin disassembly rate. We observe either a symmetric state in which the network contracts towards the center of the droplets and exhibits a spherically symmetric density and flow pattern, or a polar state in which the contraction center is localized near the droplet's boundary. In the symmetric state, the contraction center is actively maintained near the middle of the droplet, reminiscent of actin-based centering mechanisms found in living cells. During symmetry breaking, the system transitions from this symmetric state to a polar state, mimicking cellular symmetry breaking as seen for example during motility initiation or spindle migration in mammalian oocytes.