Cortactin releases the brakes in actin- based motility by enhancing WASP-VCA detachment from Arp2/3 branches

10.1016/j.cub.2011.11.010Current Biology21242092-2097CUBL

How distinct Arp2/3 complex variants regulate actin filament assembly.

The heptameric Arp2/3 complex generates branched actin filament networks that drive lamellipodium protrusion, vesicle trafficking and pathogen motility. Distinct variants of the Arp2/3 complex are now shown to have different roles in tuning actin assembly and disassembly, in concert with the prominent actin regulators cortactin and coronin

A new method to measure mechanics and dynamic assembly of branched actin networks

We measured mechanical properties and dynamic assembly of actin networks with a new method based on magnetic microscopic cylinders. Dense actin networks are grown from the cylinders' surfaces using the biochemical Arp2/3-machinery at play in the lamellipodium extension and other force-generating processes in the cell. Under a homogenous magnetic field the magnetic cylinders self-assemble into chains in which forces are attractive and depend on the intensity of the magnetic field. We show that these forces, from piconewtons to nanonewtons, are large enough to slow down the assembly of dense actin networks and controlled enough to access to their non linear mechanical responses. Deformations are measured with nanometer-resolution, well below the optical resolution. Self-assembly of the magnetic particles into chains simplifies experiments and allows for parallel measurements. The combination of accuracy and good throughput of measurements results in a method with high potential for cell and cytoskeleton mechanics. Using this method, we observed in particular a strong non linear mechanical behavior of dense branched actin networks at low forces that has not been reported previously

Co-assembly, spatiotemporal control and morphogenesis of a hybrid protein-peptide system

Controlling molecular interactions between bioinspired molecules can enable the development of new materials with higher complexity and innovative properties. Here we report on a dynamic system that emerges from the conformational modification of an elastin-like protein by peptide amphiphiles and with the capacity to access, and be maintained in, non-equilibrium for substantial periods of time. The system enables the formation of a robust membrane that displays controlled assembly and disassembly capabilities, adhesion and sealing to surfaces, self-healing and the capability to undergo morphogenesis into tubular structures with high spatiotemporal control. We use advanced microscopy along with turbidity and spectroscopic measurements to investigate the mechanism of assembly and its relation to the distinctive membrane architecture and the resulting dynamic properties. Using cell-culture experiments with endothelial and adipose-derived stem cells, we demonstrate the potential of this system to generate complex bioactive scaffolds for applications such as tissue engineering.The work was supported by the European Research Council Starting Grant (STROFUNSCAFF), the European Commission under FP7 and H2020 programs ((NMP3- LA-2011-263363, HEALTH-F4-2011-278557, PITN-GA-2012-317304, MSCA-ITN-2014- ETN- 642687, 642687 H2020-NMP-2014-646075), the Ministry of Economy and Competitiveness (Spain) (MAT2012-38043-C02-01, MAT2013-41723-R, MAT2013- 42473-R) the Junta de Castilla y Leon (VA244U13, VA313U14) and the Portuguese Foundation for Science and Technology, grants PTDC/EBB-BIO/114523/2009 and SFRH/ BD/44977/2008. Additional support was obtained from the Bilateral Program Portugal– Spain Integrated Actions 2011 (E-50/11) and Marie Curie Career Integration Grant 618335. The authors thank the European Synchrotron Research Facility for access to synchrotron beamline BM29 and P. Pernot for support during the experiments, and C. López (Centres Científics i Tecnològics University of Barcelona), C. Semino (Institut Químic de Sarrià), E. Rebollo (Advanced Fluorescence Microscopy Unit in the Molecular Biology Institute of Barcelona), J. P. Aguilar, R. Doodkorte, A. Amzour and the technical staff of the Material Characterization Laboratory and Nanovision Laboratory at the Queen Mary University of London for the constructive discussions and contributions in this study