The assembly of ATP-actin monomers into filaments lies at the base of the formation of the actin cytoskeleton in cells (figure below, left). ATP hydrolysis that occurs during this process is accompanied by a major change of the conformation of actin subunits, thus of the filament itself, has profound consequences on the regulation of the kinetics of filament assembly.
In cells, actin assembly is regulated by hundreds of Actin Binding Proteins (ABPs), that may act together synergistically or antagonistically (right). Those ABPs can bind to filament sides, filament ends, and/or monomers and have a variety of effects. We typically distinguish them based on their main functions: nucleators, proteins that modulates elongations (favoring or blocking it), proteins that promotes filament disassembly or stabilize them, or proteins that link filaments between them, creating bundles or fibers.
While ABPs can modify the mechanical state of actin filaments, external mechanical factors may in turn also affect the activity of ABPs. We believe that this mechano-chemical interplay plays a crucial role in actin network assembly in cells.
To understand how all ABPs and the mechanical context generate networks of various geometries, dynamics and life-spans, our team focuses its effort to observe and manipulate in vitro single actin filaments or small reconstituted networks in well controlled conditions. Microfluidics has proven a very strong tool to both expose filaments to different proteins solutions sequentially and expose filaments to various mechanical constraints, opening new avenues to decipher the dynamics of actin network assembly.
On the right, a sketch represents a standard microfluidics chamber with 3 inlets positioned on top of a microscope objective. In this chamber, actin filaments are grown from surface-anchored seeds and align with the flow. Tens of fluorescently labeled actin filaments can be monitored in parallel while being exposed to various biochemical conditions affecting their dynamics.