College of Science

Seminar: Bekele Gurmessa [University of San Diego]

Microscale Stress Response and Molecular Deformations in Actin Networks

Jan 16, 2018 11:00 AM to Jan 16, 2018 12:00 PM at 8-241

Actin, the most abundant protein in eukaryotic cells, is a semi-flexible biopolymer in the cytoskeleton that plays crucial structural and mechanical roles in cell stability, motion, replication, and muscle contraction. Most of these mechanically driven structural changes in cells stem from the de/polymerization of actin filaments, which are driven by ATP hydrolysis, and vary depending on the concentrations of actin monomers and crosslinking proteins. In this presentation, I will talk about our recent experimental observations on the response of (1) steady-state, sterically entangled and cross-linked actin networks and (2) non-equilibrium network during a dynamic disassembly/reassembly to localized microscale mechanical perturbations by using optical trapping - coupled with fluorescence microscopy. In the former, we actively drive a microsphere 10 micrometer through entangled/cross-linked actin networks at a constant speed and measure the resistive force that the deformed actin filaments exert on the bead during and following strain by varying the concentrations of actin filaments and cross- linkers while simultaneously capturing the video of the network. From the captured videos, we track fluorescently labeled actin segments in order to map the propagation of the initially localized perturbation field throughout the rest of the network. In the later, we couple time- resolved active microrheology with a recently developed microfluidic platform to measure the time trajectories of local viscoelastic moduli of entangled and crosslinked actin networks during dynamic disassembly and subsequent reassembly. Specifically, we chemically trigger actin de/re-polymerization while simultaneously measuring the force induced in the network by microscale oscillations of an optically trapped microsphere over the time course of dis/re- assembly. These results are essential to understanding how cells can dynamically alter their mechanical properties to enable key processes; and shed light onto the underlying principles of other dynamic, self-assembling systems and materials.

10:50 am Refreshments

11:00 Seminar

Building 8, Room 241