Microscopic origins of extensile versus contractile active stress in cytoskeletal motor-filament systems

Microscopic origins of extensile versus contractile active stress in cytoskeletal motor-filament systems

Microscopic origins of extensile versus contractile active stress in cytoskeletal motor-filament systems

Date

January 31, 2017 -
3:00pm to 4:00pm

Location

Klaus - Advanced Computing Building, Rm. 1116 West - 266 Ferst Dr NW, Atlanta, GA 30332

Affiliation

University of Colorado

Soft Condensed Matter & Physics of Living Systems Seminar: Prof. Meredith Betterton, University of Colorado.

The cytoskeleton, despite comprising relatively few building blocks, drives an impressive variety of cellular phenomena ranging from cell division to motility. These building blocks include filaments such as microtubules and actin, motor proteins such as kinesins and myosins, and static crosslinkers. Outside of cells, these same components can form novel materials exhibiting active flows and nonequilibrium contraction or extension.

Reconstituted actin-myosin mixtures typically contract, and microtubule-kinesin mixtures typically extend along the filament axis. A longstanding puzzle is the microscopic origin of active stresses in motor-filament mixtures and the mechanisms underlying the balance between contraction and extension.  Using a minimal physical model of filaments, crosslinking motors, and static crosslinkers we dissect the microscopic mechanisms of stress generation. 

We demonstrate the essential role of filament steric interactions and develop a unified picture of active forces in motor-filament systems. With this insight, we are able to tunecontractile or extensile behavior through control of motor-driven filament sliding and crosslinking. Our results help explain why flowing reconstituted motor-filament mixtures are extensile while gelled systems arecontractile. This work provides a roadmap for engineering stresses in cytoskeletal active matter and a framework for understanding the cellular cytoskeleton.