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Physics Colloquium - Friday, Nov. 21th, 2008, 4:00 P.M.

E300 Math/Science Center; Refreshments at 3:30 P.M. in Room E200

Jennifer Curtis - School of Physics, Georgia Institute of Technology

At the Invisible Rim: Polymer physics of the cell coat

Hyaluronan is a cell surface-associated polysaccharide that is a vital component in the pericellular coat, a polymer matrix attached directly to the membrane of many mammalian cells. Synthesized and extruded through the plasma membrane, hyaluronan acts as a multivalent template for interactions with a multitude of different proteins which can anchor the polymer to the cell membrane, stiffen it and/or crosslink it into a gelled meshwork. Often microns in length, the combination of hyaluronan's size and its remarkable hydrodynamic properties help regulate the porosity and malleability of the polymer matrices it forms. Cell adhesion-dependent processes including cell proliferation, migration, and cancer metastasis are highly correlated with dramatic changes in the appearance of the pericellular coat, which tends to become larger, and asymmetric, in the case of migrating cells. Despite these observations and speculations about its mechanical importance, little work has been done to characterize the structure of the pericellular coat or its viscoelastic properties in any context. We apply a suite of techniques to unravel details of pericellular coat structure and mechanics on living rat chondrocytes. Passive microrheology shows a linear increase in the stiffness of the pericellular coat towards the cell surface, while optical tweezer studies reveal viscoelastic tethers can be pulled from the coat. Correlating these results with quantitative fluorescent measurements, we characterize the possible microstructure of this crucial but neglected biopolymer network. Ultimately, these techniques will determine how cell coat transformations are correlated with biological activities, and reveal if, and how, the cell utilizes polymer physics to modulate cell adhesion-dependent activities.