title: The nanoscale architecture of force-bearing focal adhesions.
abstract: The combination of micropillar array technology to measure cellular traction forces with super-resolution imaging allowed us to obtain cellular traction force maps and simultaneously zoom in on individual focal adhesions with single-molecule accuracy. We achieved a force detection precision of 500 pN simultaneously with a mean single-molecule localization precision of 30 nm. Key to the achievement was a two-step etching process that provided an integrated spacer next to the micropillar array that permitted stable and reproducible observation of cells on micropillars within the short working distance of a high-magnification, high numerical aperture objective. In turn, we used the technology to characterize the super-resolved structure of focal adhesions during force exertion. Live-cell imaging on MCF-7 cells demonstrated the applicability of the inverted configuration of the micropillar arrays to dynamics measurements. Forces emanated from a molecular base that was localized on top of the micropillars. What appeared as a single adhesion in conventional microscopy were in fact multiple elongated adhesions emanating from only a small fraction of the adhesion on the micropillar surface. Focal adhesions were elongated in the direction of local cellular force exertion with structural features of 100-280 nm in 3T3 Fibroblasts and MCF-7 cells. The combined measure of nanoscale architecture and force exerted shows a high level of stress accumulation at a single site of adhesion.
authors.affiliation: Physics of Life Processes, Kamerligh Onnes-Huygens Laboratory, Leiden University , Niels Bohrweg 2 , 2333 CA Leiden, The Netherlands.
authors.forename: Hedde
authors.initials: H
authors.lastname: van Hoorn
authors.forename: Rolf
authors.initials: R
authors.lastname: Harkes
authors.forename: Ewa M
authors.initials: EM
authors.lastname: Spiesz
authors.forename: Cornelis
authors.initials: C
authors.lastname: Storm
authors.forename: Danny
authors.initials: D
authors.lastname: van Noort
authors.forename: Benoit
authors.initials: B
authors.lastname: Ladoux
authors.forename: Thomas
authors.initials: T
authors.lastname: Schmidt