title: Probing the stochastic, motor-driven properties of the cytoplasm using force spectrum microscopy.
abstract: Molecular motors in cells typically produce highly directed motion; however, the aggregate, incoherent effect of all active processes also creates randomly fluctuating forces, which drive diffusive-like, nonthermal motion. Here, we introduce force-spectrum-microscopy (FSM) to directly quantify random forces within the cytoplasm of cells and thereby probe stochastic motor activity. This technique combines measurements of the random motion of probe particles with independent micromechanical measurements of the cytoplasm to quantify the spectrum of force fluctuations. Using FSM, we show that force fluctuations substantially enhance intracellular movement of small and large components. The fluctuations are three times larger in malignant cells than in their benign counterparts. We further demonstrate that vimentin acts globally to anchor organelles against randomly fluctuating forces in the cytoplasm, with no effect on their magnitude. Thus, FSM has broad applications for understanding the cytoplasm and its intracellular processes in relation to cell physiology in healthy and diseased states.
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Guo
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA; Beth Israel Deaconess Medical Center, Boston, MA 02115, USA.
authors.forename: Allen J
authors.initials: AJ
authors.lastname: Ehrlicher
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA; Department of Physiology and Biophysics, Boston University, Boston, MA 02118, USA.
authors.forename: Mikkel H
authors.initials: MH
authors.lastname: Jensen
authors.affiliation: Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Malte
authors.initials: M
authors.lastname: Renz
authors.affiliation: Department of Physiology and Biophysics, Boston University, Boston, MA 02118, USA.
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Moore
authors.affiliation: Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Goldman
authors.affiliation: Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Lippincott-Schwartz
authors.affiliation: Department of Physics and Astronomy, VU University, 1081 HV Amsterdam, The Netherlands.
authors.forename: Frederick C
authors.initials: FC
authors.lastname: Mackintosh
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA; Department of Physics, Harvard University, Cambridge, MA 02138, USA. Electronic address: weitz@seas.harvard.edu.
authors.forename: David A
authors.initials: DA
authors.lastname: Weitz
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D003593:Cytoplasm / Q000737:chemistry*; D004622:Embryo, Mammalian / Q000166:cytology; D005347:Fibroblasts / Q000737:chemistry; D051379:Mice; D018625:Microscopy, Atomic Force / Q000379:methods*; D011506:Proteins / Q000737:chemistry; D014746:Vimentin / Q000737:chemistry
chemical_list: D011506:Proteins; D014746:Vimentin