title: Contractile dynamics change before morphological cues during fluorescence [corrected] illumination.
abstract: Illumination can have adverse effects on live cells. However, many experiments, e.g. traction force microscopy, rely on fluorescence microscopy. Current methods to assess undesired photo-induced cell changes rely on qualitative observation of changes in cell morphology. Here we utilize a quantitative technique to identify the effect of light on cell contractility prior to morphological changes. Fibroblasts were cultured on soft elastic hydrogels embedded with fluorescent beads. The adherent cells generated contractile forces that deform the substrate. Beads were used as fiducial markers to quantify the substrate deformation over time, which serves as a measure of cell force dynamics. We find that cells exposed to moderate fluorescence illumination (λ = 540-585 nm, I = 12.5 W/m(2), duration = 60 s) exhibit rapid force relaxation. Strikingly, cells exhibit force relaxation after only 2 s of exposure, suggesting that photo-induced relaxation occurs nearly immediately. Evidence of photo-induced morphological changes were not observed for 15-30 min after illumination. Force relaxation and morphological changes were found to depend on wavelength and intensity of excitation light. This study demonstrates that changes in cell contractility reveal evidence of a photo-induced cell response long before any morphological cues.
authors.affiliation: Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Knoll
authors.affiliation: Laboratoire Physico Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, 75005, Paris, France.|Sorbonne Universités, UPMC Univ Paris 06, 75005, Paris, France.
authors.forename: W W
authors.initials: WW
authors.lastname: Ahmed
authors.affiliation: Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Saif
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000528:radiation effects; D002460:Cell Line; D048430:Cell Shape / Q000528:radiation effects*; D005347:Fibroblasts / Q000166:cytology* / Q000528:radiation effects*; D005453:Fluorescence; D000882:Haplorhini; D008027:Light; D011336:Probability