title: Critical behavior of subcellular density organization during neutrophil activation and migration.
abstract: Physical theories of active matter continue to provide a quantitative understanding of dynamic cellular phenomena, including cell locomotion. Although various investigations of the rheology of cells have identified important viscoelastic and traction force parameters for use in these theoretical approaches, a key variable has remained elusive both in theoretical and experimental approaches: the spatiotemporal behavior of the subcellular density. The evolution of the subcellular density has been qualitatively observed for decades as it provides the source of image contrast in label-free imaging modalities (e.g., differential interference contrast, phase contrast) used to investigate cellular specimens. While these modalities directly visualize cell structure, they do not provide quantitative access to the structures being visualized. We present an established quantitative imaging approach, non-interferometric quantitative phase microscopy, to elucidate the subcellular density dynamics in neutrophils undergoing chemokinesis following uniform bacterial peptide stimulation. Through this approach, we identify a power law dependence of the neutrophil mean density on time with a critical point, suggesting a critical density is required for motility on 2D substrates. Next we elucidate a continuum law relating mean cell density, area, and total mass that is conserved during neutrophil polarization and migration. Together, our approach and quantitative findings will enable investigators to define the physics coupling cytoskeletal dynamics with subcellular density dynamics during cell migration.
authors.affiliation: Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97239.
authors.forename: Sandra M
authors.initials: SM
authors.lastname: Baker-Groberg
authors.affiliation: Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97239.
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Phillips
authors.affiliation: Department of Cell, Developmental & Cancer Biology, Oregon Health & Science University, Portland, OR 97239.
authors.forename: Laura D
authors.initials: LD
authors.lastname: Healy
authors.affiliation: Department of Cell, Developmental & Cancer Biology, Oregon Health & Science University, Portland, OR 97239.
authors.forename: Asako
authors.initials: A
authors.lastname: Itakura
authors.affiliation: Viterbi School of Engineering, Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089.
authors.forename: Juliana E
authors.initials: JE
authors.lastname: Porter
authors.affiliation: Viterbi School of Engineering, Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089 ; Department of Mathematics, University of Southern California, Los Angeles, CA 90089 ; Norris Comprehensive Cancer Center, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089.
authors.forename: Paul K
authors.initials: PK
authors.lastname: Newton
authors.affiliation: Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97239.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Nan
authors.affiliation: Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97239 ; Department of Cell, Developmental & Cancer Biology, Oregon Health & Science University, Portland, OR 97239 ; Division of Hematology and Medical Oncology, School of Medicine, Oregon Health & Science University, Portland, OR 97239.
authors.forename: Owen J T
authors.initials: OJ
authors.lastname: McCarty
keywords: Chemokinesis; active matter; motility; neutrophil; quantitative phase microscopy; rheology; subcellular density