582 | Nature | Vol 582 | 25 June 2020
Article
Cellular locomotion using environmental
topography
Anne Reversat1,7 ✉, Florian Gaertner^1 , Jack Merrin^1 , Julian Stopp^1 , Saren Tasciyan^1 ,
Juan Aguilera^1 , Ingrid de Vries^1 , Robert Hauschild^1 , Miroslav Hons1,2,8, Matthieu Piel3,4,
Andrew Callan-Jones^5 , Raphael Voituriez^6 & Michael Sixt^1 ✉Eukaryotic cells migrate by coupling the intracellular force of the actin cytoskeleton
to the environment. While force coupling is usually mediated by transmembrane
adhesion receptors, especially those of the integrin family, amoeboid cells such as
leukocytes can migrate extremely fast despite very low adhesive forces^1. Here we show
that leukocytes cannot only migrate under low adhesion but can also transmit forces
in the complete absence of transmembrane force coupling. When confined within
three-dimensional environments, they use the topographical features of the substrate
to propel themselves. Here the retrograde flow of the actin cytoskeleton follows the
texture of the substrate, creating retrograde shear forces that are sufficient to drive
the cell body forwards. Notably, adhesion-dependent and adhesion-independent
migration are not mutually exclusive, but rather are variants of the same principle of
coupling retrograde actin flow to the environment and thus can potentially operate
interchangeably and simultaneously. As adhesion-free migration is independent of
the chemical composition of the environment, it renders cells completely
autonomous in their locomotive behaviour.Mechanistic understanding of cell motility started with Abercrom-
bie’s demonstration that particles placed on the dorsal surface of a cell
undergo retrograde transport^2. The authors concluded that cellular
material is added to the front of the cell, feeding a rearwards flow, which
couples to the substrate and thereby generates friction to drag the cell
body forwards. Later studies showed that the added material is the
growing polymer of F-actin and that F-actin retrograde flow couples
via transmembrane adhesion receptors, mainly of the integrin fam-
ily. Although this adhesion-dependent principle of motility turned
out to be universal on two-dimensional (2D) surfaces, some cells can
migrate in the absence of integrin-mediated adhesion when confined
within a three-dimensional (3D) context^3 ,^4. This applies especially to
the amoeboid (shape-changing) class of cells such as leukocytes^5.
Force transmission under these conditions is not understood, and
alternative membrane-spanning molecules that mediate specific or
even unspecific friction have been suggested^6 ,^7. Notably, in his seminal
study, Abercrombie contemplated a second, qualitatively different,
scenario: backward-moving waves of deformation might passively
entangle with the applied particles (or a substrate) and propel the cell
in a manner analogous to paddling and swimming^2.
To explore adhesion-independent locomotion, we initially inves-
tigated T lymphocytes. When these cells migrate within lymphatic
organs, integrin depletion causes them to slow down by only 15%, mean-
ing that they do employ integrins but retain a substantial capacity to
transmit forces via other means^8 ,^9. We used a mouse T cell line, which
migrates vigorously in 3D environments, such as in vitro-assembled
collagen gels (Supplementary Video 1). To eliminate integrin-based
force transmission, we deleted Tln1, which encodes talin 1, a cytosolic
adaptor protein essential for integrin functionality^10 (Extended Data
Fig. 1a–c). Talin-deficient (referred to here as ‘talin KO’) cells were
completely unable to adhere to and migrate on 2D surfaces (Fig. 1a,
b, Extended Data Fig. 1d, e). However, once incorporated into 3D col-
lagen gels, their migratory characteristics were indistinguishable from
wild-type cells (Fig. 1c, Extended Data Fig. 1f, Supplementary Video 1).
In the following, we engineered artificial environments to dissect the
geometrical transition between 2D surfaces and fibrillar environments,
while keeping the chemical composition of the substrate unchanged.
We first designed a microfluidic setup to confine leukocytes between
two parallel surfaces separated by an adjustable space^11 (‘2.5D’; Fig. 1d).
While this setup supported efficient migration of wild-type cells,
talin-KO cells were unable to translocate, although they showed mor-
phological polarization (Fig. 1d, Extended Data Fig. 1g, Supplementary
Video 2). When T cells expressing the actin reporter Lifeact-GFP were
imaged with total internal reflection fluorescence (TIRF) microscopy,
actin within the rapidly moving cell body remained static in relation to
the adhesive substrate and flowed backwards in the cell frame of refer-
ence (Fig. 1e–g, Supplementary Video 3). Talin-KO cells on adhesive
substrates or wild-type cells on passivated surfaces were immobile but
showed similar actin dynamics in the cell frame of reference^8 , mean-
ing that actin slid backwards in relation to the substrate (Fig. 1e–g,
Extended Data Figs. 1g–l, 2a–c, Supplementary Video 3). These findings
demonstrate that, when placed on 2D substrates or when confinedhttps://doi.org/10.1038/s41586-020-2283-z
Received: 13 January 2018
Accepted: 9 March 2020
Published online: 13 May 2020
Check for updates(^1) Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Austria. (^2) Institute of Scientific Instruments of the Czech Academy of Sciences, Brno, Czech Republic. (^3) Institut Curie,
PSL Research University, CNRS, UMR 144, Paris, France.^4 Institut Pierre-Gilles de Gennes, PSL Research University, Paris, France.^5 Laboratoire Matière et Systèmes Complexes, UMR 7057 CNRS,
Université Paris Diderot, Paris, France.^6 Laboratoire de Physique Theorique de la Matière Condensée et Laboratoire Jean Perrin, CNRS/Université Pierre-et-Marie Curie, Paris, France.^7 Present
address: Institute of Translational Medicine, Department of Cellular and Molecular Physiology, University of Liverpool, Liverpool, UK.^8 Present address: BIOCEV, First Faculty of Medicine,
Charles University, Vestec, Czech Republic. ✉e-mail: [email protected]; [email protected]