Velocity Fields in a Collectively Migrating Epithelium

Abstract

We report quantitative measurements of the velocity field of collectively migrating cells in a motile epithelium. The migration is triggered by presenting free surface to an initially confluent monolayer by using a microstencil technique that does not damage the cells. To avoid the technical difficulties inherent in the tracking of single cells, the field is mapped using the technique of particle image velocimetry. The main relevant parameters, such as the velocity module, the order parameter, and the velocity correlation function, are then extracted from this cartography. These quantities are dynamically measured on two types of cells (collectively migrating Madin-Darby canine kidney (MDCK) cells and fibroblastlike normal rat kidney (NRK) cells), first as they approach confluence, and then when the geometrical constraints are released. In particular, for MDCK cells filling up the patterns, we observe a sharp decrease in the average velocity after the point of confluence, whereas the densification of the monolayer is much more regular. After the peeling off of the stencil, a velocity correlation length of approximately 200 microm is measured for MDCK cells versus only approximately 40 microm for the more independent NRK cells. Our conclusions are supported by parallel single-cell tracking experiments. By using the biorthogonal decomposition of the velocity field, we conclude that the velocity field of MDCK cells is very coherent in contrast with the NRK cells. The displacements in the fingers arising from the border of MDCK epithelia are very oriented along their main direction. They influence the velocity field in the epithelium over a distance of approximately 200 microm.

Emergence of collective modes and tri-dimensional structures from epithelial confinement

“…Image processing was performed with custom Matlab (Mathworks) routines. In particular, the velocity field was mapped by particle image velocimetry 22 . PIV parameters were chosen as follows: subwindows size ¼ 12 mm; overlap ¼ 75%.…”

“…2a). Typically 30 h after confluence, the displacements within the monolayer reached a very low value (UE3 mm h À 1 ) and were very local 22 ( Supplementary Movies 1 and 2). However, compared with large monolayers studied in the same conditions, the confinement induced low-frequency velocity fluctuations that superimposed to the average decrease in speed (Fig.…”

Spatio-temporal morphology changes in and quenching effects on the 2D spreading dynamics of cell colonies in both plain and methylcellulose-containing culture media

“…Cell motility was also studied by particle image velocimetry [39] using PIVlab 1.35 software [40] of MATLAB (The MathWorks, Natick, MA). Image sequences recorded for 255 min with Δt´= 15 min were filtered and analyzed with an interrogation window of 82 × 82 pixels with 50% overlap.…”

Active jamming: Self-propelled soft particles at high density

“…In the zero-temperature limit, soft repulsive disks undergo a jamming transition to mechanically stable state at φ = 0.842 in two dimensions [17]. The elastic properties of the jammed state are determined by an excess number of low frequency modes [18] which are also closely linked to the large-scale rearrangements that microscopic packings undergo when strained [19] or thermalized [20].Recent in vitro experiments on confluent monolayers of migratory epithelial and endothelial cells have revealed displacement fields and stress distributions that strongly resemble both dynamical heterogeneities of glasses and the soft modes of jammed packings [1][2][3][4][5], and an analogy between the dynamics of these living systems and that of glassy materials has been proposed [1]. Migratory cells have been successfully modeled with soft polar particles at low densities [21] as well as through a mechanical agent model at high densities [22].…”

“…What are the mechanical properties of the ensuing materials? The answers to these questions are fundamentally important for a wide range of physical and biological systems, from tissue formation [1][2][3][4][5] and vibrated granular materials [6,7] to the behavior of packed crowds [8].…”