Mechanical convergence in mixed populations of mammalian epithelial cells

Abstract Tissues consist of cells with different molecular and/or mechanical properties. Measuring the forces and stresses in mixed-cell populations is essential for understanding the mechanisms by which tissue development, homeostasis, and disease emerge from the cooperation of distinct cell types. However, many previous studies have primarily focused their mechanical measurements on dissociated cells or aggregates of a single-cell type, leaving the mechanics of mixed-cell populations largely unexplored. In the present study, we aimed to elucidate the influence of interactions between different cell types on cell mechanics by conducting in situ mechanical measurements on a monolayer of mammalian epithelial cells. Our findings revealed that while individual cell types displayed varying magnitudes of traction and intercellular stress before mixing, these mechanical values shifted in the mixed monolayer, becoming nearly indistinguishable between the cell types. Moreover, by analyzing a mixed-phase model of active tissues, we identified physical conditions under which such mechanical convergence is induced. Overall, the present study underscores the importance of in situ mechanical measurements in mixed-cell populations to deepen our understanding of the mechanics of multicellular systems. Graphical abstract Supplementary Information The online version contains supplementary material available at 10.1140/epje/s10189-024-00415-w.


Figures
Figure A1 We varied the size of the ROIs to assess potential size and positional dependencies in the measured mechanical quantities.Given that the patterns employed have a typical length R (either the radius of the circles or the side length of the square fields of view), we performed the quantification of traction, isotropic stress, and deviatoric stress in areas that have typical lengths of 0.95R and 2 3 R.In both cases, the results closely resemble those obtained in the whole domains (compare Fig. A1 with Fig. 2 and Fig. 4).

Figure A2
We tracked the traction and intercellular stress over time in regions proximal to the cells producing calcium sparks in Fig. 3. Here, we verified that the size of the area of calculation had no significant e↵ect on the evolution of the mechanical quantities surrounding calcium spark events.

Appendix B Supplementary Table
Table A1 List of parameters and their physical dimensions.

Appendix C Supplementary Videos
Video A1 Table A1: List of parameters and their physical dimensions.Names, values used in simulations, and dimensions are listed for each parameter.The mathematical model is two-dimensional and the integrand in Eq. 1 represents the energy density per area with the physical unit Pa m.In the simulations, time and length units are set as 10 min and 10 µm, respectively.See Materials and Methods for the rationale of the parameter choice.
Video A3 Numerical simulation of binary cell mixture shown in Fig. 7a.The phase field (color scale) and velocity field (blue arrows) at the indicated simulation time.Orange and yellow indicate regions occupied by cells A ( = 1) and cells B ( = 1), respectively.Parameter values are described in the legend of Fig. 7. Video A4 Numerical simulation of binary cell mixture shown in Fig. 7b.The phase field (color scale) and velocity field (blue arrows) at the indicated simulation time.Orange and yellow indicate regions occupied by cells A ( = 1) and cells B ( = 1), respectively.Parameter values are described in the legend of Fig. 7. Video A5 Numerical simulation of binary cell mixture shown in Fig. 7c.The phase field (color scale) and velocity field (blue arrows) at the indicated simulation time.Orange and yellow indicate regions occupied by cells A ( = 1) and cells B ( = 1), respectively.Parameter values are described in the legend of Fig.
Fig. A1: Quantification, in areas of typical length 0.95R and 2 3 R, of traction, isotropic stress, and deviatoric stress.(a, b) Magnitude of the tractions, in areas of typical length 0.95R, exerted by the cells in a function of time depending on the experiment types in MDCK cells (n = 3 for each plot) (a) and in MDCK-II cells (WT: n = 8, E-cad KO: n = 6, and WT+ E-cad KO: n = 8) (b).In (a), 0 hour corresponds to 6 h after the induction of RasV12 expression.WT represents the co-culture of GCaMP WT and non-tagged WT MDCK cells (light green), WT+RasV12 represents the co-culture of GCaMP WT and Myc-tagged RasV12-induced MDCK cells (blue), and RasV12 represents the co-culture of CMFDA-stained RasV12-induced and unstained RasV12 MDCK cells (red).In (b), 0 hour corresponds to 24 h after the cell seeding.WT represents the WT MDCK-II cells in single-cell colonies (light green), E-cad KO represents the E-cad KO MDCK-II cells in single-cell colonies (purple), and WT+E-cad KO represents the co-culture of WT and E-cad KO MDCK-II cells (red).(c, d) Isotropic stress, in areas of typical length 0.95R, in a function of time depending on the experiment type in MDCK cells (c) or MDCK-II cells (d), as shown respectively in (a) and (b).(e, f) Magnitude of deviatoric stress, in areas of typical length 0.95R, in a function of time depending on the experiment type in MDCK cells (e) or MDCK-II cells (f), as shown respectively in (a) and (b).(g, h) Magnitude of the tractions, in areas of typical length 2 3 R, exerted by the cells in a function of time depending on the experiment types in MDCK cells (f) or MDCK-II cells (g), as shown respectively in (a) and (b).Data is presented as the mean ± s.d.