Oxygen driven spreading and microphase separation of eukaryotic cells

J.-P. Rieu^1,*, A. Carrère¹, N. Ghazi¹, C. Anjard¹, F. Detchevery¹, O. Cochet-Escartin¹, S. Hirose³,K. Funamoto³, M. Demircigil², S. V. Calvez²

1-Institut Lumière Matière and 2- Institut Camille Jordan, Université Claude Bernard Lyon 1, Villeurbanne, France. 3- Institute of Fluid Science, Tohoku University, Sendai, Japan

Cells exhibit multiple responses to environmental stresses. A state of low oxygen (O₂) occurs frequently in soil, water and multicellular tissues and has played a pivotal evolutionary role in shaping multicellularity. We study the mechanisms of a novel behavior in the amoeba Dictyostelium discoideum (Dd) in which cells collectively regulate their motility and adhesion in response to self-generated hypoxia. 

Vertically confining a micro-colony of Dd cells in a growth medium with a coverglass triggers the propagation of a ring cells for days (Fig. C, [1]). Cells consume O2 and try to escape by aerotaxis the hypoxic zone. Below a millimetric culture medium film, Dd cells proliferate until some critical density. Then they assemble in compact domains, of about 100µm, surrounded by a dense cellular gas phase. Domains stay mobile and stable in size during several days. Their size is regulated by the O₂ atmospheric level above the dish or the medium height (Fig. A-B, [2]). 

These observations as well as microfluidic experiments with imposed O2 gradients highlight the importance of oxygen regulation and self-generated gradients as an emergent organizing principle for biological matter. The variety of cell behaviors are modeled using both mean field PDE models and Monte-Carlo Lattice models with a few measurable parameters: cell division rate, motility (diffusion constant), aerotactic speed, oxygen modulated cell-cell adhesion and consumption [1]. In particular, the new dynamical microphase separation of Dd results from a balance between a long-range repulsion, trough self-generated O₂ gradients due to O₂ consumption, and a short-range attraction due to cell-cell adhesion.

Figure: (A) Dd aggregates under a culture medium layer of varying height, with the height profile from the dish wall (left) drawn above. (B) Zoom on one aggregate surrounded by a cellular gas phase (arrows point to the first layer of cell flattened on the surface). (C) Spreading of a Dd covered spot of cells with a ring formation moving outwardly toward free O2.

[1] O. Cochet-Escartin et al, elife 2021 10:e64731

[2] A. Carrère, et al. Microphase separation of living cells. bioRxiv (2022)