Cells in interaction with their environment: The spotlight of momentum fluxes on collective and individual cell motion

I will first introduce a piece of work I did on the locomotive force & angular momentum fluxes in cell aggregates. I will in a second time present a model for the physical role of the nucleus in eukaryotic cell migration. Finally, I will present my research projects at the RDP lab (ENS-Lyon) on the incidence of cell variability on plant growth.

Dictyostelium Discoideum forms a multi-cellular 3D aggregate when starved. This aggregate, coordinated by the interior chemical waves of cAMP, migrates like a slime in which the individual cells undergo active “cortical flow”. It was already known that, paradoxically, the migrating aggregate can exert a “bulk” force whose magnitude increases with its volume rather than with its contact area with surrounding objects.

To understand the origin of such a force, we formulated a general mechanical description in terms of the momentum flux and angular momentum flux, where the fluxes are described by the force and torque at the cell-cell interfaces of arbitrary shape and interaction [1] . Applied to the steady motion of the aggregate, the theory explains how the cortical flow of the bulk cells gives rise to the force of migration through the coupling between the linear momentum and angular momentum fluxes. Our model also describes the data of migrating velocity under external force hitherto unexplained [2].

The role of the nucleus has been largely neglected, partly due to the famous experiments of keratocyte cell fragments crawling without a nucleus [3]. Recently however the nucleus has been shown to play an important role in cell motility, especially in three dimensional environments [4,5]. The nucleus is connected to the cell cytoskeleton which is known to play a key role in cell migration. Cytoskeleton elements interact with the external environment, for example through specific adhesion. Therefore, the nucleus is in contact with the external environment via the cytoskeleton.

We proposed a simplistic description of cell motility using an active gel model for the cytoskeleton, and we have been able to investigate the role played by the coupling of the cytoskeleton with the nucleus and the external milieu on cell motion and cell polarization.

I joined the RDP lab (ENS-Lyon) to work on organ size and shape regulation during the morphogenesis of plants. More precisely, I will focus on the possible role played by cellular mechanical retroactions in the regulation of cell variability, and on the interplay between different sorts of variability at different scales.

[1] Fruleux, Antoine, and Ken Sekimoto. "Mesoscopic formulas of linear and angular momentum fluxes." Physical Review E 94.1 (2016): 013004.
[2] Fruleux, Antoine, and Ken Sekimoto. In preparation.
[3] Verkhovsky, Alexander B., Tatyana M. Svitkina, and Gary G. Borisy. "Self-polarization and directional motility of cytoplasm." Current Biology 9.1 (1999): 11-S1.
[4] Khatau, Shyam B., et al. "The distinct roles of the nucleus and nucleus-cytoskeleton connections in three-dimensional cell migration." Scientific reports 2 (2012): 488.
[5] Fruleux, Antoine, and Rhoda J. Hawkins. "Physical role for the nucleus in cell migration." Journal of Physics: Condensed Matter 28.36 (2016): 363002.