An asymmetry between pushing and pulling for crawling cells

TL;DR

This paper models the asymmetry between pushing and pulling in crawling cells, revealing distinct force-velocity behaviors and the potential for cells to switch between these mechanisms based on external forces.

Contribution

It introduces a 1D active gel model demonstrating how pushing and pulling mechanisms differ and can adapt, highlighting the switchability of cellular motility strategies.

Findings

Pushing is controlled by protrusion, leading to concave force-velocity relations.

Pulling involves both protrusion and contraction, showing convex-concave force-velocity relations.

Cells can switch between pushing and pulling mechanisms depending on external forces.

Abstract

Eukaryotic cells possess motility mechanisms allowing them not only to self-propel but also to exert forces on obstacles (to push) and to carry cargoes (to pull). To study the inherent asymmetry between active pushing and pulling we model a crawling acto-myosin cell extract as a 1D layer of active gel subjected to external forces. We show that pushing is controlled by protrusion and that the macroscopic signature of the protrusion dominated motility mechanism is concavity of the force velocity relation. Instead, pulling is driven by protrusion only at small values of the pulling force and it is replaced by contraction when the pulling force is sufficiently large. This leads to more complex convex-concave structure of the force velocity relation, in particular, competition between protrusion and contraction can produce negative mobility in a biologically relevant range. The model illustrates active readjustment of the force generating machinery in response to changes in the dipole structure of external forces. The possibility of switching between complementary active mechanisms implies that if necessary 'pushers' can replace 'pullers' and visa versa.