When Self-Generated Gradients interact with Expansion by Cell Division and Diffusion. Analysis of a Minimal Model

TL;DR

This paper analyzes a minimal mathematical model of cell propagation involving self-generated signaling gradients, cell division, and diffusion, providing existence, uniqueness, and wave speed analysis, including explicit formulas and wave dynamics insights.

Contribution

It offers a rigorous mathematical analysis of a coupled diffusion-advection-reaction system with discontinuous advection, including explicit wave speed formulas and wave behavior classification.

Findings

Explicit minimal wave speed formula derived

Dichotomy between pushed and pulled waves established

Propagation speed characterized relative to minimal wave speed

Abstract

We investigate a minimal model for cell propagation involving migration along self-generated signaling gradients and cell division, which has been proposed in an earlier study. The model consists in a system of two coupled parabolic diffusion-advection-reaction equations. Because of a discontinuous advection term, the Cauchy problem should be handled with care. We first establish existence and uniqueness locally in time through the reduction of the problem to the well-posedness of an ODE, under a monotonicity condition on the signaling gradient. Then, we carry out an asymptotic analysis of the system. All positive and bounded traveling waves of the system are computed and an explicit formula for the minimal wave speed is deduced. An analysis on the inside dynamics of the wave establishes a dichotomy between pushed and pulled waves depending on the strength of the advection. We identified the minimal wave speed as the biologically relevant speed, in a weak sense, that is, the solution propagates slower, respectively faster, than the minimal wave speed, up to time extraction. Finally, we extend the study to a hyperbolic two-velocity model with persistence.