Embryonic development involves diffusion and proliferation of cells, as well as diffusionand reaction of molecules, within growing tissues. Mathematical models of these processes often involve reaction-diffusion equations on growing domains that have been primarily studied using approximate numerical solutions. Recently, we have shown how to obtain an exact solution to a single, uncoupled, linear reaction-diffusion equation on a growing domain, 0 < x < L(t), where L(t) is the domain length. The present work is an extension of our previous study, and we illustrate how to solve a system of coupled reaction-diffusion equations on a growing domain. This system of equations can be used to study the spatial and temporal distributions of different generations of cells within a population that diffuses and proliferates within a growing tissue. The exact solution is obtained by applying an uncoupling transformation, and the uncoupled equations are solved separately before applying the inverse uncoupling transformation to give the coupled solution. We present several example calculations to illustrate different types of behaviour. The first example calculation corresponds to a situation where the initially-confined population diffuses sufficiently slowly that it is PLOS 1/36 unable to reach the moving boundary at x = L(t). In contrast, the second example calculation corresponds to a situation where the initially-confined population is able to overcome the domain growth and reach the moving boundary at x = L(t). In its basic format, the uncoupling transformation at first appears to be restricted to deal only with the case where each generation of cells has a distinct proliferation rate.However, we also demonstrate how the uncoupling transformation can be used when each generation has the same proliferation rate by evaluating the exact solutions as an appropriate limit. PLOS 2/36 1 Several processes during embryonic development are associated with the migration 2 and proliferation of cells within growing tissues. A canonical example of such a process 3 is the development of the enteric nervous system (ENS) [1-5]. This involves a 4 population of precursor cells that is initially confined towards the oral end of the 5 developing gut tissue. Cells within the population undergo individual migration and 6 proliferation events, leading to a population-level front of cells that moves toward the 7 anal end of the gut [6]. The spatial distribution of the population of cells is also 8 affected by the growth of the underlying gut tissue [7, 8]. Normal development of the 9 ENS requires that the moving front reaches the anal end of the developing tissue. 10 Conversely, abnormal ENS development is thought to be associated with situations 11where the front of cells fails to reach the anal end of the tissue [6,7].
12Previous mathematical models of ENS development involve reaction-diffusion 13 equations on a growing domain [6,9]. These partial differential equation models have 14 been solved numerically, and the numerical solutions used to i...