Figure 3.

LIS width regulates autocrine signalling. a, Schematic of the epithelial LIS showing the boundary conditions regulating EGF family ligand diffusion, and example profiles of ligand concentration within the LIS. b, ERK phosphorylation elicited by compressive stress compared to 3.3-fold increasing concentrations of HB-EGF (mean ± s.e.m., n = 5). Concentrations of HB-EGF <0.33 ng ml⁻¹ had no effect on ERK phosphorylation. We thus assume that the baseline local concentration of EGF family ligands in the LIS is between 0.33 and 1.0 ng ml⁻¹. From equation (7) we predict that the result of compressive stress should be most comparable to the effect of adding exogenous HB-EGF to increase this concentration approximately tenfold, to between 3.3 and 10 ng ml⁻¹.