Fig. 3

Effect of selected model processes on target gene mRNA expression along the porto-central axis. a: A constant total Wnt concentration for each cell (1 nM) and an exponential gradient of total APC concentration increasing 5-fold from PC (20 nM) to PP (100 nM) is assumed. b: The target gene mRNA expression profiles are shown for different model setups: A: The expression profile is shown if only the signalling module is considered (Wnt/Frz/LRP complex concentration is set to 1 nM, reaction rates k ₁₀ to k ₁₆ are set to 0; this setup is equivalent to the published signalling model [54]). This model setup is successively extended by consideration of B: the receptor module without Dkk feedback and diffusion, C: the receptor module with a weak Dkk feedback (k ₁₂=2·10⁻³ min ⁻¹) and no diffusion, D: the receptor module with a stronger Dkk feedback (k ₁₂=2·10⁻² min ⁻¹) and no diffusion, E: the receptor module with a stronger Dkk feedback k ₁₂=2·10⁻² min ⁻¹) and weak diffusion (D=10 \(\frac {\mu m^{2}}{s}\)), F: the receptor module with a stronger Dkk feedback k ₁₂=2·10⁻² min ⁻¹) and stronger diffusion (D=500 \(\frac {\mu m^{2}}{s}\)). c: The PC/PP target gene mRNA expression ratios for the model setups presented in (b) are compared