Fig. 9.

Fig. 9.

Initial condition of simulated FRAP experiment in the ECS geometry and the shell geometry. (A) ECS geometry and (B) shell geometry. The lower half of the ECS is uniformly initialized with [Fgf8a]=0.001 (arbitrary unit), and the upper half (above 500 μm above the margin) with [Fgf8a]=0. To estimate the diffusive hindrance of ECS tortuosity alone, we simulate diffusion without reactions, measuring the total mass recovery in the bleached half. Fitting the recovery curve of the shell geometry to the curve of the ECS geometry, we find the ratio between the local and effective diffusion coefficient, i.e. the tortuosity factor τ_d=2.5. Scale bar: 50 μm.