A novel stochastic simulation approach enables exploration of mechanisms for regulating polarity site movement
Fig 5
Direct recruitment of polarity factors to the patch enables highly mobile clusters.
(A) Snapshots of the distribution of total active Cdc42 over a 1hr simulation. The black dot in each frame is the centroid of the polarity cluster, and the green dot is the centroid when the polarity cluster first formed. (B) Diffusivity of the centroid of the polarity patch (Dpatch) as a function of the total amount of GEF molecules in the simulations. Dpatch was obtained from the mean squared displacement (MSD) of the patch centroid by fitting the equation MSD(Δti) = 4Dpatch Δtiβ to the data, where Δti is a particular time interval, and β reflects the degree of anomalous diffusion. (C) Patch diffusivities as a function of total GEF for simulations where k2b has been decreased by a factor of 1/16 and k5a has been increased by a factor of 10 relative to the parameters in Table 1. For these simulations β ≈ 1. (D) Snapshots from a representative simulation in (C) as indicated by the red arrow. (E) Patch diffusivities as a function of total GEF for simulations where k6 has been increased to either 1 μm2/s or 50 μm2/s. With k6 = 1 μm2/s polarization is lost when the number of GEFs is below 200. With k6 = 50 μm2/s the simulations show polarization at even lower GEF amounts, in this case, β varied between 0.85 and 1. (F) Snapshots from a representative simulation in (E) as indicated by the red arrow. (G) Patch diffusivities as a function of total GEF after adding Reaction 7 to the model. β values were ≈ 0.85 for the two data points with highest mobilities, and close to 1 for the other points. (H) Snapshots from a representative simulation in (G) as indicated by the red arrow. Error bars for patch centroid diffusivities are standard errors from the least-squares fit use to compute Dpatch.