Figure 5.

Fitting of ligands and receptors mutants distributions. (A) Plot of lag-2 mRNA counts in P3.p versus P3.a in egl-20; cwn-1; cwn-2 strain and illustration of how θ_lag-2 is calculated. (B) Histograms for θ_lag-2 (blue) and maximum likelihood fits (red) for mom-4; lit-1 strain grown at 25°C for 9 h. (C) Histograms for θ_lag-2 (blue) and maximum likelihood fits (red) for P3–P10 in egl-20; cwn-1; cwn-2 and mom-5; lin-17 strains. (D) Fit parameter, g and r_f obtained using maximum likelihood for triple-ligand mutant (egl-20; cwn-1; cwn-2 strain) (white) and receptor mutant (mom-5; lin-17 strain) (black). White dotted line shows the region of parameter space giving rise to above 99.9% correct divisions. Although the parameters of WT P cells cannot be determined exactly as many combinations of parameters can give rise to 100% correct polarity, the parameters of WT P cells must lie above the white dotted line. Hence, values of g obtained for both ligands and receptors mutants are lower than that of WT P cells. (E) Abstraction of parameters’ movement in phase space as a result of mutations. (i) Decreasing ligands in WT P cells leads to reduction of g and converts correct polarity into the coexistence of correct and reverse polarity observed in the triple-ligand mutant. (magneta) (ii) Decreasing receptors slightly will lead to reduction of r_f and cells that still polarize correctly if the parameters lie within the region of correct division (white dotted line). (iii) Decreasing ligands in strains with reduced r_f would lead to loss of polarity.