Figure 4

Multivalent APC IDRs decrease the critical concentration of Axin1 for puncta formation. (A) Quantification of mCherry-Axin1 protein intensity in puncta positive cells as identified in Fig. 3B. Red bar indicates median. Blue bars indicate 25% and 75% percentiles. Cell number > 150 for each sample. Statistics was done with Kruskal–Wallis one-way analysis. All comparisons were made against the mEGFP control using Dunn’s multiple comparison test. ns, not significant; ***p < 0.001. (B–C) Models of the diffused or punctate β-catenin destruction complex in two cells expressing similar level of mCherry-Axin1 in the absence (B) or presence (C) of APC 20R2-7. In (B), the DIX domain of Axin1 may undergo reversible polymerization, however it is not able to form micrometer-sized puncta due to limited concentration and/or valency of scaffold proteins. In SW480 cells, the endogenous APC (not shown) is truncated, and could not scaffold the complex efficiently. In (C), multivalent APC 20R2-7 provides additional valency on top of the DIX polymerization, allows puncta to form at an Axin1 concentration that it normally wouldn’t form puncta (as shown in (B)). Note that the puncta or the biocondensate shown in (C) creates a separated compartment that has extremely high protein concentration while maintaining protein dynamics.