We have set up experiments in yeast to investigate how cells evolve to recover from mutations in the polarity network. Our assays consists of growth rate experiments as well as live cell microscopy experiments, where we can observe the dynamics of the different polarity proteins involved. With these experiments we have tested a mathematical model that we developed in collaboration with a theory group (Braun et al, in press Nature Comms). Our model, verified by our experiments, suggests how subsequent mutants in a previously established evolutionary trajectory can restore fitness in the polarity network. Based on these findings we realized that it may not be fair to take a modular approach but rather that evolvability may be more of a collective property of the whole cell rather than of specific modules (Glazenburg and Laan, JCS, 2023). We built computer models to test this idea (Nghe et al, Annu Rev 2020, Daalman et al, Phil Trans B 2023, Zwicker et al PNAS, 2022) and performed genome wide experiments, that showed that various redundant pathways indeed collectively respond to buffer change during evolution (Kingma et al Biorxiv 2023).
In parallel we built artificial (synthetic) systems to look for network structures or rather collective behavior by a purified a set or polarity proteins. As a first step we tested their activity (that these proteins work) in bulk assays (Tschripke et al Biorxiv 2022). Subsequently we needed proteins that can interact with lipids, as they do during polarity establishment, and therefore we developed a new method to add a hydrophobic tail to one of the proteins. After we obtained all our building blocks we studies how these proteins regulate Cdc42. To our surprise we found strong synergy between the regulatory proteins showing that even within a network of three proteins, collective behavior occurs (Tschirpke, Daalman and Laan, Biorxiv 2023).
