Wave-pinning model: active Cdc42 self-amplification with cytoplasmic depletion
Cell polarity is established by Turing-like wave-pinning of Rho GTPases (here: Cdc42). Active membrane-bound Cdc42 (u) activates itself and recruits inactive cytoplasmic Cdc42 (v), which diffuses much faster. This differential diffusion creates a single stable "pole" — the cell's front — essential for directed migration and yeast budding.