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Cell Polarity Establishment
Turing mechanism in a round cell — spontaneous symmetry breaking concentrates the activator at one pole while the inhibitor spreads globally.
How it works: The Gierer-Meinhardt model uses an activator-inhibitor reaction-diffusion system. The activator (orange) auto-catalyzes its own production and triggers inhibitor synthesis. The inhibitor (blue) diffuses much faster, creating a "long-range inhibition, short-range activation" landscape. This instability drives spontaneous symmetry breaking — a uniform initial state spontaneously collapses into a polarized pattern where the activator concentrates at one pole. The key condition for polarity: DH/DA ≫ 1. This mirrors how Cdc42, PIP2, and other polarity markers concentrate at the leading edge of migrating cells.