Buffering Global Variability of Morphogen Gradients.

Morphogen gradients determine tissue pattern by triggering differential cell responses to distinct morphogen concentrations. The strict quantitative dependence of the emerging patterns on morphogen distribution raises the challenge of buffering variability in morphogen profile to ensure a reproducible outcome. We describe the underlying principles of two modules for buffering morphogen distribution: buffering morphogen amplitude by storing excess morphogen in a limited spatial region, and buffering morphogen spread by pinning morphogen levels at a distal position through global feedback that adjusts morphogen diffusion or degradation across the tissue. We also present concrete examples of patterning systems that implement these modules.