Non-linear signaling for pattern formation?

Developmental pathways are often simplified as linear cascades of gene activation caused by initial signaling events. Recent data, however, support a more complex view in which non-linear responses to signals are important for pattern formation. First, a positive feedback loop may regulate cellular patterning in the Arabidopsis epidermis. Second, an asymmetric auxin distribution that organizes pattern in the distal root tip may be established by positive feedback.