ABSTRACT
The developmental transcription networks of well-studied organisms such as fruit flies, worms, sea urchins and humans are composed of several strong network motifs. In developmental networks, the regulation signs of the two interactions usually lead to positive feedback loops. There are two types of positive feedback loops: double-positive in which the two transcription factors activate each other, and double-negative in which the two transcription factors repress each other. In the hybrid negative feedback loop, one interaction, transcription, is slow and the other is fast. Engineers routinely use feedback in which a slow component is regulated by a fast one. The principal use of the type of feedback is to stabilize a system around a desired set point. Both coherent feedforward loops (FFLs) and positive feedback loops can provide delays and memory. FFLs provide transient memory and positive feedback can provide long-term memory.
