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. Author manuscript; available in PMC: 2010 Dec 11.
Published in final edited form as: Mol Cell. 2009 Dec 11;36(5):894–899. doi: 10.1016/j.molcel.2009.11.018

Figure 2. The incoherent feedforward loop can provide fold-change detection.

Figure 2

(A) In a simple gene regulation, two inputs with different absolute levels but identical fold-changes give two different profiles of Z transcription.

(B) In a properly designed I1-FFL (see text), two inputs with different absolute levels but identical fold-changes give two identical profiles of Z transcription (dashed and full lines overlap).

(C-D) The amplitude and duration of the response Z can be increased by slowing the dynamics of Y (C) or by introducing a delay in the response of Y to X (D).

In all the plots, time is in arbitrary units. Using typical biochemical rate constants, the response time is in the range of minutes to hours (see text). The plots were generated using equations 7-8 in Box with r=0.1, except in Fig C where r varies.