Figure 4.

Fold-change detection in miRNA-mediated incoherent FFLs. Fold-change detection allows heterogeneous cells to tolerate signal noise by relative change in their intensities (the shaded area). In other words, the two cells receive external signals (S; the green lines) with different absolute intensities but the expression of the TF and the miRNA stays at their initial levels (the red and blue lines). When S exceeds a detection threshold (the non-shaded area), which is determined by the relative change of its intensity, the TF responds to S leading to the upregulation of the miRNA and its target (the grey lines). Such a mechanism may allow for the same response of the cells when the upregulation of the TF expression differs in absolute magnitude but shows the same relative change (2-fold-changes).