Question

Compared to a direct simple regulation, what is the biological significance of a coherent FFL in regulating expression of genes? (Hint: think about what happens in response to a noise signal versus a true signal).

Answer 1

Feed forward motif is a best design for signal transduction because it excels in the noise reduction function.

Feedforward loop is a pattern of three genes.E achan of the interactions of 3 genes in FFL can be activation or repression.Based on the eight possible structural configuration of activator or repressor, 4 are coherent and other 4 are incoherent.

Coherent FFl appears with highest frequency in the organism.It rejects transient input impulses and responses only to persistent stimuli. They attains their steady states if the stimuli act over a sufficiently long time interval

coherent feedforward loop could serve as a sign-sensitive delay element: a circuit that responds rapidly to step-like stimuli in one direction and at a delay to steps in the opposite direction.

Eg, arabinose utilisation system of E coli ,The arabinose system displays sign-sensitive delay kinetics. This type of kinetics is important for making decisions based on noisy inputs by filtering out fluctuations in input stimuli, yet allowing rapid response.

This information-processing function may be performed by the feedforward loop regulation modules that are found in diverse systems from bacteria to humans.

FFLis commonly found in transcriptional networks, where a transcription factor X activates a second transcription factor Y, and both jointly regulate a gene Z.

Compared to direct regulation of gene Z by X, feedforward regulation is inherently time-delayed and buffered against noisy transcriptional inputs.