Signal Manifestation Trade-offs in Incoherent Feed-Forward Loops

Abstract

Signal processing in biological systems is delicately executed by specialised networks, which are modular assemblies of network motifs. The motifs are independently functional circuits found in enormous numbers in any living cell. A very common network motif is the feed-forward loop (FFL), which regulates a downstream node by an upstream one in a direct and an indirect way within the network. If the direct and indirect regulations go antagonistic, the motif is known as an incoherent FFL (ICFFL). The current study is aimed at exploring the reason for the variation in the evolutionary selection of the four types of ICFFLs. As comparative measures, I compute sensitivity amplification, adaptation precision and efficiency from the temporal dynamics and mutual information between the input-output nodes of the motifs at steady state. The ICFFL II performs very efficiently in adaptation but poor in information processing. On the other hand, ICFFL I and III are better in information transmission compared to adaptation efficiency. Which is the fittest among them under the pressure of natural selection? To sort out this puzzle, I take help from the multi-objective Pareto efficiency. The results, found in the Pareto task space, are in good agreement with the reported abundance level of all the types in eukaryotes as well as prokaryotes.