#20 - Building efficient signal decoders out of three-node subgraphs: an information-theoretic framework
Ayan Biswas (Bose Institute, Kolkata)
Tuesday, 01 Dec 21:15 - 22:00 CET
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Title: Building efficient signal decoders out of three-node subgraphs: an information-theoretic framework
Author(s): Md S. A. Momina, Ayan Biswasa and Suman K. Banika
Affiliation(s): aBose Institute, Kolkata
Abstract: Out of thirteen possible three-node random subgraphs, evolution has only selected the feed-forward loop (FFL) as a network motif. FFLs with 'OR' and 'AND' logic are ubiquitous in gene-transcription regulatory network (GTRN) of E. coli which uses them for metabolism and chemotaxis . Here we search for plausible interplay between the topology and dynamics of the FFL favoring its high statistical abundance in bacterial GTRN and hence propose a biochemically feasible construct containing a two-step cascade (TSC), an FFL and a fan-out (FO) architecture. The input transcription factor (TF) mediated production of the output gene-product is increased and the intermediate TF mediated production of the same is consequently decreased so that the total steady-state output population level remains fixed. We compute two- and three-variable Shannon mutual information (MI) of the direct and indirect pathways but these MI profiles remain inconclusive to answer the question in perspective. Hence, we formulate fractions of two-variable MIs out of their three-variable counterparts. These MI fractions get maximized and form a plateau for an extended FFL domain while contributions from both TSC and FO become minimum. Further, the output noise level gets minimized for FFL and forms a noise floor surrounded by high noise walls belonging to TSC and FO. These observations display universality under transformations of degradation rate-parameters and steady-state population levels of the gene-products. Therefore, we conclude that FFL acts as a better decoder of environmental signals through both of its direct and indirect signaling channels for a substantially extended parametric regime. This increased signal fidelity helps FFL to sustain its functionality in a dynamic environment and favors its selection as the only network motif in bacterial GTRN. Our result  is crucial to build functional modular circuits in vivo as stochasticity is inherent to single cells.