Identifying the sources of noise synergy and redundancy in the feed-forward loop motif
Abstract
The propagation of noise through parallel regulatory pathways is a prominent feature of feed-forward loops in genetic networks. Although the contributions of the direct and indirect regulatory pathways of feed-forward loops to output variability have been well characterized, the impact of their joint action arising from their shared input and output remains poorly understood. Here, we identify an additional component of noise that emerges specifically from this convergent nature of the pathways. Using inter-gene correlations, we reveal the regulatory basis of the additional noise and interpret it as synergy or redundancy in noise propagation, depending on whether the combined pathways amplify or suppress fluctuations. This framework not only accounts for previously observed differences in noise behavior across coherent and incoherent feed-forward loops but also provides a generalizable strategy to connect network structure with stochastic gene regulation.