Interplay of degeneracy and non-degeneracy in fluctuation propagation in coherent feed-forward loop motif

We present a stochastic framework to decipher fluctuation propagation in classes of coherent feed-forward loops (CFFLs). The systematic contribution of the direct (one-step) and indirect (two-step) pathways is considered to quantify fluctuations of the output node. We also consider both additive and multiplicative integration mechanisms of the two parallel pathways (one-step and two-step). Analytical expression of the output node's coefficient of variation shows contributions of intrinsic, one-step, two-step, and cross-interaction in closed form. We observe a diverse range of degeneracy and non-degeneracy in each of the decomposed fluctuation terms and their contribution to the overall output fluctuations of each CFFL motif. The analysis of output fluctuations reveals a maximal level of fluctuations of the CFFL motif of type 1.