Noise-induced alternative response in MAP kinase pathways with mutual inhibition

All organisms have the ability to detect and respond to changes in the environment for survival, and as a result, a variety of mechanisms, i.e., specific cellular signaling pathways, have evolved by which organisms sense their environment and respond to signals that they detect. However, an important unsolved problem in cell biology is to understand how specificity from signal to cellular response is maintained between different signal transduction pathways that share similar or identical components. Here, we show, using mathematical and computational modeling, that two typical signaling pathways in a single cell, hyperosmolar and pheromone motigen-avtivated protein kinase in the yeast, despite mutual inhibition, can respond alternatively to two costimulated signals in the fluctuated environment.