Quantifying intracellular information flow

Signalling pathways convey information about the environment which cells collect and process to make decisions. The cell’s ability to govern its functions correctly and precisely while relying on these intricate biochemical networks is surprising given the noisy cell interior, which indicates the mechanisms cells use to process information are highly sophisticated. While our understanding of the constituents of the cellular machinery and the processes taking place in the cell is steadily increasing, little is known about the information flow within the cell. Are pathways conveying only on/off signals, or is there graded information being transduced? Here, we measure and quantify the information relayed through the MAPK signalling pathway, one of the key signalling pathways in eukaryotic systems. Using a synergy of the optogenetic experimental setup and data analysis based on information theory, we quantify the input-output relationships within the MAPK signalling pathway and highlight the role of intracellular and extracellular noise, stochastic activations of the pathway and the temporal aspect of the information processing in the cell. We show that the capacity of the pathway exceeds the 1-bit value (on/off), and that collective systems of cell seem to exploit this capacity.