Quantifying information flow in cells

Cells guide their decisions relying on the information that streams through the signalling pathways into the cellular interior. Signalling pathways are interconnected cascades of biochemical reactions which form complex networks. Given the variety of cellular behaviours and responses to external stimuli, the ability to distinguish between a multitude of signals is expected. However, existing quantifications of cellular information flow reported low sensitivity for graded signals. Here, we study information flow in MAPK pathway, one of key signalling pathways in eukaryotes. Combining optogenetic experiments and data analysis based on information theory, we quantify the input-output relationships and elucidate 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 signalling pathway has a higher information capacity than previously reported, as well as bring to light the spatio-temporal aspects of information flow in a cellular popularion.