Quantifying information transmission in eukaryotic gradient sensing and chemotactic response.

Eukaryotic cells are able to sense shallow chemical gradients by surface receptors and migrate toward chemoattractant sources. The accuracy of this chemotactic response relies on the ability of cells to infer gradients from the heterogeneous distribution of receptors bound by diffusing chemical molecules. Ultimately, the precision of gradient sensing is limited by the fluctuations of signaling components, including the stochastic receptor occupancy and noisy intracellular processing. Viewing the system as a Markovian communication channel, we apply techniques from information theory to derive upper bounds on the amount of information that can be reliably transmitted through a chemotactic cell. Specifically, we derive an expression for the mutual information between the gradient direction and the spatial distribution of bound receptors. We also compute the mutual information between the gradient direction and the motility direction using three different models for cell motion. Our results can be used to quantify the information loss during the various stages of directional sensing in eukaryotic chemotaxis.