UBC Math Bio Seminar: Austin Hopkins (Online)

Cells often chemotax, directing their motion in response to a chemical signal. We develop models of strategies for chemotaxis in complex environments. Groups of cells may cooperate to sense a chemical signal. One strategy is to specialize into leader cells that sense the gradient and follower cells that follow the clusters direction. We find that this specialization can speed up cluster migration in steep gradients, where a few cells have much more information than the other cells in the cluster. Surprisingly, specialization may also be optimal in shallow gradients. There are tradeoffs between cluster speed and flexibility. Clusters with only a few leaders can take orders of magnitude more time to reorient than all-leader clusters. In addition, single cells can express multiple types of receptors with varying affinities for the same signal. Will this help chemotactic accuracy? If the environment is not variable, using multiple receptor types is less effective than a single receptor type tuned to the environment. However, as environmental variability increases, cells should hedge their bets by expressing multiple receptor types adapted to varying environments. Cells can make several measurements of the signal over time, combining them to make a consistent estimate. Remarkably, time-integration for multiple receptor types is qualitatively different from a single type, allowing cells to extract orders of magnitude more information by using a maximum likelihood estimate.