Expérimental et théorique
Paramecium is a unicellular organism that swims in fresh water by beating thousands of cilia. When it is stimulated, it often swims backward then turns and swims forward again. This “avoiding reaction” is triggered by a calcium-based action potential. For this reason, some authors have called Paramecium a “swimming neuron”. This project aims at modeling the thermal behavior in Paramecium. When placed in a thermal gradient, Paramecium tends to gather around a preferred temperature, thanks to temperature-triggered avoiding reactions. This behavior is mediated by membrane potential changes produced by cold- and heat-sensitive thermoreceptors. In addition, the preferred temperature shifts when Paramecium is left at the same temperature. A basic experimental device has been built in Laboratoire Jean Perrin to observe paramecia in controlled thermal gradients. The first part of the project is to refine this device and to film trajectories with normal paramecia, and with mutants that do not produce action potentials. The second part is to use the trajectories extracted with tracking software and build a model of thermosensitivity. Depending on time and interest, the student will have the opportunity to either investigate the electrophysiological basis of the inferred input-output mapping (by measuring electrical responses to thermal changes), or its molecular basis (by inactivating receptors either pharmacologically or genetically with RNA interference).