Video 2

Movie S2. Serial, transient signaling events during positive selection. Preselection OT1 thymocytes were loaded with the ratiometric calcium indicator dye Indo1LR and allowed to migrate into selecting thymic slices for 2 h and imaged by two-photon microscopy for 1 h starting at 4 h after thymocyte addition. Frames were collected every 20 s for 60 min. Low [Ca2+]i (green) and high [Ca2+]i (red). Graph indicates the calcium ratio (black), speed (gray), and signaling events of the corresponding thymocyte.