Video 1

Movie S1. Thymocytes undergo transient signaling events within minutes of release from Zap-70 inhibition. OT1 Zap-70(AS) preselection thymocytes were loaded with the ratiometric calcium indicator dye Indo1LR and allowed to migrate into selecting thymic slices for 2 h in the presence of 3-MB-PP1 to prevent TCR signaling. After 2 h, the inhibitor was washed out, and slices were imaged by two-photon microscopy. Frames were collected every 20 s for 15 min. Low [Ca2+]i (green) and high [Ca2+]i (red). White circles follow two examples of signaling tracks, and arrows indicate signaling events. Image volume is shown as a maximum projection along the z axis.