Behavior of CD41-GFP^low immigrants to the nascent thymus. Time-lapse fluorescence imaging of CD41-gfp embryos incubated with Bodipy TR, performed by conventional (A-G) or spinning disk (H-P) confocal microscopy. (A-G) Routes of GFP^low immigrants toward the nascent left thymus, lateral view; z-projection images of an embryo scanned through a depth of 80 μm (11 planes) every 4 minutes. Between 54 and 67 hpf (Videos S7 and S8); asterisk, GFP⁺ nonhematopoietic mesenchymal tissue; (A) Trajectories of 2 cells and their progeny in this 13 hour sequence: cell 1 (white dots), and cell 2 (blue dots) which divided at t = 450 minutes, giving 2 daughter cell routes (purple dots). (B-G) Some relevant time points; arrowheads point at the tracked cells with the same color code as in (A). (H-L) Right thymus at 96 hpf, lateral view; scanning performed every minute on a selected confocal plane (see Video S9); time is indicated in minutes and seconds; a GFP⁺ cell (arrowhead) in the PHS stops (H), moves back against the blood flow (I) and extravasates (J,K) to join the thymus (L). The dotted line in L recapitulates its trajectory; another circulating GFP⁺ cell also stops in this part of the PHS at t = 50 minutes (L), but then circulates again 18 minutes later. (M-P) Dynamics of CD41-GFP^low cells in and around the thymus at 5 dpf, ventrolateral view (Video S11); scanning performed every 90 seconds, time indicated in seconds. Dots and numbers point at cells whose trajectory during this 42-minute sequence was traced and is recapitulated in (P). White arrows indicate the position and sense of blood flow of the primary head sinus (phs), common cardinal vein (ccv), and optic vein (ov); r indicates retina; hb, hindbrain; y, yolk sac; m, muscle; and t, thymus.