Fig. 3. Emergence and fate of secondary angiogenic sprouts. Images shown are lateral views of vessels at single intersomitic positions in the mid-trunk of TG(fli-egfp)^y1 zebrafish embryos. Sequential image stacks were collected by multiphoton confocal microscopy. Time-lapse movies of the sequences in A, C, E are available as Movies 6, 7 and 9 at http://dev.biologists.org/supplemental/ The images shown in these panels are from selected frames of these movies, labeled with the time in hours:minutes from the first frame (arbitrarily designated time zero). (A) A secondary sprout (arrow) emerges from the posterior cardinal vein immediately adjacent to a primary segment (arrowhead). After an extended time it fuses with the primary vessel, lumenizes and begins to carry blood. Images are from 1.5-2.5 dpf. The dorsal aorta (DA) and posterior cardinal vein (PCV) are noted. (B) A secondary sprout (arrow) emerges from the posterior cardinal vein slightly away from the vertical myoseptum. It elongates towards and reaches the proximal part of the primary segment (arrowhead), forming a patent connection and lumenizing. Images are from 1.5-2.0 dpf. (C) A nonfunctional vestigial ventral segment connecting a primary segment to the DA (arrows) thins and then regresses completely adjacent to a large robustly patent secondary connection to the posterior cardinal vein. This vessel is thus an intersegmental vein. Images are from 1.7-2.5 dpf. (D) Explanatory diagram showing the vessels in C. (E) A secondary sprout elongates next to a primary segment, partially lumenizing but failing to connect. Images are from 1.6-2.2 dpf. Anterior is towards the right in A and B, and to the left in C-E. Primary (arrowhead) and secondary (arrowhead) intersegmental vascular segments are noted. Scale bar: 25 µm. 3D reconstructions of these images are available at http://dir.nichd.nih.gov/lmg/uvo/ISV3_D.html