Fig. 6

Actively dividing NPCs are localized more ventrally near the midline. a, c Schematic showing stage 4 telotroch animals exposed to BrdU (red) for 2 h followed by a 3 h thymidine chase (pink arrow) and sea-water incubation (blue arrow) until 24 h a and 48 h c respectively before a 2 h EdU (cyan) pulse. b, b′, b″, b.1, b.2, d, d′, d″, d.1, d.2 Confocal micrographs of BrdU pulse-chase-wait-EdU experiments showing BrdU (red) and EdU (cyan) after chase for 24 h b–b″, b.1, b.2 and 48 h d–d″, d.1, d.2. Panels b, b′, b″, d, d′, d″ represent ventral views of the trunk neuroectoderm, with anterior to the left and posterior to the right, showing single BrdU⁺b, d, EdU⁺b′, d″ and EdU/BrdU dual-labeled cells b″, d″. Panels b.1, b.2, d.1, d.2 show orthogonal sections through the ventral trunk neuroectoderm of b″ and d″ respectively. b.1 and d.1 are transverse sections through the anterior trunk neuroectoderm, while b.2 and d.2 are through the posterior trunk neuroectoderm. In b.1, b.2, d.1, and d.2, orange boxes indicate regions that have been cropped and enlarged 3 times in the respective adjacent panels for better visualization of EdU/BrdU dual-labeled cells. In b", d", b.1, b.2, d.1, d.2, closed arrowheads indicate surface EdU⁺/BrdU⁺ dual labeled cells in the trunk neuroectoderm while open arrowheads indicate subsurface dual labeling. Arrows point to the ventrolaterally located surface EdU⁺/BrdU⁺ dual labeled cells. Asterisk denotes the position of the mouth. In all orthogonal views (b.1, b.2, d.1, d.2), apical is up and basal is down and the yellow dot denotes the ventral midline. Square brackets indicate the boundaries between the neuroectoderm and neurotroch. Prototroch (pt) and telotroch (tt) are indicated by dashes. The channel visualized is indicated on the left of each figure panel. ST4tt: Stage 4 telotroch, ST5l: Stage 5 late, ST6mid: stage 6 mid. Vent, ventral. Scale bar in panels b–d″: 25 μm. Scale bar in panels b.1, b.2, d.1, d.2: 15 μm