Fig. 3: Mosaic transgenesis reveals developmental compartment restrictions of PSCs in Platynereis posterior elongation.

a Summary sketch of the protocol for creating large embryonic clones with transposase. b–g Examples of simple germ layer– or tissue-specific primary clones observed on posteriorly growing worms; 6 weeks, ventral views. Observed frequencies of integration patterns for ectoderm = 29/61, mesoderm = 6/61, pygidial ectoderm = 53/61, median neural = 13/61, endoderm = 16/61 (Supplementary Data 7). b Ectodermal clone, no pygidial or internal cell labeled. c Mesodermal clone, only the muscles are clearly visible. d Pygidial and median neural lineage clones. Most median neurites are emanating from pygidial sensory neurons. e Endodermal clone. f–i Dorsal views of a primary clone in ectoderm-derived PSCs. f General confocal stack projection, showing the position of the ectoderm-derived PSCs and uniformly labeled nascent segments; the pygidium is labeled with independent clones. Magnified confocal section views of the SAZ region, at 2 µm z-depth (g), 6.5 µm z-depth (h) and and y-z section (i). g–i show the continuity of the clonal expression of the transgene in bottleneck-shaped ectoderm-derived PSCs with large nuclei-nucleoli (yellow arrowheads), transversely elongated columnar progenitor cells and squamous epidermal differentiated cells. For all panels, green labelings are cell membranes, magenta labelings are cell nuclei. White arrows: position of the PSCs. White asterisks: background staining. Scale bars b–f = 100 µm; g–I = 10 µm.