Fig. 1

Fig. 1

Wnt signaling is active in the fli1a-positive progenitor cell population of the posterior LPM, consisting of medial kdrl-positive cells and more lateral gata1-positive cells. (A-D) Position of the progenitor cell population (A, Tg(fli1a:GFP)^y1), endothelial cells (B, Tg(kdrl:GFP)^s843, ECs) and erythrocytes (C, Tg(gata1:GFP)^la781) in the posterior LPM at 14 hpf (10ss). (a-c, a’-c’) Magnified dorsal images of the left side of the posterior LPM region caudal to the 9th somite. Scale bars 30 µm. The fli1a-positive cell population has a width of 4–5 cells (A), the kdrl-positive cell population has a width of 1–2 cells (B) and the gata1-positive cell population has a width of 3–4 cells (C). Double labeling of fli1a-positive and kdrl-positive cells (D, left panel, Tg(kdrl:GFP)^s843;(fli1a:dsRed)^y1 with immuno-labeling of dsRed) or of gata1-positive erythrocytes and kdrl-positive ECs (D, right panel, Tg(kdrl:GFP)^s843;(gata1:dsRed)^sd2 with immuno-labeling of dsRed) indicated, that kdrl-positive ECs are sorted more medially within the fli1a-positive cell population than gata1-positive cells. (E) Schematic of the posterior LPM at 14 hpf illustrating the localization of the kdrl-positive (ECs, green) and the gata1-positive (erythrocytes, red) cell populations within the fli1a-positive progenitor cell population (purple) as shown in A-D. (F-H) Time course of the migration of fli1a-positive cells from 12 to 16 hpf. Dorsal views of the posterior LPM. Images were processed either as surface rendering projections (F,G) or displayed as maximum intensity projections (H, upper panel) or using inverted colors (H, lower panel) for better visualization. Tg(fli1a:GFP)^y1 is expressed in bilateral stripes that migrate towards the midline (F). Wnt responding cells from Tg(axin2_BAC:Venus-Pest)^mu288 (G) or cre mRNA injected Tg(14TCF:loxP-STOP-loxP-dGFP)^mu202 (H, upper panel) show mesodermal expression in the developing somites and expression in bilateral stripes similar to Tg(fli1a:GFP)^y1. Double transgenic embryos for Tg(14TCF:loxP-STOP-loxP-dGFP)^mu202 and Tg(fli1a:cre)^mu225 exhibit GFP expression in a subset of fli1a-positive cells at 14 hpf (H, lower panel). Grey lines surround the region of the migrating fli1a-positive cell population.