Fig. 4

hand2 expression in the posterior lateral mesoderm.

(A–D, F–I) Two-color fluorescent in situ hybridization (A, C, F, H) and immunofluorescence (B, D, G, I) label components of the posterior mesoderm in dorsal views, anterior to the left, of three-dimensional reconstructions, as in Figure 2D–E. In embryos containing transgenes in which GFP expression is driven by the regulatory elements of hand2 (B, G) or etv2 (D, I), anti-GFP immunofluorescence was used to enhance visualization. Tg(etv2:egfp) expression was also observed in the midline neural tube, as previously reported (Proulx et al., 2010). Scale bar represents 100 μm. (E, J) Schematics depict posterior mesoderm territories, dorsal views, anterior to the left; hand2-expressing cells, IM, and medial vessel/blood progenitors are shown at 2–10 somites (E) and at 11–13 somites (J), together with lateral vessel progenitors. (A–D) hand2 is expressed lateral to the IM at the 2–10 somite stages. Embryos shown are at the 10 somite stage; similar expression patterns were seen at earlier stages. (A, B) hand2 is expressed lateral to the IM markers lhx1a (A) and Pax2a (B). (C) hand2 is expressed lateral to tal1, a marker of blood and vessel progenitors; note the unlabeled gap between expression territories. (D) A marker of vessel progenitors, Tg(etv2:egfp), lies medially adjacent to Pax2a. (F–I) Vessel progenitors arise at the interface between hand2-expressing cells and the IM at the 11–13 somite stages. (F, G) hand2 is expressed lateral to the IM marker pax2a. (H) hand2 is expressed lateral to a second territory of tal1 expression; note the presence of lateral tal1-expressing cells (arrows) immediately adjacent to hand2 expression. (I) The IM lies between two territories of etv2 expression; the more lateral etv2-expressing cells (arrows) are lateral to the IM.