GFP expression of construct 3 in the allantoid, aorta, and gonadal ridges regions. Each panel shows the image in bright field (i) and fluorescence (ii). Panel B shows fluorescence only, and panels Fi and Fii are bright field images. (A) E8 allantoid. An arrow points to the hindgut region. An arrowhead in Aii points to a group of fluorescent cells in the allantoid. (B) E9.5 embryo. An arrow points to the fluorescent streak. (C-D) E9.5 dissected aortas with some adjacent mesenchyme. (E) lateral view of an embryo (E10.5) truncated below and above the AGM region. One of the fluorescent gonadal ridges is out of focus. (F) Cross-section of E9.5 aorta and magnification of a detail; note the large fluorescent cell in Fiii, shown by an arrow in Fii. (G) Cross-section of the aorta. (Gi) AP⁺ cells in the ventral part are indicated by arrows. The box indicates the area corresponding to the fluorescence image (enlarged) shown in panel Gii. (Gii) GFP (anti-HA) staining of the same region of the adjacent section. In the panels, ao indicates aorta; al, allantoid; gr, gonadal ridge; and hg, hindgut. Note that nontransgenic control embryos (and dissected organs) were completely nonfluorescent, even with exposure times of 90 seconds (versus 8-15 seconds as used here). Original magnifications are × 100 (A), × 20 (B), × 40 (C-E), × 100 (Fi), × 400 (Fii-iii), and × 100 (G).