Figure 2.—

N signaling at the AP organizer. Three stages of wing development: (A–C) late third instar disc; (D–F) early pupal wing disc when the dorsal and ventral surfaces of the everting disc are coming into apposition (∼3 hr after pupariation); (G–I) early pupal wing (∼9–12 hr after pupariation). (A, D, and G) Su(H)lacZ expression (green) indicates N signaling both at the DV border (yellow arrowheads) and at the AP organizer (white arrowheads). The DV boundary is in the middle of the wing pouch (A), near the edge in a partially everted disc (D), and at the edge of the pupal wing (G). As development advances, Su(H)lacZ expression increases at the AP border (white arrowheads) and decreases at the DV border (yellow arrowheads). (B, E, and H) Ci expression (magenta) marks anterior cells; the posterior extent of Ci expression marks the AP border. (C, F, and I) Merged images show that Su(H)lacZ expression at the AP organizer is in Ci-expressing anterior cells; Ci staining is enhanced in enlarged views (C′ and F′) to show the position of the AP border and the coincidence of Ci and LacZ expression. (A–F) Orientation: anterior is left and ventral is up; (G–I) anterior is up and distal is right.