Figure 9.—

Expression of key genes at the AP organizer and a model for N activation by Hh. (A) Ovals represent the width of expression domains in cell diameters perpendicular to the AP axis, and oval sizes reflect expression levels. Expression domains were measured in late third instar wing discs in the ventral compartment intermediate between the edge of the wing pouch and the DV border. Antibodies were used except where lacZ insertions are indicated. (B) Hh-dependent activation of vn at the AP organizer is required for the expression of Dl in vein 3 and vein 4 stripes. N activation induces cell proliferation within the organizer at least in part through the activation of the E(spl) genes.