Fig. 2. Selective requirement for Lqf in sending DSL signals. (A) Clones of cells overexpressing Dl (marked by nuclear GFP, green) activate Notch in adjacent wild-type cells within the D compartment of the wing blade primordium, as indicated by the induction of Cut expression (red). The abnormally high levels of ectopic Dl expression generated under these conditions autonomously inhibit Notch transduction by cells within the clones. (B) Clones of lqf^- cells that overexpress Dl (green) fail to activate Notch ectopically, and interrupt normal Cut expression when they abut the DV boundary. The same result was obtained using either the lqf¹²²⁷ or lqf^BTmutation; a lqf¹²²⁷ clone is shown. (C,C') `Twin spots' comprising clones derived from the two daughters of single mother cells: one clone of each twin spot overexpresses Dl (marked by nuclear GFP, green), and induces Cut (red) in all the surrounding cells, including the cells of its sibling lqf^- clone (marked by the absence of staining for ß-Gal, blue, C'). (D) Clones of cells overexpressing Ser (green) activate Notch in adjacent wild-type cells within the V compartment, as indicated by the induction of Cut expression (red); Notch tranduction within the clone is inhibited, as in A. (E) Clones of lqf^- cells that overexpress Ser (green) fail to activate Notch ectopically, and interrupt normal Cut expression when they abut the DV boundary. (F,F') Twin spot, as in C,C', except that Ser, rather than Dl, is overexpressed, and the twin spot is located in the V compartment; Cut is expressed in all the surrounding cells, including cells of the sibling lqf^- twin clone. (G,G') Clones of lqf^- cells that ectopically express Dpp (marked by nuclear GFP, green) in a wing disc carrying the Dpp-responsive, omb-lacZ reporter gene. Dpp expressed by cells located just anterior to the AP compartment boundary functions as a gradient morphogen to control omb expression (red) in a broad, centrally located stripe flanking the boundary (see also H). Clones of lqf^- cells that ectopically express Dpp, express omb and induce surrounding clones to do the same, indicating that they are competent both to send and to receive Dpp. (H,H') Clones of lqf^- cells (marked by the absence of GFP, green) in an omb-lacZ wing disc, counterstained for both omb-lacZ (red) and Ci (blue) expression. Ci expression serves in this experiment to mark the A compartment (left); the AP boundary is shown in white. Note the presence of a large lqf^- clone in the P compartment (arrow) that has no apparent effect on the broad domain of omb expression, indicating that Dpp has moved normally through the P compartment from its source in the A compartment. Note also that clones of lqf^- cells are of similar size to their sibling twin clones (marked in this experiment by two copies of the GFP-producing transgene, and hence bright green), and have similarly wiggly borders.