Figure 2.

Presenilin is required for the transducing activity of transmembrane but not intracellular forms of Notch during wing development. Each column contains views of a single mosaic imaginal wing disk. Clones that lack PS activity are marked by GFP expression (green). These clones also express either N^ECN or N^intra, which are constitutively active in a wild-type genetic background. smc-Z expression (red) labels SMCs that will form mechanosensory bristles in the presumptive notum (n) as well as sense organs in other portions of the disk. Cut expression (blue) marks subsets of SMCs. Cut is also expressed in a thin stripe of “edge cell” straddling the dorsoventral compartment boundary (_v^d) in the wing blade, and in adepithelial cells associated with the notum. The disk shown in A contains only a single small clone and hence serves as a reference for the normal disk. Disks are shown anterior to the left and ventral down. (A) Series of views of a disk carrying one small clone of PS⁻ UAS-N^ECN-expressing cells (yellow arrow). Cells within the clone form a cluster of SMCs (marked by smc-Z and Cut expression) instead of the single SMC that would normally form at this position, indicating the absence of Notch transducing activity. Single SMCs (marked by smc-Z expression) in neighboring wild-type tissue are indicated by arrowheads. (B) This disk carries multiple PS⁻ clones that express N^ECN and display phenotypes associated with the absence of Notch transducing activity. Two clones in the notum (yellow arrows) show the formation of SMC clusters in place of single SMCs; two clones in the wing blade span the dorsoventral compartment boundary (white arrow and arrowhead) and show a cell autonomous loss of Cut expression. (C) This disk serves as a control. Clones of PS⁻ UAS-N^ECN-expressing cells were generated in the presence of a rescuing Tub-PS⁺ transgene. Restoration of Presenilin activity from the rescuing transgene reveals the constitutive activity of N^ECN within clones. In the notum, SMCs do not form, indicating that neurogenesis is suppressed. There is no overlap between the clone (green) and smc-Z expression (red); the few apparent cases are due to superimposition of the nuclear GFP and cytoplasmic smc-Z signals in different focal planes. In the wing blade, clones autonomously express Cut, indicating constitutive activity of Notch (white arrow marks a representative clone). These clones are also associated with overgrowth of neighboring, wild-type tissue, an indication that the mutant cells are ectopically expressing Wg as well as Cut. (D) This disk carries several clones of PS⁻ UAS-N^intra-expressing cells. Clones in the wing blade autonomously express Cut. The wing blade clone marked by the white arrow has also induced neighboring wild-type cells to express the smc-Z reporter, an indication that these cells are developing as wing margin bristles in response to Wg ectopically expressed by the mutant cells within the clone (see also Fig. 3C).