Fig. 1. Lqf is required for Notch signaling in the developing wing disc. (A) Structure of Lqf/Epsin. The conserved ENTH (Epsin N-terminal homology) domain, Ubiquitin-interacting motifs (UIM) and `Clathrin box' motifs (CBM), as well as the DPW and NPF tripeptide repeat domains, are shown together with their interaction partners. The position of the lqf¹²²⁷ mutation, a stop codon, is indicated. (B) Adult wing with clones of lqf^- cells associated with wing notching (asterisk) and thickened veins (arrow). (C) Adult mesonotum containing a clone of lqf^- cells (marked by the expression of a UAS-y⁺ transgene, which darkens bristles, and the mwh mutation, which splits each epidermal hair into a tuft; the clone is outlined by a red dotted line). lqf^- cells next to the clone border can form normal bristles (arrows), as opposed to multi-shafted bristles or no bristles, indicating rescue of Notch signaling by adjacent wild-type cells. (D) Wing disc containing clones of lqf^- cells, marked by nuclear GFP expression (green). Here, and in all subsequent figures, dorsal is up. Cells that abut the boundary between the dorsal (D) and ventral (V) compartments express Cut (red) in response to the activation of Notch. Cut is also expressed in isolated neural cells in more proximal portions of the wing disc. Ser produced by D cells activates Notch in V cells, and Dl produced by V cells activates Notch in D cells. Both Dl and Ser are upregulated in response to the activation of Notch, creating a positive-feedback loop responsible for Cut induction in D and V cells flanking the DV boundary. lqf^- clones that abut the DV boundary block Cut expression on both sides, indicating a failure in Notch signaling (blockage of the signal coming from either direction interrupts the feedback loop necessary for Cut expression on both sides of the boundary). (D') Higher magnification of the DV boundary, showing that Cut expression is rescued in lqf^- cells adjacent to wild-type cells along the clone border (rescued cells appear yellow).