Fig. 3. Deletion and chimeric forms of Smoothened. Green indicates Smo sequences, pink indicates Fz sequences. The chimeric and deleted forms are schematized as blocks representing extracellular CRD (leftmost), TM (center) and cytoplasmic tails (right). The transmembrane domain and myristoylate that should anchor SmoN and SmoC to membranes are indicated with zig-zags. Expression scored levels (+ versus ++) relative to endogenous Fz and/or Smo by immunofluorescence in embryos where transgene expression was driven by ptcGal4. All constructs except SmoC (indicated by asterisk) showed ratios of cell surface and internal localization similar to those of Smo and Fz at physiological levels; SmoC alone failed to outline cells. Signaling scored the ability of the transgenes to change L3/4 spacing (high) or to change L3 and A/P growth (low) in the presence of endogenous Smo. DN indicates narrowing of L3/4 spacing. FFS signaling was regulated by Wg rather than Ptc and Hh. Only Fz affected wing hair polarity. `smo^- rescue' scored ability of prdGal4 driven transgenes to restore wg and ptc expression, and segmentation in alternate segments of smo¹/smo³ embryos. nd, not determined.

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