Ptch1 and XIAP are associated in primary cilia. (A) XIAP and acetylated-tubulin (Ace-tub) expression in frontal sections of E10.5 mouse embryos. Lower panels are high magnification of white dashed square of upper panels. XIAP protein localized to primary cilia (white arrowheads) and cytoplasm in ventral forebrain neuroepithelium. Ace-tub and DAPI label primary cilia and nuclei, respectively. (B) N-terminal Flag/C-terminal EGFP-tagged Ptch1 and mCherry-tagged XIAP are stably expressed in NIH3T3FRT cells under serum starvation (SS), Sonic Hh condition medium (Shh), purmorphamine (Smo agonist, Pur) and cyclopamine (Smo antagonist, Cyc)-treated conditions. (C) Model of Ptch1 (blue) and XIAP (green circle) association with/without Hh (pink circle) ligand in primary cilia. Without Hh, Ptch1 separates from XIAP (1). Ptch1 C-terminal domain is cleaved (2) and then C-terminal product induces mitochondrial dysfunction leading to cell death (3). When Hh binds to Ptch1 (4), Hh and Ptch1 are degraded leading to cell survival (5, 6). Scale bars: 50 µm in (A); 5 µm in (B).