npg Fused dimerization transduces Hedgehog signal 1436 ORIGINAL ARTICLE Cell Research (2011) 21:1436-1451. © 2011 IBCB, SIBS, CAS All rights reserved 1001-0602/11 www.nature.com/cr npg Transduction of the Hedgehog signal through the dimerization of Fused and the nuclear translocation of Cubitus interruptus Yanyan Zhang1, Feifei Mao1, Yi Lu1, Wenqing Wu1, Lei Zhang1, Yun Zhao1 1State Key Laboratory of Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chi- nese Academy of Sciences, Shanghai 200031, China The Hedgehog (Hh) family of secreted proteins is essential for development in both vertebrates and invertebrates. As one of main morphogens during metazoan development, the graded Hh signal is transduced across the plasma membrane by Smoothened (Smo) through the differential phosphorylation of its cytoplasmic tail, leading to path- way activation and the differential expression of target genes. However, how Smo transduces the graded Hh signal via the Costal2 (Cos2)/Fused (Fu) complex remains poorly understood. Here we present a model of the cell response to a Hh gradient by translating Smo phosphorylation information to Fu dimerization and Cubitus interruptus (Ci) nuclear localization information. Our findings suggest that the phosphorylated C-terminus of Smo recruits the Cos2/ Fu complex to the membrane through the interaction between Smo and Cos2, which further induces Fu dimeriza- tion. Dimerized Fu is phosphorylated and transduces the Hh signal by phosphorylating Cos2 and Suppressor of Fu (Su(fu)). We further show that this process promotes the dissociation of the full-length Ci (Ci155) and Cos2 or Su(fu), and results in the translocation of Ci155 into the nucleus, activating the expression of target genes. Keywords: Cubitus interruptus; Drosophila; Fused; Hedgehog; morphogen Cell Research (2011) 21:1436-1451. doi:10.1038/cr.2011.136; published online 16 August 2011 Introduction One of the central questions in the developmental biol- ogy is how diverse cell types are generated and organized to form appropriate body patterns from a single cell type. A theme that has emerged from the study of model or- ganisms is that cells choose fates and form patterns based on the positional information they have received, which is often provided by the evolutionarily conserved fami- lies of secreted signaling molecules, morphogens. The Hedgehog (Hh) family of secreted proteins represents one of the major families of these signaling molecules. Members of the Hh family govern cell proliferation, dif- ferentiation and patterning in a range of tissues during development in both vertebrates and invertebrates [1]. Correspondence: Yun Zhaoa, Lei Zhangb aE-mail: yunzhao@sibs.ac.cn bE-mail: rayzhang@sibs.ac.cn Received 13 June 2011; revised 22 June 2011; accepted 5 July 2011; pub- lished online 16 August 2011 Malfunction of Hh signaling causes congenital disorders and cancers, such as birth defects, basal cell carcinoma and obesity in humans [2-4]. Thus, the study of Hh sig- naling transduction is of great importance in understand- ing the mechanism of oncogenesis and obesity, and how different thresholds of a morphogen can generate distinct development outputs. The Hh pathway, which was first elucidated in Droso- phila, is composed of a series of repressive reactions [3, 5]. In the absence of Hh, downstream gene transcription is blocked by the Hh receptor, the 12-transmembrane protein Patched (Ptc), which inhibits the function of the 12-transmembrane GPCR-like protein Smoothened (Smo) [3, 6]. Under this condition, a large protein com- plex, which contains the kinesin-related protein Costal2 (Cos2) and the Ser/Thr kinase Fused (Fu), associates with the transcription factor Cubitus interruptus (Ci) and other kinases including cAMP-dependent protein kinase (PKA), GSK3 and CKI. The full-length Ci (Ci155) is phosphorylated and processed to generate a truncated form of Ci, Ci75, which functions as a Hh pathway re- Cell Research | Vol 21 No 10 | October 2011