title: Understanding Mechanisms of GLI-Mediated Transcription during Craniofacial Development and Disease Using the Ciliopathic Mutant,talpid2.
abstract: The primary cilium is a ubiquitous, microtubule-based organelle that cells utilize to transduce molecular signals. Ciliopathies are a group of diseases that are caused by a disruption in the structure or function of the primary cilium. Over 30% of all ciliopathies are primarily defined by their craniofacial phenotypes, which typically include midfacial defects, cleft lip/palate, micrognathia, aglossia, and craniosynostosis. The frequency and severity of craniofacial phenotypes in ciliopathies emphasizes the importance of the cilium during development of the craniofacial complex. Molecularly, many ciliopathic mutants, including the aviantalpid2(ta2), report pathologically high levels of full-length GLI3 (GLI3FL), which can go on to function as an activator (GLIA), and reduced production of truncated GLI3 (GLI3T), which can go on to function as a repressor (GLIR). These observations suggest that the craniofacial phenotypes of ciliary mutants liketa2are caused either by excessive activity of the GLIAor reduced activity of GLIR. To decipher between these two scenarios, we examined GLI3 occupation at the regulatory regions of target genes and subsequent target gene expression. Usingin silicostrategies we identified consensus GLI binding regions (GBRs) in the avian genome and confirmed GLI3 binding to the regulatory regions of its targets by chromatin immunoprecipitation (ChIP). Inta2mutants, there was a strikingly low number of GLI3 target genes that had significantly increased expression in facial prominences compared to the control embryo and GLI3 occupancy at GBRs associated with target genes was largely reduced.In vitroDNA binding assays, further supported ChIP results, indicated that the excessive GLI3FLgenerated inta2mutants did not bind to GBRs. In light of these results, we explored the possibility of GLI co-regulator proteins playing a role in regulatory mechanism of GLI-mediated transcription. Taken together our studies suggest that craniofacial ciliopathic phenotypes are produced via reduced GLITproduction, allowing for target gene transcription to be mediated by the combinatorial code of GLI co-regulators.
authors: Division of Plastic Surgery, Department of Surgery, Cincinnati Children's Hospital Medical CenterCincinnati, OH, USA; Division of Developmental Biology, Department of Pediatrics, Cincinnati Children's Hospital Medical CenterCincinnati, OH, USA.
authors: Ya-Ting
authors: YT
authors: Chang
authors: Division of Developmental Biology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center Cincinnati, OH, USA.
authors: Praneet
authors: P
authors: Chaturvedi
authors: Division of Plastic Surgery, Department of Surgery, Cincinnati Children's Hospital Medical CenterCincinnati, OH, USA; Division of Developmental Biology, Department of Pediatrics, Cincinnati Children's Hospital Medical CenterCincinnati, OH, USA.
authors: Elizabeth N
authors: EN
authors: Schock
authors: Division of Plastic Surgery, Department of Surgery, Cincinnati Children's Hospital Medical CenterCincinnati, OH, USA; Division of Developmental Biology, Department of Pediatrics, Cincinnati Children's Hospital Medical CenterCincinnati, OH, USA.
authors: Samantha A
authors: SA
authors: Brugmann
keywords: GLI; c2cd3; ciliopathies; craniofacial; primary cilia; talpid2