title: The ciliogenic transcription factor RFX3 regulates early midline distribution of guidepost neurons required for corpus callosum development.
abstract: The corpus callosum (CC) is the major commissure that bridges the cerebral hemispheres. Agenesis of the CC is associated with human ciliopathies, but the origin of this default is unclear. Regulatory Factor X3 (RFX3) is a transcription factor involved in the control of ciliogenesis, and Rfx3-deficient mice show several hallmarks of ciliopathies including left-right asymmetry defects and hydrocephalus. Here we show that Rfx3-deficient mice suffer from CC agenesis associated with a marked disorganisation of guidepost neurons required for axon pathfinding across the midline. Using transplantation assays, we demonstrate that abnormalities of the mutant midline region are primarily responsible for the CC malformation. Conditional genetic inactivation shows that RFX3 is not required in guidepost cells for proper CC formation, but is required before E12.5 for proper patterning of the cortical septal boundary and hence accurate distribution of guidepost neurons at later stages. We observe focused but consistent ectopic expression of Fibroblast growth factor 8 (Fgf8) at the rostro commissural plate associated with a reduced ratio of GLIoma-associated oncogene family zinc finger 3 (GLI3) repressor to activator forms. We demonstrate on brain explant cultures that ectopic FGF8 reproduces the guidepost neuronal defects observed in Rfx3 mutants. This study unravels a crucial role of RFX3 during early brain development by indirectly regulating GLI3 activity, which leads to FGF8 upregulation and ultimately to disturbed distribution of guidepost neurons required for CC morphogenesis. Hence, the RFX3 mutant mouse model brings novel understandings of the mechanisms that underlie CC agenesis in ciliopathies.
authors.affiliation: Département de Biologie Cellulaire et de Morphologie, University of Lausanne, Lausanne, Switzerland.
authors.forename: Carine
authors.initials: C
authors.lastname: Benadiba
authors.forename: Dario
authors.initials: D
authors.lastname: Magnani
authors.forename: Mathieu
authors.initials: M
authors.lastname: Niquille
authors.forename: Laurette
authors.initials: L
authors.lastname: Morlé
authors.forename: Delphine
authors.initials: D
authors.lastname: Valloton
authors.forename: Homaira
authors.initials: H
authors.lastname: Nawabi
authors.forename: Aouatef
authors.initials: A
authors.lastname: Ait-Lounis
authors.forename: Belkacem
authors.initials: B
authors.lastname: Otsmane
authors.forename: Walter
authors.initials: W
authors.lastname: Reith
authors.forename: Thomas
authors.initials: T
authors.lastname: Theil
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Hornung
authors.forename: Cécile
authors.initials: C
authors.lastname: Lebrand
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Durand
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology; D003337:Corpus Callosum / Q000254:growth & development; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D051524:Fibroblast Growth Factor 8 / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D051741:Kruppel-Like Transcription Factors / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D009024:Morphogenesis / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D000074290:Zinc Finger Protein Gli3
chemical_list: D004268:DNA-Binding Proteins; C496457:Fgf8 protein, mouse; C465571:Gli3 protein, mouse; D051741:Kruppel-Like Transcription Factors; D009419:Nerve Tissue Proteins; C000605540:RFX3 protein, human; D000071701:Regulatory Factor X Transcription Factors; C000605541:Rfx3 protein, mouse; D014157:Transcription Factors; D000074290:Zinc Finger Protein Gli3; D051524:Fibroblast Growth Factor 8