title: A secreted WNT-ligand-binding domain of FZD5 generated by a frameshift mutation causes autosomal dominant coloboma.
abstract: Ocular coloboma is a common eye malformation resulting from incomplete fusion of the optic fissure during development. Coloboma is often associated with microphthalmia and/or contralateral anophthalmia. Coloboma shows extensive locus heterogeneity associated with causative mutations identified in genes encoding developmental transcription factors or components of signaling pathways. We report an ultra-rare, heterozygous frameshift mutation in FZD5 (p.Ala219Glufs*49) that was identified independently in two branches of a large family with autosomal dominant non-syndromic coloboma. FZD5 has a single-coding exon and consequently a transcript with this frameshift variant is not a canonical substrate for nonsense-mediated decay. FZD5 encodes a transmembrane receptor with a conserved extracellular cysteine rich domain for ligand binding. The frameshift mutation results in the production of a truncated protein, which retains the Wingless-type MMTV integration site family member-ligand-binding domain, but lacks the transmembrane domain. The truncated protein was secreted from cells, and behaved as a dominant-negative FZD5 receptor, antagonizing both canonical and non-canonical WNT signaling. Expression of the resultant mutant protein caused coloboma and microphthalmia in zebrafish, and disruption of the apical junction of the retinal neural epithelium in mouse, mimicking the phenotype of Fz5/Fz8 compound conditional knockout mutants. Our studies have revealed a conserved role of Wnt-Frizzled (FZD) signaling in ocular development and directly implicate WNT-FZD signaling both in normal closure of the human optic fissure and pathogenesis of coloboma.
authors.affiliation: Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, 6 Center Drive, Bethesda, MD 20892, USA, State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, China.
authors.forename: Chunqiao
authors.initials: C
authors.lastname: Liu
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9.
authors.forename: Sonya A
authors.initials: SA
authors.lastname: Widen
authors.affiliation: MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XU, UK.
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Williamson
authors.affiliation: Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, 6 Center Drive, Bethesda, MD 20892, USA.
authors.forename: Rinki
authors.initials: R
authors.lastname: Ratnapriya
authors.affiliation: Department of Ophthalmology, University Hospital Zurich, Frauenklinikstrasse 24, Zurich 8091, Switzerland.
authors.forename: Christina
authors.initials: C
authors.lastname: Gerth-Kahlert
authors.affiliation: MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XU, UK.
authors.forename: Joe
authors.initials: J
authors.lastname: Rainger
authors.affiliation: Unit on Pediatric, Developmental, and Genetic Eye Disease, National Eye Institute, 10 Center Drive, Bethesda, MD 20892, USA.
authors.forename: Ramakrishna P
authors.initials: RP
authors.lastname: Alur
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Alberta, Edmonton, AB, Canada T6G 2H7.
authors.forename: Erin
authors.initials: E
authors.lastname: Strachan
authors.affiliation: Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, 6 Center Drive, Bethesda, MD 20892, USA.
authors.forename: Souparnika H
authors.initials: SH
authors.lastname: Manjunath
authors.affiliation: Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, 6 Center Drive, Bethesda, MD 20892, USA.
authors.forename: Archana
authors.initials: A
authors.lastname: Balakrishnan
authors.affiliation: Welcome Trust Sanger Institute, Hinxton, Cambridge CB10 1HH, UK and.
authors.forename: James A
authors.initials: JA
authors.lastname: Floyd
authors.affiliation: Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, 6 Center Drive, Bethesda, MD 20892, USA.
authors.forename: Tiansen
authors.initials: T
authors.lastname: Li
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9, swaroopa@nei.nih.gov david.fitzpatrick@igmm.ed.ac.uk olehmann@ualberta.ca aw@ualberta.ca.
authors.forename: Andrew
authors.initials: A
authors.lastname: Waskiewicz
authors.affiliation: Unit on Pediatric, Developmental, and Genetic Eye Disease, National Eye Institute, 10 Center Drive, Bethesda, MD 20892, USA.
authors.forename: Brian P
authors.initials: BP
authors.lastname: Brooks
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Alberta, Edmonton, AB, Canada T6G 2H7, Department of Medical Genetics, University of Alberta, Edmonton, AB, Canada T6G 2H7 swaroopa@nei.nih.gov david.fitzpatrick@igmm.ed.ac.uk olehmann@ualberta.ca aw@ualberta.ca.
authors.forename: Ordan J
authors.initials: OJ
authors.lastname: Lehmann
authors.affiliation: MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XU, UK, swaroopa@nei.nih.gov david.fitzpatrick@igmm.ed.ac.uk olehmann@ualberta.ca aw@ualberta.ca.
authors.forename: David R
authors.initials: DR
authors.lastname: FitzPatrick
authors.affiliation: Neurobiology-Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, 6 Center Drive, Bethesda, MD 20892, USA, swaroopa@nei.nih.gov david.fitzpatrick@igmm.ed.ac.uk olehmann@ualberta.ca aw@ualberta.ca.
authors.forename: Anand
authors.initials: A
authors.lastname: Swaroop
mesh_terms: D000818:Animals; D004252:DNA Mutational Analysis; D005260:Female; D016368:Frameshift Mutation; D051157:Frizzled Receptors / Q000235:genetics*; D006801:Humans; D008297:Male; D051379:Mice; D008850:Microphthalmos / Q000235:genetics / Q000378:metabolism; D010375:Pedigree; D060449:Wnt Signaling Pathway; D015027:Zebrafish / Q000235:genetics / Q000378:metabolism
chemical_list: C498589:FZD5 protein, human; D051157:Frizzled Receptors; C403211:Fzd5 protein, mouse