title: Autosomal recessive GJA1 (Cx43) gene mutations cause oculodentodigital dysplasia by distinct mechanisms.
abstract: Oculodentodigital dysplasia (ODDD) is mainly an autosomal dominant human disease caused by mutations in the GJA1 gene, which encodes the gap junction protein connexin43 (Cx43). Surprisingly, there have been two autosomal recessive mutations reported that cause ODDD: a single amino acid substitution (R76H) and a premature truncation mutation (R33X). When expressed in either gap junctional intercellular communication (GJIC)-deficient HeLa cells or Cx43-expressing NRK cells, the R76H mutant trafficked to the plasma membrane to form gap junction-like plaques, whereas the R33X mutant remained diffusely localized throughout the cell, including the nucleus. As expected, the R33X mutant failed to form functional channels. In the case of the R76H mutant, dye transfer studies in HeLa cells and electrical conductance analysis in GJIC-deficient N2a cells revealed that this mutant could form functional gap junction channels, albeit with reduced macroscopic and single channel conductance. Alexa 350 dye transfer studies further revealed that the R76H mutant had no detectable negative effect on the function of co-expressed Cx26, Cx32, Cx37 or Cx40, whereas the R33X mutant exhibited significant dominant or trans-dominant effects on Cx43 and Cx40 as manifested by a reduction in wild-type connexin gap junction plaques. Taken together, our results suggest that the trans-dominant effect of R33X together with its complete inability to form a functional channel may explain why patients harboring this autosomal recessive R33X mutant exhibit greater disease burden than patients harboring the R76H mutant.
authors.affiliation: Department of Anatomy and Cell Biology, University of Western Ontario, London ON N6A-5C1, Canada.
authors.forename: Tao
authors.initials: T
authors.lastname: Huang
authors.forename: Qing
authors.initials: Q
authors.lastname: Shao
authors.forename: Andrew
authors.initials: A
authors.lastname: MacDonald
authors.forename: Li
authors.initials: L
authors.lastname: Xin
authors.forename: Robert
authors.initials: R
authors.lastname: Lorentz
authors.forename: Donglin
authors.initials: D
authors.lastname: Bai
authors.forename: Dale W
authors.initials: DW
authors.lastname: Laird
mesh_terms: D019943:Amino Acid Substitution; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D018389:Codon, Nonsense; D000072259:Connexin 26; D018031:Connexin 43 / Q000235:genetics / Q000378:metabolism*; D017630:Connexins; D019465:Craniofacial Abnormalities / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D003600:Cytosol / Q000378:metabolism; D005124:Eye Abnormalities / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D005456:Fluorescent Dyes / Q000378:metabolism; D005532:Foot Deformities, Congenital / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D017629:Gap Junctions / Q000378:metabolism / Q000473:pathology; D005808:Genes, Recessive; D006801:Humans; D008856:Microscopy, Fluorescence; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D013576:Syndactyly / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D014071:Tooth Abnormalities / Q000235:genetics / Q000378:metabolism* / Q000473:pathology
chemical_list: D018389:Codon, Nonsense; D018031:Connexin 43; D017630:Connexins; D005456:Fluorescent Dyes; C500216:GJA1 protein, human; C000607042:GJB2 protein, human; D020033:Protein Isoforms; D000072259:Connexin 26
keywords: Cx43; GJA1; Gap junctions; Oculodentodigital dysplasia