title: The human deafness-associated connexin 30 T5M mutation causes mild hearing loss and reduces biochemical coupling among cochlear non-sensory cells in knock-in mice.
abstract: Mutations in the GJB2 and GJB6 genes, respectively, coding for connexin26 (Cx26) and connexin30 (Cx30) proteins, are the most common cause for prelingual non-syndromic deafness in humans. In the inner ear, Cx26 and Cx30 are expressed in different non-sensory cell types, where they largely co-localize and may form heteromeric gap junction channels. Here, we describe the generation and characterization of a mouse model for human bilateral middle/high-frequency hearing loss based on the substitution of an evolutionarily conserved threonine by a methionine residue at position 5 near the N-terminus of Cx30 (Cx30T5M). The mutation was inserted in the mouse genome by homologous recombination in mouse embryonic stem cells. Expression of the mutated Cx30T5M protein in these transgenic mice is under the control of the endogenous Cx30 promoter and was analysed via activation of the lacZ reporter gene. When probed by auditory brainstem recordings, Cx30(T5M/T5M) mice exhibited a mild, but significant increase in their hearing thresholds of about 15 dB at all frequencies. Immunolabelling with antibodies to Cx26 or Cx30 suggested normal location of these proteins in the adult inner ear, but western blot analysis showed significantly down-regulated the expression levels of Cx26 and Cx30. In the developing cochlea, electrical coupling, probed by dual patch-clamp recordings, was normal. However, transfer of the fluorescent tracer calcein between cochlear non-sensory cells was reduced, as was intercellular Ca(2+) signalling due to spontaneous ATP release from connexin hemichannels. Our findings link hearing loss to decreased biochemical coupling due to the point-mutated Cx30 in mice.
authors.affiliation: Institut fuer Genetik, Rheinische Friedrich-Wilhelms-Universitaet Bonn, Roemerstrasse 164, D-53117 Bonn, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Schütz
authors.forename: Pietro
authors.initials: P
authors.lastname: Scimemi
authors.forename: Paromita
authors.initials: P
authors.lastname: Majumder
authors.forename: Romolo Daniele
authors.initials: RD
authors.lastname: De Siati
authors.forename: Giulia
authors.initials: G
authors.lastname: Crispino
authors.forename: Laura
authors.initials: L
authors.lastname: Rodriguez
authors.forename: Mario
authors.initials: M
authors.lastname: Bortolozzi
authors.forename: Rosamaria
authors.initials: R
authors.lastname: Santarelli
authors.forename: Anke
authors.initials: A
authors.lastname: Seydel
authors.forename: Stephan
authors.initials: S
authors.lastname: Sonntag
authors.forename: Neil
authors.initials: N
authors.lastname: Ingham
authors.forename: Karen P
authors.initials: KP
authors.lastname: Steel
authors.forename: Klaus
authors.initials: K
authors.lastname: Willecke
authors.forename: Fabio
authors.initials: F
authors.lastname: Mammano
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000375:Aging / Q000473:pathology; D000818:Animals; D020013:Calcium Signaling; D003051:Cochlea / Q000254:growth & development / Q000473:pathology* / Q000503:physiopathology*; D000072259:Connexin 26; D000075302:Connexin 30; D017630:Connexins / Q000235:genetics*; D003638:Deafness / Q000150:complications / Q000235:genetics* / Q000503:physiopathology; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D036681:Fluorescence Recovery After Photobleaching; D055879:Gene Knock-In Techniques; D006312:Hearing Loss, Bilateral / Q000150:complications / Q000235:genetics* / Q000503:physiopathology; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D009154:Mutation / Q000235:genetics*; D009925:Organ of Corti / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D010539:Permeability; D011995:Recombination, Genetic / Q000235:genetics
chemical_list: D000075302:Connexin 30; D017630:Connexins; C000607042:GJB2 protein, human; C491020:GJB6 protein, human; D000072259:Connexin 26; D000255:Adenosine Triphosphate