title: Deficiency of transcription factor Brn4 disrupts cochlear gap junction plaques in a model of DFN3 non-syndromic deafness.
abstract: Brn4, which encodes a POU transcription factor, is the gene responsible for DFN3, an X chromosome-linked, non-syndromic type of hearing loss. Brn4-deficient mice have a low endocochlear potential (EP), hearing loss, and ultrastructural alterations in spiral ligament fibrocytes, however the molecular pathology through which Brn4 deficiency causes low EP is still unclear. Mutations in the Gjb2 and Gjb6 genes encoding the gap junction proteins connexin26 (Cx26) and connexin30 (Cx30) genes, respectively, which encode gap junction proteins and are expressed in cochlear fibrocytes and non-sensory epithelial cells (i.e., cochlear supporting cells) to maintain the proper EP, are responsible for hereditary sensorineural deafness. It has been hypothesized that the gap junction in the cochlea provides an intercellular passage by which K+ is transported to maintain the EP at the high level necessary for sensory hair cell excitation. Here we analyzed the formation of gap junction plaques in cochlear supporting cells of Brn4-deficient mice at different stages by confocal microscopy and three-dimensional graphic reconstructions. Gap junctions from control mice, which are composed mainly of Cx26 and Cx30, formed linear plaques along the cell-cell junction sites with adjacent cells. These plaques formed pentagonal or hexagonal outlines of the normal inner sulcus cells and border cells. Gap junction plaques in Brn4-deficient mice did not, however, show the normal linear structure but instead formed small spots around the cell-cell junction sites. Gap junction lengths were significantly shorter, and the level of Cx26 and Cx30 was significantly reduced in Brn4-deficient mice compared with littermate controls. Thus the Brn4 mutation affected the assembly and localization of gap junction proteins at the cell borders of cochlear supporting cells, suggesting that Brn4 substantially contributes to cochlear gap junction properties to maintain the proper EP in cochleae, similar to connexin-related deafness.
authors.affiliation: Juntendo University Faculty of Medicine, Department of Otorhinolaryngology, Tokyo, Japan.
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Kidokoro
authors.affiliation: Juntendo University Faculty of Medicine, Department of Otorhinolaryngology, Tokyo, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Karasawa
authors.affiliation: BioResource Center, Institute of Physical and Chemical Research (RIKEN), Tsukuba, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Minowa
authors.affiliation: Department of Cell Biology, Japanese Foundation for Cancer Research, Cancer Institute, Tokyo, Japan.
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Sugitani
authors.affiliation: BioResource Center, Institute of Physical and Chemical Research (RIKEN), Tsukuba, Japan; Department of Cell Biology, Japanese Foundation for Cancer Research, Cancer Institute, Tokyo, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Noda
authors.affiliation: Juntendo University Faculty of Medicine, Department of Otorhinolaryngology, Tokyo, Japan.
authors.forename: Katsuhisa
authors.initials: K
authors.lastname: Ikeda
authors.affiliation: Juntendo University Faculty of Medicine, Department of Otorhinolaryngology, Tokyo, Japan.
authors.forename: Kazusaku
authors.initials: K
authors.lastname: Kamiya
mesh_terms: D000818:Animals; D003051:Cochlea / Q000378:metabolism*; D000072259:Connexin 26; D000075302:Connexin 30; D017630:Connexins / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D016057:Evoked Potentials, Auditory, Brain Stem; D017629:Gap Junctions / Q000235:genetics* / Q000378:metabolism*; D006319:Hearing Loss, Sensorineural / Q000235:genetics* / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000172:deficiency* / Q000235:genetics; D050809:POU Domain Factors / Q000172:deficiency* / Q000235:genetics
chemical_list: D000075302:Connexin 30; D017630:Connexins; C000607043:Gjb2 protein, mouse; C100629:Gjb6 protein, mouse; D009419:Nerve Tissue Proteins; D050809:POU Domain Factors; D000072259:Connexin 26; C074067:Pou3f4 protein, mouse