A claudin-9-based ion permeability barrier is essential for hearing

PLoS Genet. 2009 Aug;5(8):e1000610. doi: 10.1371/journal.pgen.1000610. Epub 2009 Aug 21.


Hereditary hearing loss is one of the most common birth defects, yet the majority of genes required for audition is thought to remain unidentified. Ethylnitrosourea (ENU)-mutagenesis has been a valuable approach for generating new animal models of deafness and discovering previously unrecognized gene functions. Here we report on the characterization of a new ENU-induced mouse mutant (nmf329) that exhibits recessively inherited deafness. We found a widespread loss of sensory hair cells in the hearing organs of nmf329 mice after the second week of life. Positional cloning revealed that the nmf329 strain carries a missense mutation in the claudin-9 gene, which encodes a tight junction protein with unknown biological function. In an epithelial cell line, heterologous expression of wild-type claudin-9 reduced the paracellular permeability to Na+ and K+, and the nmf329 mutation eliminated this ion barrier function without affecting the plasma membrane localization of claudin-9. In the nmf329 mouse line, the perilymphatic K+ concentration was found to be elevated, suggesting that the cochlear tight junctions were dysfunctional. Furthermore, the hair-cell loss in the claudin-9-defective cochlea was rescued in vitro when the explanted hearing organs were cultured in a low-K+ milieu and in vivo when the endocochlear K+-driving force was diminished by deletion of the pou3f4 gene. Overall, our data indicate that claudin-9 is required for the preservation of sensory cells in the hearing organ because claudin-9-defective tight junctions fail to shield the basolateral side of hair cells from the K+-rich endolymph. In the tight-junction complexes of hair cells, claudin-9 is localized specifically to a subdomain that is underneath more apical tight-junction strands formed by other claudins. Thus, the analysis of claudin-9 mutant mice suggests that even the deeper (subapical) tight-junction strands have biologically important ion barrier function.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport
  • Claudins
  • Cochlea / chemistry
  • Cochlea / metabolism
  • Disease Models, Animal
  • Female
  • Hair Cells, Auditory / chemistry
  • Hair Cells, Auditory / metabolism
  • Hearing Loss / genetics
  • Hearing Loss / metabolism*
  • Humans
  • Ions / chemistry
  • Ions / metabolism*
  • Male
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice
  • Mice, Inbred A
  • Mice, Transgenic
  • Mutagenesis
  • Permeability
  • Tight Junctions / chemistry
  • Tight Junctions / genetics
  • Tight Junctions / metabolism*


  • Claudins
  • Cldn9 protein, mouse
  • Ions
  • Membrane Proteins