May 2008
Volume 49, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2008
N-Terminal Mutation of Whirlin Disrupts the Usher Syndrome II (USH2) Protein Complex and Causes Retinal and Inner Ear Defects in Mice
Author Affiliations & Notes
  • J. Yang
    Harvard Med Sch, Mass Eye & Ear Infirmary, Boston, Massachusetts
    Berman-Gund Laboratory for the Study of Retinal Degenerations, Department of Ophthalmology, Retina Foundation of the Southwest, Department of Ophthalmology,
  • X. Liu
    Berman-Gund Laboratory for the Study of Retinal Degenerations, Department of Ophthalmology, Retina Foundation of the Southwest, Department of Ophthalmology,
    University of Texas Southwestern Medical Center, Dallas, Texas
  • M. Adamian
    Harvard Med Sch, Mass Eye & Ear Infirmary, Boston, Massachusetts
    Berman-Gund Laboratory for the Study of Retinal Degenerations, Department of Ophthalmology, Retina Foundation of the Southwest, Department of Ophthalmology,
  • B. S. Pawlyk
    Harvard Med Sch, Mass Eye & Ear Infirmary, Boston, Massachusetts
    Berman-Gund Laboratory for the Study of Retinal Degenerations, Department of Ophthalmology, Retina Foundation of the Southwest, Department of Ophthalmology,
  • X. Sun
    Harvard Med Sch, Mass Eye & Ear Infirmary, Boston, Massachusetts
    Berman-Gund Laboratory for the Study of Retinal Degenerations, Department of Ophthalmology, Retina Foundation of the Southwest, Department of Ophthalmology,
  • D. R. McMillan
    Eaton-Peabody Laboratory, Department of Otology and Laryngology, Department of Pediatrics,
    University of Texas Southwestern Medical Center, Dallas, Texas
  • P. C. White
    Eaton-Peabody Laboratory, Department of Otology and Laryngology, Department of Pediatrics,
    University of Texas Southwestern Medical Center, Dallas, Texas
  • M. C. Liberman
    Harvard Med Sch, Mass Eye & Ear Infirmary, Boston, Massachusetts
    Eaton-Peabody Laboratory, Department of Otology and Laryngology, Department of Pediatrics,
  • T. Li
    Harvard Med Sch, Mass Eye & Ear Infirmary, Boston, Massachusetts
    Berman-Gund Laboratory for the Study of Retinal Degenerations, Department of Ophthalmology, Retina Foundation of the Southwest, Department of Ophthalmology,
  • Footnotes
    Commercial Relationships  J. Yang, None; X. Liu, None; M. Adamian, None; B.S. Pawlyk, None; X. Sun, None; D.R. McMillan, None; P.C. White, None; M.C. Liberman, None; T. Li, None.
  • Footnotes
    Support  NIH Grants EY010309, R01 DC00188, NEI core grant P30 EY14104, Fight for Sight, and the Foundation Fighting Blindness
Investigative Ophthalmology & Visual Science May 2008, Vol.49, 4405. doi:
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      J. Yang, X. Liu, M. Adamian, B. S. Pawlyk, X. Sun, D. R. McMillan, P. C. White, M. C. Liberman, T. Li; N-Terminal Mutation of Whirlin Disrupts the Usher Syndrome II (USH2) Protein Complex and Causes Retinal and Inner Ear Defects in Mice. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4405.

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Abstract

Purpose: : Mutant alleles of the whirlin gene cause different diseases in humans. A mutation near the C-terminus results in nonsyndromic deafness, while its N-terminal mutations are responsible for USH2D, a condition with both visual and hearing defects. In this study, we investigated the underlying mechanism for the variable disease expressions involving the whirlin gene.

Methods: : Gene targeting was carried out by homologous recombination in embryonic stem cells followed by blastocyst injection of the targeted clones. Whirlin knockout mice were examined by light and scanning electron microscopy, electroretinography (ERG), and distortion product otoacoustic emissions (DPOAE) testing. Subcellular localization and expression levels of whirlin and other USH2 proteins were analyzed by immunofluorescence and Western blotting.

Results: : Whirlin colocalized with two known Ush2 proteins Ush2a and Vlgr1 at the periciliary ridge complex (PRC)-like structure in photoreceptors and at the stereocilia in hair cells. Disruption at the first exon of the whirlin gene in mice abolished the normal localization of Ush2a and Vlgr1 in photoreceptors and reduced their protein levels, indicative of destabilization. Photoreceptor outer segments were shortened and ERG amplitudes were reduced in whirlin mutant mice at 28 months of age. Localization of Ush2a and Vlgr1 in hair cells was also affected in the mutant. Stereocilia of inner ear hair cells in mutant mice were lost in the basal turn of the cochlea, and shortened or distorted in the middle turn. The threshold of hearing response was markedly elevated as demonstrated by DPOAE testing. The hearing loss appeared to be non-progressive.

Conclusions: : Whirlin forms a multi-protein complex in vivo with the two other known USH2 proteins through its N-terminal domain. A mutation in this region causes both retinal degeneration and cochlear hair cell defects in mice as in humans. Subtle differences in functional requirements and transcript/splice variant expressions between photoreceptors and inner ear hair cells may explain the variable disease expressions caused by mutations in different regions of the whirlin gene.

Keywords: photoreceptors • retinal degenerations: cell biology • protein structure/function 
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