Localization of PDZD7 to the stereocilia ankle-link associates this scaffolding protein with the Usher syndrome protein network

J Neurosci. 2012 Oct 10;32(41):14288-93. doi: 10.1523/JNEUROSCI.3071-12.2012.

Abstract

Usher syndrome is the leading cause of genetic deaf-blindness. Monoallelic mutations in PDZD7 increase the severity of Usher type II syndrome caused by mutations in USH2A and GPR98, which respectively encode usherin and GPR98. PDZ domain-containing 7 protein (PDZD7) is a paralog of the scaffolding proteins harmonin and whirlin, which are implicated in Usher type 1 and type 2 syndromes. While usherin and GPR98 have been reported to form hair cell stereocilia ankle-links, harmonin localizes to the stereocilia upper tip-link density and whirlin localizes to both tip and ankle-link regions. Here, we used mass spectrometry to show that PDZD7 is expressed in chick stereocilia at a comparable molecular abundance to GPR98. We also show by immunofluorescence and by overexpression of tagged proteins in rat and mouse hair cells that PDZD7 localizes to the ankle-link region, overlapping with usherin, whirlin, and GPR98. Finally, we show in LLC-PK1 cells that cytosolic domains of usherin and GPR98 can bind to both whirlin and PDZD7. These observations are consistent with PDZD7 being a modifier and candidate gene for USH2, and suggest that PDZD7 is a second scaffolding component of the ankle-link complex.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • COS Cells
  • Carrier Proteins / chemistry*
  • Carrier Proteins / genetics
  • Chick Embryo
  • Chlorocebus aethiops
  • Female
  • Gene Regulatory Networks / physiology*
  • Humans
  • LLC-PK1 Cells
  • Male
  • Mice
  • Mice, Transgenic
  • Molecular Sequence Data
  • PDZ Domains / physiology*
  • Rats
  • Stereocilia / chemistry*
  • Stereocilia / genetics
  • Stereocilia / metabolism
  • Swine
  • Usher Syndromes* / genetics
  • Usher Syndromes* / metabolism

Substances

  • Carrier Proteins
  • PDZD7 protein, mouse