Localization of PDZD7 to the stereocilia ankle-link associates this scaffolding protein with the Usher syndrome protein network.
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.
Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA. Mgrati@aol.com
M'hamed
M
Grati
Jung-Bum
JB
Shin
Michael D
MD
Weston
James
J
Green
Manzoor A
MA
Bhat
Peter G
PG
Gillespie
Bechara
B
Kachar
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics; D002642:Chick Embryo; D002522:Chlorocebus aethiops; D005260:Female; D053263:Gene Regulatory Networks / Q000502:physiology*; D006801:Humans; D018374:LLC-PK1 Cells; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D054731:PDZ Domains / Q000502:physiology*; D051381:Rats; D059547:Stereocilia / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013552:Swine; D052245:Usher Syndromes / Q000235:genetics / Q000378:metabolism
D002352:Carrier Proteins; C000594656:PDZD7 protein, mouse