Mouse slc9a8 mutants exhibit retinal defects due to retinal pigmented epithelium dysfunction.
OBJECTIVE
As part of a large scale systematic screen to determine the effects of gene knockout mutations in mice, a retinal phenotype was found in mice lacking the Slc9a8 gene, encoding the sodium/hydrogen ion exchange protein NHE8. We aimed to characterize the mutant phenotype and the role of sodium/hydrogen ion exchange in retinal function.


METHODS
Detailed histology characterized the pathological consequences of Slc9a8 mutation, and retinal function was assessed by electroretinography (ERG). A conditional allele was used to identify the cells in which NHE8 function is critical for retinal function, and mutant cells analyzed for the effect of the mutation on endosomes.


RESULTS
Histology of mutant retinas reveals a separation of photoreceptors from the RPE and infiltration by macrophages. There is a small reduction in photoreceptor length and a mislocalization of visual pigments. The ERG testing reveals a deficit in rod and cone pathway function. The RPE shows abnormal morphology, and mutation of Slc9a8 in only RPE cells recapitulates the mutant phenotype. The NHE8 protein localizes to endosomes, and mutant cells have much smaller recycling endosomes.


CONCLUSIONS
The NHE8 protein is required in the RPE to maintain correct regulation of endosomal volume and/or pH which is essential for the cellular integrity and subsequent function of RPE.
MRC Human Genetics Unit, MRC Institute of Genetics & Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.
Shalini
S
Jadeja
Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, The John Radcliffe Hospital, Oxford, United Kingdom.
Alun R
AR
Barnard
MRC Human Genetics Unit, MRC Institute of Genetics & Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.
Lisa
L
McKie
MRC Human Genetics Unit, MRC Institute of Genetics & Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.
Sally H
SH
Cross
Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom.
Jacqueline K
JK
White
MRC Human Genetics Unit, MRC Institute of Genetics & Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.
Morag
M
Robertson
MRC Human Genetics Unit, MRC Institute of Genetics & Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.
Peter S
PS
Budd
Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, The John Radcliffe Hospital, Oxford, United Kingdom.
Robert E
RE
MacLaren
MRC Human Genetics Unit, MRC Institute of Genetics & Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom 4Roslin Institute, University of Edinburgh, Edinburgh, United Kingdom.
Ian J
IJ
Jackson
D000818:Animals; D018929:Cell Culture Techniques; D004195:Disease Models, Animal; D004596:Electroretinography; D005455:Fluorescent Antibody Technique; D055786:Gene Knockout Techniques; D020868:Gene Silencing; D007429:Intraocular Pressure; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D009154:Mutation; D009887:Ophthalmoscopy; D010957:Plasmids; D060888:Real-Time Polymerase Chain Reaction; D012164:Retinal Diseases / Q000175:diagnosis / Q000235:genetics*; D055213:Retinal Pigment Epithelium / Q000473:pathology*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics*
C471945:Slc9a8 protein, mouse; D017923:Sodium-Hydrogen Exchangers