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1From The Jackson Laboratory, Bar Harbor, Maine; and the 2Jules Stein Eye Institute, Harbor-UCLA Medical Center, Torrance, California.
PURPOSE. Viable motheaten mutant mice (abbreviated allele symbol mev) are deficient in Src-homology 2-domain phosphatase (SHP)-1, a critical negative regulator of signal transduction in hematopoietic cells. These mice exhibit immune dysfunction, hyperproliferation of myeloid cells, and regenerative anemia. This study focused on the role of SHP-1 in retinal homeostasis.
METHODS. Ophthalmoscopy, histology, transmission electron microscopy (TEM), electroretinography (ERG), immunohistochemistry, Western blot, bone marrow transplantation, and genetic crosses were performed for phenotypic characterization and functional studies of retinal degeneration (RD) in mev/mev mice.
RESULTS. Fundus examinations of mev/mev mice revealed numerous, small white spots. Histologic examination demonstrated photoreceptor loss beginning at 3 weeks of age, and TEM revealed disorganization and reduction in the number of outer segments, as well as the presence of phagocytic cells in the subretinal space. Rod- and cone-mediated ERGs were abnormal. SHP-1 protein was expressed in mouse and human retinal lysates and was localized to the outer nuclear layer of the retina in mev/mev and control mice. Autoantibodies are not necessary for RD, as B-cell-deficient mev/mev Igh-6tm1Cgn mice had no attenuation of photoreceptor cell loss compared with age-matched mev/mev mice. Histologic examination of lungs and retinas from normal recipients of mev/mev marrow revealed the classic acidophilic macrophage pneumonia of mev/mev mice, but no retinal degeneration.
CONCLUSIONS. mev/mev mice exhibit normal retinal development with the onset of RD at 3 weeks of age and a rapidly progressive loss of photoreceptors. These findings support the hypothesis that SHP-1 plays a critical role in retinal homeostasis.
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