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S.H. Tsang, C.K. Yamashita, M.L. Woodruff, W. Lee, S. Nusinowitz, D.B. Farber; Transgenic Mice Carrying an Allele of a Human Congenital Stationary Night Blindness (Csnb) Gene . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1660.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Different mutations in the ß–subunit of cGMP–phosphodiesterase (PDEß) can lead to retinitis pigmentosa (RP) or congenital stationary night blindness (CSNB). Individuals with CSNB in the Rambusch pedigree were found to have the H258N allele of PDEß; a similar mutation was not found in RP patients. Transgenic mice with the H258N allele were generated to dissect the pathophysiological mechanisms of CSNB in the Rambusch kindred. Methods: The murine opsin promoter was used to direct expression of wild–type PDEß control and mutant transgenes and the constructs were injected into normal oocytes. The founder mice were then crossed with rd1/rd1 mice that lack the ß–subunit of cGMP–PDE to generate mice that could only synthesize transgenic PDEß. PDE activity was measured by the method of Farber and Lolley and the electroretinograms (ERG) and suction recordings were performed according to standard techniques. Results: The H258N mutation in PDEß did not dramatically alter the function of cGMP–PDE, in vivo; however, in in vitro assays, the cGMP–PDE activity of dark–adapted H258N mice showed an approximate 3–fold increase in the rate of retinal cGMP hydrolysis, from 130 nmol x min–1 x nmol rhodopsin in the wild–type controls to 319 nmol x min–1 x nmol rhodopsin in the mutant animals. While rd1/rd1 mice have severe photoreceptor degeneration as in human RP, H258N mice display features of CSNB as diagnosed by morphological and ERG studies. A fit of a rod model to the a–wave of the ERG did not reveal a significant difference between the mutant and control animals in the saturated a–wave amplitude and sensitivity of the rod–mediated photoresponse, although there was a trend in the direction of reduced amplitudes and sensitivity for the H258N mice. In contrast, H258N mice demonstrated losses in amplitude at the level of the b–wave of the ERG. Suction electrode records from isolated H258N rods were fairly normal. Conclusions: The H258N mutant allele, while rescuing retinal degeneration in the RP mouse model, causes an increase of cGMP hydrolysis in darkness. ERGs from the H258N mice are similar to ERGs from humans with the incomplete form of CSNB. These ERGs usually demonstrate a selective loss of the b–wave with relatively intact a–waves. Thus, photoreceptors appear to function fairly normally. The defect in this type of CSNB seems to lie proximal to the visual cells, possibly in the ON–bipolar cells, or their interconnections.
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