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B.A. Johnson, S. Ikeda, L.H. Pinto, A. Ikeda; Synaptic Abnormalities in 44TNJ Mice . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5351.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The synaptic interaction in the outer plexiform layer (OPL) represents the first neurological connection to generate visual information after the photoreceptors receive light stimulus. Structural and functional defects in the OPL are associated with human retinal diseases. Identifying a series of molecules involved in the development and function of this synaptic interaction may allow us to understand mechanisms that cause human retinal diseases. Initial characterization of 44TNJ mice, produced by ENU mutagenesis at the Tennessee Mouse Genome Consortium (TMGC), suggested reduced synaptic function between photoreceptor cells and second–order neurons. The purpose of this study was to characterize synaptic phenotypes in 44TNJ mice, using histological and electrophysiological methods, and to generate a high resolution genetic map of the mutant locus. Methods: To assess the synaptic morphology of 44TNJ mice, we performed marker studies to visualize different cell types, pre– and post–synaptic structures in the retina. We also analyzed synaptic development at sequential time points. Electroretinograms (ERGs) were recorded from 44TNJ and B6 control mice at 2 months of age. For genetic mapping, an F2 intercross (44TNJxAKR) was carried out to produce 300 F2 mice. The phenotypes of F2 animals were determined by histological analysis. A whole genome wide scan was performed using 74 SSLP markers. Results: In 44TNJ adult mice, second–order neurons are disorganized, ectopically extend neurites, and do not form proper synapses. Photoreceptor presynapses are also mislocalized. The developmental study showed that the morphological defects are first observed at P17. Consistent with morphological abnormalities, we observed decreased ERG responses. The gene responsible for this mutation has been mapped to distal chromosome X. Conclusions:44TNJ mice have a defect in synaptic structure and function in the OPL. We hypothesize that this gene might be important for synaptic maturation during the later stage of development or maintenance, which may be activity dependent.
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