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D.M. Sherry, R. Mitchell, H. Li; Synapse–Specific Expression of Syntaxins 1 Through 4 in the Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5338.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Syntaxins are members of the SNARE core complex mediating membrane fusion in vesicular trafficking. Syntaxins 1 through 4 are associated specifically with trafficking to the plasma membrane. In the retina, syntaxins 1 and 3 are found presynaptically in conventional and ribbon synapses, respectively (Morgans et al., 1996), suggesting that syntaxins may contribute to functional differences among synapses. To better understand the potential roles of syntaxins in retinal synaptic signaling, we examined the expression of syntaxins 1 through 4 in the mouse retina. Methods: Single and double immunolabeling for syntaxins and cell– or synapse–specific markers was examined by confocal microscopy to localize syntaxins 1 through 4 in the plexiform layers of the mouse retina. Results: All four syntaxin isoforms examined displayed a unique distribution in the synaptic layers, with little or no colocalization of isoforms. Distribution of syntaxins 1 and 3 was similar to previous reports. Syntaxin 1 was present in amacrine cells and their conventional synapses in the IPL as well as sparse terminals in the OPL. Syntaxin 3 was restricted to the glutamatergic ribbon synapses of photoreceptors in the OPL and bipolar cells in the IPL. The putative glutamatergic VGLUT3 amacrine cells did not express syntaxin 3. Syntaxin 2 was expressed in amacrine cell bodies and throughout the IPL. However, syntaxin 2 did not colocalize with syntaxin 1 or other presynaptic markers for conventional or ribbon synapses in the IPL, suggesting a potential postsynaptic role. Syntaxin 4 was present in both the OPL and IPL, but did not colocalize with any presynaptic markers. In the OPL, syntaxin 4 labeling was localized to horizontal cell processes invading the ribbon synaptic complexes of rod and cone terminals. In the IPL, syntaxin 4 was expressed in puncta that contacted the processes of dopaminergic and CD15–positive amacrine cells in S1. Additional syntaxin 4–positive puncta were diffusely distributed in the inner portion of the IPL. Syntaxin 4 also was observed in processes coursing in the INL and occasionally in cell bodies in the innermost INL, suggesting syntaxin 4 may be expressed by interplexiform cells. Conclusions: Each syntaxin isoform studied probably has a different function in synaptic signaling in the retina. Syntaxins 1 and 3 are associated with release from conventional and ribbon synapses, respectively. Syntaxin 2 is likely to have post–synaptic roles in the IPL. Syntaxin 4 is likely to have a postsynaptic role in the horizontal cells at ribbon synaptic complexes in the OPL. Syntaxin 4 may have a postsynaptic role in the IPL as well and interact with the dopaminergic amacrine cells.
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