Fig. 4. Expression and subcellular localization of SNAREs in vivo. Rat eye tissue sections were double-labeled with specific antibodies and analyzed by confocal fluorescence microscopy. In all panels, the respective SNARE is in green, staining for the double-label is in red and the nuclear stain is in blue. (A) Syntaxin 3 (green), collagen-IV (red). Note that syntaxin 3 is expressed in the photoreceptor inner segments (IS) but is not detectable in the photoreceptor outer segments (OS) or the RPE cells. RPE cells are identified by the collagen-IV-positive basement membrane (BM). (B) Syntaxin 1A (green), collagen-IV (red). Note the expression of syntaxin 1A at the apical plasma membrane of RPE cells (arrowhead) that is in contact with the photoreceptor outer segments, which themselves are negative. (C) Syntaxin 1B (green), occludin (red). Note the syntaxin 1B signal on the apical plasma membrane of the RPE cells (arrowhead) above the tight junctions identified by occludin-staining. (D) Syntaxin 2 (green), occludin (red). Note that syntaxin 2 localizes to a narrow band just underneath the occludin-positive tight junctions. Syntaxin 2 does not overlap with occludin but is instead always towards the basolateral side of the cells, indicating that it localized to a region of the lateral plasma membrane that is adjacent to the tight junctions. (E) Syntaxin 4 (green), occludin (red). Similar to syntaxin 2, syntaxin 4 localizes to a narrow band underneath the occludin-positive tight junctions (arrowhead). In addition, syntaxin 4 staining is evident at the basal plasma membrane and in intracellular vesicles that are often perinuclear. (F) Endobrevin (green), occludin (red). Note that endobrevin localizes to narrow a band underneath the tight junctions (arrowhead) in addition to localizing in small vesicles that are diffusely distributed throughout the cytoplasm of RPE cells.