P-Rex2 is expressed in the terminals of OFF- and ON-cone bipolar cells. A-C: Widefield microscopy of double labeling for P-Rex2 and Synaptotagmin 2, a marker for Type 2 OFF-cone and Type 6 ON-cone bipolar cell terminals. A: P-Rex2 is present in photoreceptor terminals in the OPL and in numerous bipolar cell terminals in the ON and OFF sublaminae of the IPL. B: Labeling for Synaptotagmin 2 reveals an extensive plexus of Type 2 OFF-cone bipolar cell terminals in the OFF sublamina of the IPL. Type 6 ON-cone bipolar cell terminals form a sparser plexus in the ON sublamina of the IPL. Labeling of horizontal and bipolar cell processes is present in the OPL and faint labeling of Type 2 bipolar cell bodies (B) is visible in the INL. C: Overlay of panels A and B shows apparent colocalization of P-Rex 2 and synaptotagmin 2 labeling in the OFF and ON sublayers of the IPL. D-F: Confocal imaging of P-Rex2 and synaptotagmin 2 labeling in the IPL confirms that P-Rex2 (panel D) and synaptotagmin 2 (panel E) colocalize in the terminals of Type 2 OFF-cone and Type 6 ON-cone bipolar cells (arrowheads) in the OFF and ON sublayers of the IPL, respectively. Panel F shows the overlay of panels D and E. Intensity of P-Rex2 labeling varies considerably among individual Type 2 and Type 6 bipolar cell terminals, with some terminals showing no P-Rex2 labeling. Single optical plane of approximately 0.3 μm thickness shown. Nuclei are counterstained with DAPI in panels A and D to illustrate the locations of the nuclear layers. ONL, outer nuclear layer; OPL, outer plexiform layer; INL, inner nuclear layer; IPL, inner plexiform layer; GCL, ganglion cell layer. Scale bars = 20 μm for A-C; 10 μm for D-F.
Sherry and Blackburn BMC Neuroscience 2013 14:70 doi:10.1186/1471-2202-14-70