Morphological evaluation of retinal ganglion cells expressing the L132C/T159C ChR2 mutant transgene in young adult cynomolgus monkeys

To characterize recombinant AAV2 （rAAV2）-mediated expression of L 132C/T 159C ChR2 mutant in retinal ganglion cells （RGCs） of young adult cynomolgus monkeys, rAAV2 vectors carrying a fusion construct of the ChR2 mutant and GFP （ChR2-GFP） were delivered to the vitreous chamber by intravitreal injection. Expression patterns of the ChR2 mutant in RGCs were examined by immunohistochemical methods three months after injection. The RNA-binding protein with multiple splicing （RBPMS） was used as an RGC specific marker to differentiate RGCs from other retinal neurons and non-neuronal cells. The numbers of RBPMS＋ and GFP＋ double-labeled RGCs in the central foveal varied with the eccentricity. The expression peaked within 100 p.m from the edge of the foveola and drastically decreased to a single superficial RGC layer approximately 300 ~tm from the edge. On average, the ratio of the double-labeled RGCs versus RBPMS＋ RGCs approached 0.324-0.15 （n=14 fields） at the central foveal region （0.1 to 0.53 mm）. We observed that the ratio reached 0.784-0.16 （n=21 fields） at peripheral retinal locations （eccentricity 〉7 mm）. This investigation demonstrates that RBPMS could serve as a valuable RGC specific marker for future investigations in this field.