Abstract
Purpose :
The pig is increasingly important for modeling human retinal disease and as a preclinical model of designing therapeutic approaches. The pig eye size and retinal anatomy is very similar to humans and non-human primates. Like primates and unlike rodents, the pig retina has a visual streak with a high density of cones and a periphery dominated by rods. Previous analysis of the changes in retinal structure and function in retinas lacking rhodopsin were published for rhodopsin knockout mice1,2 where cone density is similar across the entire retina. We wanted to determine if the absence of rhodopsin and rods had similar effects in the mouse vs the pig given the high density of cones in the pig visual streak.
Methods :
Rhodopsin KO pigs were created with a Crispr/Cas 9 approach in which 251 bp of the rhodopsin gene were deleted at in exons ? and ?. Full-field ERGs (under dark and light adapted conditions) assessed retinal function from 1 month to 1 year of age. OCTs assessed retinal morphology and were performed at the same time as the ffERG. Animals were euthanized at various ages and retinas processed for IHC and confocal imaging with an emphasis on rod and cone morphology and opsin expression.
Results :
In the rhodopsin knockout pig, no rhodopsin expression and no rod isolated function is evident at any age. In contrast, cone function develops normally; e.g., photopic b-wave amplitudes increase to ~ 400uV P120 to 150, similar to WT pigs. Pig cone function is similar up to 5 months, declines to ~ 300uV at P180 and remains unchanged through 1 year of age. Despite a lack of rhodopsin expression, rod nuclei (1 to 2 layers) remain at 1 year of age in the outer nuclear layer. Remaining rods maintain inner segments that are positive for Reep6 and cones retain inner and outer segments that express cone opsins through 1 year of age.
Conclusions :
The Rho KO pig can be used as a background to express mutant forms of rhodopsin. It also can be used to examine cone isolated signaling in a retina where rods remain but are not functional.
1. Humphries et al., Nature Genetics (1997) 15:216-219
2. Toda et al., Visual Neuroscience (1999) 16: 381-398
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.