Presence of rd8 mutation does not alter the ocular phenotype of late-onset retinal degeneration mouse model

Purpose A spontaneous frameshift mutation, c.3481delC, in the Crb1 gene is the underlying cause of dysplasia and retinal degeneration in rd8 mice. The rd8 mutation is found in C57BL/6N but not in C57BL/6J mouse sub-strains. The development of ocular pathology in single knockout Ccl2−/−, Cx3cr1−/− and in double knockout Ccl2−/−/Cx3cr1−/− mice raised on a C57BL/6 background has been reported to depend on the presence of a rd8 mutation. In this study, we investigated the influence of the rd8 mutation on the retinal pathology that we previously described in the late-onset retinal degeneration (L-ORD) mouse model with a heterozygous S163R mutation in the C1q-tumor necrosis factor-related protein-5 (Ctrp5+/−) gene that was generated on a C57BL/6J background. Methods Mouse lines carrying the Ctrp5 S163R and rd8 mutations (Ctrp5+/−;rd8/rd8), corresponding controls without the rd8 mutation (Ctrp5+/−;wt/wt), and wild-type mice with and without the rd8 mutation (Wtrd8/rd8 and Wtwt/wt, respectively) were generated by systematic breeding of mice in our L-ORD mouse colony. Genotyping the mice for the rd8 (del C at nt3481 in Crb1) and Ctrp5 S163R mutations was performed with allelic PCR or sequencing. Retinal morphology was studied with fundus imaging, histology, light microscopy, electron microscopy, and immunohistochemistry. Results Genotype analysis of the mice in L-ORD mouse colony detected the rd8 mutation in the homozygous and heterozygous state. Fundus imaging of wild-type mice without the rd8 mutation (Wtwt/wt) revealed no autofluorescence (AF) spots up to 6–8 months and few AF spots at 21months. However, the accumulation of AF lesions accelerated with age in the Ctrp5+/− mice that lack the rd8 mutation (Ctrp5+/−;wt/wt). The number of AF lesions was significantly increased (p