Typical rod–cone degeneration with moderate progression in a rhodopsin knock–in mouse model

Abstract

Abstract: : Purpose:To analyze the retinal function of a rhodopsin knock–in mouse model, generated to investigate the effects of reduced rhodopsin levels. Methods:The mice were generated by gene–targeting the rhodopsin locus with a construct containing rhodopsin cDNA flanked with a globin intron and 5' and 3' noncoding rhodopsin gene sequences. 5 rho–knock–in mice and 5 controls have been examined by Ganzfeld electroretinograms (ERGs) at the age of 5 and 13 weeks. Scotopic and photopic ERGs were performed in the anaesthetized mice. A–, b, and c–waves as well as adaptation were analyzed. Recovery after light adaptation was investigated in 11 weeks–old mice (5 knock–in, 4 controls). Results:The knock–in model displayed a typical rod–cone degeneration: Scotopic b–wave amplitudes were significantly lower at 5 and 13 weeks of age with a moderate progression, a– and c–wave amplitude reduction was more pronounced reconcilable with a primary photoreceptor problem. Cone amplitudes were not reduced at 5 weeks, but at 13 weeks of age. At that time, the cone implicit time showed a tendency to be longer than in controls. At 13 weeks, the relative ERG–amplitudes in the knock–ins were as follows: Rod: barely detectable, rod–cone: 30%, cone: 68%. The recovery of a 10 cds/qm stimulus response after light adaptation (70 cd/qm, 5 minutes) was significantly faster in knock–in mice, consistent with reduced rhodopsin levels. Conclusions:In previous papers it could be shown that rhodopsin knock–out mice (rho–/–) developed no outer segments whereas the animals with one copy (rho+/–) did so and degenerated over a long time period. With the construct presented here a typical rod–cone degeneration could be achieved with a rate of progression which makes this mouse model suitable for therapeutical trials.

Keywords: retinal degenerations: hereditary • electroretinography: non–clinical • gene/expression