Expression of Cre Recombinase in Photoreceptors Leads to Retinal Degeneration

Abstract

Abstract: : Purpose:In order to allow for conditional removal of genes in photoreceptors, we produced transgenic rhodopsin–cre and RP1–cre mice that express cre–recombinase specifically in photoreceptor cells. To determine the suitability of these mice for conditional gene targeting experiments, we characterized the retinal function and structure of the transgenic mice at different ages. Methods:Mice that express cre–recombinase in photoreceptor cells were prepared by placing the gene encoding cre–recombinase behind a 5 kb fragment from the rhodopsin promoter or a 2 kb portion of the RP1 promoter. Retinal function in the transgenic mice was evaluated at ages 1 month, 3 months and 6 months by electroretinography (ERG). Retinal structure was evaluated using histological techniques at the same time points. Results:Retinal function in rhodopsin–cre and RP1–cre mice was normal when tested at 1 month of age, but declined to 70% of normal by 3 months of age, and was barely detectable by 6 months of age, compared to non–transgenic littermate controls. This decrease in retinal function was associated with thinning of the outer nuclear layer of the retina, consistent with progressive loss of photoreceptor cells. Transgenic mice also exhibited a pigmentary retinopathy and retinal vessel attenuation, consistent with the observed retinal degeneration. Conclusions:Over–expression of cre–recombinase in photoreceptor cells leads to cell death, and retinal degeneration. This will limit the suitability of these mice for conditional gene targeting experiments. At present, it is not clear if the observed photoreceptor cell death is due to a specific effect of the cre–recombinase, or a more general effect of protein over–expression. We are creating additional photoreceptor–cre transgenic mice to evaluate these possibilities, and generate mice that will be useful for conditional gene targeting. Grant Identification: NIH (EY12910), FFB, RPB, Rosanne Silbermann Foundation, F.M. Kirby Foundation

Keywords: transgenics/knock–outs • photoreceptors • cell death/apoptosis