DDIT3 and retinal degeneration: While looking for the cellular mechanism involved in the rapid retinal degeneration observed in T17M RHO CHOP−/− mice, we tested the RHO mRNA expression and found that the levels of mouse and human RHO mRNA were significantly reduced in T17M RHO CHOP−/− compared to T17M RHO retinas, suggesting that either photoreceptor cell death or transcriptional inhibition is responsible for this down-regulation.