GTF2IRD1 regulates cone gene expression to maintain the topology and function of retinal cone photoreceptors

The mechanisms that specify cone photoreceptor cell-fate to short-wave-sensitive (S) versus medium-wave-sensitive (M) cones and maintain their nature are not fully understood. Here we report the importance of the GTF2IRD1 transcription factor in maintaining M cone cell identity and function. In the mouse, GTF2IRD1 is expressed in cell-fate determined photoreceptors at postnatal day 10. GTF2IRD1 binds to the enhancer and promoter regions of mouse M and S opsin genes, but regulates their expression differentially, suppressing S opsin expression and, through interaction with the transcription factors CRX and TR2, enhancing M opsin expression. Null mutation of Gtf2ird1 leads to altered topology of cone opsin expression in the retina, with aberrant S opsin over-expression and M opsin under-expression in M cones. Gtf2ird1 null mice also demonstrate abnormal M cone electrophysiological responses. These findings indicate a dual and specific regulatory role of GTF2IRD1 in maintaining normal M cone-specific gene expression and function. Total 16 samples were analyzed for BEN-NULL vs WT. Four biological replicates, two time points (2-week and 4-month) were used.