Figure 9.

Models of GTF2IRD1's role in M cones and rods. A, In cone precursors, transcription factors and their modulators, including TRβ2, RXRγ, and PIAS3, direct M cone cell-fate lineage determination (AI). Immature M cones are not yet morphologically developed and functional (AII). By the time M-opsin expression begins, TRβ2 expression level is significantly reduced, and GTF2IRD1 expression is increased. In M cones, GTF2IRD1 enhances M-opsin and other cone-specific gene expression in cooperation with CRX and TRβ2, whereas it suppresses S-opsin expression to maintain M cone function (AIII). B, In rods, GTF2IRD1 interacts with the enhancer and promoter regions of rhodopsin and other rod-specific genes and enhances their expression in cooperation with CRX and NRL to maintain rod function.