FIGURE 4.

Excess cone opsin-expressing cells in mice lacking RORβ isoforms. A, in situ hybridization revealed ∼2-fold increases in S opsin⁺ and M opsin⁺ cells, with many cones misplaced in the inner zones of the ONL in 2z/2z mice at 3 months of age. 1g/1g mice also showed increased cone opsin⁺ cells, most of which were in a normal location in the outer zone of the ONL. Stepwise deletion of additional RORβ isoforms in 2z/− or 1g/− compound heterozygotes further increased cone opsin⁺ cell numbers. In Rorb^−/− mice lacking both RORβ isoforms, cone opsins were overexpressed, and rhodopsin was almost completely lacking. RPE, retina pigment epithelium. Scale bar = 50 μm. B, analysis by qPCR of S opsin, M opsin, and rhodopsin mRNA in the retina of 3-month-old mice of the indicated genotypes.