Purpose. The expression of S- and M-opsins in the murine retina is altered in different transgenic mouse models with mutations in the thyroid hormone receptor (TR)-|3 gene, demonstrating an important role of thyroid hormone (TH) in retinal development. Methods. The spatial expression of S- and M-opsin was compared in congenital hypothyroidism and in two different TR mutant mouse models. One mouse model contains a ligand- binding mutation that abolishes TH binding and results in constitutive binding to nuclear corepressors. The second model contains a mutation that blocks binding of coactivators to the AF-2 domain without affecting TH binding. Results. Hypothyroid newborn mice showed an increase in S-opsin expression that was completely independent of the genotype. Concerning M-opsin expression, hypothyroidism caused a significant decrease (P < 0.01) only in wild-type animals. When TR<β1 and -β were T3-binding defective, the pattern of opsin expression was similar to TR|3 ablation, showing increased S-opsin expression in the dorsal retina and no expression of M-opsin in the entire retina. In an unexpected finding, immunostaining for both opsins was detected when both subtypes of TRβ were mutated in the helix 12 AF-2 domain. Conclusions. The results show, for the first time, that the expression of S- and M-opsin is dependent on normal thyroid hormone levels during development.
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience