Maternal hypothyroidism is associated with M-opsin developmental delay

Thyroid hormones are critical for the development of opsins involved in color vision. Hypothyroid mice show delayed M-opsin development and expanded distribution of S-opsin on the retina. However, the effects of maternal hypothyroidism on opsin development remain unknown. This study investigates the effects of congenital central hypothyroidism and maternal hypothyroidism on opsin development in thyrotropin-releasing hormone knockout (TRH−/−) mice. We examined the mRNA expression and protein distribution of S/M-opsin on postnatal days (P)12 and 17, as well as mRNA expression of type 2 and 3 iodothyronine deiodinase (DIO2 and DIO3, respectively) in the retina and type 1 iodothyronine deiodinase (DIO1) in the liver at P12 in TRH+/− mice born to TRH+/− or TRH−/− dams, and conducted S/M-opsin analysis in TRH+/+ or TRH−/− mice born to TRH+/− dams at P12, P17, and P30. M-opsin expression was lower in TRH+/− mice born to TRH−/− dams than in those born to TRH+/− dams, whereas S-opsin expression did not significantly differ between them. DIO1, DIO2, and DIO3 mRNA expression levels were not significantly different between the two groups; therefore, thyroid function in peripheral tissues in the pups was similar. S/M-opsin expression did not significantly differ between the TRH+/+ and TRH−/− mice born to TRH+/− dams on any postnatal day. These results demonstrate that maternal hypothyroidism causes M-opsin developmental delay during the early developmental stages of neonatal mice, and TRH−/− mice, a model of congenital central hypothyroidism, born to a euthyroid dam do not have delayed opsin development.