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PURPOSE. The effects of postnatal hypothyroidism on retinal development and spatial patterning of cone opsin expression were studied in Pax8-deficient mice. Pax8(-/-) mice are incapable of synthesizing thyroxine and serve as a model for congenital hypothyroidism. METHODS. Pax8(-/-), Pax8(-/-), and Pax8(-/-) littermates were studied. Serum thyroid hormone levels, body weight, and eye size were measured. Retinal cell-type-specific antibodies were used on frozen sections to examine the postnatal development of the major retinal cell classes and of retinal structure. The expression of short-wavelength-sensitive (S) and middle-to-long-wavelength-sensitive (M) cone opsins was assessed with opsin antibodies on retinal sections and whole retinas. The pattern of S opsin mRNA was assessed by in situ hybridization. RESULTS. In Pax8(-/-) mice, S opsin was upregulated in all cones, whereas M opsin was downregulated throughout the retina, the wild-type dorsoventral gradients of S and M opsin expression were absent. Otherwise, Pax8(-/-) mice showed no overt mutant phenotype in eye size, gross retinal anatomy, and the time-course of structural differentiation of retinal photoreceptors, horizontal cells, bipolars, amacrines, ganglion cells, and Muller glia cells. CONCLUSIONS. Pax8(-/-) mice show a pattern of cone opsin expression that differs substantially from the wild-type pattern, but exhibit no apparent alterations in general retinal development. The finding that a postnatal decrease in serum thyroid hormone yields changes in postnatal cone opsin expression is consistent with a ligand-dependent role of thyroid hormone receptor beta 2 in S opsin repression and M opsin activation. (Invest Ophthalmol Vis Sci. 2010;51:1719-1727) DOI:10.1167/iovs.09-3592
