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Arnold Szabo, Anna Enzsoly, Akos Lukats, Gergely Halasz, Agoston Szel; Developmental Expression of Thyroid Receptor Beta 2 in the Retina of Rat and Syrian Golden Hamster. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5422.
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Recent observations indicate that thyroid hormone plays an important role in M-cone development of the mouse. Since the mouse exhibits unique features regarding photoreceptor distribution as well as development, the question arises whether the involvement of thyroid hormone is general in cone development among the mammals. In this study we investigated the expression of the TRβ2 thyroid receptor in two rodent models in which cone development may differ from that of the mouse.
Retinas of embryonic and postnatal Sprague-Dawley rats and Syrian golden hamsters were studied. The expression of the TRβ2 thyroid receptor and that of the cone specific visual pigments were analyzed using immunocytochemistry and Western blot.
In agreement with earlier results the adult rat retina expressed visual pigments in distinct cone populations. During development, a transdifferentiation occurred and cones that initially expressed S-opsin switched to the production of M-opsin. In the Syrian golden hamster, however, no S-opsin was present at all. Rather, all retinal cones expressed M-opsin. The TRβ2 receptor was detectable in both species and its expression preceded that of the cone specific opsins. Both species exhibited TRβ2 positive cells in the neuroblast and developing photoreceptor layers in embryonic and young postnatal ages, a feature that was missing in the adult retinas. This result was confirmed by Western blotting, in which the expression of the thyroid receptor was detectable already in embryonic samples, and dropped drastically in the adult.
Our results indicate that although there are differences in cone distribution, and possibly, in cone development as well, thyroid hormone and its TRβ2 receptor play the same role in cone differentiation of both investigated species. In accordance with relevant literature data and our earlier results, this role is presumably the regulation of cone development.
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