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J. P. Canner, K. E. Beazley, M. Nurminskaya, C. J. Lagace, T. F. Linsenmayer; Thyroxine and Iron Regulate Ferritin and Ferritoid Protein Expression in Chicken Corneal Epithelium. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4302. doi: https://doi.org/.
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Previous work in our laboratory showed that in corneal epithelial (CE) cells the iron sequestering protein Ferritin (FTN) has a nuclear localization, where it confers UV protection to DNA. Subsequently, we identified and characterized the CE-specific nuclear transporter for FTN, Ferritoid (FTD). Both FTN and FTD appear to be coordinately regulated; they are expressed in a precise temporal pattern that coincides with the development of the thyroid, and their expression in culture is inhibited by the removal of iron. Others have shown that thyroid hormones play crucial roles in corneal development, as well as regulation of FTN in other tissues. Here we examine the factors that regulate FTN and FTD protein expression in CE.
To determine the contribution of iron regulatory proteins to FTN and FTD expression we preformed qRT-PCR on lysates of CE tissue harvested from staged chicken embryos. To determine if systemic factors are involved in the coordinate regulation of FTN and FTD a chorioallantoic membrane (CAM) assay was utilized in which donor corneas of one age were explanted to hosts of another age. To examine specific factors involved, we cultured whole corneas in the presence or absence of thyroxine and iron. Organ cultures were analyzed by western blot, immunofluorescent labeling, and qRT-PCR.
During the development of the chicken CE there is no significant transcriptional increase in any iron regulating proteins. CAM assays showed that donor corneas responded to influences from the host in regards to FTN/FTD protein expression. Corneas cultured with 10% serum expressed FTN/FTD proteins, while insignificant protein expression was observed in serum free conditions with or without the addition of either FeSO4 or thyroxine. However, the addition of both factors together increase FTN/FTD protein expression greater than 20 and 10 fold, respectively.
These results demonstrate that in the developing CE the coordinate regulation of FTN/FTD protein expression involves systemic factors and that iron and thyroxine are sufficient to direct FTN/FTD synthesis.
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