Heterogeneous expression of transketolase in ocular tissues

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Abstract
PURPOSE. Previous studies have shown that transketolase is preferentially expressed in the corneal epithelium and comprises up to 10% of the soluble protein of the mature mouse cornea. The aim of this study is to evaluate the expression and distribution of TKT in the different ocular tissues. METHODS. We have used in situ hybridization and immunohistochemistry to localize TKT mRNA and protein in the developing and adult mouse eye. RESULTS. TKT were found to be widely distributed throughout the adult mouse eye. Among the ocular tissues examined, the corneal epithelium exhibited the highest levels of TKT mRNA and protein. Within the epithelial layer, TKT mRNA and protein were differentially distributed with the highest expression occurring in basal cells and the lowest in apical cells, suggesting that TKT expression in the corneal epithelium may be differentiation-related. Enriched expression of TKT was also found in the cornea endothelium, lens epithelium, ciliary body, and iris. Low basal levels of expression were observed in the limbus and conjunctiva. In contrast to the adult eye, TKT expression in the one-day-old mouse eye was homogeneous at low, but detectable levels, suggesting that TKT expression is developmentally regulated in the cornea as well as in the other ocular tissues. In the healing corneal epithelium, TKT expression in the single cell layer of the leading edge was completely suppressed until the cells began to stratify, at which point TKT expression increased markedly. CONCLUSIONS. The results presented here suggest that TKT is differentially expressed and developmentally regulated in the various tissues that comprise the eye.