Role of glycosaminoglycan-synthesizing enzymes in corneal transparency

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cDNAs of some glycosyltransferases and sulfotransferases which are involved in biosynthesis of glycosaminoglycan chain were cloned from chick corneal cells.(2)N-Acetylglucosamine 6-sulfotransferase (GlcNAc6ST) : GlcNAc6ST is involved in a sulfation of GlcNAc residue of keratan sulfate chain. This enzyme could be a marker for the corneal differentiation. Most part (90%) of the sequence of ORF of the cDNA has been determined. The sequence showed 83.0% homology with human GlcNAc6ST-1, but not with human cornea-specific GlcNAc6ST-5. Furthermore, 300 bps of 5'-region of the sequence showed very low homology even with the GlcNAc6ST-1.(3)Chondroitin synthasae and β-glucosyltransferases (Gal-T) : Chondroitin synthase is involved in the elongation of chondroitin chain and Gal-T in the elongation of keratan sulfate chain. Both enzymes could be marker for the dedifferentiation or transdifferentiation from cornea. The sequences of ORFs of both cDNAs have been determined. The sequence of chick chondroitin synthase cDNA showed 82.0% homology with human chondroitin synthase-1, while that of chick Gal-T was identical with chick Gal-T I reported previously. Expression levels of these two enzymes in cultured stromal cells were examined by real-time PCR method. The levels of the two enzymes did not changed so much during the passage of culture (tertiary culture).