How does Proteoglycan synthesis by coraeal stromacytes respond to changes in environment around the cells?

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1. Immunohistochemically, keratan sulfate (KS) was first detected in corneal stroma on Day 6 of chick embryonic age, but this KS was undersulfated. The sulfation of KS increased on Day 8.2. When the stromacytes were cultured in vitro, the degree of sulfation of KS decreased markedly but the syntheses of KS backbone and core protein of KS proteoglycan were maintained. On the other hand, the sulfation of chondroitin sulfate increased.3. N-Acetylglucosaminyl sulfotransferase which may be involved in the sulfation of KS, was purified 887-fold with a 8.4% yield from 2-day-old chick corneas. The enzyme specifically transferred a sulfate to GlcNAc at the nonreducing end but not to internal GlcNAc. When the stromacytes were cultured in vitro, the activity of this enzyme specifically, markedly decreased.4. β-Glucuronyltransferase which may be involved in the elongation of chondroitin chain, was purified 389-fold with a 11% yield from 2-day-old chick corneas. This enzyme activity toward chondro-heptasaccharide was 10-fold higher than that toward chondro-pentasaccharide.5. β-Galactosyltransferase activity toward 6-sulfo-GlcNAcβl-3Gal which is the disaceharide unit of KS, was found in chick corneas. This enzyme may be a novel β-galactosyltransferase.6. Almost a whole of open reading frame (ORF) of cDNA of chick corneal chondroitin 6-sulfotransferase was determined for the nucleotide sequence and the predicted amino acid sequence, 3'-Side half of ORF of cDNA of chick coraeal chondroitin 4-sulfotransferase was determined for the nucleotide sequence and the predicted amino acid sequence.