Functional Analysis of the Chondroitin 6-Sulfotransferase Gene in Relation to Lymphocyte Subpopulations, Brain Development, and Oversulfated Chondroitin Sulfates*

Chondroitin 6-sulfotransferase (C6ST) catalyzes the transfer of sulfate to position 6 of theN-acetylgalactosamine residue of chondroitin. To obtain direct evidence regarding the function of C6ST and its product, chondroitin 6-sulfate, in vivo, we isolated the mouse C6ST gene (C6st) and generated mice deficient in this gene (C6st−/− ) by embryonic stem cell technology.C6st−/− mice were born at approximately the expected frequency and were viable through adulthood. In the spleen ofC6st−/− mice, the level of chondroitin 6-sulfate became almost undetectable. Analyses of these knockout mice provided insights into the biosynthesis of oversulfated chondroitin sulfates in mice; chondroitin sulfate D in the brain of null mice and the cartilage and telencephalon of null embryos disappeared, whereas the chondroitin sulfate E level in the spleen and brain of the null mice was unchanged. Despite the disappearance of chondroitin sulfate D structure, brain development was normal in theC6st−/− mice. Further analysis revealed that the number of CD62L+CD44low T lymphocytes corresponding to naive T lymphocytes in the spleen of 5–6-week-oldC6st−/− mice was significantly decreased, whereas those in other secondary lymphoid organs were unchanged. This finding suggested that chondroitin 6-sulfate plays a role in the maintenance of naive T lymphocytes in the spleen of young mice.