Abstract The expression of glyco-chains is precisely regulated in a time-and-space dependent manner. We summarize two types of regulation: kidney tubular cell-specific regulation of core 2 β1-6GlcNAc transferase by the Gsl5 gene, and the suppression of N-glycolylneuraminic acid (NeuGc) by the regulation of CMP-NeuAc hydroxylase activity. The Gsl5 gene identified by genetic analysis on the basis of the polymorphic expression of kidney glycolipids among inbred strains of mice regulates β1,6-GlcNAc transferase activity. The GlcNAc transferase transfers GlcNAc on Galβ1-3GalNAcβ-and also synthesizes core 2 structure, GlcNAcβ1-6(Galβ1-3)GalNAcα-. Immunohistochemistry with anti-core 2-Lex monoclonal antibody demonstrated that the lysosome-like vesicles of the proximal tubule cells were clearly stained in a Gsl5 wild-type mouse. Western blotting confirmed that the positive staining was due to the microsomal glycoproteins. These results, together with those of in situ hybridization, confirmed that the Gsl5 gene controls the expression of β-1,6-GlcNAc transferase mRNA in a proximal tubular cell-specific manner. The expression of NeuGc is controlled by the activity of CMP-NeuAc hydroxylation, which requires three enzyme proteins, cytochrome b5, cytochrome b5 reductase, and a terminal hydroxylase, in the presence of NADH. We cloned mouse and human hydroxylase cDNAs. Mouse brain contains a very high amount of NeuAc, but the hydroxylase mRNA is not detectable by Northern blotting. Surprisingly, the same phenotype is conserved in humans, even though humans have lost the ability to produce intact hydroxylase enzyme, due to the deletion of 92 bp in the genome.