Rat brain glycosyltransferase activities during postnatal development

Sulfated glucuronic acid-containing glycoconjugates are temporally and spatially regulated antigens in the developing mammalian nervous system

Monoclonal antibody 4F4, which was raised against a cell suspension of embryonic rat forebrain, reacts with acidic glycolipids and several high-molecular-weight glycoproteins in rodent brain. The major reactive glycolipid is maximally expressed at Embryonic Day 15 (E15) and is no longer detectable at Postnatal Day 14 (P14) in the rat. 4F4 antibody reacts with a glucuronic acid- and sulfate-containing lipid isolated from human sciatic nerve as well as with lipids from mouse and rat embryonic brain tissue. Although the glycolipid disappears postnatally, the immunoreactive glycoproteins continue to be expressed in brain until adulthood. Both sciatic nerve and embryonic brain glycolipids are hydrolyzed by glucuronidase/sulfatase treatment but are insensitive to all other glycosidases tested. In addition, the observed 4F4 reactivity with extracted glycolipids, glycoproteins, and tissue sections of embryonic brain is identical to the reactivity demonstrated by HNK-1 antibodies. Immunocytochemical studies in developing brain showed stage-specific distribution of this carbohydrate antigen. At E10 in the mouse, immunoreactivity is associated with the mantle layer of the neural tube. At E15 in the cortex, the most intense staining is associated with the molecular layer and the subplate, and weaker staining is seen in the intermediate zone and cortical plate, suggesting that the antigen is highly concentrated on postmigratory cells in the embryonic nervous system.

Dolichol kinase and the regulation of dolichyl phosphate levels in developing brain

The developmental changes of dolichol kinase activity and dolichyl phosphate levels have been studied in rat brain. Because both dolichol kinase activity and dolichyl phosphate were enriched in microsomes, detailed study of this subcellular fraction was carried out. Dolichol kinase specific activity in brain microsomes increased postnatally 3-fold to a maximum at ca. 30 days of age. This increase was observed whether exogenous dolichol was present or not and whether Zn2+ or Ca2+ was utilized as the cation for the enzyme. Zn2+ was the most effective cation in developing brain, as we have shown previously for adult brain (Sakakihara, Y. and Volpe, J.J., J. Biol. Chem., 260 (1985) 15413-15419). Although the Vmax for the enzyme increased by three-fold with development, the Km for dolichol and for CTP did not change, indicating that the developmental increase was not related to an alteration in catalytic efficiency of the enzyme. A striking and parallel increase in dolichyl phosphate levels in brain microsomes was defined with development. Levels were lowest in one-day-old animals and then increased ca. 13-fold to a maximum at 30 days of postnatal age. The parallel increase in dolichol kinase activity and dolichyl phosphate levels in microsomes of developing brain suggests that dolichol kinase is the principal determinant of cellular levels of dolichyl phosphate, the critical intermediate in the dolichol-linked pathway to glycoproteins.

Study of circadian correlations between acetylcholine muscarinic receptor and brain glycosyltransferases by multivariate analysis

Circadian variations of the acetylcholine muscarinic receptor and some glycosyltransferases were studied in brain using multivariate analysis. Highly significant correlations exist between fucosyltransferase, sialyltransferase and galactosyltransferase and to a lesser extent between both of these enzymes and acetylcholine receptor. No correlation appeared between these enzymes and dolichol phosphate mannose synthase.

Modifications involved in brain glycoconjugate metabolism induced by neonatal capsaicin treatment

Neonatal capsaicin treatment induces significant changes in rat brain glycoconjugate metabolism. All glycosyltransferase activity involved either in glycoprotein or glycolipid biosynthesis was strongly enhanced. Higher enzymatic activities were obtained when capsaicin-treated rats (T1) had received an additional capsaicin dose (T2). In this case, the fucosyl and galactosyltransferase activities were markedly increased. However, the enhancement of sialyltransferase activity only affects the biosynthesis of glycoproteins and is not correlated with a significant change in ganglioside content. The present results suggest that the modulation of the microsomal glycosyltransferase activity, after capsaicin treatment, could not be stated up through a direct lipid interaction or a change in membrane properties because the phospholipid brain content is not significantly modified.