Determination of major sialylated N-glycans and identification of branched sialylated N-glycans that dynamically change their content during development in the mouse cerebral cortex

Oligosaccharides of glycoproteins expressed on the cell surface play important roles in cell-cell interactions, particularly sialylated N-glycans having a negative charge, which interact with sialic acid-binding immunoglobulin-like lectins (siglecs). The entire structure of sialylated N-glycans expressed in the mouse brain, particularly the linkage type of sialic acid residues attached to the backbone N-glycans, has not yet been elucidated. An improved method to analyze pyridylaminated sugar chains using high performance liquid chromatography (HPLC) was developed to determine the entire structure of sialylated N-linked sugar chains expressed in the adult and developing mouse cerebral cortices. Three classes of sialylated sugar chains were prevalent: 1) N-glycans containing alpha(2-3)-sialyl linkages on a type 2 antennary (Gal beta(1-4)GlcNAc), 2) sialylated N-glycans with alpha(2-6)-sialyl linkages on a type 2 antennary, and 3) a branched sialylated N-glycan with a [Gal beta(1-3){NeuAc alpha(2-6)}GlcNAc-] structure, which was absent at embryonic day 12 but then increased during development. This branched type sialylated N-glycan structure comprised approximately 2 % of the total N-glycans in the adult brain. Some N-glycans (containing type 2 antennary) were found to change their type of sialic acid linkage from alpha(2-6)-Gal to alpha(2-3)-Gal. Thus, the linkages and expression levels of sialylated N-glycans change dramatically during brain development.