Ligand, modulatory, and co-receptor functions of neural glycans.

Glycans exist at the surface of neural cells primarily as modifications to proteins and lipids. The broad range of functions attributed to neural glycans reflects the immense diversity of glycan structures found in neural tissue. Most glycan functions can be sorted into three non-exclusive categories: ligand, modulatory, and/or co-receptor. Classic models, that have proposed functions for glycans as adhesive ligands, are evolving to incorporate sometimes subtle, but extremely robust, effects on cell survival, differentiation, and physiology. Over the past decade, the identification of new glycan structures and unsuspected biosynthetic pathways has demonstrated that glycans modulate cell-signaling pathways and function as co-receptors for receptor-ligand interactions. In some contexts, the distinction between adhesion and signaling has become blurred. This review summarizes major recent advances in neuroglycobiology related to glycan expression and function.