A Bird's-eye View of Glycan Diversity

To explain the diverse structures, distributions, and properties of glycans, it is necessary to study them from various perspectives. Glycans with unusual structures in humans may be found in other species, and evolutionary analyses can provide insight into the significance of glycan diversity. For instance, (Gala1-4Gal)-bearing glycoprotein expression was initially reported in pigeons and a few additional animals. However, we demonstrated that the glycoproteins with Gala1-4Gal epitopes are expressed in many birds belonging to the main avian clade (Neoaves), accounting for 95% of modern birds. We cloned cDNAs of an alpha 1,4-galactosyltransferase, which produce this carbohydrate antigens, from a pigeon liver cDNA library, and inferred how this glycans were acquired or lost during vertebrate evolution ranging from fish to birds and mammals, based on cDNA sequences and DNA databases. Since the Human Genome Project, the availability of whole genome sequence data has grown enormously, and the number and scope of target species has expanded. Combined with dramatically improved analytical techniques for glycans, it is possible to investigate the mechanism underlying glycan diversity and the roles of various glycans acquired during vertebrate evolution.