Glycomic survey mapping of zebrafish identifies unique sialylation pattern

Functional genomics and proteomics studies of the developmental glycobiology of zebrafish are greatly hampered by the current lack of knowledge on its glycosylation profile. To furnish the requisite structural basis for a more insightful functional delineation and genetic manipulation, we have initiated a survey mapping of the possible expression of stage-specific glycoconjugates in zebrafish. High-sensitivity mass spectrometry (MS) analysis in conjunction with the usual array of enzymatic and chemical derivatization was employed as the principal method for rapid differential mapping of the glycolipids and sequentially liberated N- and O-glycans from the total extracts. We demonstrated that all developmental stages of the zebrafish under investigation, from fertilized eggs to hatched embryos, synthesize oligomannosyl types of N-glycans, as well as complex types with additionally beta4-galactosylated, Neu5Ac/Neu5Gc monosialylated Lewis x termini. A combination of collision-induced dissociation (CID)-MS/MS and nuclear magnetic resonance (NMR) analyses led to the identification of an abundant and unusual mucin-type O-glycosylation, based on a novel sequence Fucalpha1-3GalNAcbeta1-4(Neu5Ac/Neu5Gcalpha2-3)Galbeta1-3GalNAc. This core structure may be further oligosialylated, but exclusively in the earlier development stages. Similarly, MS and MS/MS analyses of the extracted glycolipid fraction revealed the presence of a heterogeneous family of oligosialylated lactosylceramide compounds. In contrast to the O-glycans, these glycolipids only appear in the later development stages, suggesting a complex pattern of regulation for sialyltransferase activities during zebrafish embryogenesis.