Zebrafish appears as a relevant model for the functional study of glycoconjugates along vertebrate's development. Indeed, as a prelude to such studies, we have previously identified a vast array of potentially stage-specific glycoconjugates, which structures are reminiscent of glycosylation pathways common to all vertebrates. In the present study, we have focused on the identification and regulation of major protein and lipids associated alpha2-8-linked oligosialic acids motifs in the early development of zebrafish. By a combination of partial hydrolysis, anion exchange HPLC-FD and mass spectrometry, we demonstrated that glycoproteins and glycolipids differed by the extent and the nature of their substituting oligosialylated sequences. Furthermore, relative quantifications showed that alpha2-8-linked sialylation was differentially regulated in both families of glycoconjugates along development. Accordingly, we established that alpha2,8-sialyltransferase mRNA levels was directly correlated with changes of alpha2,8-sialylation status of glycolipids, but independent of those observed on major glycoproteins that appear to originate from the mother.
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[Show abstract][Hide abstract]ABSTRACT: Developmental events can be monitored at the cellular and molecular levels by using noninvasive imaging techniques. Among the biomolecules that might be targeted for imaging analysis, glycans occupy a privileged position by virtue of their primary location on the cell surface. We previously described a chemical method to image glycans during zebrafish larval development; however, we were unable to detect glycans during the first 24 hours of embryogenesis, a very dynamic period in development. Here we report an approach to the imaging of glycans that enables their visualization in the enveloping layer during the early stages of zebrafish embryogenesis. We microinjected embryos with azidosugars at the one-cell stage, allowed the zebrafish to develop, and detected the metabolically labeled glycans with copper-free click chemistry. Mucin-type O-glycans could be imaged as early as 7 hours postfertilization, during the gastrula stage of development. Additionally, we used a nonmetabolic approach to label sialylated glycans with an independent chemistry, enabling the simultaneous imaging of these two distinct classes of glycans. Imaging analysis of glycan trafficking revealed dramatic reorganization of glycans on the second time scale, including rapid migration to the cleavage furrow of mitotic cells. These studies yield insight into the biosynthesis and dynamics of glycans in the enveloping layer during embryogenesis and provide a platform for imaging other biomolecular targets by microinjection of appropriately functionalized biosynthetic precursors.
Full-text · Article · Jun 2010 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract]ABSTRACT: Glycosylation analysis of nonmammalian sources often springs surprises and conjures up intriguing views of evolutionary adaptation. Many of the constituents of snake venoms are known to be glycosylated and yet very few were fully characterized and accorded specific functions. In the process of glycomic screening through the venoms from Asian pit vipers, a partially O-acetylated NeuAcα2-8NeuAcα2-3Galβ1-4GlcNAcβ1-terminal epitope was found to be the predominant glycosylation characteristic of the snake venom produced by the monotypic Deinagkistrodon acutus, with acutobin, a highly specific fibrinogenase, being identified as a primary protein carrier. Full structural definition and glycosylation site mapping were completed through advanced mass spectrometry analyses at both the glycan and glycopeptide levels in conjunction with chemical and enzymatic cleavages. Although similar occurrence of such terminal disialyl cap on the N-glycans of several mammalian glycoproteins has been implicated, most of these correspond to only minor constituents of the full glycomic heterogeneity and remain poorly characterized. In contrast, each antennae of the hybrid- and complex-type N-glycans derived from acutobin was found to be rather homogeneously disialylated. With up to eight sialic acids evenly distributed on nonextended tetraantennary core structure, these unusual N-glycans are among those of highest sialic acid density ever identified without actually carrying polysialic acid chains. It remains to be tested whether they may serve as multivalent disialyl ligands for several of the human Siglecs and thus meddle with the natural immuno-recognition systems of snakebite victims, apart from affecting the general efficacy of acutobin as anticoagulant in biomedical applications.
[Show abstract][Hide abstract]ABSTRACT: Sialic acids (Sia) form the nonreducing end of the bulk of cell surface-expressed glycoconjugates. They are, therefore, major
elements in intercellular communication processes. The addition of Sia to glycoconjugates requires metabolic activation to
CMP-Sia, catalyzed by CMP-Sia synthetase (CMAS). This highly conserved enzyme is located in the cell nucleus in all vertebrates
investigated to date, but its nuclear function remains elusive. Here, we describe the identification and characterization
of two Cmas enzymes in Danio rerio (dreCmas), one of which is exclusively localized in the cytosol. We show that the two cmas genes most likely originated from the third whole genome duplication, which occurred at the base of teleost radiation. cmas paralogues were maintained in fishes of the Otocephala clade, whereas one copy got subsequently lost in Euteleostei (e.g. rainbow trout). In zebrafish, the two genes exhibited a distinct spatial expression pattern. The products of these genes
(dreCmas1 and dreCmas2) diverged not only with respect to subcellular localization but also in substrate specificity. Nuclear
dreCmas1 favored N-acetylneuraminic acid, whereas the cytosolic dreCmas2 showed highest affinity for 5-deamino-neuraminic acid. The subcellular
localization was confirmed for the endogenous enzymes in fractionated zebrafish lysates. Nuclear entry of dreCmas1 was mediated
by a bipartite nuclear localization signal, which seemed irrelevant for other enzymatic functions. With the current demonstration
that in zebrafish two subfunctionalized cmas paralogues co-exist, we introduce a novel and unique model to detail the roles that CMAS has in the nucleus and in the sialylation
pathways of animal cells.
Full-text · Article · Feb 2012 · Journal of Biological Chemistry