Novel Zebrafish Mono-α2,8-sialyltransferase (ST8Sia VIII): An Evolutionary Perspective of α2,8-Sialylation.

Lan-Yi Chang,Kay Khoo,Pierre-André Gilormini,Yann Guérardel,Anne Harduin-Lepers,Maxence Noel,Anne-Marie Mir,Philippe Delannoy,Daniel Petit,Christophe Biot,Cédric Lion,Elin Teppa,Virginie Cogez,Mathieu Decloquement

doi:10.3390/ijms20030622

Abstract

The mammalian mono-α2,8-sialyltransferase ST8Sia VI has been shown to catalyze the transfer of a unique sialic acid residues onto core 1 O-glycans leading to the formation of di-sialylated O-glycosylproteins and to a lesser extent to diSia motifs onto glycolipids like GD1a. Previous studies also reported the identification of an orthologue of the ST8SIA6 gene in the zebrafish genome. Trying to get insights into the biosynthesis and function of the oligo-sialylated glycoproteins during zebrafish development, we cloned and studied this fish α2,8-sialyltransferase homologue. In situ hybridization experiments demonstrate that expression of this gene is always detectable during zebrafish development both in the central nervous system and in non-neuronal tissues. Intriguingly, using biochemical approaches and the newly developed in vitro MicroPlate Sialyltransferase Assay (MPSA), we found that the zebrafish recombinant enzyme does not synthetize diSia motifs on glycoproteins or glycolipids as the human homologue does. Using comparative genomics and molecular phylogeny approaches, we show in this work that the human ST8Sia VI orthologue has disappeared in the ray-finned fish and that the homologue described in fish correspond to a new subfamily of α2,8-sialyltransferase named ST8Sia VIII that was not maintained in Chondrichtyes and Sarcopterygii.

Highlights

Sialic acids are acidic monosaccharides mostly found at the outermost level of glycolipids and glycoproteins
To summarize on the oligosialylation status of glycoconjugates during zebrafish development, it was shown that expression of glycoprotein-associated diSia motifs rapidly decreased following fertilization, whereas glycolipid-associated oligoSia structures followed a reverse trend with an onset of expression at 24 hpf
Sequence similarity network and synteny/paralogy analyses, we showed that the human ST8Sia VI orthologue disappeared in teleosts fish genomes, whereas another distinct mono-α2,8-sialyltransferase subfamily renamed ST8Sia VIII was present in Teleost fishes and had disappeared in Chondrichtyes and Sarcopterygii

Summary

Introduction

Sialic acids are acidic monosaccharides mostly found at the outermost level of glycolipids and glycoproteins. Structural analysis clearly established that only Neu5Gc could be further elongated with another Sia residue generating Neu5Gcα2-8Neu5Gc and Neu5Acα2-8Neu5Gc di-sialylated motifs [18,20] suggesting high specificity of the enzymes involved in the synthesis of these zebrafish α2,8-sialylated epitopes This unusual di-sialylated structure disappeared 24 h post fertilization (hpf) from the developing embryo. To summarize on the oligosialylation status of glycoconjugates during zebrafish development, it was shown that expression of glycoprotein-associated diSia motifs rapidly decreased following fertilization, whereas glycolipid-associated oligoSia (diSia and triSia) structures followed a reverse trend with an onset of expression at 24 hpf This pattern of oligosialylation did not correlate with the temporal expression of associated mono- oligo- and poly-α2,8-sialyltransferases and what we knew of their enzymatic activity suggesting other regulatory mechanisms [20]. Oligosialylation was exclusively detected in brain gangliosides, in agreement with the high expression level of all α2,8-sialyltransferases identified in the zebrafish genome [21]

Methods

Results

Conclusion