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Bisecting Galactose as a Feature of N-Glycans of Wild-type and Mutant Caenorhabditis elegans.

ABSTRACT: The N-glycosylation of the model nematode Caenorhabditis elegans has proven to be highly variable and rather complex; it is an example to contradict the existing impression that "simple" organisms possess also a rather simple glycomic capacity. In previous studies in a number of laboratories, N-glycans with up to four fucose residues have been detected. However, although the linkage of three fucose residues to the N,N'-diacetylchitobiosyl core has been proven by structural and enzymatic analyses, the nature of the fourth fucose has remained uncertain. By constructing a triple mutant with deletions in the three genes responsible for core fucosylation (fut-1, fut-6 and fut-8), we have produced a nematode strain lacking products of these enzymes, but still retaining maximally one fucose residue on its N-glycans. Using mass spectrometry and HPLC in conjunction with chemical and enzymatic treatments as well as NMR, we examined a set of α-mannosidase-resistant N-glycans. Within this glycomic subpool, we can reveal that the core β-mannose can be trisubstituted and so carries not only the ubiquitous α1,3- and α1,6-mannose residues, but also a "bisecting" β-galactose, which is substoichiometrically modified with fucose or methylfucose. In addition, the α1,3-mannose can also be α-galactosylated. Our data, showing the presence of novel N-glycan modifications, will enable more targeted studies to understand the biological functions and interactions of nematode glycans.

SUBMITTER: Yan S

PROVIDER: S-EPMC4523199 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:RET/GDNF and ET3/EDNRB regulate cell survival, differentiation and migration of neural crest-derived cells. Many signalling mediators of RET have been characterized but the target genes at the end of the signalling cascade are largely unknown. Since the RET/EDNRB crosstalk has been previously shown, we used a Caenorhabditis elegans knockout strain of Nep-1, a homologue of human ECE1 (endothelin-converting enzyme-1), to identify new target genes. Transcriptome comparison between wild-type and Nep-1 strains at different stages identified vit-3 as a differentially expressed gene. Molecular studies of the vit3 mammalian homologue, Apoliporotein B (APOB), were performed in the murine Neuro2a cell line, a model of ENS development. Apob expression in Neuro2a is specifically activated by the RET/GDNF signalling pathway, since Ret silencing abolished Apob increase, and this effect is induced by MAPK P38 kinase activation. Mouse Apob promoter study revealed that there is a p53-dependent repressor element in the promoter region which blocks Apob expression and we show that actually p53 binds to this region. We demonstrated that RET/GDNF and EDNRB/endothelin 3 (ET-3) cooperate in inducing neuronal differentiation resulting in Apob activation. We also show that Apob expression is downregulated in mouse embryos homozygous for the mutation RetC620R and presenting a severe HSCR phenotype, whereas heterozygous mice, phenotypically normal, present a significant increase in Apob expression. These data suggest that Apob has an important role in RET-mediated neuronal development and APOB decrease may have an impact in human disorders where RET absence has been already identified, such as HSCR and Parkinson disease. Gene expression analysis using Affymetrix GeneChip C. elegans arrays in order to identify genes up- or down-regulated in nep-1 strains, homologue of human ECE1 (endothelin-converting enzyme 1). Comparison of the transcriptomes between wt and nep-1 strains in larval stage L3 and adult C. elegans.

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Bisecting Galactose as a Feature of N-Glycans of Wild-type and Mutant Caenorhabditis elegans.

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