Among them, disrupted synthesis or transfer of LLO underlies the most prevalent disorder, CDG type I (CDG-I)( Jaeken and Péanne, 2017). The analysis of the clinical and metabolic consequences of each defect is challenging as the underlying mutated enzymes or transporters are often involved in multiple and intricate pathways( Freeze et al., 2014). N-linked glycan undergoes final modifications in the ER and Golgi compartments.ĭisrupting the N-glycosylation process in humans causes congenital disorders of glycosylation (CDG), a wide and highly heterogeneous group of inherited metabolic disorders ( Ng and Freeze, 2018) ( Freeze et al., 2014) ( Jaeken and Péanne, 2017). Then, the oligosaccharyltransferase (OST) complex transfers en bloc the oligosaccharide part of the LLO to Asn residues on specific sites (Asn-X-Ser/Thr, X≠Pro) in nascent glycoproteins( Chavan and Lennarz, 2006). This LLO comprises a sequential assembly of 14 monosaccharides (Glc 3Man 9GlcNAc 2) on top of the phosphorylated lipid carrier dolichol. Protein N-glycosylation begins in the endoplasmic reticulum (ER), where a tightly controlled and conserved biosynthetic pathway synthesizes a precursor named the lipid-linked oligosaccharide (LLO). This template-independent process shows distinct glycosylation patterns that vary by protein and physiological context( Dennis et al., 2009). Nearly all proteins transported through the secretory pathway undergo N-glycosylation, particularly to regulate cell surface abundance and cellular interactions( Dennis et al., 2009). Protein N-glycosylation, one of the most abundant post-translational modification, helps direct various cellular functions, such as protein folding, stability, trafficking and localization( Cherepanova and Gilmore, 2016) ( Freeze et al., 2014).
Our results link high N-glycan multiplicity to fine-tuned neural cell adhesion during mammalian brain development. As IgSF-CAM adhesion proteins are critical for neuron adhesion and highly N-glycosylated, we observed impaired IgSF-CAM-mediated neurite outgrowth and axon guidance in Srd5a3 mutant cerebellum. Using proteomic approaches, we identified that Srd5a3 loss affects a subset of glycoproteins with high N-glycans multiplicity per protein and decreased protein abundance or N-glycosylation level. In addition to motor coordination defects and abnormal granule cell development, Srd5a3 deletion causes mild N-glycosylation impairment without significantly altering ER homeostasis. We generated a cerebellum specific knockout mouse for Srd5a3, a gene involved in the initiation of N-glycosylation. However, little is known about the molecular mechanisms underlying these defects. Impairing the N-glycosylation pathway at early steps produces broad neurological symptoms identified in congenital disorders of glycosylation. Proper brain development relies highly on protein N-glycosylation to sustain neuronal migration, axon guidance and synaptic physiology.
Medina-Cano D.Cantagrel V.2018Transcriptomic analysis of the developing cerebellum in a mouse model for SRD5A3-CDG available at EMBL-EBI Array Express (accession no. Medina-Cano DLipecka JGuerrera ICCantagrel V2018GlycoProteomics in CDG (congenital disorder of glycosylation) available at EBI PRIDE (accession no.
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Proteomics and Glycoproteomics data are included within supplementary files 1, 2 and 3 and full proteomics and glycoproteomics data are available via ProteomeXchange with identifier PXD009906. Total proteomics and glycoproteomics data are available via ProteomeXchange with identifier PXD009906.Įxpression microarray data are publicly available at ArrayExpress accession number E-MTAB-6861. DOI: 10.7554/eLife.38309.020 Data Availability Statementįull transcriptomic data is publicly available at ArrayExpress (accession no.
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