N-Glycosylation Is Required for Secretion and Mitosis in C. elegans

Abstract

N-glycosylation of proteins is an essential process, and N-glucans serve as important beacons in protein folding and ER associated degradation. More importantly, N-glycosylation increases the structural repertoire of proteins because the addition of the N-glucan on proteins will serve as a base for further sugar additions in the Golgi apparatus, and hence complex three-dimensional structures can be build. N-glycosylation is mediated by the ER-resident OST complex, which is essential throughout eukaryotes. Partial knockdown of conserved OST complex members, such as C. elegans RIBO-1, led to an embryonic lethal phenotype. Although the ER morphology was not grossly altered in ribo-1(RNAi) oocytes and embryos, secretion of yolk and of the yolk receptor RME-2 was perturbed in those worms. Perhaps as a consequence of reduced arrival of N-glycosylated proteins at the plasma membrane, cytokinesis occurred less efficiently leading to multinuclear cells. Unexpectedly, we detected a chromosome segregation defect in ribo-1(RNAi) embryos suggesting an essential role of at least one N-glycosylated protein in metaphase-anaphase transition.

Attenuation of N-glycosylation causes polarity and adhesion defects in the C. elegans embryo

“…Over 80% of plasma membrane proteins are N-glycosylated in the ER, and this modification is essential for protein folding, function and stability. We have previously shown that depletion of OST complex components leads to secretion defects (Stevens and Spang, 2013). Here, we report that N-glycosylation is important for cell adhesion and cell polarity, suggesting a role for N-glycosylated proteins in the compartmentalization of the plasma membrane.…”

“…We have reported previously that reduced N-glycosylation leads to severe cytokinesis defects and delayed development (Stevens and Spang, 2013). The embryos that were able to successfully complete cytokinesis under those conditions, lost the adhesion between AB and P1 cells ( Fig.…”

“…Bob Goldstein (Department of Biology, University of North Carolina, Chapel Hill, NC) provided LP172 {hmr-1 (cp21[hmr-1::gfp+LoxP]) I}. RNAi feeding experiments and embryo fixation were performed as described previously (Stevens and Spang, 2013). qPCR (Fig.…”

“…Immunostaining and FM4-64 staining HMR-1 and MAGI-1 were detected according to Hadwiger et al (2010) with modifications from Stevens and Spang (2013). α-HMR-1 (Developmental Studies Hybridoma Bank; DSHB) was diluted 1:10 and α-MAGI-1 1:5000 (Stetak and Hajnal, 2011).…”

“…We have shown previously that, under these conditions, the concentration of the plasma membrane-localized yolk receptor RME-2 is strongly reduced (Stevens and Spang, 2013), suggesting that the concentration of plasma membrane proteins in general might be reduced in ribo-1(RNAi) zygotes. Upon fertilization and, hence, establishment of plasma membrane domains in the zygote, the protein concentration might be too low to provide a sufficient density of proteins in the different domains (Fig.…”