Membrane microdomain formation is crucial in epiboly during gastrulation of medaka

Rapid Trimming of Cell Surface Polysialic Acid (PolySia) by Exovesicular Sialidase Triggers Release of Preexisting Surface Neurotrophin

As acidic glycocalyx on primary mouse microglial cells and a mouse microglial cell line Ra2, expression of polysialic acid (polySia/PSA), a polymer of the sialic acid Neu5Ac (N-acetylneuraminic acid), was demonstrated. PolySia is known to modulate cell adhesion, migration, and localization of neurotrophins mainly on neural cells. PolySia on Ra2 cells disappeared very rapidly after an inflammatory stimulus. Results of knockdown and inhibitor studies indicated that rapid surface clearance of polySia was achieved by secretion of endogenous sialidase Neu1 as an exovesicular component. Neu1-mediated polySia turnover was accompanied by the release of brain-derived neurotrophic factor normally retained by polySia molecules. Introduction of a single oxygen atom change into polySia by exogenous feeding of the non-neural sialic acid Neu5Gc (N-glycolylneuraminic acid) caused resistance to Neu1-induced polySia turnover and also inhibited the associated release of brain-derived neurotrophic factor. These results indicate the importance of rapid turnover of the polySia glycocalyx by exovesicular sialidases in neurotrophin regulation.

Discovery, primary, and crystal structures and capacitation-related properties of a prostate-derived heparin-binding protein WGA16 from boar sperm

Mammalian sperm acquire fertility through a functional maturation process called capacitation, where sperm membrane molecules are drastically remodeled. In this study, we found that a wheat germ agglutinin (WGA)-reactive protein on lipid rafts, named WGA16, is removed from the sperm surface on capacitation. WGA16 is a prostate-derived seminal plasma protein that has never been reported and is deposited on the sperm surface in the male reproductive tract. Based on protein and cDNA sequences for purified WGA16, it is a homologue of human zymogen granule protein 16 (ZG16) belonging to the Jacalin-related lectin (JRL) family in crystal and primary structures. A glycan array shows that WGA16 binds heparin through a basic patch containing Lys-53/Lys-73 residues but not the conventional lectin domain of the JRL family. WGA16 is glycosylated, contrary to other ZG16 members, and comparative mass spectrometry clearly shows its unique N-glycosylation profile among seminal plasma proteins. It has exposed GlcNAc and GalNAc residues without additional Gal residues. The GlcNAc/GalNAc residues can work as binding ligands for a sperm surface galactosyltransferase, which actually galactosylates WGA16 in situ in the presence of UDP-Gal. Interestingly, surface removal of WGA16 is experimentally induced by either UDP-Gal or heparin. In the crystal structure, N-glycosylated sites and a potential heparin-binding site face opposite sides. This geography of two functional sites suggest that WGA16 is deposited on the sperm surface through interaction between its N-glycans and the surface galactosyltransferase, whereas its heparin-binding domain may be involved in binding to sulfated glycosaminoglycans in the female tract, enabling removal of WGA16 from the sperm surface.

Membrane microdomains from early gastrula embryos of medaka, Oryzias latipes, are a platform of E-cadherin- and carbohydrate-mediated cell-cell interactions during epiboly

Formation of membrane microdomain is critical for cell migration (epiboly) during gastrulation of medaka fish [Adachi et al. (Biochem. Biophys. Res. Commun. 358:848-853, 2007)]. In this study, we characterized membrane microdomain from gastrula embryos to understand its roles in epiboly. A cell adhesion molecule (E-cadherin), its associated protein (beta-catenin), transducer proteins (PLCgamma, cSrc), and a cytoskeleton protein (beta-actin) were enriched in the membrane microdomain. Le(X)-containing glycolipids and glycoproteins (Le(X)-gp) were exclusively enriched in the membrane microdomain. Interestingly, the isolated membrane microdomain had the ability to bind to each other in the presence of Ca(2+). This membrane microdomain binding was achieved through the E-cadherin homophilic and the Le(X)-glycan-mediated interactions. E-cadherin and Le(X)-gp were co-localized on the same membrane microdomain, suggesting that these two interactions are operative at the same time. Thus, the membrane microdomain functions as a platform of the E-cadherin- and Le(X)-glycan-mediated cell adhesion and signal transduction.

A sugar rush for developmental biology

The EMBO Workshop on Glycoscience and Development, organised by Philippe Delannoy, Yann Guérardel, Tony Merry and Jean-Claude Michalski, was held in the picturesque, contemplative environment of Les Minimes, a converted seventeenth century Flemish convent in Lille, France, in December 2007. A cross-section of researchers, both confirmed `glycomaniacs' and those newer to the field, discussed and debated recent advances in the field of glycobiology. Presentations ranged from the clinical applications of glycobiology to novel approaches for unravelling carbohydrate biosynthesis in developmental settings and models, such as the fruit fly, nematode and zebrafish.