Changes in glycoconjugate expression during early chick embryo development: A lectin‐binding study
Authors: Griffith C. M. , Sanders E. J. 
Published: May 2005

A selection of lectins was used to investigate developmentally regulated changes in the distribution of cell surface oligosaccharides during the gastrulation and neurulation stages of early chick embryo development. Lectins from three specificity classes were used: glucose/mannose specificity (concanavalin A [Con A], Lens culinaris agglutinin [LCA], Pisum sativum agglutinin [PSA]); N‐acetylglucosamine specificity (Lycopersicon esculentum agglutinin [LEA], wheat germ agglutinin [WGA], succinylated WGA [sWGA]); N‐acetylgalactosamine/galactose specificity (Dolichos biflorus agglutinin [DBA], soybean agglutinin [SBA], Sophora japonica agglutinin [SJA], Bandeiraea (Griffonia) simplicifolia lectin I [BSL I], peanut agglutinin [PNA], Artocarpus integrifolia lectin [Jacalin], Ricinus communis agglutinin‐1 [RCA‐1], Erythrina cristagalli lectin [ECL]). At gastrulation stages, patterns of lectin binding could be distinguished in the epiblast, mesoderm, and endoderm cell layers. The primitive streak failed to bind any of the lectins, but LEA and WGA bound to the epiblast in regions lateral to the streak, indicating the loss of some glucosamine residues medially in preparation for the ingression movements of gastrulation. Several lectins showed marked binding to the mesoderm cells after their passage through the primitive streak; these were LCA, PSA, WGA, sWGA, BSL, and most particularly PNA. Therefore, the epithelial‐mesenchymal transformation from epiblast to mesoderm at the primitive streak is accompanied by cell surface oligosaccharide changes in the epiblast and mesoderm that involve all classes of lectins including the PNA‐binding sequence Galβ1‐3GalNAc. Ultrastructurally, PNA was shown to bind extracellularly to matrix fibrils. Jacalin, having the same sugar specificity as PNA, but binding to serine/threonine linked chains rather than asparagine linked chains showed no binding to the mesoderm. The endoderm layer most clearly bound WGA and BSL.

At neurulation stages, medio‐lateral domains in the ectoderm could again be demonstrated. Neural plate cells bound only PNA, although the hinge point of the neural plate, the future floor plate, failed to bind PNA unless pre‐treated with neuraminidase to remove sialic acid residues. Caudally, where the primitive streak persisted, all mesoderm cells reacted very strongly with PNA, but rostrally this binding became more restricted to the mesodermal regions immediately adjacent to the streak. This mesodermal PNA‐binding was abolished by hyaluronidase pre‐treatment, suggesting extracellular matrix association, whereas the neural plate binding was unaffected by this treatment, suggesting a more intimate developmentally regulated association with the cell surface of early neural cells. Neuraminidase treatment and sWGA‐binding indicated patterns of sialylation on cells of several tissues at the later stages of development. These sialic acid residues had the effect of masking both PNA and ECL reactivity. The latter, specific for sequences of the poly‐N‐lactosamine series, (Galβ1‐4GlcNAc)n, bound to mesoderm only after removal of sialic acids. Basement membranes bound lectins of glucose/mannose and galactose specificities at both stages, and RCA‐binding was localized ultrastructurally to the fibronectin‐rich interstitial bodies of the lamina densa.