Cytochemistry of the cell surface and extracellular matrix during early embryonic development

Lectin-binding patterns in the embryonic human paraxial mesenchyme

The paraxial mesenchyme in seven human embryos aged between Carnegie stages 12 and 17 was studied by lectin histochemistry with the lectins AIA, Con A, GSA II, LFA, LTA, PNA, RCA I, SBA, SNA, WGA. The paraxial mesenchyme was found to be segmented into sclerotomes by intersegmental vessels and from late stage 12 by intrasclerotomal clefts dividing each sclerotome into a cranial and caudal half. The lectins Con A, GSA II, LFA, LTA, SBA and SNA did not react at all in the paraxial mesenchyme. Staining for AIA, PNA, RCA I and WGA was found in the developing sclerotomes. However, no differences in the staining pattern between the two sclerotomal halves could be seen. It was striking that in contrast to the chick embryo no differences in binding for PNA between the cranial and caudal sclerotomal parts was observed. These findings reveal that PNA-binding sites do not play the same functional role in segmented axonal outgrowth and neural crest immigration into cranial sclerotomal halves in the human embryo, as found in chick embryonic development. Beginning with the stage 16-embryo, the already condensed caudal sclerotomal halves express Con A-, RCA- and PNA-binding sites. The staining for PNA in particular marked the differentiation of chondrogenous structures developing in this half. From the late stage 12 or stage 13, the walls of intersegmental and other vessels showed binding sites for AIA, PNA, RCA I, SNA and WGA.

Histochemical investigations on lectin binding in normal and irradiated mouse embryos

Lectin binding in normal and irradiated embryonic mouse tissues on day 10 of gestation was studied by peroxidase techniques. Specific binding of Dolichos biflorus lectin (DBA) was detected in the mesodermal blood vessels and in the otic vesicles. The amount of DBA as well as that of soybean agglutinin (SBA) and peanut agglutinin (PNA) increased after exposure to low doses of radiation (0.25, 0.50 and 0.75 Gy). The modifying influence of ionizing radiation was observed in the pituitary region, in the otic vesicles and in the blood vessel endothelium. The greatest effect appeared in the pituitary region at 0.75 Gy, while in the otic vesicles it appeared at 0.50 Gy. A dose-effect relationship was established for the DBA lectin affinity of the vascular endothelium. In comparison to DBA, SBA and PNA displayed more extensive staining after irradiation. The reactivity of these lectins appeared especially pronounced on the blood vessels within the central nervous system and in the luminal surface of the ependymal cells. It is of interest that maximal binding for PNA was observed at 0.25 Gy and for SBA at 0.50 Gy at the junctions between neuroepithelial cells.

Changes in glycoconjugate expression during early chick embryo development: a lectin-binding study

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 Gal beta 1-3GalNAc. 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Lectin binding pattern in the embryonal and early fetal human vertebral column

Paraffin sections from vertebral columns of ten human embryos and fetuses ranging from stage 16 to the 12th week were stained with the FITC-coupled lectins PNA, RCA I, Con A and WGA in order to investigate changes in carbohydrate-binding sites during vertebral development. PNA revealed a specific binding site in the vertebral body blastema in the precartilaginous stage of development. Beginning with the 25-mm CRL embryo, PNA-binding sites occurred in the developing fibrous annulus and the inner zone of the intervertebral discs. The first binding sites for RCA I were seen in the extracellular matrix of vertebral bodies during the cartilaginous stage of vertebral development. During early ossification of the vertebrae, staining for RCA I-binding sites in the cytoplasm of the chondrocytes and the area around the future cartilaginous end-plates was observed. Con A bound to the chondrocyte cytoplasm, and also very strongly to notochordal cells in all developmental stages examined. WGA-binding sites appeared simultaneously with cartilage formation. Connective tissue components, e.g. ligaments, were diffusely stained by WGA. Also this lectin showed an affinity for vertebral body chondrocytes. We discuss the biochemical aspects of these lectin-binding sites, and their possible roles in the differentiation process of the human vertebral column. The results of this first lectin histochemical study on human vertebral development are compared with related results in other species.

The distribution of cell surface glycoconjugates during mouse secondary neurulation

During secondary neurulation in the mouse, the neural tube develops from the tail bud by caudal extension of the primary neurocoele. The mesenchymal cells of the tail bud become radially arranged around the neurocoele and undergo a mesenchymal to epithelial transformation to form a neuroepithelium. In order to study the expression of glycoconjugates during the morphogenesis of the secondary neural tube, 14 lectins were applied to serial sections of tail buds at various stages of development. In general, binding was fairly homogeneous during the early stages of tail bud development. However, as development progressed, several lectins became localized to specific structures. The changes were observed to parallel the ongoing development of the secondary neuraxis. sWGA, which is N-acetylglucosamine (GlcNAc) specific, bound mainly to the luminal surface of the secondary neurocoele and to a lesser extent, the notochord. WGA, which has both GlcNAc and sialic acid specificities, showed most intense binding at the luminal and abluminal surfaces of the secondary neurocoele. Binding by the lectin PNA was restricted to the extracellular matrix around the developing secondary neural tube. A comparison of the lectin binding patterns in mouse with those previously reported in chick, demonstrates a less elaborate pattern of lectin binding in murine embryos. This may suggest a less complex expression of glycoconjugates in rodents, in keeping with their comparatively simpler mechanism of secondary neurulation.

The binding pattern of peanut lectin associated with sclerotome migration and the formation of the vertebral axis in the chick embryo

Lectins have been used extensively to detect changes in carbohydrate moieties on the surfaces of embryonic cells during early development. Peanut agglutinin (PNA) in particular has been used to investigate changes related to cell differentiation. PNA has also been used to differentiate between the rostral and caudal sclerotome halves which have been shown to be functionally different, with neural crest cells and neurites traversing only the rostral half during their migration. In this study, we have sectioned and stained chick embryos between 3 and 8 days of age with PNA to examine the distribution of PNA binding sites associated with the vertebral column during this period and also to determine the fates of the rostral and caudal sclerotome halves. Ultrastructural localisation of PNA-gold conjugate showed that binding sites for this lectin were present intracellularly and extracellularly both on cell surfaces and in the matrix. At the light microscope level, a clear banding pattern emerged after staining with PNA which consisted of alternating light and dark staining along the entire length of the vertebral axis of the embryo. In the younger embryos, a simple banding pattern emerged where the rostral sclerotome half of each segment stained only lightly while the caudal half stained darkly. This banding pattern was present throughout the 6 day period of development and could be traced continuously but grew more complex as the sclerotome cells migrated to surround the notochord and neural tube and as the dorsal root ganglia developed. The rostral sclerotome half was found to contribute to the caudal part of one vertebral body and its neural arch, while the caudal sclerotome half was found to contribute to the intervertebral disc, the rostral half of the next caudal vertebra, and part of its neural arch.

The primitive streak

The emphasis of this review is on the primitive streak of the chick embryo, collated with such information as is available on the mouse embryo. Little modern work has been published on any reptile primitive streak. The following topics are considered: evolutionary significance; formation of the primitive streak; ingression and de-epithelialisation; the basal lamina; migration from the primitive streak of the endoderm and mesoderm; the role of the extracellular matrix; changes in cell adhesiveness; regression of the primitive streak and its role in body patterning; the primitive streak and induction.