Localization of endogenous galactoside-binding lectin during morphogenesis of Xenopus laevis

Production of a monoclonal antibody by in vitro immunization that recognizes a native chondroitin sulfate epitope in the embryonic chick limb and heart

We report the production of a monoclonal antibody (d1C4) by in vitro immunization that has immunoreactivity with a native chondroitin sulfate epitope in embryonic chick limb and heart. Murine lymphocytes were stimulated by direct exposure to unfixed, unsolubilized precartilage mesenchymal aggregates in high-density micromass culture derived from Stage 22-23 chick limb buds. Specificity of d1C4 reactivity was demonstrated by sensitivity of immunohistochemical staining to pretreatment with chondroitinase ABC or AC, preferential immunoreactivity with chondroitin-6-sulfate glycosaminoglycan (CS-C GAG) in ELISA, and competition of immunohistochemical staining with CS-C GAG. Immunohistochemical analysis of the expression of the d1C4 epitope revealed a striking localization of immunoreactivity in the extracellular matrix (ECM) of precartilage aggregates of chick limb mesenchyme in high-density micromass culture by 16 hr and the prechondrogenic limb core at Stage 23 in vivo. Immunoreactivity in both cultured limb mesenchyme and the embryonic limb continued through differentiation of prechondrogenic condensations into cartilage tissue. In the developing chick heart, d1C4 staining was found throughout the ECM of atrioventricular cushion tissue by Stage 25, but was localized to mesenchyme adjacent to the myocardium in the outflow tract cushions. There was an abrupt demarcation between d1C4-reactive intracardiac mesenchyme and unreactive extracardiac mesenchyme of the dorsal mesocardium in the Stage 22 embryo. This study demonstrates the efficacy of in vitro immunization of lymphocytes for the production of MAbs to native ECM constituents, such as CS-GAGs. Immunohistochemical data utilizing d1C4 suggest that CS-GAGs bearing this epitope may be important in early morphogenetic events leading to cartilage differentiation in the limb and valvuloseptal morphogenesis in the heart.

The primary structure and carbohydrate specificity of a beta-galactosyl-binding lectin from toad (Bufo arenarum Hensel) ovary reveal closer similarities to the mammalian galectin-1 than to the galectin from the clawed frog Xenopus laevis

The detailed characterization of a galectin from the toad (Bufo arenarum Hensel) ovary in its primary structure, carbohydrate specificity, and overall biochemical properties has provided novel information pertaining to structural and evolutionary aspects of the galectin family. The lectin consists of identical single-chain polypeptide subunits composed of 134 amino acids (calculated mass, 14,797 daltons), and its N-terminal residue, alanine, is N-acetylated. When compared to the sequences of known galectins, the B. arenarum galectin exhibited the highest identity (48% for the whole molecule and 77% for the carbohydrate recognition domain (CRD)) with the bovine spleen galectin-1, but surprisingly less identity (38% for the whole molecule and 47% for the CRD) with a galectin from Xenopus laevis skin (Marschal, P., Herrmann, J., Leffler, H., Barondes, S. H., and Cooper, D. N. W. (1992) J. Biol. Chem. 267, 12942-12949). Unlike the X. laevis galectin, the binding activity of the B. arenarum galectin for N-acetyllactosamine, the human blood group A tetrasaccharide and Galbeta1,3GalNAc relative to lactose, was in agreement with that observed for the galectin-1 subgroup and those galectins having "conserved" (type I) CRDs (Ahmed, H., and Vasta, G. R. (1994) Glycobiology 4, 545-549). Moreover, the toad galectin shares three of the six cysteine residues that are conserved in all mammalian galectins-1, but not in the galectins from X. laevis, fish, and invertebrates described so far. Based on the homologies of the B. arenarum galectin with the bovine spleen galectin-1 and X. laevis skin galectin, it should be concluded that within the galectin family the correlation between conservation of primary structure and phylogenetic distances among the source species may not be a direct one as proposed elsewhere (Hirabayashi, J., and Kasai, K. (1993) Glycobiology 3, 297-304). Furthermore, galectins with conserved (type I) CRDs, represented by the B. arenarum ovary galectin, and those with "variable" (type II) CRDs, represented by the X. laevis 16-kDa galectin, clearly constitute distinct subgroups in the extant amphibian taxa and may have diverged early in the evolution of chordate lineages.

Confrontation of developing melanophore bars of dark and white axolotls with endogenous dark-embryo mannose-binding lectin correlates with melanophore bar disruption

Lectins are carbohydrate-binding proteins suggested to be important in embryonic cell adhesion/differentiation. Dark and white axolotls contain an endogenous mannose-binding lectin that is especially prevalent during larval melanophore pattern formation (Martha et al., 1990). To determine if this lectin can alter melanophore patterning, lectin extracts have been isolated from Dark embryos by affinity chromatography. The main protein band is 44K on SDS-PAGE. Dark and white embryos at the early chromatophore migration stage have been confronted with Dark lectin or its nonmetabolized inhibitor, 2-deoxyglucose (2-DG). The barred melanophore pattern of both genotypes is disrupted by lectin or 2-DG treatment suggesting that endogenous mannose-binding lectin and its receptor participate in bar formation.

Probing the functions of endogenous lectins: effects of a monoclonal antibody against the neural crest-stage lectin of Xenopus laevis on trunk development

Trunk neural crest of Xenopus laevis has been confronted prior to migration with whole or fragments of a monoclonal antibody raised against the carbohydrate-binding site of the endogenous neural crest-stage galactoside binding lectin (Milos et al.: Anat. Embryol., 182:319-327 '90). External fin formation was inhibited in confronted regions but extensive internal matrix develops suggesting interiorization of fin tissue. In the regions of missing fin, the myotomes overgrew the neural tube and dorsal root ganglion neuronal numbers became more variable. Melanophore numbers in regions of missing fin did not change but a significantly greater proportion of the pigment cells localized on the muscle surface that had overgrown the neural tube suggesting that the pigment cell population redistributed itself to occupy a greater myotomal area.

Changing complexity of endogenous lectin activities during juvenile development of Xenopus laevis

Galactoside-binding lectin has been isolated from whole Xenopus laevis embryos and tadpoles at four development stages: st. 24-26, 32, 41 and 47. The main lectin activity at st. 24-26 is β-galactoside specific, producing a 34/35.5K doublet on SDS-PAGE. Later in development, lectin activities specific for a wide range of other sugars appear concommitant with the detection of a number of new protein bands on SDS-PAGE gels. The greatest variety of new lectin activities exists at st. 32 when lectins specific for all of the main sugar families found in nature are detected. After this stage and up to st. 47 (the beginning of metamorphosis), fewer different lectin activities are again detected. The results suggest that a complex, developmentally regulated battery of different lectins are present during early Xenopus development, perhaps with stage-specific roles to play in the control of tissue morphogenesis.