Characterization of the Xenopus Galectin Family

Abstract

We have isolated six novel galectin cDNAs from a Xenopus laevis kidney cDNA library. The newly identified X. laevis galectins (xgalectins) comprise one proto type (xgalectin-Vb), one chimera type (xgalectin-VIIa), and four tandem repeat types (xgalectin-IIb, -IIIb, -VIa, and -VIIIa). Thus, together with those mentioned in our previous work (Shoji, H., Nishi, N., Hirashima, M., and Nakamura, T. (2002) Glycobiology 12, 163-172), the 12 xgalectins are classified into three types based on their domain structures, as in mammals. The xgalectins whose counterparts in other species have not been identified (xgalectin-IVa, -Vb, and -VIa) were confirmed to possess lactose-binding activity by expression of their recombinant forms. This shows that they truly function as animal lectins. The protein purification study revealed that the major xgalectins in kidney are xgalectinIb, -IIa, -IIb, -IIIa, and -VIIa. The mRNAs of xgalectin-IIb, -IIIb, -Vb, and -VIa were localized to specific adult tissues, whereas those of xgalectin-VIIa and -VIIIa were broadly distributed. The temporal expression patterns of the mRNAs of the 12 xgalectins during embryogenesis were analyzed and categorized into three groups: 1) mRNA observed to exist throughout embryogenesis, i.e. maternal mRNA also exists (xgalectin-Ia, -IIa, -IIIa, -IIIb, -Va, -VIIa, and -VIIIa); 2) mRNA observed from the gastrula stage (xgalectin-VIa); and 3) mRNA observed from the tail bud or the tadpole stage (xgalectin-Ib, -IIb, -IVa, and -Vb). The mRNA of the most abundant xgalectin in embryos, xgalectin-VIIa, was localized to the surface layer of embryos, the epidermis, the cement gland, and various placodes. Xgalectin-VIIa protein was also observed to exist throughout embryogenesis by Western blot analysis with specific antiserum. These results show that the expression of each member is spatiotemporally regulated from eggs to adulthood, suggesting that galectins play multiple roles not only in adults, but also in development.Galectins comprise a family of animal lectins that bind to ␤-galactoside-containing carbohydrate moieties of glycoconjugates (1, 2). Fourteen galectins have been isolated from mammals and are classified into the proto, chimera, and tandem repeat types based on their structures (3-8). Proto-type galectins contain one carbohydrate recognition domain (CRD), 1 a structurally conserved domain that specifically recognizes a ␤-galactoside-containing carbohydrate; and chimera-type galectins consist of one CRD and an N-terminal elongating protein domain. Mammalian galectin-1 (proto type) and -3 (chimera type) are the most extensively studied galectins (9). They have been proposed to play roles in tissue organization, development, immunity, and cancer growth and metastasis by regulating such processes as cell adhesion and apoptosis. Tandem repeat-type galectins contain two CRDs covalently linked through a unique link peptide. Tandem repeat-type galectins are less well understood, but they have been shown to be expressed in a tissue-specific manner in adult animals ...

Heterologous expression of newly identified galectin-8 from sea urchin embryos produces recombinant protein with lactose binding specificity and anti-adhesive activity

“…By qPCR, we found that Pl - gal-8 transcripts showed a developmental upregulation at gastrula and pluteus stages. This finding is in accordance with the important role attributed to galectins in controlling morphogenetic events during embryogenesis 36 and particularly with the role assigned to carbohydrates and carbohydrate-bearing molecules in supporting cell-cell interactions during sea urchin gastrulation 37 . For example, the binding of secondary mesenchyme cells to the blastocoel roof is prevented by D-mannose like residues, resulting in the inhibition of gastrulation 37 .…”

Mutational Tuning of Galectin-3 Specificity and Biological Function

“…All the fluorescein-tagged saccharides have previously been described (19). Plasmids encoding human galectin-3 in pET-3c were as described (34), Xenopus galectin-3 (galectin VIIa (35)) in pET-11a was kindly provided by Dr. Hiroki Shoji, Kagawa University, Japan, and mouse galectin-3 in pIN III ompA2 (36) was kindly provided by Professor John L. Wang, Michigan State University.…”

Roles of galectins in infection

“…Most metazoans are endowed with a complex galectin repertoire, with members exhibiting multiple isoforms 53 and subtle variations in carbohydrate specificity. This, together with the plasticity observed in sugar binding 47 , suggests that there is substantial diversity in their glycan-recognition properties.…”