Lectin Histochemistry Shows Fucosylated Glycoconjugates in the Primordial Germ Cells ofXenopusEmbryos

Abstract

Previous works have shown that glycoconjugates with terminal fucose (Fuc) are located in the primordial germ cells (PGCs) of some mammals and might play a role in the migration and adhesion processes during development. The aim of this work was to identify the terminal Fuc moieties of Xenopus PGCs by means of three Fuc-binding lectins: from asparagus pea (LTA), gorse seed (UEA-I), and orange peel fungus (AAA). The histochemical procedures were also carried out after deglycosylation pretreatments: β-elimination with NaOH to remove O-linked oligosaccharides; incubation with PNGase F to remove N-linked carbohydrate chains; and incubation with α(1,2)- and α(1,6)-fucosidase. The PGCs were always negative for LTA and UEA-I, two lectins that have the highest affinity for Fuc α(1,2)-linked. However, the PGCs were strongly labeled with AAA, which preferentially binds to Fuc with α(1,3) or α(1,4) linkages and to Fuc α(1,6)-linked to the proximal N-acetylglucosamine. There was fainter labeling with AAA when the sections were preincubated with α(1,6)-fucosidase, but the labeling remained strong when the sections were pretreated with α(1,2)fucosidase. When the β-elimination procedure was carried out, the PGC labeling with AAA was slight. If the PNGase F incubation was performed, the PGCs remained moderately positive for AAA. These data suggest that the Xenopus PGCs have Fuc moieties in O- and N-linked oligosaccharides, including Fuc α(1,6) linked to the innermost GlcNAc, and that the Fuc was not in α(1,2)-linkage.