Localization and Characterization of Lectins in Yolk Platelets of Xenopus Oocytes: (Xenopus oocyte/yolk lectin/endocytosis/immunohistochemistry/biochemistry).

The localization and characteristics of yolk platelet lectins (YLs) in Xenopus laevis oocytes were studied with antiserum against cortical granule lectins (CGLs) as a probe. In oocytes at stages I, II and III-IV, specific, immunofluorescent staining for the lectins was observed on the cortical cytoplasm extending about 2, 4 and 20 μm, respectively, from the egg surface. In stage III-IV oocytes, the superficial layer of the yolk platelets was also stained. The cortical cytoplasm included cortical granules, coated pits, coated vesicles, multivesicular bodies and primordial yolk platelets. The YLs were incorporated into the oocytes by endocytosis as demonstrated using gold-labeled YLs. On PAGE, native YLs gave two bands of CGL-like proteins and proteins that appeared as a single diffuse band. The YLs and the CGLs shared antigenicity and hemagglutination activity specific to D-galactoside residues. However, the proteins of the diffuse band had little or no activity for either hemagglutination or jelly-precipitation, suggesting that they were monomers with a single reactive site. These results indicate that the YLs are supplied to the oocytes, presumably from extracellular sources, polymerized to CGL-like molecules in the cortical cytoplasm and accumulated in the superficial layer of the yolk platelets.