Oviductal Localization of the Cortical Granule Lectin Ligand Involved in the Block to Polyspermy of Xenopus Laevis

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Abstract
The fertilization layer of Xenopus laevis is formed upon egg activation by the binding of the cortical granule lectin (CGL) to its ligand in the egg extracellular matrix. Using Western blotting methods with biotinylated CGL as a probe, oviductal tissue extracts were examined to determine the site of origin of the CGL ligand. Three glycoprotein ligands of Mrs= > 250,000, 160,000, and 90,000 (reduced samples) were localized to the pars convoluta oviduct immediately posterior to the pars recta oviduct. The binding of CGL to these glycoproteins was inhibited in the presence of 200 mM galactose, but not with 200 mM mannose indicating a specific lectin interaction. The Mrs= > 250,000 and 90,000 glycoproteins were linked by disulfide bonds. In addition, these ligands were secreted from a more anterior region of the pars convoluta oviduct than the Mr=160,000 ligand. No binding of CGL was detected to pars recta secretory granule lysate components. The highest molecular weight CGL ligand seen in the pars convoluta corresponded to the CGL ligand in isolated fertilization envelopes. Thus, the CGL ligand involved in the formation of the fertilization layer is a product of the pars convoluta oviduct.

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