Distribution of carbohydrates in the zona pellucida of human oocytes

The purpose of the present study was to investigate the distribution pattern of carbohydrates in the zona pellucida of human oocytes using lectins and ruthenium red as histochemical probes. For lectin analyses, oocytes that failed to undergo fertilization following in vitro insemination were collected, washed, fixed with glutaraldehyde and embedded in araldite. For ruthenium red labelling, the oocytes were fixed with glutaraldehyde containing ruthenium red, post-fixed with OsO4 and embedded in araldite. Araldite sections (1 micron) were de-resined with sodium methoxide, rehydrated, labelled with ten different biotinylated lectins as probes and avidin-biotin-peroxidase complex as visualant, and examined under a light microscope. The zonae pellucidae of all oocytes studied exhibited a common lectin-binding pattern, expressed in intense binding of lectins from Concanavalia ensiformis (ConA), Lens culinaris (LCA), Ricinus communis (RCA-I), wheat germ agglutinin (WGA), and of succinylated WGA (S-WGA). Peanut lectin (PNA) bound to the zona pellucida only after neuraminidase treatment, whereas the lectins from Griffonia simplisifolia (GS-I), Dolichos biflorus (DBA), Ulex europhaeus (UEA-I) and soybean (SBA) did not bind at all. There was almost no binding of ruthenium red to the matrix of the zona pellucida. The results indicate that the human zona pellucida is characterized by normally exposed mannosyl, N-acetylglucosaminyl and beta-galactosyl residues. In addition, it contains masked beta Gal-(1-3)GalNAc sugar sequences that can be exposed only after removing terminal sialic acid residues.(ABSTRACT TRUNCATED AT 250 WORDS)