POSTFERTILIZATION CHANGES IN THE ZONA-PELLUCIDA GLYCOPROTEINS OF RAT EGGS

The zona pellucida (ZP) is the extracellular coat surrounding the mamm alian egg. Numerous evidence supports the role of ZP carbohydrate resi dues as the specific sperm receptors. In this study we used lectins to study different distribution patterns of carbohydrate residues in the rat ZP, and to follow changes at fertilization. ZP were collected fro m follicular, ovulated, and fertilized eggs, incubated with one of 11 different biotin-labeled lectins, followed by avidin-fluorescein iso t hiocyanate (FITC) complex, and visualized by epifluorescent microscopy . For electron microscope (EM) histochemistry, eggs were embedded in L R white and ultra thin sections were stained with the complex Ricinus communis lectin (RCA-1)-colloidal gold. Some lectins (RCA-I, Glycine m ax) bound to the entire ZP while others were restricted to the inner o r outer zones [Griffonia simplicifolia, Concanovalia ensiformis, Triti cum vulgaris (WGA), succinyl-WGA]. Other lectins (Lens culinaris, Ulex europhaeus) were totally excluded. The RCA-1 binding pattern changed following sperm penetration, from homogeneous in ZP of ovulated eggs ( 57%) to uneven in ZP of fertilized (71%) or activated (68%) eggs. Our results demonstrate an uneven distribution of different sugar residues in the rat ZP, and a post-fertilization change in the distribution of beta-galactose, which is specifically recognized by RCA-I, presumably correlated with other changes in the ZP that lead to the block to pol yspermy.