Post-fertilization changes in the zona pellucida glycoproteins of rat eggs

Abstract

The zona pellucida (ZP) is the extracellular coat surrounding the mammalian egg. Numerous evidence supports the role of ZP carbohydrate residues 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 from follicular, ovulated, and fertilized eggs, incubated with one of 11 different biotin-labeled lectins, followed by avidin-fluorescein isothiocyanate (FITC) complex, and visualized by epifluorescent microscopy. For electron microscope (EM) histochemistry, eggs were embedded in LR white and ultrathin sections were stained with the complex Ricinus communis lectin (RCA-1)-colloidal gold. Some lectins (RCA-I, Glycine max) bound to the entire ZP while others were restricted to the inner or outer zones [Griffonia simplicifolia, Concanovalia ensiformis, Triticum 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 polyspermy.

Cellular and molecular mechanisms leading to cortical reaction and polyspermy block in mammalian eggs

“…Sperm receptors ZP3 and ZP2 are modified to become ZP2f and ZP3f by CG exudates shortly after fertilization and thus polyspermy is prevented (McLeskey et al, 1998;Wassamman, 1994). An uneven distribution of different sugar residues in the rat ZP and postfertilization changes in the distribution of ␤-galactose are supposed to be correlated with polyspermy block (Raz et al, 1996). Identified CG contents that may be involved in zona reaction are described as follows.…”