Ultrastructural and histochemical changes in the murine zona pellucida during the final stages of oocyte maturation prior to ovulation

Abstract

The ultrastructural morphology of the mouse zona pellucida was studied in preovulatory follicles from the ovaries of immature mice treated with exogenous gonadotrophins. The ovaries were fixed in the presence of cetylpyridinium chloride, which precipitates carbohydrates, so that their loss during fixation and processing is substantially reduced. The semi-thin araldite sections obtained from osmicated material were viewed by conventional light microscopy, while the ultra-thin sections were examined by transmission electron microscopy. A parallel series of semi-thin sections of non-osmicated ovaries was deresined and subsequently stained with periodic acid Schiff (PAS). The morphological appearance of the zona pellucida in preovulatory oocytes changed during the final stages of oocyte maturation. A close correlation was observed between the ultrastructural appearance of the zona pellucida and that observed following PAS staining during the period studied. Real differences were observed in the location, density, and distribution of glycoconjugates within the zona pellucida during the final stages of oocyte maturation prior to and immediately following germinal vesicle breakdown. Similar changes in the zona were observed in adult females autopsied during proestrus and oestrus. The changes in the density and distribution of glycoconjugates are likely to have important consequences for fertilization by affecting sperm-zona binding and sperm-egg interactions.

Distribution of lectin‐binding glycosidic residues in the hamster follicular oocytes and their modifications in the zona pellucida after ovulation

“…Furthermore, the absence of labeling by PNA and DSA over the secretory granules of the non-ciliated secretory cells in the hamster oviduct and the marked decrease in the density of labeling by the same lectins over both inner and outer ZP of ovulated oocytes led us to exclude the oviduct as a possible effector in the modi®cations of galactosyl sugar residues after ovulation. Therefore, we are tempted to consider these modi®cations as an indication of redistribution of pre-existing ZP glycocomponents in response to hormonal triggering of ovulation by gonadotropins (Talbot, 1984;Kaufman et al, 1989). Similar assumption can apply to the sialic acid (Neu5Ac) residues despite the moderate intensity of labeling by MAA over the non-ciliated secretory granules of the oviduct.…”

Pyriform cell differentiation in Podarcis sicula is accompanied by the appearance of surface glycoproteins bearing α‐galNAc terminated chains

“…Indeed, the Podarcis ZP, which was found to be rich in GalNAc, GluNAc, Man, and Gal residues, exhibited the same lectin-binding pattern throughout oocyte growth. In mammals, differences in the carbohydrate composition and/or spatial distribution within the ZP of preantral, antral, and ovulated oo- cytes have been extensively documented in several species (Kaufman et al, 1989;Roux and Kan, 1991;Shalgi et al, 1991;Araki et al, 1992;Aviles et al, 1994;Parillo et al, 1998;Parillo and Verini Supplizi, 1999). Such differences have generally been related to the unequal distribution and composition of sperm receptors that are localized in the mammalian ZP (Bleil and Wassarman, 1980;Yamagata, 1985;Wassarman, 1995).…”

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

“…Identical distribution patterns were obtained after exposing isolated ZP or small fragments of ZP to the lectins, suggesting that the results observed reflected specific binding of the lectin examined, and were not affected by factors such as the lectin size, thickness or permeability of the ZP. An uneven distribution of sugar residues in mammalian ZP was also demonstrated using post-embedding labeling with lectins in the rat , hamster (Roux and Kan 1991), and by different reactivity to periodic acid-Schiff staining in the mouse (Kaufman et al 1989). Accordingly, differences between inner and outer surfaces of the ZP were demonstrated in the hamster (Phillips and Shalgi 1980;Ahuja and Bolwell 1983), and in the house musk shrew (Suprasert et al 1989).…”

“…In several species, a maturational process of the ZP was demonstrated (mouse, Kaufman et al 1989; hamster, Oikawa Kan et al 1990;Kimura et al 1991;Roux and Kan 1991;rat, Shalgi et al 1991). The postembedding EM-labeling method used in some of these studies has the advantage of allowing an even accessibility to receptors throughout the entire thickness of the ZP.…”