Study of the growth regulation of preimplantation mouse embryos using concanavalin A

Characterization, fate, and function of hamster cortical granule components

Little is known about the composition and function of mammalian cortical granules. In this study, lectins were used as tools to: (1) estimate the number and molecular weight of glycoconjugates in hamster cortical granules and show what sugars are associated with each glycoconjugate; (2) identify cortical granule components that remain associated with the oolemma, cortical granule envelope, and/or zona pellucida of fertilized oocytes and preimplantation embryos; and (3) examine the role of cortical granule glycoconjugates in preimplantation embryogenesis. Microscopic examination of unfertilized oocytes revealed that the lectins PNA, DBA, WGA, RCA(120), Con A, and LCA bound to hamster cortical granules. Moreover, LCA and Con A labeled the zona pellucida, cortical granule envelope, and plasma membrane of fertilized and artificially activated oocytes and two and eight cell embryos. Lectin blots of unfertilized oocytes had at least 12 glycoconjugates that were recognized by one or more lectins. Nine of these glycoconjugates are found in the cortical granule envelope and/or are associated with the zona pellucida and plasma membrane following fertilization. In vivo functional studies showed that the binding of Con A to one or more mannosylated cortical granule components inhibited blastomere cleavage in two-cell embryos. Our data show that hamster cortical granules contain approximately 12 glycoconjugates of which nine remain associated extracellularly with the fertilized oocyte after the cortical reaction and that one or more play a role in regulating cleavage divisions.

Mammalian cortical granules: contents, fate, and function

Recent studies have extended our knowledge regarding the contents of mammalian cortical granules (CG) and their function in postfertilization events. Cytochemical staining has demonstrated the presence of carbohydrates within mammalian CG, and lectin-binding studies have shown that these carbohydrates include alpha-D-mannose, alpha-D-GalNAc, and galactose residues in the hamster, alpha-D-mannose in the mouse and cat, and beta-D-Gal(1,3)-D-GalNAc in the pig. Following fertilization and artificial activation, mannosylated material is released from CG and can be found on the oolemma and within the perivitelline space (PVS) of hamster oocytes. Fertilized or artificially activated rabbit, mouse, and human oocytes also release mannosylated, fucosylated and sialylated, and fucosylated material, respectively, which localizes to the oolemma. These glycosylated materials are probably of CG origin, although they have not been directly localized to the CG in rabbit, mice, and humans. The function(s) of the glycosylated material released from mammalian oocytes is not known, although it may participate in blocking polyspermy at the level of the plasma membrane, PVS, and/or zona pellucida (ZP), or it may facilitate preimplantation embryonic development. Proteinases, including tissue plasminogen activator, are also released from mammalian oocytes following fertilization and artificial activation, suggesting that they are of CG origin. These proteinases modify the ZP such that it is no longer receptive to sperm, and some proteinases have been suggested to bring about ZP hardening (an increased resistance to denaturing agents) by an unknown mechanism. Mouse ZP may also be hardened by an ovoperoxidase (cross-links tyrosine residues) cytochemically identified in mouse CG and CG exudate. The phenomena of ZP hardening in mammalian zygotes is not well understood but is likely to function in blocking polyspermic penetration of the ZP and/or in protecting embryos during preimplantation development. Recently, a 75 kD protein (p75) has been immunocytochemically localized to mouse CG and to the PVS of fertilized oocytes and two-cell embryos. The identity and function of p75 remains to be determined. Heparin binding placental protein may also be a CG component, since it is released from hamster oocytes following fertilization. It has not, however, been directly demonstrated to be a CG component, and its functions in fertilization and/or early embryonic development have yet to be defined.

Lectin-induced abnormalities of mouse blastocyst hatching and outgrowth in vitro

We have examined the role of cell surface glycoconjugates during mouse blastocyst maturation, hatching, attachment, and outgrowth by monitoring the influence of six lectins on blastocyst development in vitro. Two lectins, concanavalin A and wheat germ agglutinin were toxic to blastocysts at the concentrations used. Bandierea simplicifolia lectin 1 (BSL-1) induced abnormal growth, developmental arrest at the hatching stage, and some disruption of cell contacts. Culture with Lotus tetragonolobus lectin-1 (LTA-1) also disrupted cell contacts and caused developmental arrest. The remaining lectins, Dolichos biflorus agglutinin (DBA) and Ulex europaeus agglutinin (UEA), retarded blastocyst hatching and outgrowth but did not induce any major defects, although differentiation of the inner cell mass was limited by both. This study demonstrates that very low concentrations of lectins can disrupt blastocyst development, suggesting that exposed surface saccharide moieties may be involved in interactions between blastomeres and their environment.

Detection of differences in surface carbohydrates of unfertilized and fertilized golden hamster eggs using potato agglutinin

Changes in the surface carbohydrate moieties of zonae pellucidae and naked vitelli isolated from unfertilized and fertilized hamster eggs were examined through potato agglutinin (STA)-mediated agglutination and binding of FITC-STA as a marker. The results indicated that the stereochemical properties of the saccharide residues within STA-binding sites on the outer surface of the zona pellucida, inner region of the zona pellucida, and the surface of the ooplasmic membrane were different in unfertilized and fertilized eggs, that part of the differences between the two kinds of eggs could be visualized with FITC-STA and that, on the basis of these data, if we use STA as a probe to analyze the surface change following fertilization, we may be able to analyze these changes to a substantial degree.

Ultrastructural study of concanavalin-A binding to the surface of preimplantation mouse embryos

Receptors for Con-A were labelled (using the peroxidase-diaminobenzidine technique) on the plasma membrane of unfertilized and fertilized mouse eggs, cleavage stage embryos, trophoblast and inner cell mass (ICM) of the blastocyst. Embryos were exposed to Con-A concentrations of 10 microgram/ml, 50 microgram/ml, or 1,000 microgram/ml and the lowest concentration was observed to be the most suitable for discerning differences between stages of embryonic development. On the surface of unfertilized and fertilized eggs and 2-cell embryos, reaction product appeared as a thin, discontinuous layer. The surface of 4- and 16-cell stage embryos had a thicker, continuous, although non-uniform, layer of the reaction product. On the surface of the cells of the late morula, and on the trophoblastic cells of the blastocyst, clustering of reaction product was observed. Cells of ICM of intact blastocyst were free of the reaction product, showing that either Con-A and/or peroxidase cannot penetrate tight junctions between trophoblastic cells. Reaction product in the form of a thin, uniform layer covered the free surface of the cells of the ICM after they had been isolated (using immunosurgery) and exposed to 50 microgram/ml of Con-A. The amount and distribution of Con-A receptors is discussed, along with their redistribution and mobility in relation to the agglutinability of preimplantation mouse embryos.