ULTRASTRUCTURAL-LOCALIZATION OF LECTIN RECEPTORS IN THE PREIMPLANTATION OVINE EMBRYO

Background: Preimplantation development of mammalia is characterized b y cell surface changes functioning in intercellular communication and adhesion. The glycoconjugate role in cellular interactions has been an alysed for several groups but not in sheep embryos. The binding patter ns of eleven lectins during sheep preimplantation development were inv estigated and the role of glycoconjugates in early development was dis cussed. Methods: Ultrathin sections from preimplantation ovine embryos (3-7 days) were incubated with different colloidal gold conjugated le ctins and the frequency of gold particles on the cell membrane, some o rganelles, and the zona pellucida was evaluated. Results and Conclusio ns: We observed a higher staining of WGA, DBA, and SBA lectins in the intercellular contact zone with respect to the free cell surface of bl astomeres during cleavage. This indicates that the N-acetyl galactosam ine and N-acetyl glucosamine residues may be involved in sheep morula compaction. In contrast, the trophoblast cell displays an increase of staining of some lectins previously identified during cleavage (LcH, W GA, SBA, MPA, and PNA) on the free membrane, and a lack of sugar resid ues in the intercellular surface. This polarization of the trophoblast cell surface is not observed in the inner cell mass and could provide a mechanism for differentiation within the blastocyst. Intracytoplasm ic vesicles show a cytochemical identity with lysosomes in the blastoc yst (abundant GlcNAc and Man/Glc residues) that may reflect a function al relationship between both organelles in an intracellular cycle. The zona pellucida presents abundant GlaNAc, GlcNAc, and Gal residues dur ing preimplantation ovine development. (C) 1994 Wiley-Liss, Inc.