Lectin-binding sites in isolated equine cumulus-oocyte complexes. Differential expression of glycosidic residues in complexes recovered with compact or expanded cumulus

Equine cumulus-oocyte complexes (COCs) were analyzed by means of 13 lectins to evaluate their glycoconjugate patterns and to verify differences between COCs recovered with compact (Cp) and expanded (Exp) cumulus. Cumulus cells showed a similar staining pattern in both Cp and Exp COCs with all lectins used, except for a higher reactivity with SNA and GSA II in Cp COCs and SBA in Exp COCs. The zona pellucida (ZP) showed (1) uniform staining with MAL II, RCA120, and SBA in both Cp and Exp COCs, (2) trilaminar binding pattern with WGA as well as higher Con A reactivity in the outer region of both types of COCs, (3) uniform staining with PNA only in Exp COCs, (4) uniform and trilaminar binding pattern with SNA in Cp and Exp COCs, respectively, and (5) major reactivity with GSA II in Exp COCs. Ooplasm showed similar staining intensity with Con A, HPA, GSA I-B4, and WGA in both Cp and Exp COCs, with stronger reactivity to GSA II in Exp COCs, whereas SNA, UEA I, and LTA binding sites were present only in Cp COCs. Oocyte cortical granules of both Cp and Exp COCs reacted with Con A and WGA. These results suggest that, in the mare, viable (Cp) and atretic (Exp) COCs display different glycoconjugate staining pattern, which may account for the different maturation and developmental competence of COCs.