Differential expression of lectin binding sites in equine compact and expanded cumuli oocytes

(Cp) or expanded (Ex) cumuli. Cp-oocytes nave lower meiotic competence, slower rate of maturation, reduced ability to respond to activation stimuli and reduced male pronucleus formation rate after ICSI when compared to Ex-oocytes. Glycoconjugates play a key role in oocyte maturation and fertilization. We here investigated the glycoconjugate expression in equine Cp and Ex cumuli by lectin histochemistry. Cumulus-enclosed oocytes from abbattoir ovaries were fixed in Bouin's solution and embedded in paraffin wax after in vitro maturation. Sections (5 um thick) were stained with il lectins (SNA, PNA, DBA, RCA120, SBA, HPA, Con A, GSA I-B4, GSA II, UEA I, LTA). The ooplasm of Cp-oocytes showed a major reactivity for SNA, SBA, HPA, GSA I-B4 with respectto Ex ones,whereas botri type of oocytes displayed same affinity for DBA, Con A, GSA II and no binding sites for PNA, DBA, RCA120, UEA I, LTA. The zona pellucida of botri Cp and Ex oocytes were unreactive for GSA I-B4, GSA II, UEA I, ITA whereas in Cp oocytes showed no binding sites for SNA and PNA, a lower staining with RCA120 and a higher reactivity for HPA than Ex ones. Corona radiata cells from both oocytes types did not react with DBA, showed same reactivity with SNA, RCA120, GSA I-B4, and GSA II. In Cp-oocytes, it did not react with PNA but showed major affinity for SBA, HPA, Con A, UEA I, and LTA. The different glycoprotein pattern observed between equine Cp and Ex oocytes may be related to their different meiotic and developmental competence. Research supportated by MIUR COFIN-PRIN 2003