HETEROGENEITY OF THE ZONA-PELLUCIDA CARBOHYDRATE DISTRIBUTION IN HUMAN OOCYTES FAILING TO FERTILIZE IN-VITRO

The mammalian zona pellucida contains several glycoproteins whose olig osaccharide moieties are known to play a key role in the interaction w ith spermatozoa, Since zona pellucida defects may represent one of the most likely causes of failed fertilization in human in-vitro reproduc tion, we have studied the carbohydrate composition and distribution ov er the human zona pellucida by means of lectins, Donated, not insemina ted cumulus-oocyte complexes, from cohorts with high fertilization rat es, and fertilization-failed oocytes from cohorts inseminated with pro ven fertile donor semen, were analysed using 11 fluorescein-labelled l ectins, on deplasticized semi-thin epoxy sections. Results showed that wheat germ agglutinin (WGA), Maclura pomifera (MPA) and Pisum sativum (PSA) bound to the extracellular matrix bordering the zona pellucida- corona radiata interface of cumulus-oocytes complexes, while the zona pellucida was labelled by WGA, Concanavalin A (ConA) and PSA, WGA labe lling and correlative electron microscopy on the cumulus-oocyte comple xes demonstrated that this lectin is a useful tool to trace the cortic al granule distribution in the human oocyte, Surprisingly, in the fail ed-fertilized oocytes the zona pellucida was also labelled by MPA and showed three different patterns: (i) labelling of the zona pellucida o uter surface; (ii) uniform labelling; (iii) labelling of an outer zona pellucida layer with variable thickness, Comparative analysis of WGA and MPA labelling on single failed-fertilized oocytes demonstrated tha t MPA zona pellucida patterns are not related to the cortical reaction . The nature and meaning of the MPA pattern of failed-fertilized oocyt es were discussed in the light of zona pellucida defects impairing spe rm receptivity.