Confocal and fluorescence microscopic study using lectins of the distribution of cortical granules during the maturation and fertilization of pig oocytes

Abstract

A study was carried out to determine whether pig cortical granules (CGs) could be visualized using fluorescein isothiocyanate (FITC)-labelled lectins. Following labelling with FITC-labelled peanut agglutinin (FITC-PNA), fluorescent spots were observed that had a distribution during maturation and fertilization entirely consistent with that observed by electron microscopy. For the first 18 h of in vitro maturation, most of the fluorescent spots of FITC-PNA were distributed throughout the cortical cytoplasm. Thereafter, the CGs underwent centrifugal migration to form a monolayer next to the plasma membrane. Following penetration by sperm, fluorescent spots were extruded into the perivitelline space, where they aggregated forming fluorescent clumps, which subsequently formed a reticulate structure surrounding the egg. Fluorescence was gradually lost such that by 18 h after insemination none could be detected in 70% of the eggs. The results indicate that CGs in pig oocytes contain galactosyl-rich glycoconjugates and that FITC-PNA is a useful probe for their rapid visualization and examination.