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

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Abstract
A study was carried out to determine whether pig cortical granules (CGs) could be visualized using fluorescein isothiocyanate (FITC)‐labelled lec‐tins. 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.