Distribution of Cortical Granules in Porcine Oocytes Inseminated In Vitro at Various Times of Culture for Maturation In Vitro

Abstract

The distribution of cortical granules (CGs) during in vitro maturation of porcine oocytes was investigated with a confocal laser microscope. The incidence of exocytosis of CGs in oocytes inseminated at various maturation stages was also investigated to determine the dependency of the block of polyspermy on the zona reaction in porcine oocytes matured in vitro. CGs were synthesized but not yet transported beneath the oolemma at 18 h of culture (GVBD stage). CGs transported beneath the oolemma were found at 30 h of culture (at stages metaphase I to anaphase I). From 24 h to 36 h of culture, when a dramatic change in the pattern of distribution of CGs was observed, oocytes were inseminated. Although there was no difference among the groups in the rate of oocytes penetrated, the rate of polyspermy decreased as the culture period of the oocytes was prolonged to more than 30 h. It can be concluded from the results that the oocytes in which cortical granules have been transported beneath the oolemma can react to some degree against excessive penetration of spermatozoa, but polyspermy could not be avoided completely. This may reflect the incomplete amount of CGs synthesized during culture or the incompleteness of exocytosis of CGs in the oocytes matured in vitro.