In this study we investigated the effects of gravity over 1 G on the distribution of cortical granules (CGs) in mouse oocytes. We had found eggs incubated in a centrifuge culture medium showing a high rate of polyspermy, but there had been no difference between 2 G and 3 G loads in the incidence of polyspermy. We focused on cortical granules (CGs) which are known to act as a protection against polyspermy. The CG-free area of mouse oocytes subjected to increased G, when compared to that of

more »

... l oocytes, was found to be significantly larger. Therefore, it can be assumed that the increased G caused an abnormal CG distribution which resulted in a high incidence of polyspermy in oocytes subjected to increased G. Further, as the centrifugation force was increased, the CGs free area of oocytes did not tend to expand. Observation was facilitated by using FITC-LCA fluorescent dye and TEM.