Fig. 8. Effect of MCD-mediated removal of cholesterol and its repletion on Xenopus egg fertilization. A group of Xenopus unfertilized eggs (30 eggs) were untreated (control), pretreated with 25 mM MCD (middle) or pretreated with 25 mM MCD then treated with cholesterol (right), and subjected to insemination as in Fig. 7A. The appearance of sperm entry point and cortical contraction (a marker of egg activation) were scored after microscopic observation. Number of positive eggs/total number of eggs tested is indicated.