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Cell Cycle, Cell Death, and Senescence

Expression of Bcl-x_S in Xenopus Oocytes Induces BH3-Dependent and Caspase-Dependent Cytochrome c Release and Apoptosis¹

¹ Department of Neurobiochemistry, George S. Wise Faculty of Life Sciences and ² Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel

Requests for reprints: Reuven Stein, Department of Neurobiochemistry, George S. Wise Faculty of Life Sciences, Tel-Aviv University, 69978 Tel-Aviv, Israel. Phone: 972-3-640-8608; Fax: 972-3-640-7643. E-mail: reuvens{at}post.tau.ac.il

The mechanism of action of pro-apoptotic proteins is difficult to study in vivo because of their death effect, which makes it problematic to obtain sufficient homogeneous experimental material for biochemical analysis. We show here that pro-apoptotic genes expressed in Xenopus oocytes constitute a useful in vivo system for studying their mechanism of action. In the present study, we used this system to study the death effects of Bcl-x_S, a pro-apoptotic member of the Bcl-2 family. The results showed that expression of Bcl-x_S in oocytes induces oocyte death by a caspase-dependent mechanism, which includes BH3-dependent cytochrome c release and is inhibited by co-expression of the anti-apoptotic proteins Bcl-2 and Bcl-x_L. The release of cytochrome c was found to be dependent on caspase activity. Bcl-x_S was localized mainly in the mitochondria, and Bcl-x_S transmembrane and BH3 domains were required for its apoptotic effect. These findings suggest that Bcl-x_S induces apoptosis in Xenopus oocytes mainly by its presence in the mitochondria, where it induces BH3- and caspase-dependent release of cytochrome c, which leads to oocyte death.

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