Although the outlines of the death circuitry in cells are rapidly emerging, our current models undoubtedly are sim- plistic. It seems highly likely that there are additional pathways, driven by other activator caspases and their corresponding adaptors--neither of the above pathways accounts for the culling of autoreactive thymocytes, for example. Significant differences probably will emerge in the circuitry of various cell types and there may be cross-talk between pathways as well as feedback loops to amplify or dampen signals. Much remains to be established, particularly about how Bcl-2-related proteins regulate the caspase cascade. Further gene targeting currently on line and crosses of mutant mice hold great promise for unraveling the cellular secrets of life and death.
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