Conditional gene expression: a new tool for the transplantologist

The ability to generate genetically manipulated mice has revolutionized the study of development, cell biology, immunobiology and transplantation. Conventional gene targeting approaches lead to inactivation of the target gene in all tissues. This approach often has unintended consequences, such as embryonic lethality, which preclude studying the originally intended tissue. Newer approaches allowing conditional gene expression in a tissue-specific or temporally controlled fashion have the advantage of normal development with gene deletion only in the desired tissues. While nuances to these techniques continue to be developed, the underlying concepts remain consistent. This minireview focuses on the use of conditional gene targeting in mice using the Cre-loxP system and drug inducible gene expression using the tetracycline system.