Hundreds of mice have been generated with Cre expressed under control of tissue or cell specific promoters, allowing space/anatomical control of the recombination. And other mice were generated to check the correct recombination. Conversely, relatively few systems allow temporal control. Current solutions include the "activation" of Cre by a ligand given opportunely at selected time. Particularly, I read about:
- The exploitation of a tetracycline-responsive promoter (St Onge, 1996);
- The use a fusion protein to obtain modulation of Cre activity by steroids like ecdysone (No et al., 1996) or tamoxifen (Danielian et al., 1998);
- A dimerizable approach, in which two Cre mojeties complement upon binding to a rapamycin molecule (Jullien et al., 2007).
Recently, I read about noninvasive in vivo local heating by means of high-intensity focused ultrasound (HIFU) . Deckers and colleagues, implemented such technique in combination with a heat-inducible promoter [heat shock protein 70 (HSP70)] driving luciferase expression. They monitored local hypertermia with MRI thermometry and evaluated gene induction by bioluminescence imaging. Nice. Really cool. Now I'm wondering how can I convince my boss to buy one HIFU, one MRI and one more BLI workstation instead of just another syringe to inject tetracycline?!
R. Deckers, B. Quesson, J. Arsaut, S. Eimer, F. Couillaud, C. T. W. Moonen (2009). Image-guided, noninvasive, spatiotemporal control of gene expression Proceedings of the National Academy of Sciences, 106 (4), 1175-1180 DOI: 10.1073/pnas.0806936106