Project 1: Conditional clock gene regulation of mammalian circadian rhythms

Dr. Joseph Takahashi and Dr. Michael Menaker, Project Leaders

This project will test the role of the central SCN pacemaker in the control of peripheral rhythms using tissue-specific inducible regulation of circadian clock gene expression. Specifically, we will test whether central (SCN) manipulation of circadian rhythms is sufficient to regulate circadian rhythms in the body or whether both central and peripheral rhythms can be regulated more efficiently in concert.

We propose to utilize the powerful in vivo inducible transgene methods developed by Bujard and colleagues (tetracycline Transactivator (tTA) system) to regulate clock gene expression conditionally in a tissue-specific and temporal manner. We have identified a set of genes whose promoters can be used to drive tTA expression in the SCN. These “drivers” have expression patterns restricted to the brain, and thus can be used to test central vs. peripheral control of circadian rhythms on behavior as well as in specific tissues. As a proof of principle of this approach, we will first validate this approach by conditional rescue of the Clock locus in the SCN of mutant mice. This will test the hypothesis that the SCN (and brain) are sufficient to drive wild-type circadian rhythms of locomotor activity while the body and peripheral organs remain mutant. In addition, we will be able to rescue Clock gene function in peripheral tissues such as the liver and skeletal muscle to test potential effects on behavior and to determine whether “local” tissue-specific rescue of Clock function is sufficient to generate normal circadian rhythms in these tissues in the presence or absence of wild-type SCN function. Conditional experiments of this type will open new avenues of investigation concerning the integration of circadian systems biology not previously possible. They will also provide important reagents for the field to test the role of circadian components in the context of the intact organism.