System-Driven and Oscillator-Dependent Circadian Transcription in Mice with a Conditionally Active Liver Clock
Figure 1
Conditional Repression of Bmal1 Transcription in Hepatocytes
(A) Hepatocyte-specific, Dox-dependent expression of HA-REV-ERBα was achieved by placing a 5′-HA-tagged REV-ERBα cDNA transgene under the control of seven TREs (Tet-responsive elements). In the liver of mice expressing the tetracycline (Tet)-responsive transactivator (tTA) from the hepatocyte-specific C/ebpβ-LAP locus control region, HA-Rev-erbα transcription is constitutively repressed in the absence of the tetracycline analog Dox (tet-off system). This leads to an attenuation of circadian oscillator function, since Bmal1 is required for circadian rhythm generation.
(B) LAP-tTA/TRE-Rev-erbα double transgenic mice display high HA-Rev-erbα mRNA and protein levels throughout the day in the absence of Dox (−Dox). In the presence 3 g/kg Dox in the food (+Dox), neither HA-Rev-erbα mRNA nor protein can be detected.
(C) The levels of both Bmal1 mRNA and BMAL1 protein are dramatically down-regulated in the absence of Dox (compare the lanes on the left to those on the right).