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Cellular/Molecular Biology of Biological Clocks

Carl Johnson
Department of Biology
615-322-2384 (office)

My lab studies daily biological clocks in a variety of organisms, and we use luminescence as a tool to monitor these clocks. In mammals, our lab uses transgenic mice and mammalian fibroblasts expressing different kinds of light-emitting enzymes (“luciferases”) to monitor rhythms of gene expression and calcium levels by the rhythmic glow of the reporter luciferase. Therefore, our lab uses luminescence as a tool to monitor circadian rhythms in the brain and in cell cultures. These studies are directed towards understanding the calcium signal transduction pathway to the core clock and the role of clock genes in the fundamental mammalian clockwork. We have recently extended our studies to the genetics of the human biological clock. We are examining clock gene polymorphisms in human populations to determine how the neurogenetics of the biological clock affects our ability to adapt to shiftwork cycles and how it caninfluence mental health (esp. depression).

My laboratory also studies rhythmic behavior in bacteria (specifically, blue-green algae). To study the clock mechanism in cyanobacteria, we used a bacterial luciferase reporter as a genetic marker in order to find other genes that control clock function. My lab, in collaboration with labs in Japan and Texas A&M, has identified three bacterial genes that are essential for biological clock function. In collaboration with Drs. Martin Egli and Phoebe Stewart at Vanderbilt, we study the structural biology of these bacterial clock proteins. The three purified proteins exhibit circadian oscillations in a test tube! Therefore, the Johnson/Egli/Stewart labs are taking advantage of our past structural work to analyze and explain how these proteins can oscillate in vitro. Furthermore, my lab is using clock mutants of the bacteria to provide the first rigorous evidence for the adaptive significance of circadian clocks in fitness.

Finally, we developed a new method for measuring protein-protein interactions based upon the resonance energy between a luciferase and a fluorescent protein. This method is called Bioluminescence Resonance Energy Transfer, or BRET. This technique has allowed the development of novel reporters for intracellular calcium and hydrogen ions. A bright future is envisioned for BRET.

For more information, please visit the lab website.