Shin Yamazaki, Ph.D. - US grants

[unreadable] DESCRIPTION (provided by applicant): Circadian rhythms, which measure time on a scale of 24 h, are the overt consequences of biological clocks. When isolated from environmental time cues, a circadian oscillator free-runs with its own period which is usually different from 24 h. However, in the presence of the natural cycle of light and temperature, circadian oscillators are adjusted to exactly 24 h. Because these two major environmental signals are closely associated in nature, it is not surprising that the entraining effect of temperature cycles mimics that of the light-dark cycle in fungi, plants and poikilotherms. Most scientists, however, would predict that homeotherms would not be affected by temperature. Nevertheless, using Per1-luc transgenic rats to measure circadian fluctuations of Per1 from cultured suprachiasmatic nuclei (SCN), we have shown that the isolated SCN can be entrained by temperature cycles with an amplitude as low as 1 [unreadable]C, well within the range of the normal brain temperature rhythm of rodents (1 to 1.5 [unreadable]C). One of the unique and fundamental phenomena in circadian rhythms is temperature compensation; rhythms exhibit similar cycle durations over a wide range of temperatures. Although this phenomenon was discovered nearly 50 years ago, the biochemical or molecular mechanisms mediating this phenomenon are still not known. It was previously shown that the rhythms in the SCN and retina in mammals are temperature compensated. Our lab recently demonstrated that temperature compensation also exists in peripheral cells. In this proposal, the two major impacts of temperature on the mammalian circadian system: entrainment and compensation will be analyzed. The hypothesis that temperature entrainment is mediated by changing Per1 mRNA levels, whereas temperature compensation is affected by different degradation rates of mRNAs in three Period genes will be studied. [unreadable] The overall goal of our proposal is to identify molecular targets in the clock mechanism responsible for the demonstrated temperature effects. Information obtained in this proposal will be essential for the informed use of circadian approaches to the understanding and treatment of circadian-related concerns in humans, such as shift work, jet-lag, and chrono-cancer therapy. [unreadable] [unreadable]

Our internal biological clocks are synchronized with our external surroundings and regulate our daily (circadian) rhythms of behavior and physiology. The mammalian circadian system is composed of multiple clocks located in the brain and throughout the body. Most studies have investigated the central clock in the brain, which synchronizes to the environmental cycle of light and dark. In contrast, other clocks, such as those that respond to feeding time, are "black box" mysteries because their locations in the body are unknown. In this project, behavioral, molecular, and mathematical approaches will be combined to investigate the timekeeping mechanisms of these elusive clocks and how they functionally interact with the circadian system to control behavior. These studies will identify genes that are important for timekeeping in these clocks and future studies evaluating the expression patterns of these genes could lead to the identification of the location(s) of these oscillators, which could transform our understanding of the function of the circadian system.

This research is a unique opportunity for undergraduate and post-doctoral trainees to participate in a project that will address long-standing speculation about biological timekeeping. The studies will teach trainees about the value of experimental observation, creativity, and using multiple technical approaches when developing and testing hypotheses. Trainees from all academic levels, including a postdoctoral fellow, undergraduate students and high school students, and from diverse demographic backgrounds, including women and underrepresented minorities, will be immersed in an environment rich in the study of circadian biology. Finally, this project will provide opportunities for community outreach, because lab members organize and operate the biological clocks booth at free events for children of all economic and racial backgrounds.

Project Summary Circadian rhythms are fundamental to living organisms. The mammalian circadian system is a multi-oscillatory system composed of a master pacemaker located in the hypothalamic suprachiasmatic nucleus (SCN) and many other oscillators located in peripheral organs. The SCN entrains to the environmental light-dark cycle and adjusts physiological and behavioral rhythms accordingly. Another putative pacemaker, the food-entrainable oscillator (FEO), entrains to feeding cycles. This oscillator is located outside of the SCN and controls food anticipatory activity. For more than 90 years the anatomical locus of the FEO has eluded scientists. However, recent studies have revealed the FEO oscillates without canonical circadian genes. We will capitalize on this discovery by performing non-biased screening for the brain area responsible for FEO timekeeping in mice without functional circadian genes. Successful completion of the proposed experiments will be a long-awaited advance; one essential to identifying the neural basis of anticipatory feeding behavior. This is necessary to understand the non-canonical molecular circadian timekeeping mechanisms and the function of the FEO. Disruption of the clock system with shiftwork and/or artificial light at night has been implicated as a risk factor for human diseases. In addition, sleep and circadian rhythms are impaired in several neurological disorders. An innovative approach to treating people with sleep and circadian related disorders is to regulate the timing of meals. Therefore, understanding the mechanistic basis of the FEO (how the rhythm is generated and synchronized to the environment) is necessary for developing strategies to treat and prevent diseases caused by circadian disruptions.

Project Summary Circadian rhythms are fundamental to living organisms. The mammalian circadian system, which controls daily rhythms of behavior and physiology, is a multi-oscillatory system composed of a master pacemaker in the hypothalamic suprachiasmatic nucleus (SCN) and many other oscillators in peripheral organs. However, the SCN is not the only pacemaker. When arousing stimuli are present, circadian behavior rhythms are observed even when circadian clocks in the SCN and peripheral tissues are disabled. The molecular mechanisms, anatomical loci, and functional significance of these extra-SCN pacemakers are not known. We have assembled molecular and imaging toolsets and technologies to identify the neural circuitry and physiological outputs of those extra-SCN pacemakers. The proposed studies will uncover the functional significance of the enigmatic extra-SCN circadian pacemakers in mammals. The discovery of the loci and physiological roles of the extra-SCN pacemakers will expand our understanding of the molecular and physiological processes of the circadian system. Importantly, our studies will investigate how the SCN and extra-SCN pacemakers interact to regulate feeding and sleep. Disruption of circadian rhythms and sleep by shiftwork and exposure to artificial light at night increases the risk of human diseases. In addition, sleep and circadian rhythms are impaired in several neurological disorders and in persons with drug addictions. Therefore, understanding how extra-SCN pacemakers control circadian rhythms will elucidate novel processes that could be manipulated to manage circadian disruption in humans.