There’s a season for everything, King Solomon reportedly said: a time to be born and a time to die, a time for war and a time for peace. Modern science says there’s also the best time to wake up – at 6 am, when metabolism starts running; the best time for love – at 8 am, when sex hormones are about to peak; the best time to see a dentist – at 2 pm, when sensitivity to pain drops; and the worst time to drive – at 2 am, when the body is geared for its deepest sleep.
Such peaks and valleys are determined by internal biological “clocks” that operate in approximately 24-hour cycles known as circadian, from Latin,
circa diem, meaning “approximately a day.” These clocks regulate the daily fluctuations in heartbeat, blood pressure, kidney function, body temperature, sleeping and waking, sensory perception and the secretion of many hormones. The body’s master circadian clock, residing in the brain, synchronizes a multitude of peripheral clocks present not only in every organ in the body but in every single cell. “Our body is a collection of myriad microscopic clocks that all ‘tick’ in unison,” says
Dr. Gad Asher, who recently joined the Weizmann Institute’s Biological Chemistry Department. “Moreover, amazingly enough, these clocks function perfectly well even when the cells are cultured in a laboratory dish.”
A major aim of Asher’s new lab at the Institute is to find out why we need circadian clocks and how they function. Though science does not yet have an answer to these questions, it’s obvious that the clocks are vital. For one, studies suggest that shift workers tend to have a higher incidence of cancer, diabetes and obesity, as well as signs of accelerated aging, apparently because their circadian clocks are disrupted by work patterns that don’t follow the regular day-and-night cycle. Another indication of the clocks’ importance is their survival throughout millions of years of evolution, from plants and bacteria to humans: Such survival generally means that a mechanism is important enough for nature to keep. Finally, as many as 15 percent of all genes have circadian rhythms. “That’s an incredibly high number – it means that various processes in our bodies run entirely differently at different times of the day,” says Asher.
One striking example of such a process was discovered by accident, as often happens in science, in the lab of Prof. Ueli Schibler at the University of Geneva. Several years before Asher joined that lab to conduct his postdoctoral research, Schibler’s team had discovered that a protein called DBP could be purified in unusually high amounts from liver cells. But after the scientists had already published these findings in a prestigious journal, something seemed to go terribly wrong. When they repeated the same experiments, they suddenly couldn’t purify the protein at all. After a brief spell of panic, the quandary was resolved. It turned out that the original experiments had been performed by a student who used to come to the lab at 6 am, as was the custom in his Swiss peasant family. In contrast, the follow-up experiments were conducted by an American student who, needing a rest after late-night partying, used to start work at 2 pm. It so happened that the liver protein under study was regulated by the circadian clock: Its early-morning production was a hundred times higher than in the afternoon.
This fascinating discovery gave rise to an entire series of in-depth studies of circadian clocks in Schibler’s Geneva lab. “Geneva is a world leader in all types of clock – not just the Swiss cuckoo clocks, but circadian clocks as well,” says Asher.
Among the major questions addressed by Asher’s current studies is how circadian clocks are regulated. It’s known that the master clock in the brain is reset every day by light-dark cycles. As for the clocks in peripheral organs, the major cues for their synchronization are feeding times; it therefore seems that peripheral clocks are extremely sensitive to the metabolic state of cells. While working in Prof. Schibler’s lab, Asher discovered that a protein called SIRT1, which plays a central role in cellular metabolism, also controls the circadian clocks’ function. This discovery, according to the journal Cell, suggests that the SIRT1 might be the “missing link” between metabolism and circadian clocks. In his lab at Weizmann, Asher now intends to expand his studies into the relationship between metabolic factors and circadian mechanisms.
Asher’s ultimate goal is to clarify how circadian clocks work at the molecular and cellular levels, and how the central clock in the brain synchronizes peripheral clocks in other organs. His studies are aimed at answering fundamental biological questions that are related to a wide variety of physiological and pathological conditions – from jetlag and sleep disturbances to cancer, diabetes, obesity and aging.
Devoted to science
Born in Ramat Gan, Gad Asher started out by studying mathematics as part of a special program at Tel Aviv University to promote excellence, but then switched to medicine, earning his M.D. degree with distinction in 1998. Already as a medical student, he was fascinated by biological research, spending three summer internships at the Weizmann Institute. While working as a resident internist at the Tel Aviv Sourasky Medical Center, he began doctoral studies in the Weizmann Institute’s Department of Molecular Genetics under the guidance of Prof. Yosef Shaul. Upon earning his Ph.D. degree in 2006, he decided to devote himself entirely to science. After four years of postdoctoral research at the University of Geneva, Switzerland, he joined the Weizmann faculty as a Senior Scientist in May 2011. Outside the lab, he plays classical piano and enjoys bicycle racing and mountain climbing.
Dr. Gad Asher's research is supported by the estate of Dorothy Geller; Ms. Rudolfine Steindling, Austria; and the Willner Family Leadership Institute.
A team of Weizmann Institute scientists has turned the tables on an autoimmune disease. In such diseases,
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The Science of the Slow Slip
Slow quakes, says Dr. Eran Bouchbinder of the Chemical Physics Department (Faculty of Chemistry), appear to be a common occurrence. It is only the recent development of novel geophysical and laboratory measurement techniques that have enabled scientists to uncover their existence and prevalence. Researchers are eager to understand the physical principles underlying the slow quakes: Are they governed by the same physics as their fast counterparts? What is actually determining their speed? There is some evidence that in certain cases, slow quakes may be precursors of the fast ones, though no one can say, as yet, how to identify those that might presage a major event.
Both types of earthquake involve frictional interfaces – the surfaces where the plates meet. Such interfaces are present in a great number of physical systems and play a central role in phenomena occurring on widely disparate scales, ranging from nano-machines and tiny biological motors to the geophysical scale of earthquakes. The strength and stability of these interfaces is an issue of fundamental importance; when frictional interfaces fail, it could spell trouble.
According to conventional models, frictional resistance decreases as the sliding speed rises: The faster something slides the easier the sliding becomes. This is why an interfacial rupture tends to accelerate until it approaches the limit – the speed of sound. But the new model Bouchbinder and his team proposed allows for a different scenario: Frictional resistance first acts as in the standard model, decreasing with increasing sliding speed; but at some point the effect is reversed, and friction begins to progressively rise again. The slow quake phenomenon, says Bouchbinder, should occur around that point in the model at which friction levels reach their minimum and begin to swing upwards. The speed of the rupture, in this case, is determined by the frictional properties of the interface alone, rather than by the speed of sound, and thus can be orders of magnitude slower.
Bouchbinder and his team now plan to continue testing their mathematical model with more complicated calculations and to compare their predictions to experimental measurements, in hopes of providing a useful tool for better understanding the failure of frictional interfaces, including those that result in earthquakes.