How the biological clock of the body works. Why was the Nobel Prize in Medicine awarded in 2017?
Geoffrey Hall, Michael Rosebash and Michael Young website
Three American scientists shared the highest scientific award for research on the mechanism of the internal clock in living organisms
Life on Earth is adapted to the rotation of our planet around the Sun. For many years we have known about the existence inside living organisms, including humans, of a biological clock that helps to anticipate the daily rhythm and adapt to it. But how exactly does this clock work? American geneticists and chronobiologists have been able to look inside this mechanism and shed light on its hidden workings. Their discoveries explain how plants, animals and humans adjust their biological rhythms to keep in sync with the Earth's daily rotation cycle.
Using fruit flies as test subjects, the 2017 Nobel Prize winners have isolated a gene that controls the normal circadian rhythm in living things. They also showed how this gene encodes a protein that accumulates in the cell at night and breaks down during the day, thereby forcing it to follow this rhythm. Subsequently, they identified additional protein components that control the mechanism of self-sustaining "clocks" inside the cell. And now we know that the biological clock functions according to the same principle both inside individual cells and inside multicellular organisms, for example, humans.
Due to its exceptional accuracy, our internal clock adjusts our physiology to such different phases of the day - morning, afternoon, evening and night. This clock regulates important functions such as behavior, hormone levels, sleep, body temperature and metabolism. Our well-being suffers when the external environment and internal clocks are out of sync. An example is the so-called jet lag that occurs with travelers who move from one time zone to another, and then cannot adapt to the shift of day and night for a long time. They sleep during daylight hours and cannot sleep in the dark. Today, there is also a lot of evidence that a chronic mismatch between lifestyle and natural biorhythms increases the risk of various diseases.
Our internal clock cannot be fooled
Experiment by Jean-Jacques d "Ortois de Mairan Nobel Committee
Most living organisms clearly adapt to daily changes in the environment. One of the first to prove the existence of this adaptation back in the 18th century was the French astronomer Jean-Jacques d "Ortois de Mayran. He watched a mimosa bush and found that its leaves turn after the sun during the day and close with sunset. The scientist wondered what would What happened if the plant was in constant darkness?After a simple experiment, the researcher found that, regardless of the presence of sunlight, the leaves of the experimental mimosa continue to make their usual daily movements.As it turned out, plants have their own internal clock.
More recent studies have shown that not only plants, but also animals and humans are subject to the work of biological clocks, which help to adapt our physiology to daily changes. This adaptation is called the circadian rhythm. The term comes from the Latin words circa - "about" and dies - "day". But how exactly this biological clock works has long been a mystery.
Discovery of the "clock gene"
In the 1970s, the American physicist, biologist, and psychogeneticist Seymour Benzer, along with his student Ronald Konopka, investigated whether it was possible to isolate the genes that control the circadian rhythm in fruit flies. The scientists were able to show that mutations in a gene unknown to them disrupt this rhythm in experimental insects. They called it the period genome. But how did this gene affect the circadian rhythm?
The 2017 Nobel Prize winners also conducted experiments on fruit flies. Their goal was to discover the mechanism of the internal clock. In 1984, Jeffrey Hall and Michael Rozbash, who worked closely with each other at Brandeis University in Boston, and Michael Young of Rockefeller University in New York, successfully isolated the period gene. Hall and Rosebash then found that the PER protein encoded by this gene accumulates in cells during the night and is destroyed during the day. Thus, the level of this protein fluctuates during the 24-hour cycle in sync with the circadian rhythm. The "pendulum" of the internal cellular clock was discovered.
Self-adjusting clockwork
A simplified diagram of the work in the cell of proteins that regulate the circadian rhythm Nobel Committee
The next key goal was to understand how these circadian fluctuations can be generated and maintained. Hall and Rozbash suggested that the PER protein during the diurnal cycle blocks the activity of the period gene. They believed that with the help of an inhibitory feedback loop, the PER protein could periodically prevent its own synthesis and thereby regulate its level in a continuous cyclical rhythm.
Only a few elements were missing to build this curious model. To block the activity of the period gene, the PER protein produced in the cytoplasm would have to reach the cell nucleus, where the genetic material is contained. The experiments of Hall and Rozbash showed that this protein actually accumulates in the nucleus at night. But how does he get there? This question was answered in 1994 by Michael Young, who discovered the second key "clock gene" that encodes the TIM protein necessary for maintaining a normal circadian rhythm. In simple and elegant work, he showed that when TIM is bound to PER, these two proteins are able to enter the cell nucleus, where they actually block the period gene to close the inhibitory feedback loop.
Such a regulatory mechanism explained how this fluctuation in cellular protein levels arose, but did not solve all the questions. For example, it was necessary to establish what controls the frequency of daily fluctuations. To solve this problem, Michael Young isolated another gene that codes for the DBT protein; it delays the accumulation of the PER protein. Thus, it was possible to understand how this fluctuation is regulated in order to coincide as closely as possible with the 24-hour cycle.
These discoveries made by today's laureates underlie the key principles of the functioning of the biological clock. Subsequently, other molecular components of this mechanism were discovered. They explain the stability of its work and the principle of operation. For example, Hall, Rosebash, and Young discovered additional proteins needed to activate the period gene, as well as the mechanism by which daylight synchronizes the biological clock.
The influence of circadian rhythms on human life
Human Circadian Rhythm Nobel Committee
The biological clock is involved in many aspects of our complex physiology. We now know that all multicellular organisms, including humans, use similar mechanisms to control circadian rhythms. Much of our genes are regulated by the biological clock, so a carefully tuned circadian rhythm adapts our physiology to the different phases of the day. Thanks to the seminal work of today's three Nobel laureates, circadian biology has evolved into a vast and dynamic field of research that studies the impact of circadian rhythms on our health and well-being. And we received one more confirmation that it is still better to sleep at night, even if you are an inveterate "owl". It's healthier.
Reference
Geoffrey Hall was born in 1945 in New York, USA. He received his doctorate in 1971 from the University of Washington (Seattle, Washington). Until 1973, he was a professor at the California Institute of Technology (Pasadena, California). Since 1974 he has been working at Brandeis University (Waltham, Massachusetts). In 2002, he began collaborating with the University of Maine.
Michael Rozbash was born in 1944 in Kansas City, USA. He received his doctorate from the Massachusetts Institute of Technology (Cambridge, Massachusetts). For the next three years he was a doctoral student at the University of Edinburgh in Scotland. Since 1974 he has been working at Brandeis University (Waltham, Massachusetts).
Michael Young was born in 1949 in Miami, USA. He completed his doctoral studies at the University of Texas (Austin, Texas) in 1975. Until 1977, he was a postdoctoral fellow at Stanford University (Palo Alto, California). In 1978 he joined the faculty of Rockefeller University in New York.
Translation of materials from the Royal Swedish Academy of Sciences.
The annual Nobel Week began in Stockholm on Monday with the announcement of the prize winners in Physiology or Medicine. The Nobel Committee announced that the 2017 Prize went to researchers Jeffrey Hall, Michael Rosbash and Michael Young for
the discovery of molecular mechanisms that control circadian rhythms - cyclic fluctuations in the intensity of various biological processes associated with the change of day and night.
Life on Earth is adapted to the rotation of the planet. It has long been established that all living organisms, from plants to humans, have a biological clock that allows the body to adapt to the changes that occur during the day in the environment. The first observations in this area were made at the beginning of our era, more thorough research began in the 18th century.
By the 20th century, the circadian rhythms of plants and animals had been studied quite fully, but it remained a secret how exactly the “internal clock” worked. This secret was revealed to the American geneticists and chronobiologists Hall, Rosbash and Yang.
Fruit flies have become a model organism for research. A team of researchers managed to find in them a gene that controls biological rhythms.
Scientists have found that this gene encodes a protein that accumulates in cells during the night and is destroyed during the day.
Subsequently, they identified other elements responsible for the self-regulation of the "cellular clock" and proved that the biological clock works in a similar way in other multicellular organisms, including humans.
The internal clock adapts our physiology to completely different times of the day. Our behavior, sleep, metabolism, body temperature, hormone levels depend on them. Our well-being deteriorates when there is a discrepancy between the work of the internal clock and the environment. So, the body reacts to a sharp change in the time zone with insomnia, fatigue, and a headache. The jet lag syndrome, jet lag, has been included in the International Classification of Diseases for several decades. The mismatch of lifestyle with the rhythms dictated by the body leads to an increased risk of developing many diseases.
The first documented experiments with internal clocks were carried out in the 18th century by the French astronomer Jean-Jacques de Meran. He found that the leaves of the mimosa drop with the advent of darkness and straighten out again in the morning. When de Meran decided to test how the plant would behave without access to light, it turned out that mimosa leaves fell and rose regardless of the light - these phenomena were associated with a change in the time of day.
Later, scientists found that other living organisms also have similar phenomena that adjust the body to changes in conditions during the day.
They were called circadian rhythms, from the words circa - "around" and dies - "day". In the 1970s, physicist and molecular biologist Seymour Benzer wondered if the gene controlling circadian rhythms could be identified. He managed to do this, the gene was named period, but the control mechanism remained unknown.
In 1984, Hall, Rooibach and Young managed to recognize him.
They isolated the necessary gene and found that it is responsible for the accumulation and destruction of the protein associated with it (PER) in cells, depending on the time of day.
The next task for the researchers was to understand how circadian fluctuations are generated and maintained. Hall and Rosbash suggested that the accumulation of protein blocks the operation of the gene, thereby regulating the content of protein in cells.
However, in order to block the work of the gene, the protein formed in the cytoplasm must reach the cell nucleus, where the genetic material is located. It turned out that PER does build into the kernel at night, but how does it get there?
In 1994, Young discovered another gene, timeless, that codes for the TIM protein, which is essential for normal circadian rhythms.
He found that when TIM binds to PER, they are able to enter the cell nucleus, where they block the operation of the period gene due to feedback inhibition.
But some questions still remained unanswered. For example, what controlled the frequency of circadian fluctuations? Young later discovered another gene, doubletime, responsible for the formation of the DBT protein, which delayed the accumulation of the PER protein. All of these discoveries have helped to understand how fluctuations are adapted to the 24-hour daily cycle.
Subsequently, Hall, Rooibas and Young made several more discoveries that supplemented and refined the previous ones.
For example, they identified a number of proteins required to activate the period gene, and also uncovered the mechanism by which the internal clock is synchronized with light.
The most likely contenders for the Nobel Prize in this area were virologist Yuan Chang and her husband, oncologist Patrick Moore, who discovered the herpes virus type 8 associated with Kaposi's sarcoma; Professor Lewis Cantley, who discovered the signaling pathways of phosphoinositide-3-kinase enzymes and studied their role in tumor growth; and Professor Carl Friston, who made a major contribution to the analysis of brain imaging data.
In 2016, the winner of the Japanese Yoshinori Ohsumi Prize for the discovery of the mechanism of autophagy, the process of degradation and processing of intracellular debris.
In 2017, the Nobel Prize in Medicine was awarded to three American scientists who discovered the molecular mechanisms responsible for the circadian rhythm - the human biological clock. These mechanisms regulate sleep and wakefulness, the functioning of the hormonal system, body temperature and other parameters of the human body that change depending on the time of day. Read more about the discovery of scientists in the material RT.
Winners of the Nobel Prize in Physiology or Medicine Reuters Jonas Ekstromer
The Nobel Committee of the Karolinska Institute in Stockholm on Monday, October 2, announced that the 2017 Nobel Prize in Physiology or Medicine was awarded to American scientists Michael Young, Geoffrey Hall and Michael Rosbash for their discoveries of the molecular mechanisms that control the circadian rhythm.
"They were able to get inside the body's biological clock and explain how it works," the committee said.
Circadian rhythms are called cyclic fluctuations of various physiological and biochemical processes in the body associated with the change of day and night. In almost every organ of the human body, there are cells that have an individual molecular clockwork, and therefore, circadian rhythms are a biological clock.
According to a release from the Karolinska Institute, Young, Hall and Rosbash have isolated a gene in fruit flies that controls the release of a particular protein depending on the time of day.
“Thus, scientists were able to identify the protein compounds that are involved in the operation of this mechanism, and to understand the work of the independent mechanics of this phenomenon inside each individual cell. We now know that the biological clock works on the same principle in the cells of other multicellular organisms, including humans, ”the committee that awarded the prize says in a release.
- Drosophila fly
- globallookpress.com
- imagebroker/Alfred Schauhuber
The presence of a biological clock in living organisms was established at the end of the last century. They are located in the so-called suprachiasmatic nucleus of the hypothalamus of the brain. The nucleus receives information about the level of light from receptors on the retina and sends a signal to other organs using nerve impulses and hormonal changes.
In addition, some cells of the nucleus, like the cells of other organs, have their own biological clock, the work of which is provided by proteins, the activity of which varies depending on the time of day. The activity of these proteins determines the synthesis of other protein bonds that generate circadian rhythms of the vital activity of individual cells and entire organs. For example, staying indoors with bright lights at night can shift the circadian rhythm, activating protein synthesis of the PER genes, which usually begins in the morning.
Also, the liver plays a significant role in circadian rhythms in the body of mammals. For example, rodents like mice or rats are nocturnal animals and eat at night. But if food becomes available only during the day, their liver circadian cycle shifts by 12 hours.
Rhythm of life
Circadian rhythms are daily changes in body activity. They include the regulation of sleep and wakefulness, hormone secretion, body temperature and other parameters that change in accordance with the circadian rhythm, explains Alexander Melnikov, a somnologist. He noted that researchers have been developing in this direction for several decades.
“First of all, it should be noted that this discovery is neither yesterday nor today. These studies have been carried out for many decades - from the 80s of the last century to the present - and have made it possible to discover one of the deep mechanisms that regulate the nature of the human body and other living beings. The mechanism that scientists have discovered is very important for influencing the daily rhythm of the body, ”Melnikov said.
- pixabay.com
According to the expert, these processes occur not only because of the change of day and night. Even in the conditions of the polar night, circadian rhythms will continue to operate.
“These factors are very important, but very often they are disturbed in people. These processes are regulated at the gene level, which was confirmed by the prize winners. Nowadays, people very often change time zones and are exposed to various stresses associated with sudden changes in the circadian rhythm. The intense rhythm of modern life can affect the correct adjustment and opportunities for rest of the body, ”concluded Melnikov. He is confident that the study of Yang, Hall and Rosbash provides an opportunity to develop new mechanisms for influencing the rhythms of the human body.
Award history
The founder of the award, Alfred Nobel, in his will entrusted the selection of the laureate in physiology and medicine to the Karolinska Institute in Stockholm, founded in 1810 and one of the leading educational and scientific medical centers in the world. The University's Nobel Committee consists of five permanent members, who, in turn, have the right to invite experts for consultations. There were 361 names on the list of nominees for the award this year.
The Nobel Prize in Medicine has been awarded 107 times to 211 scientists. Its first laureate was in 1901 the German physician Emil Adolf von Behring, who developed a method of immunization against diphtheria. The Committee of the Karolinska Institute considers the most significant prize of 1945, awarded to the British scientists Fleming, Cheyne and Flory for the discovery of penicillin. Some awards have become obsolete over time, such as the award awarded in 1949 for the development of the lobotomy method.
In 2017, the prize was increased from SEK 8 million to SEK 9 million (about $1.12 million).
The award ceremony will traditionally take place on December 10, the day of the death of Alfred Nobel. Prizes in the fields of physiology and medicine, physics, chemistry and literature will be awarded in Stockholm. The Peace Prize, according to Nobel's will, is awarded on the same day in Oslo.
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The Nobel Committee has announced the winners of the 2017 Physiology or Medicine Prize today. This year the award will once again travel to the US, with Michael Young of the Rockefeller University in New York, Michael Rosbash of Brandeis University and Geoffrey Hall of the University of Maine sharing the award. According to the decision of the Nobel Committee, these researchers were awarded "for their discoveries of the molecular mechanisms that control circadian rhythms."
It must be said that in the entire 117-year history of the Nobel Prize, this is perhaps the first prize for the study of the sleep-wake cycle, as well as for anything related to sleep in general. The famous somnologist Nathaniel Kleitman did not receive the award, and Eugene Azerinsky, who made the most outstanding discovery in this area, who discovered REM sleep (REM - rapid eye movement, fast sleep phase), generally received only a PhD degree for his achievement. It is not surprising that in numerous forecasts (we will talk about them in our note) there were any names and any research topics, but not those that attracted the attention of the Nobel Committee.
What was the award for?
So, what are circadian rhythms and what exactly did the laureates discover, who, according to the secretary of the Nobel Committee, greeted the news of the award with the words “Are you kidding me?”.
Geoffrey Hall, Michael Rosbash, Michael Young
Circa diem translated from Latin as "around the day". It so happened that we live on planet Earth, where day is replaced by night. And in the course of adapting to different conditions of day and night, organisms developed internal biological clocks - the rhythms of the biochemical and physiological activity of the organism. It was only in the 1980s that it was possible to show that these rhythms had an exclusively internal nature by sending mushrooms into orbit. Neurospora crassa. Then it became clear that circadian rhythms do not depend on external light or other geophysical signals.
The genetic mechanism of circadian rhythms was discovered in the 1960s–1970s by Seymour Benzer and Ronald Konopka, who studied mutant lines of fruit flies with different circadian rhythms: in wild-type flies, circadian rhythm fluctuations had a period of 24 hours, in some mutants - 19 hours, in others - 29 hours, and the third had no rhythm at all. It turned out that rhythms are regulated by the gene PER - period. The next step, which helped to understand how such fluctuations in the circadian rhythm are created and maintained, was taken by the current laureates.
Self-adjusting clockwork
Geoffrey Hall and Michael Rosbash suggested that the gene encoded period PER protein blocks the work of its own gene, and such a feedback loop allows the protein to prevent its own synthesis and cyclically, continuously regulate its level in cells.
The picture shows the sequence of events over 24 hours of fluctuation. When the gene is active, PER mRNA is produced. It exits the nucleus into the cytoplasm, becoming a template for the production of the PER protein. The PER protein accumulates in the cell nucleus when the activity of the period gene is blocked. This closes the feedback loop.
The model was very attractive, but a few pieces of the puzzle were missing to complete the picture. To block the activity of a gene, the protein needs to get into the nucleus of the cell, where the genetic material is stored. Jeffrey Hall and Michael Rosbash showed that the PER protein accumulates overnight in the nucleus, but did not understand how it managed to get there. In 1994, Michael Young discovered the second circadian rhythm gene, timeless(English "timeless"). It codes for the TIM protein, which is essential for our internal clock to function properly. In his elegant experiment, Young demonstrated that only by binding to each other, TIM and PER paired can enter the cell nucleus, where they block the gene period.
Simplified illustration of the molecular components of circadian rhythms
This feedback mechanism explained the reason for the appearance of oscillations, but it was not clear what controls their frequency. Michael Young found another gene double time. It contains the DBT protein, which can delay the accumulation of the PER protein. This is how fluctuations are “debugged” so that they coincide with the daily cycle. These discoveries revolutionized our understanding of the key mechanisms of the human biological clock. Over the following years, other proteins were found that influence this mechanism and maintain its stable operation.
For example, this year's laureates have discovered additional proteins that make a gene period work, and proteins, with the help of which light synchronizes the biological clock (or causes jetlag in case of a sharp change in time zones).
About the award
Recall that the Nobel Prize in Physiology or Medicine (it is worth noting that in the original name in place of “and” the preposition “or” sounds) is one of the five prizes determined by the testament of Alfred Nobel in 1895 and, if you follow the letter of the document, should be awarded annually "for a discovery or invention in the field of physiology or medicine" made in the previous year and brought the maximum benefit to mankind. However, the "principle of last year" was not respected, it seems, almost never.
Now the prize in physiology or medicine is traditionally awarded at the very beginning of the Nobel week, on the first Monday in October. It was first awarded in 1901 for the development of a serum therapy for diphtheria. In total, the prize has been awarded 108 times in history, in nine cases: in 1915, 1916, 1917, 1918, 1921, 1925, 1940, 1941 and 1942, the prize was not awarded.
Between 1901 and 2017, the prize was awarded to 214 scientists, a dozen of whom are women. So far, there has not been a case that someone has received a prize in medicine twice, although there have been cases when an already current laureate has been nominated (for example, ours). Excluding the 2017 award, the average age of the laureate was 58 years. The youngest Nobel laureate in the field of physiology and medicine was the 1923 laureate Frederick Banting (award for the discovery of insulin, age 32), the oldest was the 1966 laureate Peyton Rose (award for the discovery of oncogenic viruses, age 87 years).
The first Nobel Prize in 2017, which is traditionally awarded for achievements in the field of physiology and medicine, went to American scientists for the discovery of a molecular mechanism that provides all living beings with their own "biological clock". This is the case when literally everyone can judge the significance of scientific achievements, marked by the most prestigious award: there is no person who would not be familiar with the change in the rhythms of sleep and wakefulness. Read about how these watches are arranged and how we managed to figure out their mechanism in our material.
Last year, the Nobel Prize Committee in Physiology or Medicine surprised the public - against the backdrop of increased interest in CRISPR / Cas and oncoimmunology, an award for deeply fundamental work done by methods of classical genetics on baker's yeast. This time, the committee again did not follow the fashion and noted the fundamental work done on an even more classic genetic object - Drosophila. Prize winners Geoffrey Hall, Michael Rosbash and Michael Young, working with flies, have described the molecular mechanism underlying circadian rhythms, one of the most important adaptations of biological beings to life on planet Earth.
What is a biological clock?
Circadian rhythms are the result of the circadian, or biological clock. The biological clock is not a metaphor, but a chain of proteins and genes, which is closed according to the principle of negative feedback and makes daily fluctuations with a cycle of approximately 24 hours - in accordance with the duration of the earth's day. This chain is quite conservative in animals, and the principle of the clock is the same in all living organisms - which have them. Currently, it is reliably known about the presence of an internal oscillator in animals, plants, fungi and cyanobacteria, although some rhythmic fluctuations in biochemical parameters are also found in other bacteria. For example, the presence of circadian rhythms is assumed in bacteria that form the human intestinal microbiome - they are regulated, apparently, by host metabolites.
In the vast majority of terrestrial organisms, the biological clock is regulated by light - so they make us sleep at night, and stay awake and eat during the day. When the light regime changes (for example, as a result of a transatlantic flight), they adjust to the new regime. In a modern person who lives in conditions of round-the-clock artificial lighting, circadian rhythms are often disturbed. According to experts from the US National Toxicology Program, shifted work hours to evening and night hours are fraught with serious health risks for people. Among the disorders associated with disruption of circadian rhythms are sleep and eating disorders, depression, impaired immunity, an increased likelihood of developing cardiovascular disease, cancer, obesity and diabetes.
The human daily cycle: the wakefulness phase begins at dawn, when the body releases the hormone cortisol. The consequence of this is an increase in blood pressure and a high concentration of attention. The best coordination of movements and reaction time are observed during the day. By evening, there is a slight increase in body temperature and pressure. The transition to the sleep phase is regulated by the release of the hormone melatonin, which is caused by a natural decrease in light. After midnight, the deepest phase of sleep normally begins. During the night, body temperature decreases and by morning reaches its minimum value.
Let us consider in more detail the structure of the biological clock in mammals. The higher command center, or “master clock,” is located in the suprachiasmatic nucleus of the hypothalamus. Information about illumination enters there through the eyes - the retina contains special cells that communicate directly with the suprachiasmatic nucleus. The neurons of this nucleus give commands to the rest of the brain, for example, regulate the production of the “sleep hormone” melatonin by the pineal gland. Despite the presence of a single command center, every cell of the body has its own clock. The “master clock” is just what is needed in order to synchronize or reconfigure the peripheral clock.
Schematic diagram of the diurnal cycle of animals (left) consists of phases of sleep and wakefulness, coinciding with the feeding phase. On the right is shown how this cycle is realized at the molecular level - by reverse negative regulation of clock genes.
Takahashi JS / Nat Rev Genet. 2017
The key gears in the clock are the CLOCK and BMAL1 transcription activators and the PER repressors (from period) and CRY (from cryptochrome). The CLOCK-BMAL1 pair activates the expression of genes encoding PER (of which there are three in humans) and CRY (of which there are two in humans). This happens during the day and corresponds to the state of wakefulness of the body. By evening, PER and CRY proteins accumulate in the cell, which enter the nucleus and suppress the activity of their own genes, interfering with activators. The lifetime of these proteins is short, so their concentration drops rapidly, and by morning CLOCK-BMAL1 are again able to activate PER and CRY transcription. So the cycle repeats.
The CLOCK-BMAL1 pair regulates expression not only of the PER and CRY pairs. Among their targets are also a couple of proteins that suppress the activity of CLOCK and BMAL1 themselves, as well as three transcription factors that control many other genes that are not directly related to the work of the clock. Rhythmic fluctuations in the concentrations of regulatory proteins lead to the fact that from 5 to 20 percent of mammalian genes are subject to daily regulation.
And here are the flies?
Almost all of the genes mentioned and the whole mechanism as a whole was described using the example of a fruit fly - American scientists, including the current Nobel Prize winners: Jeffrey Hall, Michael Rosbash and Michael Young, did this.
The life of Drosophila, starting from the stage of hatching from the pupa, is strictly regulated by the biological clock. Flies fly, feed and mate only during the day, and "sleep" at night. In addition, during the first half of the 20th century, Drosophila was the main model object for geneticists, so by the second half, scientists had accumulated sufficient tools for studying fly genes.
The first mutations in genes associated with circadian rhythms were described in 1971 in a paper by Ronald Konopka and Seymour Benzer, who worked at the California Institute of Technology. Through random mutagenesis, the researchers managed to obtain three lines of flies with a violation of the circadian cycle: for some flies, there were as if there were 28 hours in a day (mutation per L), for others - 19 ( per S), and the flies from the third group had no periodicity in behavior at all ( per 0). All three mutations fell into the same DNA region, which the authors called period.
In the mid-80s, Gen. period was independently isolated and described in two laboratories - the laboratory of Michael Young at Rockefeller University and at Brandeis University, where Rosbash and Hall worked. In the future, all three did not lose interest in this topic, complementing each other's research. Scientists have found that the introduction of a normal copy of the gene into the brain of "arrhythmic" flies with a mutation per 0 restores their circadian rhythm. Further studies showed that an increase in copies of this gene shortens the daily cycle, and mutations that lead to a decrease in the activity of the PER protein lengthen it.
In the early 90s, Young's employees received flies with a mutation timeless (Tim). The TIM protein has been identified as a PER partner in the regulation of Drosophila circadian rhythms. It should be clarified that this protein does not work in mammals - its function is performed by the above-mentioned CRY. The PER-TIM pair performs the same function in flies as the PER-CRY pair does in humans - basically repressing its own transcription. Continuing to analyze arrhythmic mutants, Hall and Rosbash found genes clock and cycle- the latter is a mouse analogue of the BMAL1 factor and, together with the CLOCK protein, activates gene expression per and Tim. Based on the results of the research, Hall and Rosbash proposed a model of inverse negative regulation, which is currently accepted.
In addition to the main proteins involved in the formation of the circadian rhythm, a gene for "fine tuning" of the clock was discovered in Young's laboratory - double time(dbt), the product of which regulates the activity of PER and TIM.
Separately, it is worth mentioning the discovery of the CRY protein, which replaces TIM in mammals. Drosophila also has this protein, and it was described specifically on flies. It turned out that if the flies were illuminated with bright light before dark, their circadian cycle shifted slightly (apparently, this also works in humans). Hall and Rosbash's team found that the TIM protein is photosensitive and is rapidly destroyed even by a short light pulse. In search of an explanation for the phenomenon, scientists have identified a mutation cry baby, which canceled the lighting effect. A detailed study of the fly cry gene (from cryptochrome) showed that it is very similar to the circadian photoreceptors of plants already known at that time. It turned out that the CRY protein perceives light, binds to TIM and contributes to the destruction of the latter, thus prolonging the “wakefulness” phase. In mammals, CRY appears to function as a TIM and is not a photoreceptor, but in mice, turning off CRY has been shown, as in flies, to cause a phase shift in the sleep-wake cycle.
