Navigation Links
Bioclocks work by controlling chromosome coiling

There is a new twist on the question of how biological clocks work.

In recent years, scientists have discovered that biological clocks help organize a dizzying array of biochemical processes in the body. Despite a number of hypotheses, exactly how the microscopic pacemakers in every cell in the body exert such a widespread influence has remained a mystery.

Now, a new study provides direct evidence that biological clocks can influence the activity of a large number of different genes in an ingenious fashion, simply by causing chromosomes to coil more tightly during the day and to relax at night.

The idea that the whole genome is oscillating is really cool, enthuses Vanderbilt Professor of Biological Sciences Carl Johnson, who headed the research that was published online Nov. 13 in the Proceedings of the National Academy of Sciences. The fact that oscillations can act as a regulatory mechanism is telling us something important about how DNA works: It is something DNA jockeys really need to think about.

Johnsons team, which consisted of Senior Lecturer Mark A Woelfle, Assistant Research Professor Yao Xu and graduate student Ximing Qin, performed the study with cyanobacteria (blue-green algae), the simplest organism known to possess a biological clock. The chromosomes in cyanobacteria are organized in circular molecules of DNA. In their relaxed state, they form a single loop. But, within the cell, they are usually supercoiled into a series of small helical loops. There are even two families of special enzymes, called gyrases and topoisomerases, whose function is coiling and uncoiling DNA.

The researchers focused on small, non-essential pieces of DNA in the cyanobacteria called plasmids that occur naturally in the cyanobacteria. Because a plasmid should behave in the same fashion as the larger and more unwieldy chromosome, the scientists consider it to be a good proxy of the behavior of the chromosome itself.

When the plasmid is relaxed, it is open and uncoiled and, when it is supercoiled, it is twisted into a smaller, more condensed state. So, the researchers used a standard method, called gel electrophoresis, to measure the extent of a plasmids supercoiling during different points in the day/night cycle.

The researchers found a distinct day/night cycle: The plasmid is smaller and more tightly wound during periods of light than they are during periods of darkness. They also found that this rhythmic condensation disappears when the cyanobacteria are kept in constant darkness.

This is one of the first pieces of evidence that the biological clock exerts its effect on DNA structure through the coiling of the chromosome and that this, in turn, allows it to regulate all the genes in the organism, says Woelfle.

Some cyanobacteria use their biological clocks to control two basic processes. During the day, they use photosynthesis to turn sunlight into chemical energy. During the night, they remove nitrogen from the atmosphere and incorporate it into a chemical compound that they can use to make proteins.

According to the Johnson labs oscilloid model, the genes that are involved in photosynthesis should be located in regions of the chromosome that are turned on by the tighter coiling in the DNA during the day and turned off during the night when the DNA is more relaxed. By the same token, the genes that are involved in nitrogen fixation should be located in regions of the chromosome that are turned off during the day when the DNA is tightly coiled and turned on during the night when it is more relaxed.

The researchers see no reason why the bioclocks in higher organisms, including humans, do not operate in a similar fashion. This could be a universal theme that we are just starting to decipher, says Woelfle.

The DNA in higher organisms is much larger than that in cyanobacteria and it is linear, not circular. Stretched end-to-end, the genome in a mammalian cell is about six feet long. In order to fit into a microscopic cell, the DNA must be tightly packed into a series of small coils, something like microscopic Slinkies.

Previous studies have shown that in higher organisms between 5 to 10 percent of genes in the genome are controlled by the bioclock, compared to 100 percent of genes in the cyanobacteria. In the case of the higher organisms, the bioclocks control is likely to be local rather than the global situation in cyanobacteria.

With a circular chromosome (as in cyanobacteria), twisting it at any point affects the entire molecule. When you twist a linear chromosome at a certain point, however, the effect only extends for a limited distance in either direction because the ends are not connected. That fits neatly with the idea that the bioclocks influence on linear chromosomes is limited to certain specific regions, regions where the specific genes that it regulates are located.


Contact: David F. Salisbury
Vanderbilt University  

Related biology news :

1. Controlling for size may also prevent cancer
2. UT Southwestern researchers identify hundreds of genes controlling female fertility
3. Hot spots the key to controlling European carp in Australia
4. Grant supports study of abnormal ring-shaped chromosomes
5. X-effect: female chromosome confirmed a prime driver of speciation
Post Your Comments:
Related Image:
Bioclocks work by controlling chromosome coiling
(Date:10/27/2015)... In the present market scenario, security is ... industry verticals such as banking, healthcare, defense, electronic gadgets, ... for secure & simplified access control and growing rate ... of bank accounts, misuse of users, , and so ... laptops, and smartphones are expected to provide potential opportunities ...
(Date:10/27/2015)... Synaptics Inc. (NASDAQ: SYNA ), the leader ... adopted the Synaptics ® ClearPad ® Series ... newest flagship smartphones, the Nexus 5X by LG and ... --> --> Synaptics works closely with ... in the joint development of next generation technologies. Together, ...
(Date:10/26/2015)... and LAS VEGAS , Oct. ... Labs , an innovator in modern authentication and a ... announced the launch of its latest version of the ... enabling organizations to use standards-based authentication that supports existing ... S3 Authentication Suite is ideal for organizations deploying customer-facing ...
Breaking Biology News(10 mins):
(Date:11/26/2015)... November 26, 2015 ... Accutest Research Laboratories, a leading ... Organization (CRO), has formed a strategic ... - Temple Health for joint work ... (Photo: ) , --> ...
(Date:11/25/2015)...  PharmAthene, Inc. (NYSE MKT: PIP) announced  today that ... plan (Rights Plan) in an effort to preserve the ... Section 382 of the Internal Revenue Code (Code). ... of its NOLs could be substantially limited if the ... 382 of the Code. In general, an ownership change ...
(Date:11/25/2015)... and HOLLISTON, Mass. , Nov. 25, ... HART ), a biotechnology company developing bioengineered organ ... Jim McGorry will present at the LD Micro ... at 2:30 p.m. PT. The presentation will be webcast ... days. Management will also be available at the conference ...
(Date:11/25/2015)... ... November 25, 2015 , ... A long-standing partnership between the ... has been formalized with the signing of a Memorandum of Understanding. , AMA ... Capt. Karl Minter and Capt. Albert Glenn Tuesday, November 24, 2015, at AMA ...
Breaking Biology Technology: