Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

What inspires yeast cells to divide?

01.08.2002


Rockefeller researchers discover unexpected trigger

Often in science a novel set of experiments comes along that forces researchers to abandon old models in exchange for new ones that better fit their observations. This is the case in a new Nature report by Rockefeller University researchers, which finds that past models of cellular division in the simple yeast organism were focused on the wrong protein.

Until now, scientists thought that yeast cells began dividing into two separate cells upon the destruction of a "cyclin" protein called Clb5. But the new research shows that a related protein called Clb2 is in fact the real trigger.



"To our surprise, the current model of cyclins and cellular division in yeast does not appear to hold true," says Ralph Wäsch, M.D., a postdoctoral researcher at Rockefeller and first author of the paper. "We found that replicating cells do divide in the presence of Clb5, which means that its destruction cannot be the signal for division. What’s more, we show that replicating cells cannot divide in the presence of Clb2."

In addition to providing fundamental insight into the "cell cycle," the process by which all cells from yeast to human create exact duplicates of themselves, the findings have implications for treating cancer - which is characterized by a cell cycle gone awry.

"Yeast and human cells share many of the same cell cycle mechanisms," says Frederick R. Cross, Ph.D., head of the Laboratory of Yeast Molecular Genetics and principal author of the paper. "Because of this and because they are easier to work with, yeast organisms are ideal models for studying how the cell cycle may normally work in humans, as well as how it might malfunction in cancer."

How cells reproduce

All eukaryotic cells (cells that contain a nucleus) must undergo some form of a cell cycle in order to grow and reproduce. During this process, two crucial events must occur within a cell’s nucleus: replication of the DNA, called S-phase, and separation of the resulting chromosomes into two groups, called mitosis or M-phase. Completing the cell cycle are two periods of rest, which take place just before both S- and M-phase, and are called G1 and G2, respectively.

Only when the cell senses that these events have transpired without error will it exit mitosis and divide into two daughter cells. At this point, the process either begins anew, or a cell enters a state of dormancy, called G0.

How a cell moves from one phase to the next depends on periodic waves of cyclins: low levels prepare DNA for replication, higher levels trigger S-phase and mitosis, and a drastic drop in cyclin number signals the cell to begin dividing. Equally important to this process are the proteins that cyclins bind to and activate, called cyclin-dependent kinases (CDKs). Once activated, CDKs carry out the specific cellular tasks required for growth and division.

Cancer arises when the body fails to properly regulate this process. For example, healthy cells respond to DNA-damaging agents, such as sunlight or cigarette smoke, by halting their cell cycle while the damage is repaired, or by committing a type of cell suicide called apoptosis. But cancerous cells have lost this system of checks and balances, resulting in uncontrolled cell growth, DNA damage and eventually tumors. This breakdown in the cell cycle is caused by genetic mutations that lead to abnormal quantities of cell cycle proteins, such as the cyclins.

Cellular oscillators

The latest findings also suggest a new way of thinking about a yeast cell’s "oscillators." Oscillators are protein complexes that control the ebb and flow of cyclins within a cell’s nucleus, thereby ensuring an orderly progression through the cell cycle. During mitosis, they signal the cell to destroy certain cyclins, which then forces it to exit mitosis and begin division. In both human and yeast cells, there are two oscillators: the Cdc20 oscillator and the Cdh1 oscillator.

Previously, scientists thought that the Cdc20 oscillator controlled chromosome separation as well as mitotic exit via elimination of Clb5, while the Cdh1 oscillator was thought to complete exit from mitosis by destroying Clb2.

But the new Nature report tells a different story. It shows that the Cdc20 oscillator dictates exit from mitosis via elimination of Clb2, not Clb5. "Previous experiments showing the destruction of Clb5 to be the primary trigger for cell division were not flawed," says Wäsch. "Rather, the conclusions drawn from them were incorrect. We can now go back and reinterpret those experiments as meaning only that the elimination of Clb5 can act as a trigger for mitotic exit under experimental conditions. But we now know that the essential trigger is the direct destruction of Clb2 by Cdc20."

The researchers say that the destruction of Clb5 may instead be required for proper chromosome maintenance.

Interestingly, the results also suggest how the two oscillators may have evolved. According to the researchers, the first oscillator appears to control both chromosome separation and mitotic exit, while the second mainly oversees the break between cycles of growth and division, G1. Because G1 provides higher organisms with the ability to create different types of cells, the researchers speculate that this second oscillator may represent a necessary step in the evolution of both yeast and humans.


This research is funded by Deutsche Krebshilfe, a German cancer research foundation, and the National Institutes of Health.

John D. Rockefeller founded Rockefeller University in 1901 as The Rockefeller Institute for Medical Research. Rockefeller scientists have made significant achievements, including the discovery that DNA is the carrier of genetic information. The University has ties to 21 Nobel laureates, six of which are on campus. Rockefeller University scientists have received this award for two consecutive years: neurobiologist Paul Greengard, Ph.D., in 2000 and cell biologist Günter Blobel, M.D., Ph.D., in 1999, both in Physiology or Medicine. At present, 33 faculty are elected members of the U.S. National Academy of Sciences. Celebrating its Centennial anniversary in 2001, Rockefeller - the nation’s first biomedical research center - continues to lead the field in both scientific inquiry and the development of tomorrow’s scientists.


Whitney Clavin | ErekAlert!

More articles from Life Sciences:

nachricht A room with a view - or how cultural differences matter in room size perception
25.04.2017 | Max-Planck-Institut für biologische Kybernetik

nachricht Studying a catalyst for blood cancers
25.04.2017 | University of Miami Miller School of Medicine

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Early organic carbon got deep burial in mantle

25.04.2017 | Earth Sciences

A room with a view - or how cultural differences matter in room size perception

25.04.2017 | Life Sciences

Warm winds: New insight into what weakens Antarctic ice shelves

25.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>