Slicing chromosomes leads to new insights into cell division

May 29, 2009

(PhysOrg.com) -- By using ultrafast laser pulses to slice off pieces of chromosomes and observe how the chromosomes behave, biomedical engineers at the University of Michigan have gained pivotal insights into mitosis, the process of cell division.

Their findings could help scientists better understand genetic diseases, aging and cancer.

Cells in plants, , and animals—including those in the human body—divide through mitosis, during which the DNA-containing separate between the resulting daughter cells. Forces in a structure called the mitotic spindle guide the replicated chromosomes to opposing sides as one cell eventually becomes two.

"Each cell needs the right number of chromosomes. It’s central to life in general and very important in terms of disease," said Alan Hunt, an associate professor in the Department of Biomedical Engineering and an author of a paper describing these findings published in .

"One of the really important fundamental questions in biology is how do chromosomes get properly segregated when cells divide. What are the forces that move chromosomes around during this process? Where do they come from and what guides the movements?"

Hunt’s results validate the theory that "polar ejection forces" are at play. Scientists had hypothesized that the direction and magnitude of these forces might provide physical cues guiding chromosome movements. In this capacity, polar ejection forces would play a central role separating chromosomes in dividing cells, but no one had established a direct link until now.

Polar ejection forces are thought to arise out of the interaction between protein motors on the arms of chromosomes that push against cells’ microtubules. Microtubules are long, thin tubes that form a central component of the cytoskeleton and the mitotic spindle. They serve as intracellular structural supports and as railways along which molecular motors move cargoes such as chromosomes.

Hunt’s group hypothesized that polar ejection forces should be proportional to the chromosome’s size, and therefore could be predictably changed by altering the size of the chromosomes. Using newts as a model organism, they cut off pieces of the chromosomes’ arms.

"We asked what the relationship is between the size of the fragment we removed and the direction the chromosome moved," Hunt said. "Not only did we observe a relationship, we established that polar ejection forces were in fact a direct cue that guided chromosomal movements in mitosis."

To achieve this, Hunt performed "nanoscale surgery," as he calls it, taking advantage of the unprecedented precision of femtosecond pulses of laser light. A femtosecond is one billionth of one millionth of a second. The chromosomes he altered were only micrometers long, and the slices across the chromosomes were only nanometers thick. A nanometer is one-billionth of a meter, about a million times thinner than a human hair.

Understanding how chromosome guidance occurs allows scientists to determine how failures lead to genetic diseases, aging and cancer. When cells don’t properly divide, they usually die. But survival can cause cancer or aging-related disorders. Likewise, such as Down’s syndrome result from improper chromosome segregation.

Mitosis, Hunt says, is one of the most important targets of chemotherapy.

"By knowing how chromosomes move, we can better understand how these drugs interfere with those movements and we can design experiments to screen for new drugs," Hunt said. "It will also allow us to have a better handle on what makes these drugs work. There are a lot of drugs that interfere with mitosis, but only a few are good for cancer therapy."

More information: The paper is called, "The Distribution of Polar Ejection Forces Determines the Amplitude of Chromosome Directional Instability." It is published in the May 26 print edition of Current Biology.

Provided by University of Michigan (news : web)

Explore further: How does enzymatic pretreatment affect the nanostructure and reaction space of lignocellulosic biomass?

add to favorites email to friend print save as pdf

Related Stories

Researchers shed light on shrinking of chromosomes

Jun 11, 2007

A human cell contains an enormous 1.8 metres of DNA partitioned into 46 chromosomes. These have to be copied and distributed equally into two daughter cells at every division. Condensation, the shortening of chromosomes, ...

A unique arrangement for egg cell division

Aug 09, 2007

Which genes are passed on from mother to child is decided very early on during the maturation of the egg cell in the ovary. In a cell division process that is unique to egg cells, half of the chromosomes are eliminated from ...

Researchers identify potential cancer target

Jan 16, 2009

(PhysOrg.com) -- Dartmouth Medical School researchers have found two proteins that work in concert to ensure proper chromosome segregation during cell division. Their study is in the January 2009 issue of ...

Scientists deconstruct cell division

Feb 08, 2009

The last step of the cell cycle is the brief but spectacularly dynamic and complicated mitosis phase, which leads to the duplication of one mother cell into two daughter cells. In mitosis, the chromosomes ...

Hotspots found for chromosome gene swapping

Nov 29, 2007

Crossovers and double-strand DNA breaks do not occur randomly on yeast chromosomes during meiosis, but are greatly influenced by the proximity of the chromosome’s telomere, according to research in the laboratory of Whitehead ...

Recommended for you

Quest to unravel mysteries of our gene network

18 hours ago

There are roughly 27,000 genes in the human body, all but a relative few of them connected through an intricate and complex network that plays a dominant role in shaping our physiological structure and functions.

EU court clears stem cell patenting

20 hours ago

A human egg used to produce stem cells but unable to develop into a viable embryo can be patented, the European Court of Justice ruled on Thursday.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.