Photos and Graphics Click for larger images

Video Quicktime Movie (10.2 Mb) Real Player (2.2 Mb) Video Script

March 1, 2001

COLLEGE STATION – Researchers at Texas A&M University studying the tips of chromosomes in a lowly weed have new insights that likely will lead to advances in human medicine.

"Much of the plant genome is very similar to the human genome," said Dr. Dorothy Shippen, Texas A&M associate professor of biochemistry and biophysics. "Also, because we can do these wonderful genetic tricks in plants, we think that much of what we learn in the plant system will be ultimately translatable, and perhaps have significant impact, in human medicine."

The findings, by Shippen, colleagues Drs. Tom McKnight and Lawrence Griffing of Texas A&M's biology department, and postdoctoral fellow Dr. Karel Riha, are in the current issue of Science magazine.

Telomeres seal the ends of chromosomes in plants and animals much like the plastic tip on the end of a shoelace. Like the plastic tip that wears out allowing the lace to fray and become hard to use, so does the telomere break down in most cells in the human body over time. For about 10 years, scientists have been looking at telomere in humans for connections to cancer and aging.

"The integrity of the shoelace is maintained in large part because of this plastic tip," Shippen said. "In the same way, the telomere provides the stability for the chromosomes through many divisions of the cell."

The team used Arabidopsis, a weed commonly used in research because of its wealth of genetic tools and relatively small genome. The Arabidopsis genome recently was completely mapped thus allowing scientists to make better comparisons, McKnight said.

To examine what differences telomeres make in plants, the team generated an Arabidopsis mutant without functional telomeres.

"The enzyme, telomerase, which is required for maintaining these structures on the ends of chromosomes has been eliminated from the plant," she said. "Now we are following the consequences of not having telomeres, and we are finding some remarkable features in these plants."

One key difference between plants and animals, Shippen noted, is that plants continue to live for a long time despite the catastrophic events they endure without telomeres.

"The plants are able to take considerable genomic abuse which is a remarkable finding and differentiates, in a fundamental way, plants from animals," she said.

In similar studies of animal systems, cells have not been able to tolerate what a plant cell can. "Mammals have to keep a stable genome more than plants," Riha said.

"In animals, there is a strictly regulated pattern of development, and there is no way of turning back," McKnight added. "But plants are always making new organs throughout their lives. Plants are more flexible."

The plant model developed in Shippen's lab should provide scientists with greater insights about how telomeres allow chromosomes to become stabilized. Those insights will lead to discoveries in human medicine.

"Telomeres are essential timekeepers for how many times a cell can divide," she explained. "There's a strong correlation between telomeres and the ability of cancer cells to divide.

"So, if we can understand what a cell sees in terms of telomere structure and function that allows it to decide if a telomere is functional or not in plants, we hope that will be translatable to understanding how cell division is controlled in humans," she said.