The Mouse shall show the way

Some amazing research is being done in two different labs, but with one common thread: the mouse. What these two research groups learn may greatly affect world health.

See also: Of Mice and Men

By Charlotte Crystal

Mice live fast lives. They generally are born, grow old and die within two years, their limited longevity making them ideal for medical research.

“By using mice in experiments, you can speed up your studies, seeing effects in a month that would take years to show up in people,” said Stuart Berr, an assistant professor of radiology and biomedical engineering.

Mice also serve as good proxies for humans in medical research since about 99 percent of the approximately 30,000 genes in humans and mice are essentially identical, inherited from a common ancestor some 75 million years ago. So genetically engineered mice, in which individual genes either have been added – as in “transgenic” mice – or subtracted – as in “knock-out” mice – have become an important tool for scientists studying how human genes work.

That’s why an estimated 25 million mice now are used in research laboratories around the world. One of the largest suppliers, The Jackson Laboratory in Bar Harbor, Maine, alone sold 1.9 million mice in its most recent fiscal year to research labs, including many at U.Va., said Joyce Peterson, a Jackson spokeswoman. And demand for the nonprofit institute’s 3,000 strains of mice is rising by 10 percent a year, she said.

By studying mice that have survived heart attacks – or a myriad of other human ailments – researchers can identify new avenues for treatment of human disease, said Fred Epstein, an associate professor of radiology and biomedical engineering who works with Berr.

According to the American Heart Association, cardiovascular disease affects more than 61 million Americans and is the leading cause of death in the United States, claiming more than 900,000 lives a year.

So, researchers in the U.S. and around the world are seeking new treatments for cardiovascular disease. But the labor is long and paths are many, some of which lead nowhere. How can researchers identify the most promising approaches?
That’s where Berr’s expertise comes in. Berr helps researchers analyze the results of their experiments by adapting medical imaging tools to make the measurements they need.

He helps U.Va. researchers with three different methods of medical imaging that have been adapted for use with small animals:

• A magnetic resonance imaging, or MRI, system that has been adapted to show an image of a tiny mouse heart beating very fast.

• A system developed by Mark Williams, associate professor of radiology, that combines high-resolution, three-dimensional X-ray scans with images of radioactively labeled compounds that travel to specific targets (e.g., the lungs, a tumor, etc.).

• A bioluminescence scanner that allows researchers to track cells that have been labeled with light-emitting proteins, such as firefly luciferase. The images of firefly light are superimposed onto regular photographs to identify the regions of interest.

Since 1999, Brent French, a molecular biologist and associate professor of biomedical engineering, has worked closely with Berr to adapt MRI to mouse research at U.Va. Since then, the cardiac MRI team has developed several MRI methods for mouse cardiac research that enable investigators to better understand what happens during a heart attack and explore ways to minimize the damage after a heart attack.

Another member of the team, Zequan Yang, assistant professor of research in biomedical engineering, is studying the role of inflammation in heart attacks. “By studying the response to heart attack in transgenic and ‘knock-out’ mice, we can learn what role individual genes play in the process,” Yang said.

The technical barriers are high. Unlike human hearts, which beat 60 to 80 times a minute in an average adult, a mouse heart beats about 500 times a minute. And at 7 millimeters long – about the size of Thomas Jefferson’s head on a nickel – a mouse heart is about a 1,000th the size of a human heart. So, the equipment must be sensitive, accurate and fast.

The team is working to acquire and display data so that particular measurements of a pumping heart can be made and shown as two-dimensional movies.

One of the questions Berr is exploring with French and Epstein is the effect that a small heart attack has on the rest of the heart. Not only does the heart attack itself kill and damage muscle tissue, but the gene expression of the muscle also changes, causing further loss of muscle function.

These mouse heart images show baseline cardiac function.

Another researcher, Chris Kramer, associate professor of radiology and director of cardiac MRI for the U.Va. Health System, is working on a related question. After a heart attack, the left ventricle, which pumps the oxygenated blood to the rest of the body, remodels itself. Kramer is trying to understand how the heart knows to change its shape.

The MRI technology that Berr has adapted allows researchers to see differences in hearts after heart attacks.

“What we’ve seen is that there are three areas of impact – the immediate area, in which the tissue has been killed outright; the adjacent area; and the area remote from the dead muscle tissue,” said Wesley Gilson, a graduate student studying with Epstein and French. Gilson is measuring the impact of a heart attack on the motion of the nearby heart muscle wall in genetically manipulated mice. Epstein said “Once we understand which genes are involved, we can go on to develop targeted drugs for use in humans.”

Of Mice and Men

By Elizabeth Kiem

The scientific contribution of the laboratory mouse just got even greater.

Two years after the celebrated breakthrough of the human genome project, scientists now have something to compare it with: a working draft of the genome of the common mouse.

“Its impact comes from being the second one. With the human one, we had nothing to compare it with,” said Sonia Pearson-White, director of U.Va.’s Transgenic Mouse Core Facility.

Comparing the two genetic maps turned up only about 300 genes, or 1 percent, that are unique to either species. Many portions of the genome show identical ordering, allowing geneticists to fill in holes in the human map.

“If there is a big area that is known to be syntenic [falling on the same chromosome] they can use the sequences to align and help close the gap,” said Pearson-White.

Studying the portions of the sequencing that diverge allows biologists insight into evolutionary processes. Pearson-White noted that many of the genes found in mice but not humans serve olfactory functions that humans have discarded.

Medical researchers will focus more closely on the shared genotypes. As many as 90 percent of the genes implicated in human diseases like cancer, hypertension and diabetes appear to be shared. This validates the role of the transgenic mouse in medical experiments.

“The key to all this is understanding all the genetics in the mouse, because You can do a lot of breeding studies in mice,” said Dr. Jerry Nadler, chief of endocrinology and metabolism. Nadler’s work is in understanding the gene or genes that are responsible for the destruction of cells that produce insulin, resulting in diabetes.

At the Transgenic Mouse Core Facility, Pearson-White assists U.Va. researchers in creating models of human diseases in mice. The process, known as a “knock-out,” involves injecting mutated embryonic stem cells into mice embryos, which will transmit the mutation into subsequent generations. No other species will pass on the mutation through the germ lines.

“[We] don’t understand why we can’t do it in other species. Nor is it understood why it works in the mouse,” said Pearson-White.

Before last month, when the mouse genome became publicly available, biologists had to clone large portions of DNA in order to narrow down the mutation target. That is slow and painstaking legwork.

“Now what you can do is go on-line and have the sequence. Then all you have to do is a couple of quick experiments to verify it,” said Pearson-White. “I would say it’s taken six months to a year off of approaching a knock-out, and that is just incredibly valuable.”

In addition to running the Core Facility for genetic research on mice, Pearson-White is head of a team that is studying a gene that regulates growth and differentiation of stem cells. For her work, the most important revelation of the mouse genome was the evidence that much of the genetic coding shared by mice and humans dictates regulatory function, as opposed to cell building.

“That was one of the surprises, that there were so many things that weren’t just coding for proteins that were conserved,” she said. “What are these conserved regions? What are they telling us about what is important for the regulation of a gene?”

The mouse genome, published in Nature magazine, is available on-line at http://www.ensembl.org/Mus_musculus/. It joins fruit flies and roundworms on the list of mapped genetic codes.