Deep. When the ferritin gene is expressed in the brain of a mouse, it shows up as a dark region under MRI.

Making Cells Magnetic

A new technique that creates tiny magnets in cells may enable MRI scans to visualize gene expression in living organisms. The technique may also one day help scientists visualize therapeutic gene delivery in humans.

At present, gene expression is imaged with the help of "reporters" such as green fluorescent protein, which causes cells to fluoresce when specific genes are turned on. But the technique is limited to the areas of the body that light can penetrate, like the skin. As an alternative, scientists have considered using magnetic resonance imaging (MRI), which detects differences in magnetic fields between tissues. But because the magnetic fluid injected into the body in traditional MRI does not penetrate well into cells and tissue, this method also prevents scientists from visualizing cells deep within the body.

To surmount the problem, Eric Ahrens and his colleagues at Carnegie Mellon University in Pittsburgh, Pennsylvania, wondered if they could force cells to make their own magnetic agent. The search led them to ferritin, an iron-containing protein found in all organisms. When the team injected a virus containing the ferritin gene into mouse brains, an MRI scan revealed a dark patch, indicating that the new reporter gene was turned on. Ahrens, whose group reports its findings in the April issue of Nature Medicine, says the method could someday be used to track the delivery of therapeutic transgenes into the body.

In the meantime, this proof-of-concept is a milestone. "The development of reporter gene for MRI has been an elusive goal for a long time," says Jeff Bulte, a molecular imaging scientist at Johns Hopkins University in Baltimore, Maryland. "This is the first study to basically show this works."

Related sites
Paper abstract
Ahrens's website