Genetic ‘dimmer Switch’ may Revolutionise Gene Therapy

by VR Sreeraman on Jul 29 2007 1:55 PM

Biomedical engineers at Boston University have devised a genetic dimmer switch that can be tuned to produce large or small quantities of a protein, or not at all, in mammal cells.

Professor James Collins, Professor Charles Cantor and doctoral candidate Tara Deans, who invented the switch, used more complex mammalian cells, from hamsters and mice, in their research.

Described in the journal Cell, the genetic dimmer switch has several new design features that extend possible applications into areas from basic research to gene therapy.

“There are a number of technologies available to regulate gene expression, but they each come with limitations. One of the central problems is you can’t get a really tight ‘off’ state,” said Collins.

Even when genetic switches are turned off, a trickle of the protein that is meant to be repressed still gets made. Some genetic switches get around this by entirely snipping out a gene to stop production of a specific protein, but this approach is irreversible.

In order to tackle these challenges, “Tara came up with a design that really combined two different technologies to repress or shut down gene expression,” Collins added, “We said, okay, we’ve got these two technologies, both that give a pretty good ‘off,’ why not try to combine them together to get a really clear and strong ‘off.’”

The first strategy, a repressor protein, sits on DNA like a roadblock and prevents any gene product or messenger RNA (mRNA) from being made. If any mRNA gets past this repressor, the second technique, interfering RNA (RNAi) attaches to the functional mRNA, rendering it useless. The cell cannot turn it into protein.

“I was delighted to see that when the two systems are coupled, it is possible to completely turn a gene’s function off,” said Deans.

The switch is also reversible and tuneable. Just by adding a chemical, Isopropyl-a-thiogalactopyranoside, the repressor components can be blocked and the gene turned on again. The gene’s activity can be tuned up or down by adjusting the amount of this chemical.

When the researchers hooked the dimmer switch up to the gene for diphtheria toxin and inserted it into cells, they found that the cells could survive for weeks with the switch turned off. Upon flipping the switch, the production of toxin was triggered, leading to cell death.

The researchers could also delicately tune gene expression when they installed the switch alongside a gene that leads to apoptosis, programmed cell death. They gradually increased the gene’s activity until they met and passed a certain threshold concentration of the gene’s product.

According to researchers, the switch may hold promise for therapeutic applications.

“It gives a really nice regulator scheme for cell and gene therapy. I think in the coming decades we’ll increasingly see these therapies being introduced as part of routine medical practice,” said Collins.