Written by Kathleen Doheny
Updated on April 19, 2007
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FRIDAY, July 19, 2002 (HealthDayNews) -- For biologists, an ongoing challenge is how to deliver foreign DNA into cells in the lab without damaging the cells in the process.
Now, German researchers think they've found the answer. They used a high-intensity, near-infrared laser to "cut" a tiny hole in mammal cells, insert a loop of DNA, and complete the process without cell damage.
They report on the technique in the new issue of Nature. The approach is expected to help those involved in gene therapy and gene expression studies.
"To our knowledge, to date, the femtosecond pulsed near-infrared laser [the one they used] has not been used for targeted transfection of cells," says Uday K. Tirlapur, one of the researchers and a cell biologist at the Institute of Anatomy II, Friedrich-Schiller-University in Jena, Germany.
"Earlier laser techniques have been based on UV lasers with long pulse durations, in nanoseconds. It is known that with longer pulse durations, such as in case of UV lasers, there are photothermal and photomechanical effects," he says. There is often damage, he explains, and it's often not confined to a tiny spot.
Besides using lasers, scientists have tried to transfer DNA into cells by microinjection and other techniques.
One practical application of the laser method of transfection -- defined as the transferring of DNA into a cell and its expression -- is to help the process of gene therapy, in which disease is treated either by replacing damaged or abnormal genes with normal ones or by providing new genetic instructions that help fight the specific disease.
The researchers used Chinese hamster ovarian and rat-kangaroo epithelial cells in the study. They achieved a 100 percent transfection rate, they report.
After the loop of DNA was inside the cell, the DNA encoded a protein that glows a green color when light irradiates it. The researchers followed the transmission of the DNA to the inside of the cell simply by watching it turn green. They report the cells then grew and divided normally.
A gene therapy expert says the new technique is promising, though it has some limitations.
"It seem to me it's certainly an improvement over current methods of laser transfection," says Joanne Douglas, an assistant professor at the Gene Therapy Center at the University of Alabama at Birmingham. "It uses a longer wave length and a shorter time to disrupt the cell membrane, which is good because it causes less cell damage."
She adds that "with this technique they are able to introduce DNA into individual cells in populations in tissue culture," Douglas says. That's ideal, she says, if the aim is to introduce individual genes into individual cells.
However, if the aim is to introduce one gene into several cells, she says, "the disadvantage is going to be that it's rather time-consuming and inefficient. Another limitation is that it can only be used in vitro, in the lab. Very often we want to do gene transfer within the body. It wouldn't be suitable for that. It would be necessary [in that case] to remove the cell, grow it in tissue culture, transfect them by this laser and reintroduce them into the body."
Overall, however, she praises the report. "Their laser is great for introducing DNA into individually targeted cells, a great improvement over other techniques, much less disruptive."
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