The adage that "you are what you eat" has taken on a whole new meaning. Researchers in Germany claim that DNA fed to a mouse can survive digestion and invade cells throughout its body. Because food contains DNA, this may be a way for species to acquire genes, they argue.
The surprising results were announced by Walter Dorfler of the University of Cologne at the International Congress on Cell iology in San Francisco last month. "We're taking in DNA in food every day," he says. "In my mind the question became: why isn't DNA incorporated all the time in animals?"
Textboods say that DNA in food should be digested and destroyed. But Dorfler and his student Rainer Schubbert found that when they fed a bacterial virus called M13 to a mouse, sections of its genetic material, about 700 DNA "letters" long -- large enough to contain a gene -- survived to emerge in faeces.
The researchers wondered whether a few of these genetic snippets had managed to penetrate the mouse's cells. They took cells from the mice and probed them with a dye molecule that lights up when it binds to the M13 NDNA. The probe lit up inside cells not only from the intessstine, but the spleen, white blood cells and liver. "They weren't hard to find," says Dorfler. "In some cases as much as one cell in a thousand had viral DNA."
Usually the DNA does not stay long inside the cells. After 18 hours, most cells had somehow ejected the viral intruders. But Dorfler speculates that occasionally some foreign DNA may remain.
Other researchers are sceptical. "It's amazing that this DNA could get all the way into the blood," says Rudolf Jaenisch, a geneticist at the Massachusetts Institute of Technology. He warns that the German team's results are "very preliminary" and that they have not been able to determine how much DNA is absorbed by the cells. Jaenisch suspects that the amounts would be so small that any effect on a cell is minimal."
TRANSFER OF FOREIGN GENE TO MICRO-ORGANISM
It was reported in 1994 that gene transfer can occur from plants to micro-organisms. Genetically engineered oilseed rape, black mustard, thorn-apple and sweet peas all containing an antibiotic-resistance gene were grown together with the fungus Aspergillus niger or their leaves were added to the soil. The fungus was shown to have incorporated the antibiotic-resistance gene in all co-culture experiments (Hoffmann T, Golz C & Schieder O (1994) Foreign DNA sequences are received by a wild-type strain of Aspergillus niger after co-culture with transgenic higher plants. Curr. Genet. 27: 70-76.). It is worth noting that micro- organisms can transfer genes through several mechanisms to other unrelated micro-organisms.