Heating from sonic waves can turn on genes in the body, demonstrate researchers at the University Victor Segalen Bordeaux in France and their colleagues. Using mice engineered with a bioluminescent gene containing a heat-sensitive stretch of DNA, they focused high-intensity ultrasound pulses on a 0.5-millimeter-wide patch of the mice's legs, heating up that area just below the skin's surface to about 43 degrees Celsius (109 degrees Fahrenheit). Light given off revealed that the gene became active. The technique could help gene therapy, which introduces beneficial DNA into patients. When and where these genes are expressed is paramount, and currently small-molecule drugs and ionizing radiation are employed to switch genes on. But chemicals are not precise, and rays can trigger cancer. The challenge for ultrasound activation, published January 27 by the Proceedings of the National Academy of Sciences USA, is safely getting the waves deep enough to reach organs.