Crossing a bacterium’s viral defense system with a flower’s response to the sun yields a light-based trigger for genes. This type of control could enable deeper study of specific genes’ functions, create complex systems for growing tissue and perhaps healing technologies, according to researchers at Duke University. “This technology should allow a scientist to pick any gene on any chromosome and turn it on or off with light, which has the potential to transform what can be done with genetic engineering” said doctoral student Lauren Polstein. “The advantage of doing this with light is we can quickly and easily control when the gene gets turned on or off and the level to which it is activated by varying the light’s intensity. We can also target where the gene gets turned on by shining the light in specific patterns, for example by passing the light through a stencil.” Researchers demonstrate their new technique to control genes by shining light through a “Duke D” stencil to turn on fluorescent genes in cells. Courtesy of Duke University. The optogenetic technique targets specific genes using an emerging genetic engineering system called CRISPR/Cas9. Discovered as the system bacteria use to identify viral invaders and slice up their DNA, the system was used by researchers to precisely target specific genetic sequences. The researchers then turned to another branch of the evolutionary tree to make the system light-activated. In many plants, two proteins lock together in the presence of light, allowing plants to sense the length of day, which determines biological functions like flowering. By attaching the CRISPR/Cas9 system to one of these proteins and gene-activating proteins to the other, the team was able to turn several different genes on or off just by shining blue light on the cells. “The light-sensitive interacting proteins exist independently in plants,” said professor Dr. Charles Gersbach. “What we’ve done is attached the CRISPR and the activator to each of them. This builds on similar systems developed by us and others, but because we’re now using CRISPR to target particular genes, it’s easier, faster and cheaper than other technologies.” The technique could allow scientists to precisely control the level of a gene’s activity from its natural position in chromosomal DNA, which would allow them to get a more accurate interpretation of the gene’s role. The light-induced system could also provide more control over how stem cell cultures differentiate into various types of tissues. By creating different patterns of gene expression, Gersbach hopes the system can be used in tissue engineering. “One of the limitations of tissue engineering right now is that typical methods make a chunk of bone, cartilage or muscle, but that’s not what tissues look like naturally,” Gersbach said. “There are several cell types mixed together, gradients of tissues between interfaces, and blood vessels and neurons that penetrate through them.” “We want to spatially control where different tissues get made in a cell population, and that way create multitissue constructs that potentially better represent normal physiology,” he said. In the more distant future the technique could even be used to regenerate wounded tissue, Gersbach said. “Far, far down the road, you could envision the type of device you’d see on Star Trek where you wave a flashlight over a wound and it heals,” he said. “Obviously that’s not currently possible, but this type of technology that creates much better control over biological systems could move us in that direction.” Funding for the work came from the National Institutes of Health, National Science Foundation and American Heart Association. The research was published in Nature Chemical Biology (doi: 10.1038/nchembio.1753). For more information, visit www.duke.edu.