Rewriting genetic information to prevent disease
For the last few years, scientists have been studying an ancient but only recently understood mechanism of bacterial immunity that has the potential to provide immeasurable benefits to plant and animal health.
The phenomenon known as CRISPR (for Clustered Regularly Interspaced Short Palindromic Repeats) is a natural immune system found in many bacteria with the ability to identify and destroy the genomes of invading viruses and plasmids.
Researchers are trying to harness this system for gene editing and regulation, a process that could transform "the genome of plants or animals in ways that will improve their health, or introduce genetic changes that will resist disease of climate change," says Jennifer Doudna, a Howard Hughes Medical Institute investigator and professor of biochemistry, biophysics and structural biology at the University of California, Berkeley. "The explosion of research using this technique has been amazing."
Doudna, collaborating with Emmanuelle Charpentier of Sweden's Helmholtz Center for Infection Research and Umeå University, identified how the system works and engineered it in new ways that broadened its scope. The two researchers, who described their work in a 2012 paper in the journal Science, developed a technique that enables the rewriting of genetic information and the correction of mutations that otherwise can cause disease, and also can knock out the cell's ability to make harmful proteins, she says.
"Many labs have shown in principle that this can be used to correct such mutations as those that occur in cystic fibrosis, or sickle cell disease," she says. "They are showing it in cell lines and lab animals. We're still some period of time away from using this in humans, but the pace in the field has been truly remarkable, and really exciting to see."
However, Doudna was among a group of leading biologists who recently called for a global moratorium on the use of the technique outside of research settings in order to give scientists, ethicists and the public time to better understand its implications. The scientists, writing in the journal Science, worry that its dramatic potential could prompt physicians to use it before experts can assess its safety and ethical ramifications. Their concern is that once in play, changes in the genome would last the life of an individual, and be passed on to future generations. While the scientists support continued laboratory research into the process, they fear that countries with regulations less stringent than the United States could use the technique in ways that could produce troubling consequences.
Many bacteria have this CRISPR-based immune system capable of identifying and destroying hostile invaders. Doudna and Charpentier showed that, in doing so, CRISPR produces the protein Cas9, a DNA-cutting enzyme guided by RNA, which relies on two short RNA guide sequences to find foreign DNA, then cleaves, or cuts, the target sequences, thereby muting the genes of the invaders.
Cas9 has evolved to provide protection against viruses that could infect the bacterium, and uses pieces of RNA derived from CRISPRS to direct its activity. The system is specific and efficient enough to stave off viral infections in bacteria.
Doudna and her colleagues programmed the process so that it can be directed by a single short RNA molecule; researchers who use it to edit genomes can customize the RNA so that it sends Cas9 to cleave, like "scissors," at their chosen location in the genome.
"When we figured out how it worked, we realized we could alter the design of RNA and program Cas9 to recognize any DNA sequence," she says. "One can therefore target Cas9 to any region of a genome simply by providing a short guide RNA that can pair with the region of interest. Once targeted, different versions of Cas9 can be used to activate or inhibit genes, as well as make target cuts within the genome. Depending on the experimental design, research can use these latter cuts to either disrupt genes or replace them with newly engineered versions."
Recently Douda and Charpentier and four other scientists received the Breakthrough Prize in life sciences, which honors transformative advances toward understanding living systems and extending human life. The prizes recognize pioneering work in physics, genetics, cosmology, neurology and mathematics, and carry a $3 million award for each researcher. The Breakthrough committee specifically cited Doudna and Charpentier for their advances in understanding the CRISPR mechanism.
Doudna has been the recipient of several National Science Foundation (NSF) grants to support her research in recent years totaling more than $1.5 million. In 2000, she received NSF's prestigious $500,000 Alan T. Waterman Award, which recognizes an outstanding young researcher in any field of science or engineering supported by NSF.
She also was a founder of the Innovative Genomics Initiative, established in 2014 at the Li Ka Shing Center for Genomic Engineering at UC Berkeley. Its goal is to promote and support genome editing research and technology in both academic and commercial research communities.
"We have a team of scientists working with various collaborative partners," she says. "We want to ensure that the technology gets into as many hands as possible, and explore ways to make it even better. We are trying to bring about fundamental change in biological and biomedical research by enabling scientists to read and write in genomes with equal ease. It's a bold new effort that embraces a new era in genomic engineering."