If you’ve eaten a pizza, cheeseburger, or yogurt since 2011, then you have consumed a dairy product enhanced by a new technology that has transformed agriculture, food, medicine, and the biotechnology industry. The use of this technology, known as clustered regularly interspaced short palindromic repeats, or CRISPR, has skyrocketed during the last 10 years. One of its proponents came to NIEHS to talk about its unlimited possibilities.
Rodolphe Barrangou, Ph.D., associate professor in the Department of Food, Bioprocessing and Nutrition Sciences at North Carolina State University in Raleigh, focused on CRISPR research, his own and that of others, in a Sept. 7 presentation. The seminar was hosted by the NIEHS Predictive Toxicology and Disease Faculty, one of several cross-divisional faculties designed to implement the institute’s strategic plan and advance research and public health.
The CRISPR-Cas system
Barrangou said CRISPR refers to a part of DNA naturally found in many bacteria and most archaea — single-celled organisms that lack a nucleus. It is a series of short, repeated sequences, approximately 30-36 nucleotides long. The function of these repeats is to fend off viruses, called bacteriophage. Together with CRISPR-associated sequences, or Cas proteins, CRISPR-Cas functions as part of the bacterial immune system.
According to Barrangou, when a virus injects its DNA into a bacterium, the region known as CRISPR makes RNAs with sequences that mirror the viral sequence. These RNAs direct Cas proteins to cut the matching sequence from the virus. The process makes the invader harmless, and the bacterium resistant to that virus. Once scientists determined they could use the CRISPR-Cas system as a molecular scalpel, they found all sorts of uses for it.
"You can make precise cuts in your target DNA, which opened up the field of gene editing," Barrangou said. "It is fast, efficient, and affordable."
Riding the CRISPR craze
With CRISPR-Cas, scientists can delete, insert, or knock out DNA, making a programmable system that binds very tightly to DNA. Barrangou said scientists can target any stretch of a DNA sequence in an organism and repress transcription of that sequence, which would turn off that particular gene. Or they can target the gene’s activator and turn up the rate of transcription, inducing the gene to make more of its protein.
The specificity of Cas offers even more options as a research tool. Scientists can tether a pharmaceutical compound to DNA and deliver it exactly where they want it, or connect a fluorescent molecule and see where in a cell that DNA sequence is found. Researchers have used CRISPR to make changes in a variety of organisms (see image below), remove HIV-1 from human cells in vitro, or turn bacterial systems against themselves, producing an antimicrobial agent that is more than 99.99 percent effective.
Barrangou said uses in food have produced mushrooms that do not turn brown on grocery store shelves, and hardier cultures for cheese and yogurt. These products are not considered genetically modified organisms, because no DNA was transferred into their cells. Instead, scientists allow dairy bacteria to use their own internal CRISPR to naturally vaccinate themselves against viruses, or use complexes made of Cas protein and guide-RNAs to get the desired result.
He acknowledged that some may want to use the technology to edit the human germline, or the group of cells that give rise to eggs or sperm. An open discussion about the ethics of doing so is already ongoing, he pointed out.
"Everyone, not just scientists, has an opinion on the topic," Barrangou said. "Establishing certain guidelines as it pertains to CRISPR and humans should be addressed."