Jennifer Doudna, a professor of chemistry and of biochemistry and molecular biology at the University of California, Berkeley known for co-discovering the CRISPR-Cas9 genome-editing technology, gave the 2018 George E. Palade Memorial Lecture in Cell Biology to a packed auditorium on Thursday afternoon.
Dedicated to preeminent cell biologist and former Yale faculty member George Palade, the Palade Memorial Lecture has invited a distinguished scientist to give the speak every year since 2009. This year, Doudna’s talk drew an outstanding crowd to the School of Medicine’s Mary S. Harkness Auditorium; there was no standing room in the 450-seat space and over 100 people watched a live broadcast in the Anlyan Center’s auditorium. In the lecture, she spoke about her initial discovery of CRISPR as a novel tool to edit DNA, recent findings on its mechanism and current clinical directions of CRISPR.
“My work on CRISPR really came out of fundamental curiosity-driven research going on in a handful of labs around the world that led in a very unexpected direction: gene-editing technology,” Doudna told the audience.
Doudna, a Howard Hughes Medical Institute investigator and executive director of the Innovative Genomics Institute, was introduced by molecular biophysics and biochemistry professor Joan Steitz, who served as an early mentor to the renowned biochemist, who taught in Yale’s molecular biophysics and biochemistry department from 1994 to 2002.
“Whenever a paper from Jennifer’s lab comes out, you know that it’s going to have some very important message and use very elegant structural and biochemical technique to support this message,” Steitz said in her introduction.
Doudna began her research career with a focus on RNA, particularly ribozymes, or RNA sequences that serve as enzymes to catalyze biochemical reactions — Steitz’s main research area at Yale. She shared that she started to investigate CRISPR in 2005, after Jillian Banfield, a colleague at Berkeley, reached out to her. Banfield had discovered unusual repeating sequences in microbes, called “clustered regularly interspaced short palindromic repeats,” or CRISPR for short.
These sequences, they later learned, included snippets of DNA from viruses that had previously infected the bacteria. After the bacteria incorporated this viral DNA into their immune systems, they could then destroy the same virus if it invaded again using a protein called Cas9.
Doudna next discovered that this system could be co-opted to edit genomes instead of killing viruses. A specific guide RNA sequence could bring Cas9 to a targeted location on the genome, inducing Cas9, to cleave that DNA, like a highly precise pair of molecular scissors.
Researchers could then take advantage of the cell’s DNA repair mechanism to knock out the gene or insert a new desired sequence, Doudna explained.
Doudna described her lab’s recent studies on Cas9’s mechanisms for recognizing and cleaving DNA sequences. For instance, the lab is trying to elucidate how Cas9 can unwind DNA without any external energy source, Doudna said.
Finally, Doudna shared research in her lab by graduate student Janice Chen investigating the Cas12a protein, which acts in a similar fashion to Cas9 by making double-stranded cuts in DNA.
A key difference between the two, however, is that once Cas12a binds to the targeted sequence and makes a cut, the protein continues to cut DNA nonspecifically, like a renegade lawn mower. This results in high degradation of DNA sequences upon target-guided activation, according to the lab’s research.
According to Doudna, a potential explanation is that Cas12a only has one active site in the protein, unlike Cas9, which has two. This may make the protein more dynamic, able to cleave single-stranded DNA sequences in a nonspecific manner.
The mechanism of Cas12 family proteins offers significant clinical applications, Doudna said.
“We think this could be a really interesting way to detect different kinds of DNA sequences, not only for detecting infectious DNA but also DNA that might be associated with tumor cells, for example,” Doudna said.
Her lab has already harnessed Cas12a technology for detecting infections such as human papillomavirus and Zika. Creating a tool called DETECTR, the team has demonstrated that they can rapidly and accurately identify different types of HPV in patient samples.
“It was a terrific lecture — a blend of the fundamental discovery, more recent results regarding mechanism of action and finally, a new application of how it can be used in the clinic,” said Chris Burd, deputy chairman of cell biology at the School of Medicine.
Palade was the first chairman of the cell biology department at the School of Medicine.
Amy Xiong | amy.xiong@yale.edu