CRISPR/Cas9 is used primarily to correct genetic mutations, but can also be used to understand the genetic causes of--and develop potential treatments for--diseases such as cancer and dementia. To that end, UC Berkeley scientists have developed a faster, more efficient way to edit the genes of mice using CRISPR.
Researchers delete or modify specific genes in lab animals, usually mice, to model human diseases. The gold standard involves editing genes inside mouse stem cells in the fertilized egg or embryo, using these cells to create “mosaic” mice and then breeding the mice to achieve a pure genetic strain. It has a low output: "Sometimes people collect more than 100 embryos just to generate one or two mice with desirable gene editing," said Lin He, a UC Berkeley associate professor of molecular and cell biology, in a statement.
The Berkeley team’s method, dubbed CRISPR-EZ, eliminates a time-consuming step: using microscopic needles to deliver gene-editing molecules into a fertilized egg. Instead, the researchers used electroporation to create holes in embryos through which the molecules can pass. Directly injecting Cas9 proteins also cuts down on the uncertainty of microinjecting mRNA and guide RNA, which relies on the hope that the former will translate into the Cas9 protein it codes for and that the protein will combine with the guide RNA.
“I think this technology could greatly reduce the technical barrier for this type of effort and will allow people to focus more on the science rather than be consumed by the process of genetically engineering mice,” He said.
In a pilot experiment, He’s team created many more gene-edited mice using CRISPR-EZ compared to microinjection. Electroporation appeared to do less damage than microinjection to mouse embryos, resulting in a higher live birth rate--30 to 50% of the embryos led to live births compared to the 10 to 15% typically resulting from microinjection. And injecting preassembled Cas9 proteins achieved a higher rate, 88%, of mice born with both copies of the target gene edited.
“In the not too distant past, it would cost at least $25,000 and take at least 6 months to make a knockout mouse,” said Russell Vance, a UC Berkeley professor of molecular and cell biology and director of the Cancer Research Laboratory, where the transgenic mouse work was performed. “With CRISPR, and improvements such as CRISPR-EZ, the costs and time have both dropped at least 10-fold. These technical innovations make the mouse an even more powerful tool for modeling human diseases.”