A Brief History of CRISPR
CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats, which are segments of prokaryotic DNA containing short repetitions of base sequences. These are part of a bacterial defense system that, together with CRISPR-associated (Cas) proteins, forms the basis for CRISPR-Cas9 genome editing technology. It essentially targets the virus's genetic material to stop its propagation.
CRISPR molecules can be used together with the Cas9 protein (Cas mean CRISPR Associated Protein) to form the CRISPR-Cas9 technology. This technology is leveraged for editing genes inside living cells and organisms using modifying CRISPR sequences.
A key advantage of the technique is that it allows to target very precisely the DNA area that is getting edited, something previous techniques could not manage. The inventors of CRISPR-Cas9 earned the 2020 Nobel Prize in Chemistry.
But Cas-9 is not the only possible way to use CRISPR. There is also Cas13, which can be used for editing RNA. And the one concerning this article, Cas12a
Cas12a vs Cas9
This will explain Cas12a as much as possible in a way understandable by a non-biochemist so that some details will be somewhat simplified, and we can first look at what CRISPR-Cas12a is.
CRISPR-Cas12a is a different system from Cas9 in a few aspects:
- Provide alternative cutting sites to what Cas9 can do.
- Non-technical translation: hard-to-solve problems with Cas9 could be workable with Cas12a
- It cuts DNA in a way that leaves a “sticky” section of DNA instead of the “blunt” cut of Cas9, and can be cut multiple times.
- Non-technical translation: It results in higher chances of gene editing happening.
- There is no need for a transactivating crRNA (tracrRNA) for Cas12a, contrary to Cas9. Due to the smaller size, it would allow for easier multiplex genome editing.
- Non-technical translation: more than one gene can be modified at once with CAs12a
Cas12a2 Unique Properties
With CRISPR-Cas12a, researchers thought they had a new, slightly different version of the now better-understood CRISPR-Cas9. It had a lot of interesting usage due to these variations, but it was still the same basic mechanism.
And then came Cas12a2.
The last number, “2” at the end, is for a variant of Cas12a that appeared to have very different properties. In fact, it is acting way differently from “normal” Cas12a than Cas12a is from Cas9.
The CRISPR-Cas systems are designed to attack foreign genes and protect bacteria from viruses. Researchers have re-purposed this capacity into gene editing. What Cas12a2 does is very different. When it detects viral RNA, it starts to attack ALL nucleic acids inside the cell. Most of the time, it will kill the cell affected, protecting the rest of the bacteria colony and blocking the replication of the virus.
This entirely new mechanism got its discoverers a spot in the prestigious publication Nature in early January 2023 in 2 different papers (something pretty much career-making for any biologist).
The reason behind the enthusiasm of Nature reviewers is pretty simple. The cas12a2 mechanism allows the creation of a tool to “programmably kill cells.”
The first application could be much more efficient editing using the other CRISPR method. Combining Cas12a2 with other CRISPR-Cas systems could boost the efficiency of CRISPR gene editing through counterselection.
It could also be very efficient at detecting virus RNA. So, a second application is that CAs12a2 could be turned into a quasi-perfect test to detect viruses. The published paper already demonstrates a proof-of-concept of this idea.
CAs12a2-based tests would combine the very high sensitivity of a PCR test with the easiness and cheapness of a home test. All without requiring complex machinery.
The best part is that it can be tuned to detect virtually any RNA viruses, a family that contains viruses like COVID-19, the Flu, Ebola, and Zika, as well as any mutation that would evade the initial batch of tests.
All that would be needed to design a new test would be to know the virus's genome and design custom crRNA sequences. Something that can be done in just a few weeks, as the pandemic showed us.
So, at the current level of understanding of Cas12a2, testing seems to be a straightforward application.
The third possible application could be in using CRISPR-Cas12a2 in cancer treatment. A theoretical example could be to program Cas12a2 to react to genetic sequences specific to the cancer cell only, forcing the cancer cell to “suicide.” However, this application might be further down the line than the others due to the complexity of cancer cells' genetics.
CRISPR technology is still in its infancy, with entirely new mechanisms to uncover. It took the researcher working on Cas12a2 7 years to get good enough results to understand it. CRISPR-Cas12a2 has just been published and is still a long way from reaching commercialization. I would not be surprised if other variants of CRISPR-Cas systems are still hidden in the preliminary results of other research teams worldwide.
Cas12a2 will be a space to study attentively in the context of testing technology, forming potentially a threat to antigen testing and PCR testing in the long run.
It could also combined with other CRISPR techniques to make them more efficient or solve technical roadblocks. Overall, Cas12a2 seems a good reason to be more optimistic about CRISPR technology in general and its potential to change medicine. Including in testing, something no one had even envisioned until January 2023.