CRISPR is the basis of a revolutionary gene editing system. One day it could make it
possible to do everything from resurrect extinct species to develop cures for chronic disease. It's
built on a natural adaptation found in the DNA of bacteria and single-celled organisms
CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats.
They're really just bits of genetic code with a specific recognizable format.
They contain a sequence that shows up over and over again though it's often reversed each time.
That's what makes it palindromic. Palindromes are words that can be read the same backwards
and forwards. Palindromes are common in DNA some serve as backups for damage to our genetic code
while others are common in cancer mutations. With CRISPR a group of enzymes recognize
certain repeats and break the DNA there to insert important information in the middle.
These insertions are called spacers and they contain the genetic code of different viruses that
have invaded in the past. Such previous invasions served a very important evolutionary purpose
immunizing against foreign threats. Researchers first discovered CRISPR and e coli in the 1980s
when e. coli survives viral attacks it incorporates some of the virus DNA into its
own genetic code. E. coli isn't unique in this strategy. Between the 1980s and 2000 scientists
found that lots of bacteria and single-celled organisms incorporate viral DNA. This way
cells use these sequences as templates for transcribing complementary strands of RNA.
When viruses matching the template sequence enter the cell, the complementary RNA binds to them and
directs a series of CRISPR-associated enzymes or Cas enzymes to attack cutting invader DNA at the
binding site. That neutralizes the viral threat. The CRISPR Cas system is incredibly effective
it's also easy to manipulate letting us alter a cell's genetic code however we want.
In 2012, French microbiologist Emmanuel Charpentier and American biochemist Jennifer
Doudna discovered that Cas enzymes, specifically Cas9, can be reprogrammed to cut nearly any part
of the genome using RNA sequences made in the lab. Those guide RNA molecules tell Caz9 where
to cut DNA in a cell. For their discovery, Charpentier and Doudna won the Nobel prize
in chemistry in 2020 and the use of CRISPR has taken off in science since their breakthrough.
But scientists are still far from realizing CRISPR's potential. Cas9 is great at suppressing
or knocking out unwanted genes, but for most medical purposes it's not enough to cut unwanted
DNA out. Scientists need to control how the DNA repairs itself. Left to their own devices cells
tend to repair broken DNA using a method that introduces lots of random errors. Researchers can
provide cells with templates to guide the repair process but they're still working on making that
more reliable. Researchers have found lots of applications for CRISPR in animals like making
disease-resistant chicken and pigs and mosquitoes that can't bite or lay eggs. But they've got many
projects underway, like making disease resistant crops for example, including wine grapes.
Even more ambitiously, they're working to genetically alter pigs so their organs could
be transplanted into humans and bring extinct species like the passenger pigeon back to life
by tweaking the genomes of similar birds alive today. When it comes to the human genome though
scientists have been more hesitant. Editing our own DNA could easily end up causing more problems
than it solves. While Cas9 reliably cuts DNA where we want it to, recent experiments have shown that
it can also affect genes far off target. And even if we could get it to work reliably many
experts have flagged ethical concerns about using the technology for eugenics and designer babies.
If parents can one day pay scientists to edit their baby's DNA making them stronger or smarter,
CRISPR could make the world even more unequal and prejudiced. In 2018, Chinese researcher He Jiankui
claimed he'd use CRISPR to make HIV-resistant children. Whether or not he succeeded his work
violated China's national health commission rules and he was sentenced to three years in prison.
Using CRISPR on babies is widely illegal but there are some cases where using CRISPR on
humans may be worth the risk. In 2020 American researchers began the first clinical trials
injecting CRISPR directly into humans aiming to repair a genetic mutation that causes blindness.
Many researchers hope CRISPR-based therapies could eventually cure hereditary diseases.
They've already seen promising results in various animal studies, though given the risks
of editing the human genome we're still a ways off from widespread use of CRISPR in medicine.
CRISPR has given science a tool to reliably tinker with a code of life, but the question remains:
can we do so safely and ethically while avoiding the unintended consequences of such power?