CRISPR-Cas is a powerful new technology that is revolutionising biology. It's like cut and paste for DNA. Using CRISPR-Cas,
(or CRISPR for short) scientists can delete, tweak or completely replace
the genes of any organism. And they can do it more cheaply,
easily and efficiently than ever before. Researchers are already trying to use CRISPR to introduce genes for
disease resistance into wheat; insert malaria blocking genes
into mosquitoes; and remove HIV genes from
infected cells in humans. Scientists didn't design CRISPR themselves. Instead, they borrowed it from
microbes like bacteria and archaea. These micro-organisms use the
CRISPR system as a defense mechanism against invading parasites like viruses. It works like this: When a virus attacks a bacterium,
it introduces its own DNA into the cell. DNA contains the instructions for life. It's made up of four different chemical units, which the cell reads like a code. Some viruses use their DNA to hijack
the bacterium's cellular machinery, and make more copies of themselves. They eventually burst out of the cell
and spread to other bacteria. But with CRISPR-Cas,
the bacterium can fight back! The Cas part of CRISPR-Cas is an enzyme
that works like molecular scissors. The bacterium uses Cas
to cut the invading DNA into two, disabling the virus. Next, the bacterium inserts a section
of the intruder viral DNA into a special area of its own genome. Over time, the bacterium uses this area to build up a library of 'bad guys'. It forms a kind of parasite hit list, so that it can recognise them
if they attack again in the future. The bacterium copies these sequences
into related molecules called RNA. Each RNA guide is combined
with a Cas enzyme, turning the molecular scissors
into precise targeted weapons. Now, when they encounter a piece of DNA
inside the cell that matches the sequence on the guide, Cas will snip the intruder DNA
and disable it. Before we discovered CRISPR, we thought that the immune systems
of bacteria were simple crude tools
that worked for everything. But now we know their defences
are much more sophisticated. CRISPR-Cas forms what's known as
an adaptive immune system; much like our own. With it, the bacteria can form
immune 'memories' of invaders, and respond more quickly and precisely
if they attack in the future. Once they figured out what CRISPR was
and how it worked, scientists realized they could
take it out of microbes and use it as a gene editing tool
in any organism. You take a Cas enzyme,
and provide your own RNA guide molecule which matches the genetic sequence
of the gene you want to edit. If you introduce this into a cell, Cas will then snip the host's genome
in precisely the place you specify. This ends up disabling the gene. Scientists have even worked out
how to get the cell to stitch a new gene
into the place of the cut one. Scientists can do these things already
with other tools, but CRISPR just makes things easier,
quicker and much more accessible. At its most basic level,
CRISPR allows scientists to study individual genes, by seeing what happens
when you turn them off. But using CRISPR to accurately edit
the genomes of plants, microbes, animals and humans
opens up almost endless possibilities. Selectively killing
antibiotic-resistant bacteria; engineering the body's cells
to fight cancer; even editing pig genes
so that we can use their organs for human transplants. The precise nature of CRISPR
means we could even use it to eliminate certain genetic diseases
in humans. These kinds of applications
are still some way off. Even though CRISPR is powerful,
it can still make mistakes, sometimes missing its targets,
or making unwanted edits. And there are ethical concerns about what should and shouldn't be allowed
with this kind of technology, especially when it comes to
modifying the human genome. CRISPR has come a long way
since its origins in tiny microbes, but it really does have the potential
to change the world. The CRISPR revolution
is well and truly here, and it's only just beginning.
