New technology lets scientists easily rewrite living organisms’ genetic code

With a few easy tweaks, scientists can cut-and-paste DNA inside living cells, thanks to a promising new technique that could make possible everything from testing new drugs or curing genetic diseases. And researchers just discovered a way to make the process a whole lot cheaper and easier, according to a study published Thursday in the journal Developmental Cell. For less than US$100, the new process allows scientists to make some of the key materials needed to modify an organism’s entire genome, or its complete set of DNA, the researchers said.

The advance is based on a technique that allows scientists to narrow in on a specific gene and cut-and-paste bits of DNA to change its function, known as CRISPR-Cas9. Jennifer Doudna at UC Berkeley and her colleagues first discovered this natural process that bacteria use to protect themselves against invading viruses. But the technique is much more powerful than that — it basically gives scientists the ability to rewrite specific chunks of an organism’s genetic code, including that of humans.

Here’s how it works: When a bacterium encounters DNA from a virus, it makes a strand of RNA, a molecular cousin to DNA, that matches the sequence of the viral DNA, known as a guide RNA. The guide RNA latches onto a protein (the Cas9 part of the CRISPR-Cas9 name), and together they search for the matching virus. When they find a match, the protein, which acts like a pair of scissors, cuts up the viral DNA, destroying it.

The same process can be used to cut-and-paste DNA into virtually any type of living cell. For example, instead of using the protein scissors to cut a virus, they can be used to cut out DNA in a human cell and replace it with DNA of the scientist’s choosing. In this way, it would be possible to swap out a defective version of a gene for a healthy one.

Humans have roughly 20,000 to 25,000 genes, which encode proteins that perform vital jobs in our cells. But our genetic blueprint has a lot of other DNA whose purpose is less obvious. The successor to the human genome project, the Encyclopedia of DNA Elements (ENCODE), has identified what 80 percent of our complete set of DNA does, but the rest remains a mystery.

In the new study, the researchers developed a method that makes it easier to create the guide molecules that home in on the DNA someone wants to tweak. The researchers hilariously named the process “CRISPR-EATING”, which stands for “Everything Available Turned Into New Guides”.

To demonstrate the technique, the researchers converted nearly 90 percent of the DNA of the common stomach bacterium E. coli (the harmless variety, not the kind that can make you sick) into 40,000 different guide molecules. Each of these molecules can be used to target any bit of DNA a researcher might want to modify. For example, if a scientist wants to figure out what a particular gene does, all he or she has to do is cut it out and see what happens. Thousands of these guides can be injected into different cells at once, a process known as genetic screening. These screens can reveal which forms of a gene are present, and whether any of them could lead to disease. Source: New technology lets scientists easily rewrite living organisms’ genetic code

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