Scientists usually shy away from using the word miracle. Unless they’re talking about the gene-editing tool called CRISPR, that is. “You can do anything with CRISPR,” some say. Others just call it amazing.
CRISPR stands for “clustered regularly interspaced short palindromic repeats.” Those repeats are elements of the genetic code in DNA. Cas9 is an enzyme that can cut apart DNA. Bacteria fight off viruses by wielding the Cas9 enzyme to reorder those repeated genetic segments. Scientists recently figured out how bacteria do this. Now, in the lab, they use a similar approach to turn the microbe’s virus-fighting system into the hottest new lab tool.
This CRISPR/Cas9 tool was first described in 2012 and 2013. Science labs around the world soon started using it to alter an organism’s genome - the entire set of its genes.
This tool can quickly and efficiently tweak almost any gene in any plant or animal. Researchers already have used it to fix genetic diseases in animals, to combat viruses and to sterilize mosquitoes. They have also used it to prepare pig organs for human transplants and to beef up the muscles in beagles.
So far CRISPR’s biggest impact has been felt in basic biology labs. This low-cost gene editor is easy to use. That has made it possible for researchers to delve into the basic mysteries of life. And they can do it in ways that used to be difficult if not impossible.
Robert Reed is a developmental biologist at Cornell University in Ithaca, N.Y. He likens CRISPR to a computer mouse. “You can just point it at a place in the genome and you can do anything you want at that spot.”
Anything, that is, as long as it involves cutting DNA. CRISPR/Cas9 in its original form is a homing device (the CRISPR part) that guides molecular scissors (the Cas9 enzyme) to a target section of DNA. Together, they work as a genetic-engineering cruise missile that disables or repairs a gene, or inserts something new where the Cas9 scissors has made some cuts.
Here’s how it works
Scientists start with RNA. That’s a molecule that can read the genetic information in DNA. The RNA finds the spot in the nucleus of a cell where some cut-and/or-paste activity should take place. (The nucleus is a compartment in a cell where most of the genetic material is stored.) This guide RNA shepherds Cas9 to the precise spot on DNA where a cut is called for. Cas9 then locks onto the double-stranded DNA and unzips it.
This allows the guide RNA to pair up with some region of the DNA it has targeted. Cas9 snips the DNA at this spot. This creates a break in both strands of the DNA molecule. The cell, sensing a problem, repairs the break.
Fixing the break might disable a gene (the easiest thing to do). Alternatively, this repair might fix a mistake or even insert a new gene (a much more difficult process).
Cells usually repair a break in their DNA by gluing the loose ends back together. That’s a sloppy process. It often results in a mistake that disables some gene. That may not sound useful - but sometimes it is.
Scientists cut DNA with CRISPR/Cas9 to make gene changes, or mutations. By comparing cells with and without the mutation, scientists can sometimes figure out what a protein’s normal role is. Or a new mutation may help them understand genetic diseases. CRISPR/Cas9 also can be useful in human cells by disabling certain genes - ones, for instance, that play a role in inherited diseases. Read more...