Key Vocabulary: gene, genome, genetic engineering, embryo, enzyme, DNA, RNA, genetic disorder, mutation
Next Generation Science Standards:
- HS-LS1-1. Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells.
Classroom Activity: CRISPR_Cas9 Article Guide
A recent breakthrough has scientists both excited and anxious about the future of genetics. CRISPR/Cas9 is a technique that allows researchers to edit genes with relative ease and precision. The method has been quickly refined in recent years and a new study in the journal Nature show promise in applying CRISPR/Cas9 in humans. A team led by Shoukhrat Mitalipov of Oregon Health and Science University used the technology to edit a gene in human embryos linked to a heart disorder called hypertrophic cardiomyopathy. This development was a big step towards being able to modify the human genome and could potentially have huge consequences for the future of genetic engineering.
What is CRISPR/Cas9?
CRISPR/Cas9 is part of the defense mechanism used by bacteria to protect themselves from viruses. Any time a bacteria’s immune system manages to kill an invading virus, it produces enzymes that chop up the viral DNA into little bits. The bacteria then stores those bits of DNA in its own genome, using it as a reference against future viral attacks, like a list of most wanted criminals. Scientists call this stored DNA Clustered Regularly Interspaced Short Palindromic Repeats or CRISPR.
When a new infection occurs, the bacteria will produce a special enzyme called Cas9 to carry around a copy of those stored bits of viral DNA. If those Cas9 enzymes come across a virus with a sequence that matches, the enzyme then begins to chopping up the virus’s DNA, neutralizing the attack and keeping the bacteria safe.
But what does this have to do with gene editing? In 2011, a research team led by Jennifer Doudna and Emmanuelle Charpentier found out they attach any sequence of RNA to the Cas9 enzyme, it would chop up anything that it found a match – even if it was in the bacteria’s own genome. The team quickly discovered they could cut out any gene sequence they wanted.
Soon research teams around the world started using the technique. In 2013, scientists showed they could edit the genomes in cultured mouse and human cells. Undesirable genes could be “turned off” while more desirable genes could be inserted into a genome and be “turned on”.
However what makes the CRISPR-Cas9 technique so revolutionary is its precision. Gene editing has been around for several years, but previous methods were time and cost intensive. CRISPR/Cas9 will cut out anything you tell it to quickly and easily, potentially making the process much cheaper and more widespread.
The technology has many in the scientific community excited about the potential applications. Since the process is fairly inexpensive, it would allow gene editing to become much more widespread. It could give researchers the power to choose which genes are expressed and which are not.
This means that anything within a genome is up for editing. If researchers are able to identify which sequences cause colon cancer or Alzheimer’s, those sequences could be simply cut out using the CRISPR/Cas9 method. Potentially any genetic disorder could be simply cut out and replaced. The technique could also be used to target antibiotic resistant bacteria, which have become difficult to treat, and in some cases, fatal infections. CRISPR/Cas9 could be used to cut up the bacteria’s genes, causing them to self-destruct.
But the potential applications aren’t limited to medicine. Genes are the basis for how proteins are expressed, and, ultimately, how any living thing functions. CRISPR/Cas9 could be used with any living organism whose powers we wish to harness. Plants could be modified to yield more crops and make them more nutritious or withstand higher temperatures and drought, things that many third world countries will be facing by the end of the 21st century as the planet continues to warm. CRISPR could even allow us to bring back species that have since gone extinct.
Understandably, there are a lot of ethical concerns that surround around this technology. While gene editing animals and plants could lead to more productive agriculture, it would also be a drastic move from traditional breeding to altering an entire species. And though we may be able to save loved ones from heartbreaking diseases such as cancer or Alzheimer’s, CRISPR/Cas9 could one day be used to edit our own genes to fit our desires.
We could design our children to have our eyes and our partner’s hair. But why stop at looks? Parents could potentially edit their children’s DNA to give them superior memory skills or athletic talent. Families with the means to do so will be able to give their children a genetic advantage over others in their generation. The rich would get richer, not just financially, but genetically as well.
All that being said, clinical trials with humans are still probably a long way off. Researchers are still struggling with what are called “off-target effects”, where other mutations occur around the edited sequence. CRISPR/Cas9 must have a much higher success rate in the lab before a clinical trial is conducted.
However, the scientific community and society as a whole need to ask the question of how far we take this technology. Biology has been in the genetic age since the 1950’s, but we’ve never been able to design genes and traits according to our own imagination. And while accurate and effective gene editing software could solve many medical challenges, we, as a society, may not be ready for this responsibility.
- This animation from MIT gives a nice visualization on how CRISPR/Cas9 works
- Science Friday interviewed CRISPR pioneer Jennifer Doudna and Shoukhrat Mitalipov. Both segments run about 17 minutes.