What is CRISPR gene editing?
In the short (roughly 50 year) history of genetics, I have always thought that there must be a lot we can learn from bacteria. These genetically simple organisms conduct incredibly complex feats in order to survive and proliferate. Bacteria have been conducting genetic modifications (aka mutation) since the beginning of time; one recent example being the ease by which pathogenic bacteria evade or inactivate our antibiotic drugs. These are purposeful, not random mutations. Pretty cool for a single cell.
In the late 1980’s scientists were surprised to find repeating sequences of bacterial DNA without an obvious task assignment. That sent molecular biologists running to their labs, and in 2002, it was learned that these sequences were part of the bacterial immune system. The segments were called Clustered Regularly Interspaced Short Palindromic Repeats or CRISPR.
We have to be careful using words like “system,” since that conjures up the complex activity of organs, blood cells and tissues. In this case, the system is purely genetic, and that, to say the least was rather intriguing.
Intrigue attracts brilliant minds, and scientists soon learned how this mechanism worked. Interspersed in the repeated sequences were “spacers” that matched pieces of DNA from viral invaders. Some bacteria, it turns out, have an adaptive immune system that can be passed to future generations. If the bacterium is invaded by the same virus, DNA in the spacers is converted to RNA, forming a structure that binds to strands of DNA in the invading virus, literally slicing into the helix and destroying the virus’ ability to proliferate. Cool!
You have to know that the inability to slice specific sequences of DNA has been a stumbling block for geneticists. Gene editing tools have been time consuming, expensive and far from perfect, as evidenced by the fact that not a single genetic disease has been cured.
CRISPR provides the perfect tool because this cellular defense system can be used to edit genomes, not just kill viruses. Scientists are now creating “guide RNA” to attach to virtually any point on the genome, and CRISPR protein scissors remove the DNA at that spot. These segments of DNA can be deleted or added, just as a film editor might cut a film and splice in new frames.
If you’re not feeling a bit uneasy about this yet, here’s the headline from a CRISPR ad I received this morning from Sigma-aldrich, a major provider of laboratory supplies.
“Access affordable targeted genome editing for mouse, human, and rat.”
Yeah… labs now have the ability to edit heritable DNA. And if this technology is usable by a small biotech team like mine, imagine what is going on in sophisticated privately held (unregulated) facilities around the world.
Bottom line, This is the proverbial double-edged sword. In March, 2017 the first human was cured of an inherited DNA defect that causes sickle cell anemia. This portends the quick (in our lifetime) end to genetic disorders including cystic fibrosis, hemochromatosis, Tay–Sachs disease and hemophilia.
And it also opens up a Pandora’s box of ethical and moral dilemmas for which we are woefully unprepared. If scientists can eliminate inherited defects, that means they can manipulate any region of the human genome. And as many have noted, “If it can be done, it will be done,” Welcome to the brave new world. Fasten your seat belts.
For scientists who want the details, go to https://phys.org/news/2017-04-accurate-dna-method.html#jCp.