The CRISPR-Cas System

It’s about time I covered CRISPR, don’t you think? It’s the hottest topic in science since space-tardigrades! Once again, no, water bears can’t live in space naked, they have to be in a dry tun. Back to CRISPR though, this new gene editing technology isn’t actually new at all. Bacteria have been using it as an adaptive immune system to remember past viral infections.

Some History and Terminology

CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats. They are exactly what their name says they are… In 1987, scientists noticed these repeating sequences in E. Coli and eventually, other scientists discovered associated genes. These CRISPR associated (Cas) genes code for nucleases and helicases and are pretty much the same in bacteria and archaea. These enzymes recognize and cut up viral DNA and stores a tiny piece of it in the bacteria genome… for the next invasion. This is called immunological memory.

Remember Old Invasions

The job of the cell is the make enzymes and proteins. Genes code for these enzymes and proteins. If a wide variety of organisms share the same set of genes, then these genes must be pretty darn important. Maybe, they even share the same function. It wasn’t until 2007, some 30 years later, that scientists realized that the CRISPR-Cas system was an adaptive immune system for bacteria. For those who aren’t familiar, the adaptive immune system remembers (immunological memory!) attacks from the past.

crispr
The Vaccine: Used to help our adaptive immune systems create antibodies. Instead of using the actual disease (and making us sick), vaccines use a disabled version of the virus/bacteria. Our immune systems react the same way, but without all the sick and dying stuff.

Handling Mutating Viruses

In Parasite Evie, I talked about how viruses invade other cells. Bacteria cells evolved the CRISPR-Cas system as a way to remember old viral attacks and protect against future attacks (from the same virus). Of course, viruses mutate, so Cas13 (one of the Cas genes) puts the bacteria to sleep, stopping the growth of the virus. You can think of Cas13 like an on/off button for a printer. If there’s a paper jam, you turn the printer off, fix the jam, then turn the printer back on again. If you keep trying to print stuff, you’ll break the printer.

Gene Editing with CRISPR

In 2013, scientists realized that we could use the CRISPR-Cas system to edit genomes. Why? Because this system is extremely precise. It uses RNA to exactly match up with a sequence of DNA and then snips it (using the Cas enzymes). You could, for example, snip out a gene that codes for the protein that HIV binds to. The person would be born “immune” to HIV. This type of technology comes with its own list of concerns, mainly because any changes made to the genome will be passed down. Plus, proteins have different roles in the body, you may inadvertently be shortening someone’s life span.

CRISPR Ethics

This is always a sticky subject because nature operates on a different set of rules than humans. Animals kill each other for food and sometimes for… well, who knows. Humans have built societies based on the one rule of “don’t murder each other for food or for any other reasons”.

Animals abandon sick babies or kill/eat babies that aren’t theirs. Males of some species lead large groups of females, mating with them at will and sometimes, without consent. Females of some species eat the males after copulation. You get the idea. None of this would fly in human society.

Our innovations and advances in medicine have allowed us to defy and rise above nature and her ways. Vaccines and antibiotics allowed hundreds to live when they should have been wiped out by smallpox and other diseases. Without scientific discoveries, most of us would have died as babies. So the question remains: how much can we tamper with nature before it’s too much?