Biology has changed

You may have heard of CRISPR. If not, check out this popular article in the New York Times about banning it for editing the human genome (specifically the germline – the part of the genome passed to the next generation), or an earlier article that nicely summarizes how the technique works. Basically, it is a technique that scientists can use to specifically rewrite the genetic code of an organism.

That is SO COOL.

Okay, we did have some ways for doing this already. But most of the GMOs you hear about are made by chopping DNA out of one organism and shoving it into another (or literally shooting it) and crossing your fingers that it works. With CRISPR, you can just make some RNA, attach it on a Cas9 enzyme, and the enzyme will write it into whatever organism you choose. But I get ahead of myself. What is CRISPR? What is Cas9? Why is there a picture of Dexter at the top? Do you really want to read this whole post? (Yes you do, if you care about science.)

CRISPR is actually an acronym that I will not break down because it doesn’t really help explain anything. What you need to know is that it was discovered as bacteria’s adaptive immune system. Humans have an innate immune system and an adaptive one. The innate is always there and consists of generalized protection like your skin and natural killer cells. The adaptive is the learning, specific immune system. B cells can remember diseases you have gotten before and produce antibodies that fight off that infection quicker the next time you get it. Vaccines work by tricking B cells into preparing for things like measles and the flu. Bacteria were not thought to have any adaptive immune system until very recently. Some Japanese scientists noticed weird chunks of DNA separated by short spacers in bacterial DNA in the late 80s. Some very smart people figured out that the bacteria was actually chopping DNA out of viruses that attacked it and saving it in its own genome so it could remember how to beat that virus the next time.

That. Read that last sentence again. That is the crazy part. It’s like some alien that eats the brains of its victims and learns all of their secrets. These bacteria collect virus DNA like microscopic Dexters (see, the photo makes sense now) and store it as a record of their victims. Now this is useful in itself. You have a nice continuous record of all the viruses this bacteria and its ancestors have faced. But the important part for us it the way it uses those stored DNA segments. When foreign DNA enters the bacteria it needs to decide whether to use it or lose it (bacteria are notorious for stealing any old DNA they pick up). So the bacteria brings a copy of the stored DNA segments to the new DNA using a protein called Cas9. It then compares stored DNA to new DNA. If they match? CHOP. The dangerous virus is gone.

Scientists have figured out how to attach any DNA segment they make to Cas9 and send it into any organism they choose to. It works for bacteria, plants, lab rats, and even humans. But there’s where it gets tricky. Because now all those Gattaca-esque designer baby dystopian futures are a little bit closer to reality. We can edit out portions of the genome that we know cause problems in the next generation, and we can edit in positive traits, like long eyelashes and not entering the subway car before others have gotten off (not sure about that second gene, but New Yorkers would thank you if you found it). This could move quickly for remedying diseases, but scientists hope that everyone will use caution. Our knowledge of how human genetics works has moved rapidly, but is still a long way from complete. Some sections of DNA have multiple effects that we just can not predict yet. But that’s not even the coolest part.

CRISPR

Diagram of the CRISPR system in a bacterium. (1)Foreign DNA is stored in the CRISPR array. (2) DNA is attached to Cas proteins as crRNA. (3) If new DNA matches crRNA, Cas cleaves it.

Since invasive species are my topic of study, I have always thought of ways to improve the way we control them. An effective control of invasive species must 1) completely remove the population of the species, 2) not be excessively expensive, and 3) be very specific to the organism. Pesticides are good at 1 and 2, having people manually kill invasives is good for 3, and biological control is not bad at all if done right. A gene drive could potentially destroy any sexually reproducing population in a few generations. Yes, you read that right. A gene drive is the process of making a gene spread rapidly through a population by ensuring that it is preferentially passed to the next generation. Mosquitoes are the first species in the cross-hairs for this. We can use CRISPR to engineer mosquitoes in the lab that carry a deadly gene. We release them into the wild and they mate with wild mosquitoes. The first generation doesn’t die because the gene is recessive, but due to biased inheritance, it spreads through the population. When the genes start meeting each other, the mosquitoes start dying. Simple as that. Of course, we will need a few more years of testing until we get there, but it’s coming. (In the meantime, check this out)

So, pay attention when you see CRISPR in the news. I expect many of the big breakthroughs in the next few years will come from it. And just hope that no one figures out a way to make a CRISPR specific enough to target a single individual’s DNA. That would make the most specific poison possible. And hope that I don’t get put on any government watchlists with that last comment.

Photo credits: PNA Bio (http://pnabio.com/products/CRISPR_Cas9.htm)
Deviantart user rumonica (https://www.pinterest.com/hayleyqs1116/dexter/)

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