Light-Activated Cas9 Activation, Lobsters, and Cas9: A History

Today I Learned:
1) In March, a pair of researchers at Duke published a nifty system for activating target gene expression in the presence of light using a Cas9-based system. It’s pretty simple — they fused a light-activated transcriptional activator from Arabidopsis (the standard plant model organism) to inactivated cas9 (dCas9). Light-activated activator + targeting protein = targeted light-activation.

I guess we already had light-activation in the form of “traditional” optogenetics using channelrhodopsins, but those always struck me as pretty heavy-handed… for channelrhodopsin to work, it has to wildly change the cell’s salt balance, which seems like Not A Good Thing. This seems much more elegant.

2) Facts about lobsters!

2a) Lobster molting is pretty cool! The lobster actually sheds some of its digestive system during molting. As part of that process, the lobster dissolves a tooth-like thing at the back of its middle gut (lobsters have three guts) that normally helps break down food. The redissolved minerals are employed in the quick regrowing of the lobster’s shell.

2b) Background reading: http://www.smbc-comics.com/?id=3169

Now, serious question: where else might evolution put excretory organs? Set a five minute timer and list out all the better places to urinate from than where we do. I highly recommend taking the time to do this before proceeding — it’s a fun little exercise.

Ok? Done?

Did you write down “at the base of the antennae”? Because that’s where lobsters pee from.

2c) Lobsters can growl… but we have no idea why. They don’t seem to growl during social interactions, and as far as I know nobody’s come up with a better hypothesis.

2d) Lobsters can live a really long time — more than 50 years! — yet show none of the skeletal dysfunctions of aging that mammals show. Of course, it’s hard to directly compare the aging of species as dissimilar as humans and lobsters, but to anybody who argues that aging is “an inevitable breakdown of physiological processes”… “lobsters”, I reply. Also “tortoises”, but that’s a TIL for a different day.

Thanks to Lady Jade Beacham for pointing me to http://www.lobsters.org/tlcbio/biology.html, from which I got the content of this TIL.

3) So, speaking of Cas9 from #1, today I learned that a bunch of people figured out how it works independently. The one most biologists know about is Jennifer Doudna, who definitely figured out Cas9. Working off of CRISPR research from as early as 2007, Doudna and her lab worked out how Cas9 does its thing, then immediately realized that it was going to be huge and took it to Science, who fast-tracked it and published within the month.

The other relatively famous discoverer of cas9 is Feng Zhang, an MIT scientist who claims to have independently discovered Cas9’s function. He published definitively after Doudna, but he *patented* the enzyme first. That patent has been under dispute ever since.

Then there’s University of Lithuania researcher Virginijus Siksnys. He *also* jumped off of 2007 research and in 2012, figured out how Cas9 works. Unlike Doudna, he submitted his findings to PNAS, and unlike Science, PNAS did not fast-track the paper. As a result, Doudna’s paper came out first. Between Doudna’s precedency and her prior fame as an RNA biologist, Doudna got all the press and Siksnys remains largely unknown. (to be fair, Doudna did more in her paper — she not only elucidated the mechanism of cas9 and suggested its use as a tool for molecular biologists, but her lab also developed a modified version with a fused tracrRNA/guide RNA, which makes the thing much more convenient to work with).