Sequencing the frog that can save lives
TL; DR: The genome sequence of the North American Wood Frog will tell us a lot about the genetic control of freezing and reanimating whole organisms. My friend and colleague, Dr. Andor Kiss is crowdfunding this project. If you would like to help, please go to experiment.com. You will get acknowledged by name in the paper. To learn more on why this is cool and important, read below.
Eighteen people die each day in the US waiting for an organ transplant. Every ten minutes, a person gets added to the waiting list. The need for improvement in organ donations is real.
Why are these statistics so grim? Even when a potentially good match is found (which can take months or years), there is a very short window between the time an organ is donated, and the time it can be transplanted. The maximum viability time for a human kidney is estimated at 35 hours; a liver 20, and a lung less than 10. This time constraint also limits the availability of matching organs. Just imagine if we could freeze and thaw organs without the risk of killing them, keeping them viable for months or even years. The time patients need to wait would be shorter, and, also, better matches may be found as the number of frozen organs increase. If we could learn to freeze organs without damaging them, we would revolutionize organ transplant in the same way refrigeration and freezing revolutionized the food industry. Today, however, freezing organs is not an option: once an organ is frozen, there is irreversible and widespread damage from the formation of ice crystals. Cells shrivel and collapse, blood vessels disintegrate, connective tissue rips apart.
But there are animals that can freeze and re-animate multiple times. In fact, if you live in the northern parts of North America, you have probably seen one, and almost surely heard it: the North American Wood Frog. The Wood Frog can freeze solid and then thaw – multiple times – with no ill effect. During this freeze event, the frog dumps glucose (a sugar) and high levels of urea (an acid normally found in urine) into its bloodstream. The glucose pulls water out of the cells and causes ice to freeze outside of the cells – a type of cryo-dehydration. This is to prevent ice forming inside the cells, where it would cause irreparable damage. The urea is thought to do two things – one, it also protects the cells integrity from damage, and two, it helps slow down the frog’s metabolism. The fact that the frog can freeze in and of itself is pretty spectacular – no heartbeat, no brain activity, no movement. When it thaws, the animal spontaneously reanimates.
What seems even more bizarre about this animal is that once the frog is acclimated to summer, freezing it will simply kill it. We think that there is some sort of seasonal trigger for winter and the possibility of freezing. There must therefore be a change of gene expression between the summer and winter frogs. One could think of this animal as its own experimental control! So to understand how the Wood Frog can survive freezing, we just pick frogs from different seasons, and see the difference in RNA expression. This can clue us into what makes a freeze-adapted frog different than a non-freeze adapted one. Andor has actually been doing that, and will be talking about it next week at the American Physiological Society Meeting in San Diego (if you’re there, walk up to him and say “hi”). But what Andor doesn’t have, is a good reference genome. Nothing close to the Wood Frog has been sequenced yet. Xenopus is a genus of frogs used in laboratories whose genomes have been sequeenced. But as a reference for Wood Frog, the Xenopus genomes aren’t good — the two species are too far apart.
Even more interesting, having the genome of the wood frog will enable studies of the different epigenetic patterns between summer and winter frogs. The control of gene expression is ultimately what Andor is interested in sorting out, and it’s likely that the epigenetics is involved: changes in the DNA that are not in the actual sequence, (like methylation) and affect the production of RNA and proteins. Additionally, because we don’t know the wood frog genome yet, we may find gene family expansions and contractions, novel genes that impart the freeze tolerance to the animal that we cannot possibly predict using a hypothesis driven approach.
And it can all be done relatively cheaply. For less than $4,000 (which is what Andor is asking for), one can do a vertebrate genome. That makes it feasible for a single researcher to (a) build the library, and (b) having the sequencing done. Annotation, of course, is another story, but we are planning a jamboree for that. Stay tuned.
Interested? The project is not too expensive, only $4,000! Any little bit helps a lot. Please go to the science crowdfunding site experiment.com, and give something. You will get acknowledged by name in the paper as part of the “Wood Frog Sequencing Consortium”. Thank you!
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