If you have ever done any research with the model organism Drosophila, you will immediately understand what an incredibly big deal this latest paper from PNAS is.
Conversion of the chill susceptible fruit fly larva (Drosophila melanogaster) to a freeze-tolerant organism
Kostal et al report a protocol for preserving fruit fly larvae at -5 degrees C. Freezing time was pretty short (75 minutes according to the Materials and Methods) but this is a significant step toward the long-term-storage promised land currently dominated by worms (C. elegans), bacteria, and cultured mammalian cells.
A little more context for those who don’t get how cool this is. Let’s say you spend a couple of years creating a genetically engineered fruit fly that expresses human huntington disease proteins, which allows you to do ground-breaking world-saving research (test new drugs and dissect how the disease works) in an easy-to-grow little organism. All you have to do is keep this genetically modified “species” (or strain) alive for, say, five more years.
Problem is, after keeping flies in a plastic bottle “fly house” for three weeks, fly carcasses accumulate, fungus starts growing, and the flies’ numbers start declining. The easy solution is to take a few flies and start a new fly bottle. Problem solved! Until a few weeks later, when you have to restart a new fly bottle. This “fly passaging” approach is fine if you don’t plan on ever stopping, being away for more than three weeks, doing non-fly experiments, or if you only have one or two genetically modified strains.
Try 50. That’s about how many unique fly strains I had to maintain during the last couple years of my Ph.D. thesis work. How about 38,424…that’s how many are maintained at the Bloomington Drosophila Stock Center (as of 2011). In the mean time, my C. elegans, human cell culture, and bacteria research neighbors got to keep their organisms in the freezer until they were ready to use them again.
Colleagues: Hey Karmella, why don’t you come out to happy hour with us? You won’t believe it…Mos Def is D.J.ing and Dave Chapelle is doing impromptu stand-up with Justin Timberlake!
Me: Can’t go. Passaging flies.
Why is freezing flies so hard? They are tropical insects. Evolution didn’t deal them cryopreservation cards. A 7 degree drop in temperature from the optimal 25 degrees will slow down their metabolism significantly (that’s actually a trick Drosophologists use to extend the life cycle clock).
How did Kostal et al do it? It appears that the secret is diet. They took cues from the biology of the subarctic fly Chymomyza costata, and fed Drosophila fly larvae a proline-, trehalose-, and glycerol-enriched diet. Glycerol, by the way, is what you add to bacterial cultures to prevent ice crystals from damaging the cells when they are frozen. Preliminary tests show that the thawed Drosophila larvae grow into healthy adults.
Even though I don’t do fly work anymore, I’m anxious to see how long the larvae can be cryogenically preserved. So far this is really cool, and time will tell (I owe the pun-ishment jar a dollar for that one).