X-Message-Number: 32239
Date: Sat, 19 Dec 2009 11:51:04 -0800 (PST)
From: 
Subject: Why Some Insects Can Survive Freezing: Huge X-Ray Microscope ...

[It has nothing to do with conventional cryoprotectants.]

Why Some Insects Can Survive Freezing: Huge X-Ray Microscope Provides Clues

ScienceDaily (Dec. 18, 2009) - Using a microscope the size of a football field, 
researchers from The University of Western Ontario are studying why some insects
can survive freezing, while others cannot.


Why is this important? Because the common fruit fly (Drosophila melanogaster) is
one of the bugs that cannot survive freezing and the little creature just so 
happens to share much of the same genetic makeup as humans, therefore finding a 
way to freeze them for research purposes is a top priority for geneticists the 
world over (about 75 per cent of known human disease genes have a recognizable 
match in the genetic code of fruit flies).
And why the large microscope?

"It's the only one in the world that's set up for this kind of imaging on 
insects," says lead researcher Brent Sinclair of his team's use of the Advanced 
Photon Source (APS), located near Chicago, Illinois. The APS generates 
high-energy x-rays that allow Sinclair and his collaborators to film the 
formation and spread of ice in real time as the maggots freeze.

An assistant professor in Western's Department of Biology, Sinclair explains 
that the physical processes of ice formation seem to be consistent among species
that do and don't survive freezing. However, it seems that the insects that 
survive freezing have some control over the process of ice formation. They 
freeze at consistently higher temperatures than those that don't.

Sinclair says this implies that the main adaptations required to survive 
freezing are at the cellular or biochemical level, rather than because of 
fundamental structural differences.

"We're comparing Chymomyza amoena, an insect native to Ontario that survives 
freezing, with Drosophila melanogaster, because they're very close relatives," 
says Sinclair. "The idea is to find the magic bullet which allows some bugs to 
survive freezing and some don't. That's the goal here."

The Western-led research was published in the journal PLoS ONE, an 
peer-reviewed, open-access resource from the Public Library of Science.



_________________________________________________________________________________
PLoS One.;4(12):e8259.

Synchrotron X-Ray Visualisation of Ice Formation in Insects during Lethal and 
Non-Lethal Freezing.

Sinclair BJ, Gibbs AG, Lee WK, Rajamohan A, Roberts SP, Socha JJ. Department of 
Biology, The University of Western Ontario, London, Ontario, Canada.

    Although the biochemical correlates of freeze tolerance in insects are 
    becoming well-known, the process of ice formation in vivo is subject to 
    speculation. We used synchrotron x-rays to directly visualise real-time ice 
    formation at 3.3 Hz in intact insects. We observed freezing in diapausing 
    3(rd) instar larvae of Chymomyza amoena (Diptera: Drosophilidae), which 
    survive freezing if it occurs above -14 degrees C, and non-diapausing 3(rd) 
    instar larvae of C. amoena and Drosophila melanogaster (Diptera: 
    Drosophilidae), neither of which survive freezing. Freezing was readily 
    observed in all larvae, and on one occasion the gut was seen to freeze 
    separately from the haemocoel. There were no apparent qualitative 
    differences in ice formation between freeze tolerant and non-freeze tolerant
    larvae. The time to complete freezing was positively related to temperature
    of nucleation (supercooling point, SCP), and SCP declined with decreasing 
    body size, although this relationship was less strong in diapausing C. 
    amoena. Nucleation generally occurred at a contact point with the 
    thermocouple or chamber wall in non-diapausing larvae, but at random in 
    diapausing larvae, suggesting that the latter have some control over ice 
    nucleation. There were no apparent differences between freeze tolerant and 
    non-freeze tolerant larvae in tracheal displacement or distension of the 
    body during freezing, although there was markedly more distension in D. 
    melanogaster than in C. amoena regardless of diapause state. We conclude 
    that although control of ice nucleation appears to be important in freeze 
    tolerant individuals, the physical ice formation process itself does not 
    differ among larvae that can and cannot survive freezing. This suggests that
    a focus on cellular and biochemical mechanisms is appropriate and may 
    reveal the primary adaptations allowing freeze tolerance in insects.
PMID: 20011523 [PubMed - in process]
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http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0008259

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