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Microarray Study Offers Genetic Clues to Insect Cold Tolerance

NEW YORK (GenomeWeb News) – A team of scientists led by members of the British Antarctic Survey is using gene expression studies to uncover the genetic basis for a type of cold tolerance called cryoprotective dehydration.

The team developed cDNA microarrays to study gene expression in insects called Arctic springtails, or Megaphorura arctica, that had been dehydrated by cold or salt conditions or were recovering from such dehydration.

The paper, which appeared online today in BMC Genomics, suggests cryoprotective dehydration — and recovery from this process — involves several pathways governing everything from cellular protection and tissue remodeling to energy production.

"This is the first in-depth molecular study on the underlying cold survival mechanisms in this species," Melody Clark, a researcher with the British Antarctic Survey, said in a statement. "Such information is not only of interest to ecologists, but also to the medical field of cryobiology."

Genetics and genomics have increasingly played a role in the British Antarctic Survey's efforts. For the latest study, researchers were interested in exploring the genetics behind a form of cold survival called cryoprotective dehydration, in which organisms lose water until they can withstand dramatic temperature drops.

Although cryoprotective dehydration has been fairly well characterized physiologically, the authors noted, the genetics behind this process remain relatively murky. To begin exploring this problem, Clark and her colleagues developed a cDNA microarray based on 6,912 M. arctica clones.

They then used the microarray to assess Arctic springtails collected in Norway under a variety of conditions to look for genes that were differentially regulated in response to cold- or salt-induced dehydration or recovery from such dehydration.

The researchers detected gene expression changes associated with each of the conditions tested. In the insects that had been exposed to below freezing temperatures, they noted, about 10.8 percent of the genes were up- or down- regulated. In contrast, after previously frozen insects recovered at warmer temperatures, 32.4 percent of genes were differentially expressed.

Some, but not all, of the expression changes that occurred in response to cold-induced dehydration overlapped with those observed in insects dehydrated by salt treatment.

The team also detected a duplication in trehalose 6-phosphate synthase, or TPS — a gene that codes for an enzyme involved in making the sugar and natural antifreeze trehalose. And, they noted, TPS regulation appeared to coincide with changes in at least 53 other clones tested, including expressed sequence tags representing genes involved in cellular signaling and membrane trafficking.

Overall, the gene expression patterns detected suggest that cryoprotective dehydration and recovery involve changes in the way Arctic springtails make and transport trehalose as well as alterations in processes related to protecting cells from damage, cell membrane remodeling, tissue repair, and energy production.

The researchers' follow-up experiments using quantitative PCR also implicated an enzyme called glutathione-S-transferase as a protective factor for insects during the freezing process.

Although they noted that such analyses are more challenging in non-model organisms that have not yet had their full genomes sequenced, the researchers expressed enthusiasm about the potential of such studies to turn up genes relevant to cold tolerance in M. arctica.

"Understanding how animals survive harsh cold environments will hopefully provide novel solutions for medical research and preserving tissues for transplant operations," Clark said in a statement.

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