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Miami scientists, alumnus study extreme dehydration tolerance in Antarctic insect: part of first-ever genome sequencing of an Antarctic animal
Written by Susan Meikle
Miami University scientists have long had a research presence in the Antarctic. Nick Teets (Miami ’07) has been a part of that research since he was a sophomore at Miami working with faculty mentor Rick Lee, University Distinguished Professor of Zoology.
Teets, who received his doctorate in entomology at Ohio State University in December, is a lead author, along with Lee, Yuta Kawarasaki, doctoral student in zoology, and an international team of researchers, on a recent study of the Antarctic insect Belgica antartica and the gene expression changes that enable it to be extremely tolerant of dehydration. Their study is part of a first-ever genome sequencing of an Antarctic animal.
Their paper was published in the Dec. 11, 2012 issue of Proceedings of the National Academy of Sciences (PNAS).
The other co-authors are Justin Peyton, doctoral student at OSU; David Denlinger, Distinguished Professor of Entomology at OSU (and adviser of Teets and Peyton); Joanna Kelley, geneticist from Stanford University; and Herve Colinet and David Renault, researchers from the Université de Rennes in France and Catholic University of Louvain, Belgium, respectively.
Lee and Denlinger have collaborated and led research expeditions to the Antarctic since 2004. Teets joined them and Kawarasaki on the 2009-2010 and the 2010-2011 expeditions. The team researches the physiological and biochemical mechanisms underlying the ecological success of the wingless midge, Belgica antarctica, the southernmost insect indigenous to the continent of Antarctica. The larvae of this species, only 2-7 mm long, represent the largest animals that remain on land year-round on the continent.
Extreme Dehydration Tolerance And The Polar Insect Belgica antarctica
Polar insects face near-constant desiccating conditions, as water is frozen and thus unavailable most of the year, explained the study authors.
Belgica antarctica is a model of success in adaptation to the environmental stresses of the Antarctic. Larvae of B. antarctica are remarkably tolerant of dehydration, surviving freezing of its body fluids; dehydration to 35 percent of its original body weight; and immersion in sea water for up to six days, among other stresses.
Overwintering midge larvae are capable of undergoing a distinct form of dehydration – cryoprotective dehydration - allowing them to remain unfrozen at subzero temperatures.
In their study, they used RNA sequencing to quantify genome-wide changes in response to dehydration in B. antarctica.
Gene Expression Changes in Response to Dehydration
The researchers found that "gene expression changes in response to dehydration indicated up-regulation of cellular recycling pathways with concurrent down-regulation of genes involved in general metabolism and ATP production."
In other words, explained Teets, “if dehydration makes a specific mRNA more abundant (I.e. up-regulated), we can reasonably conclude that the function of that gene is important for surviving dehydration.”
“Conversely, if a gene is down-regulated, that either means the gene is not needed to survive dehydration, or that keeping that gene active is detrimental to survival.”
Genes related to cellular recycling pathways – such as autophagy (breakdown of cellular components) - were turned on in response to dehydration. The researchers hypothesize that this serves an “important function by limiting cell death and turnover of macromolecules during dehydration, especially during the Antarctic winter” and “likely serves to conserve energy during prolonged dehydration.”
Conversely, they found down- regulation of genes related to general metabolism and ATP (energy) production. These mechanisms may be particularly important to overwintering larvae, contributing to energy conservation during the Antarctic winter.
Comparative Genomics: Two Polar Species, Different Gene Responses “Show How Little We Know About Molecular Adaptations In Polar Species”
The researchers also used comparative genomics to compare B. antarctica with another polar species, the Arctic collembolan (springtail) Megaphorura arctica.
“We compared our gene expression results with a transcriptomic (genome-wide expression profiling) dataset for M. arctica. Although these species are adapted to similar environments, our analysis indicated very little overlap in expression profiles between these two arthropods.
Thus, the transcript signature for a particular group is more dependent on the species than the dehydration treatment it experienced.”
"These results indicate that although both species have adapted to extremely dry and cold polar conditions, they have done so using markedly different molecular mechanisms,” Lee explained.
“These data emphasize how little we know about molecular adaptations in polar species."
First-Ever Genome Sequencing of an Antarctic Animal
This study is the first-ever genome sequencing of a Antarctic animal, according to Lee and Teets.
“This transcriptomics study was conducted in conjunction with an ongoing genome sequencing project for Belgica antarctica,“ Teets said. “The RNA-sequencing data were collected for two purposes, one for measuring gene expression in response to dehydration, but also to help us assemble the genome.”
“A couple years ago we were approached by a researcher at Stanford, Joanna Kelley – a co-author of this paper - who is interested in the genomes of extreme organisms.
We had been planning on sequencing the transcriptome all along, so now with her help we also have a draft genome for B. Antarctica,” Teets explained.
Prior to beginning this work, sequences were available for approximately 125 genes in this species. Now, with the combined efforts of this study and the ongoing genome project, “we have sequences for over 13,000 genes, and have quantified expression levels of all these genes in response to environmental extremes,” Teets said.
“The information in this genome will not only help with our physiological studies, it will allow us to do some really neat population genetics studies to quantify gene flow between populations of Belgica and look for signs of local adaptation.“
Miami Scientists and Antarctic Research
Miami researchers have had a long presence in the Antarctic, beginning with geochemist Bill Green, professor emeritus of interdisciplinary studies, more than 30 years ago.
Read the four-part series about the research of Rick Lee, Distinguished Professor of Zoology and his team from Miami and Ohio State University; Yuta Kawarasaki, doctoral student in zoology (who spent Feb.-June 2012 at Palmer Station, Antarctica); Rachael Morgan-Kiss, assistant professor of microbiology, and her team of graduate students; and Bill Green.
Rachael Morgan-Kiss Antarctic Research BLOG and VIDEO
Rachael Morgan-Kiss, assistant professor of microbiology, has conducted research in Antarctica since 2005. Her main study sites are located in the McMurdo Dry Valleys, permanently ice-capped lakes in Antarctica.
Morgan-Kiss and her graduate students Jenna Dolhi, Wei Li and Amber Siebenaler recently returned from their Oct.-Dec. 2012 expedition to Antarctica.
View photos and read their Antarctic Research Blog.
Watch a video of their research in the field.
Read more about Nick Teets and his undergraduate experience at Miami.