|Rinehart, Joseph - Joe|
Submitted to: Journal of Comparative Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2008
Publication Date: 5/1/2009
Citation: Lopez-Martinez, G., Benoit, J.B., Rinehart, J.P., Elnitsky, M.A., Lee, R.E., Denlinger, D.L. 2009. Dehydration, Rehydration and Overhydration Alter Patterns of Gene Expression in the Antarctic Midge, Belgica antarctica. Journal of Comparative Physiology B. 179(4):481-491.
Interpretive Summary: Antarctica, being the coldest and driest continent on earth, contains some of the earth’s most inhospitable environments. Although an abundance of animals have adapted to life in the sea in this part of the world, few animals have adapted to living on the continent itself. One exception is the midge Belgica antarctica, which at ¼ of an inch long, is Antarctica’s largest free-living, year-round inhabitant. Previously, our research team has studied desiccation tolerance of this insect at the whole organism level. This study investigates how the expression pattern of several important genes is changed during dehydration, rehydration, and even overhydration (adding more water to the insect’s body that it had originally). Our data show that several stress-related genes respond to these stresses, as do genes that affect cell structure, and genes that are involved in maintaining water balance across membranes. These results suggest that several important cellular mechanisms are responsive to these varying conditions in this species, and that these processes must work together to protect this insect from the rigors of living on the harsh continent.
Technical Abstract: We investigated molecular responses elicited by three types of dehydration (fast, slow and cryoprotective), rehydration and overhydration in larvae of the Antarctic midge, Belgica antarctica. The larvae spend most the year encased in ice but during the austral summer are vulnerable to summer storms, osmotic stress from ocean spray and drying conditions due to wind and intense sunlight. Using suppressive subtractive hybridization (SSH), we obtained clones that were potentially responsive to dehydration and then used northern blots to evaluate the gene’s responsiveness to different dehydration rates and hydration states. Among the genes most responsive to changes in the hydration state were those encoding heat shock proteins (smHsp, Hsp70, Hsp90), antioxidants (superoxide dismutase, catalase), detoxification (metallothionein, cytochrome p450), genes involved in altering cell membranes (fatty acid desaturase, phospholipase A2 activating protein, fatty acyl CoA desaturase) and the cytoskeleton (actin, muscle-specific actin), and several additional genes including a zinc-finger protein, pacifastin and VATPase. Among the three types of dehydration evaluated, fast dehydration elicited the strongest response (more genes, higher expression), followed by cryoprotective dehydration and slow dehydration. During rehydration most, but not all, genes that were expressed during dehydration continued to be expressed; fatty acid desaturase was the only gene to be uniquely upregulated in response to rehydration. All genes examined, except VATPase, were upregulated in response to overhydration. The midge larvae are thus responding quickly to water loss and gain by expressing genes that encode proteins contributing to maintenance of proper protein function, protection and overall cell homeostasis during times of osmotic flux, a challenge that is particularly acute in this Antarctic environment.