|Rinehart, Joseph - Joe|
|HAYWARD, SCOTT A|
Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2006
Publication Date: 9/19/2006
Citation: Rinehart, J.P., Hayward, S.L., Elnitsky, M.A., Sandro, L.H., Lee, R.E., Denlinger, D.L. 2006. Continuous upregulation of heat shock proteins in larvae, but not adults, of a polar insect. Proceedings of the National Academy of Sciences. 103(38):14223-14227.
Interpretive Summary: Antarctica has one of the earth’s most extreme environments. While many animals have adapted to life in the sea in this part of the world, few have adapted to the extremes of living on the land year round. One exception is the fly Belgica antarctica, which at a length of 1/8 of an inch, is the largest animal to live on the continent all year. During its two year lifespan, it survives as a larva during lengthy Antarctic winter encased in ice. During the summer, adults emerge and are present for a brief 1-2 week period, experiencing surprisingly high temperatures in the process. The research presented in this paper investigates the survival strategies used by the different stages of this insect. All animals, including adult Belgica antartica, are able to produce specific proteins when they are stressed, which help them survive. They then turn these proteins off when normal conditions return. In contrast, the larvae of Belgica antarctica express these proteins all the time, in anticipation of the long Antarctic winter. Thus, the midge larvae, but not the adults, have adopted the unusual strategy of expressing their heat shock proteins continuously. The change in production of stress proteins is one of what surely is many mechanisms that have allowed this insect to adapt to the harsh conditions of the Antarctic continent.
Technical Abstract: Antarctica is one of the earth’s most inhospitable environments. Though an abundance of animals have adapted to life associated with the sea in this part of the world, few animals have adapted to the rigors of a terrestrial existence. One exception is the flightless midge Belgica antarctica which, at a length of 2 mm, is the largest free-living animal on the continent. As a larva this midge survives the lengthy austral winter encased in ice, and during the austral summer it is subjected to wildly varying and surprising high temperatures. Here we report a fascinating dichotomy in survival strategies exploited by this insect. As a larva, it exhibits constituative upregulation of heat shock proteins (small hsp, hsp70, hsp90) which is concurrent with a high inherent tolerance to temperature stress. High or low temperature exposure will not further upregulate these genes, nor further enhance thermotolerance. Conversely, the adult, which lives for 1-2 weeks during the summer, exhibits no constitutive upregulation, but the hsps are readily upregulated in response to high temperatures, resulting in enhanced thermotolerance, and consequently exhibits lower intrinsic tolerance to high temperatures. Thus, the midge larvae, but not the adults, have adopted the unusual strategy of expressing their heat shock proteins continuously.