Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2007
Publication Date: 7/3/2007
Citation: Rinehart, J.P., Aiqing, L., Yocum, G.D., Robich, R.M., Hayward, S.A., Denlinger, D.L. 2007. Upregulation of Heat Shock Proteins is Essential for Cold Survival during Insect Diapause. Proceedings of the National Academy of Sciences. 104(27):11130-11137.
Interpretive Summary: Winter poses a major challenge for insects. To be successful in environments with distinct seasons, insects must grow and reproduce only for a few months during the summer and then survive the remainder of the year without feeding, while dealing with the stresses that winter brings to them. Most insects survive winter by entering diapause, a state that is characterized by, among other things, an increase in stress tolerance. Several years ago, we identified two stress proteins that appear to be present at higher levels (upregulated) in diapausing flesh flies. Since that time, other researchers have shown similar results in a handful of species. However, several questions remain unanswered. Are other stress proteins also upregulated during diapause? Do many other species, especially pest species upregulate similar proteins during diapause? And finally, is there a direct link between the presence of these proteins and the increased stress tolerance seen in diapausing insects? This paper helps to answer these key questions. Using molecular techniques we have found several other types of stress proteins that are upregulated during diapause in the flesh fly. We have also found that one specific stress protein, called heat shock protein 70, is expressed at higher levels during diapause in several different species, including some pest species. Finally, using RNA interference, a technique by which the upregulation of a specific protein can be blocked, we have established a direct link between stress protein upregulation and diapause stress tolerance. Therefore these stress proteins are a vital part of winter survival for many insects.
Technical Abstract: Diapause, the dormancy common to overwintering insects, evokes a unique pattern of gene expression. In the flesh fly most, but not all, of the fly’s heat shock proteins (Hsps) are upregulated. The diapause upregulated Hsps include two members of the Hsp70 family, one member of the Hsp60 family (TCP-1), at least four members of the small Hsp family, and a small Hsp pseudogene. Expression of an Hsp70 cognate, Hsc70, is uninfluenced by diapause, and Hsp90 is actually downregulated during diapause, thus diapause differs from common stress responses that elicit synchronous upregulation of all Hsps. Upregulation of the Hsps begins at the onset of diapause, persists throughout the overwintering period, and ceases within hours after the fly receives the signal to reinitiate development. The upregulation of Hsps appears to be common to diapause in species representing diverse insect orders including Diptera, Lepidoptera, Coleoptera and Hymenoptera, as well as in diapauses that occur in different developmental stages (embryo, larva, pupa, adult). Suppressing expression of Hsp23 and Hsp70 in flies using RNA interference did not alter the decision to enter diapause nor the duration of diapause, but it had a profound effect on the pupa’s ability to survive low temperatures. We thus propose that upregulation of Hsps during diapause is a major factor contributing to cold-hardiness of overwintering insects.