Protein chaperones and winter cold hardiness in insects: heat shock proteins and glucose regulated proteins in freeze-tolerant and freeze-avoiding species.
Two species of insects with different overwintering strategies were chosen as model organisms to assess the role of chaperone proteins in insect cold hardiness. Epiblema scudderiana, a freeze-avoiding gall moth, and Eurosta solidaginis, a freeze-tolerant gall fly, were used to compare and contrast the two overwintering strategies; both species overwinter in the diapause stage as last instar larvae inside galls on the stems of goldenrod plants. The research reported in this thesis analyzed changes in molecular chaperone levels over the winter season in insects sampled from outdoors as well as in larvae given laboratory exposures to subzero temperatures and hypoxia. Multiple proteins in the heat shock (Hsp10, Hsp40, Hsp60, Hsp70, Hsp110) and glucose-regulated (Grp75, Grp78, Grp94, Grp170) families of chaperones were assessed as well as other chaperones (TCP-1, αA- and αB-crystallins). The heat shock transcription factor (HSF-1) was also analyzed. Despite an overall suppression of transcription and translation during winter diapause, selected chaperone proteins were differentially expressed in the larvae in response to low temperatures, freeze/thaw, or hypoxia exposures. Most of the chaperones were up-regulated directly or indirectly by subzero temperature and/or anoxia exposures to enhance their actions in the stabilization, repair or elimination of misfolded or denatured proteins. These chaperones function incytoplasmic, endoplasmic reticulum and mitochondrial compartments, indicating that multiple endogenous pathways are engaged in maintaining and/or restoring cellular homeostasis in the larvae in response to these insults. Elevated HSF-1 levels indicated that Hsp enhancement in the larvae was due to up-regulation of the genes involved.