This dissertation focuses on patterns of protein synthesis that are linked to several different stress responses in insects. These include the overwintering dormancy response of insects, known as diapause; the response of insects to rapid drops in temperature, known as rapid cold hardening (RCH), and responses of an Antarctic insect to desiccation and rehydration.
Proteomics, the comprehensive study of all proteins in an organism, has proven to be a powerful technique for studying changes in protein abundance during various stresses. However, only a few studies have used proteomics to examine diapause and stress responses in insects. The primary focus of this work is to identify proteins associated with diapause, low temperature and desiccation. The flesh fly, Sarcophaga crassipalpis, and the midge, Belgica antarctica, were used as model organisms.
A proteomic analysis of pupal brains in S. crassipalpis revealed that heat shock proteins (Hsp) were among the most conspicuous brain proteins present in higher amounts during diapause. While the mRNAs encoding Hsps were previously known to be associated with diapause, other proteins identified during this study were not known to be linked to diapause, thus suggesting that the proteomic approach nicely supplements work done at the transcript level. A gene encoding neuropeptide like precursor 4 in S. crassipalpis showed close association with diapause, suggesting a potential role for this gene in initiating and maintaining diapause. Changes in brain proteins following pupal diapause termination in S. crassipalpis showed an increase in abundance of myo-inositol-1-phosphate synthase (Inos). The elevation of Inos at diapause termination is likely downstream of the physiological regulation that initiates development. During RCH, an increase in ATP synthase suggests that an elevation of ATP is an important component of this response, and a small Hsp increase suggests that at least one of the Hsps is actually mobilized during RCH, rather that after RCH as previously assumed. Proteomics of B. antarctica larvae indicate that both desiccation and rehydration elicit synthesis of contractile and cytoskeletal proteins that are likely to be involved in the body contraction and cytoskeleton rearrangements that are associated with survival of changes in body water content.