Insect Heat Shock Proteins During Stress and Diapause

Abstract

Insect heat shock proteins include ATP-independent small heat shock proteins and the larger ATP-dependent proteins, Hsp70, Hsp90, and Hsp60. In concert with cochaperones and accessory proteins, heat shock proteins mediate essential activities such as protein folding, localization, and degradation. Heat shock proteins are synthesized constitutively in insects and induced by stressors such as heat, cold, crowding, and anoxia. Synthesis depends on the physiological state of the insect, but the common function of heat shock proteins, often working in networks, is to maintain cell homeostasis through interaction with substrate proteins. Stress-induced expression of heat shock protein genes occurs in a background of protein synthesis inhibition, but in the course of diapause, a state of dormancy and increased stress tolerance, these genes undergo differential regulation without the general disruption of protein production. During diapause, when ATP concentrations are low, heat shock proteins may sequester rather than fold proteins.

Response of heat shock protein genes of the oriental fruit moth under diapause and thermal stress reveals multiple patterns dependent on the nature of stress exposure

“…Hsp70 is considered as an important stress chaperone under adverse conditions, being expressed at a high level under thermal stress (Colinet et al 2010;Fu et al 2014;King and MacRae 2015;Moribe et al 2010). However, unlike in several other insects (Colinet et al 2010;Wang and Kang 2005;Zhang and Denlinger 2010), GmHsp70 was not upregulated under cold stress.…”

“…This may reflect the role of molecular chaperons in the first line of defense of an insect to prevent irreversible denaturation of proteins and vital enzymes (Arrigo 2013;King and MacRae 2015). GmHsp70/ 90 were also highly expressed in the fat body, suggesting a role of chaperone function in stress signal detection in tissue during development (Krebs and Feder 1998), but these functional roles remain speculative in the absence of additional data including changes in protein levels.…”

“…Some conserved large Hsps do not have these highly variable terminal sequences and may show slower rates of evolution because they have pleiotropic effects on development and because there is less redundancy in this group due to the smaller number of genes comprising the various families; in contrast, sHsps can be deleted without marked deleterious effects, at least in Drosophila (Morrow and Tanguay 2015). Homologous sequences of Hsp70 and Hsp90 can show similar functions across different insects (King and MacRae 2015).…”

Stress tolerance during diapause and quiescence of the brine shrimp, Artemia

“…The sHSPs, on the other hand, are ATP-independent chaperones that prevent irreversible denaturation of other proteins but are not otherwise actively engaged in their subsequent processing (Haslbeck and Vierling 2015). The ATP-dependent chaperones may sequester partially denatured proteins when ATP is limiting and, with the sHSPs, constitute a protective network during diapause and quiescence (King and MacRae 2015). Stress tolerance in cysts depends on molecular chaperones, a proposal first occasioned by the response of A. franciscana to heat (Miller and McLennan 1988a, b).…”

“…Upon liberation from females, cysts undergo profound reduction in metabolism and enter diapause, a state of developmental arrest and greatly enhanced stress tolerance (Clegg 1967(Clegg , 1997Clegg and Jackson 1998;King and MacRae 2012;Duan et al 2014). Diapause occurs in animals other than Artemia, most commonly in insects, and initiates in anticipation of adverse environmental conditions signaled by day length, perhaps via changes in circadian clock gene expression (Nambu et al 2004;MacRae 2010;King and MacRae 2015;Meuti et al 2015).…”