chapter 1 - Bentham Science

Role of Conventional and Unconventional Stress Proteins HPFP: Recent Advances in Insects and Other Arthropods Vol. 1 129
During the insect stress response, individuals first, if possible, utilize highly adaptive behavioral,
biochemical, molecular and/or physiological responses to preemptively avoid or respond to damage
induced by stress. This preemptive response is usually limited to dormancy preparation that occurs prior to
episodes of prolonged unfavorable conditions. Second, proteins and other factors that prevent interactions
between damaged proteins and other biochemical molecules are increased during stress. Lastly, proteins are
required to return insects to their normal, pre-stress physiological and metabolic levels by repairing stress
damage to allow development and reproduction to progress. Differences in the levels and variations of the
reactions among insects are responsible for diversity of stress tolerance between species and within
individual populations.
What defines an insect “stress” protein? Typically “stress” proteins are those that have been documented to
increase in transcript level, abundance, phosphorylation or activity when insects are exposed to or
recovering from stress. Heat shock proteins (Hsps) and antioxidant enzymes (AOEs) are typical examples
of stress proteins; these are usually increased during or immediately after exposure to adverse conditions
then decrease after recovery. Recent studies, particularly large scale transcriptome and proteome projects,
have shown that other proteins not typically associated with stress are critical to tolerance, response and
recovery from stressful periods. Aquaporins (AQPs), as an example, are critical for the movement of water
and other molecules across the cell membrane [8-10], and have been recently linked to cold, dehydration
and freezing tolerance in multiple organisms [11, 12, 341, 344, 345]. Thus, AQPs are not usually classified
as “stress” proteins, but seem to be critical for stress tolerance. Many previous reviews have focused on one
type of stress response, along with the associated stress proteins, in insects or arthropods such as
dehydration [2, 4, 13-15], diapause [16-21], heat tolerance [22, 23] and cold tolerance [24-28,].
Alternatively, the focus is one type of stress protein across multiple organisms, such as Hsps [29]. Recently,
Chown and Nicolson [23] published a comprehensive book on the physiological ecology of insects that
provides an excellent synopsis of insect stress tolerance. This chapter seeks to expand on these previous
works by providing a comprehensive depiction of proteins involved in the response of insects and other
closely-related arthropods to environmental stress. Particularly, the role of proteins notprimarily associated
with traumatic conditionsare described during the insect stress response. To do so, we provide information
on factors that cause insect stress, stress signaling and transcriptional regulation, proteins involved in the
typical stress response (e.g. Hsps and AOEs), structural changes (e.g. actin and myosin) known to
accompany stress, proteins important for regulating fluid movement and buffering damage associated with
changes in water levels (aquaporins and late embryogenesis abundant, LEA, proteins), ice-active proteins
(IAPs; antifreeze proteins and ice nucleating proteins), physiological traits such as aging, metabolism and
reproduction that are altered by stress and other biochemical factors that function in conjunction with stress
proteins to alleviate stress-induced damage.
INSECT STRESSES
Any abiotic or biotic period that results in negative consequences toward the fitness of that organism can be
defined as stress. Most studies on insect stress have focused on three main abiotic pressures, cold, heat and
dehydration, or in preparation for extended harsh periods (diapause). In Table 1, we have included a list of
behavioral, biochemical, molecular and physiological changes that have been documented during
preparation for stressful periods, i.e. initiation of dormancy (aestivation and diapause) or in direct response
to cold, dehydration and heat in insects. Biotic stresses such as a microbial infections or parasitoid
infestations have been shown to induce the immune response and other stress pathways [30-34], but are not
discussed in this review. Detailed information on the immune response of insects and other arthropods can
be viewed in Chapter 3 of this book. Additionally, we have not included information on studies involving
chemical toxicity (pesticide, heavy metals, etc.) since this stress is usually due to environmental
contanmination by humans or restricted to specialized habitats. Thus, the focal point of this review is on
proteins involved in the response of insects and other similar invertebrates to environmental stress.
Early studies on insect stress response examined either short periods of stress or the effects of long-term
acclimation (or diapause) on cold, heat and dehydration tolerance [2, 4, 15, 18, 20-22, 24, 25, 35, 36]. The
discovery of rapid cold hardening (RCH) by Lee et al. [37], a process by which insects become more