Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology

Laboratory selection at different temperatures modifies heat-shock transcription factor (HSF) activation in Drosophila melanogaster

The magnitude and time course of activation of the heat-shock transcription factor (HSF) differ among Drosophila melanogaster lines evolving at 18 degrees C, 25 degrees C or 28 degrees C for more than 20 years. At lower heat-shock temperatures (27–35 degrees C), flies from the 18 degrees C population had higher levels of activated HSF (as detected by an electrophoretic mobility shift assay) than those reared at 25 degrees C and 28 degrees C. At higher temperatures (36 and 37 degrees C), however, the 28 degrees C flies had the highest levels of HSF. These differences persisted after one generation of acclimation at 25 degrees C, suggesting that phenotypic plasticity was limited. In addition, larvae from the 28 degrees C lines activated HSF less rapidly after a 35 degrees C heat shock than those from the 18 degrees C and 25 degrees C populations. These results are similar but not identical to previously reported differences in expression of Hsp70 (the major heat-inducible stress protein in Drosophila melanogaster) among the experimental lines. We conclude that HSF activation evolves rapidly during laboratory culture at diverse temperatures and could play an important role in the evolution of the heat-shock response.

Activity of plant extracts on the respiratory burst and the stress protein synthesis

Aqueous, methanol and dichloromethane extracts from Artemisia copa, Baccharis grisebachii, Baccharis incarum, Baccharis latifolia, Mutisia kurtzii and Pluchea sagittalis, plants used in the Traditional Medicine of South America, are studied for activity on the respiratory burst and the inducible heat shock protein of 72 kD (hsp72) synthesis. Activity on the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), as well as on hsp72 synthesis was measured by flow cytometry in human neutrophils. Cells were stimulated using hydrogen peroxide, phorbol-12-myristate-13-acetate (PMA) or formyl-methionyl-leucyl-phenylalanine (FMLP) for ROS generation, and sodium nitroprusside (SNP) or PMA in the presence of calmodulin inhibitor W-13 for RNS. The production of hsp72 was induced by heat, PMA, H2O2 and SNP. The best inhibitory activity was shown by the dichloromethane extracts of Baccharis grisebachii and Pluchea sagittalis that were active in all the assays. The aqueous extract of Pluchea sagittalis was also active in most assays. The aqueous extract from Mutisia kurtzii caused a clear increase of the hsp72 production and showed prooxidant activity.

Closterovirus encoded HSP70 homolog and p61 in addition to both coat proteins function in efficient virion assembly

Assembly of the viral genome into virions is a critical process of the virus life cycle often defining the ability of the virus to move within the plant and to be transmitted horizontally to other plants. Closteroviridae virions are polar helical rods assembled primarily by a major coat protein, but with a related minor coat protein at one end. The Closteroviridae is the only virus family that encodes a protein with similarity to cellular chaperones, a 70-kDa heat-shock protein homolog (HSP70h). We examined the involvement of gene products of Citrus tristeza virus (CTV) in virion formation and found that the chaperone-like protein plus the p61 and both coat proteins were required for efficient virion assembly. Competency of virion assembly of different CTV mutants was assayed by their ability to be serially passaged in Nicotiana benthamiana protoplasts using crude sap as inoculum, and complete and partial virus particles were analyzed by serologically specific electron microscopy. Deletion mutagenesis revealed that p33, p6, p18, p13, p20, and p23 genes were not needed for virion formation. However, deletion of either minor- or major-coat protein resulted in formation of short particles which failed to be serially transferred in protoplasts, suggesting that both coat proteins are required for efficient virion assembly. Deletion or mutation of HSP70h and/or p61 dramatically reduced passage and formation of full-length virions. Frameshift mutations suggested that the HSP70h and p61 proteins, not the RNA sequences, were needed for virion assembly. Substitution of the key amino acid residues in the ATPase domain of HSP70h, Asp(7) to Lys or Glu(180) to Arg, reduced assembly, suggesting that the chaperone-like ATPase activity is involved in assembly. Both HSP70h and p61 proteins appeared to contribute equally to assembly, consistent with coordinate functions of these proteins in closterovirus virion formation. The requirement of two accessory proteins in addition to both coat proteins for efficient assembly is uniquely complex for helical virions.

Genome-wide study of aging and oxidative stress response in Drosophila melanogaster

Aging is a universal but poorly understood biological process. Free radicals accumulate with age and have been proposed to be a major cause of aging. We measured genome-wide changes in transcript levels as a function of age in Drosophila melanogaster and compared these changes with those caused by paraquat, a free-radical generator. A number of genes exhibited changes in transcript levels with both age and paraquat treatment. We also found genes whose transcript levels changed with age but not with paraquat treatment. This study suggests that free radicals play an important role in regulating transcript levels in aging but that they are not the only factors. This genome-wide survey also identifies candidates for molecular markers of aging.

Reproductive costs of heat shock protein in transgenic Drosophila melanogaster

Senescence may evolve when genes have antagonistic effects between early reproduction and later age-specific mortality. Although widely consistent with data of quantitative genetics, this model has yet to be validated with the identification of a specific locus presenting such trade-offs. The molecular chaperone hsp70 may be a candidate for such a gene. Heat induced expression of the Hsp70 protein in adults decreases rates of age-specific mortality during normal aging, while maternally experienced heat shock depresses the production of mature progeny. Here we show that maternal heat shock reduces the proportion of egg hatch but not the viability of successfully hatched offspring. To assess whether heat induced maternal expression of hsp70 causes reduced egg hatch, we measured the proportion of eggs that hatch from females engineered to overexpress hsp70 transgenes. We used the same transgenic strains that extend longevity upon hsp70 expression and found that Hsp70 is sufficient to suppress egg hatch. The proportion of egg hatch as a function of hsp70 expression was not reduced in the first eggs laid after maternal heat shock, but appears in later laid eggs, which were at preoogenic and early vitellogenic stages during the maternal expression of hsp70. The contervailing effects of hsp70 upon fecundity and subsequent age-specific mortality exemplify antagonistic pleiotropy, and this trade-off could contribute to the evolution of Drosophila senescence.

Requirement of heat shock protein 90 in mesangial cell mitogenesis

BACKGROUND

Hyperplasia of mesangial cells (MCs) is a frequent finding in glomerulonephritis. Heat shock protein 90 (HSP90) is a major cellular chaperone that assists protein folding under physiological and stress conditions.

METHODS

To identify genes that are potentially involved in the pathogenesis of glomerulonephritis, we analyzed glomerular gene expression in mesangioproliferative rat anti-Thy1.1 nephritis by representational difference analysis (RDA). Expression of HSP90beta in anti-Thy1.1 nephritis was studied by Northern and Western blot analyses and immunohistochemistry. In cultured rat MCs, the requirement of HSP90 for mitogenic signaling steps and MC replication was studied by incubation with the specific HSP90 inhibitor geldanamycin.

RESULTS

By RDA, a cDNA fragment homologous to HSP90beta was identified. Glomerular mRNA and protein expression of HSP90beta was markedly and transiently up-regulated during the course of anti-Thy1.1 nephritis, with a maximum at day 6, coinciding with the peak of MC proliferation. By immunohistochemistry, HSP90beta expression in normal glomeruli was detected in podocytes. However, in anti-Thy1.1 nephritis, glomerular HSP90beta protein expression was strongly and transiently increased in mesangial localization. In vitro, mitogenic stimulation of rat MCs led to the induction of HSP90beta mRNA and protein. Incubation of MCs with geldanamycin dose-dependently inhibited DNA synthesis and replication. Moreover, geldanamycin interfered with mitogen-induced phosphorylation of extracellular signal-regulated kinase and transcription of c-fos and Egr-1, but not with transactivation of STAT1 transcription factor. Cell cycle analysis of serum-stimulated MCs revealed that geldanamycin inhibited kinase activity of cyclin D1/CDK4 complexes and blocked progression in the G0/G1 phase and at the S/G2 phase transition.

CONCLUSIONS

The up-regulation of HSP90beta in anti-Thy1.1 nephritis may reflect its functional involvement in phenotypical alterations of MCs in mesangioproliferative glomerulonephritis. Our in vitro studies indicate that HSP90 governs the capacity of MCs to respond to proliferative stimuli by regulating critical mitogenic signaling steps necessary for G1 entry and S-phase progression.

Variation in the expression of Hsp70, the major heat-shock protein, and thermotolerance in larval and adult selection lines of Drosophila melanogaster

(1) Lines of Drosophila melanogaster were "laboratory naturally" or artificially selected under five thermal regimes. (2) Hsp70 expression per unit protein after heat hardening and heat-shock resistance with and without prior hardening were measured. (3) Differences between the selection regimes in the responses of these traits suggest that thermal resistance can be changed independently of inducible Hsp70 expression. (4) Adult males had higher survival than females but did not differ in inducible Hsp70 expression per unit protein after heat hardening. (5) Larvae expressed less Hsp70 per unit protein than adults after heat hardening.

Heat-shock protein 90 is down-regulated during pupal diapause in the flesh fly, Sarcophaga crassipalpis, but remains responsive to thermal stress

Heat-shock protein 23 (hsp23) and hsp70 are both known to be strongly up-regulated during pupal diapause in the flesh fly Sarcophaga crassipalpis. This prompted us to investigate whether hsp90 was also up-regulated during diapause. To test this possibility, we developed a partial clone of a hsp90 family member for use as a probe in Northern blot hybridization. Both high and low temperature exposure up-regulated hsp90 transcripts in nondiapausing individuals. In contrast to hsp23 and hsp70, hsp90 was down-regulated following entry into diapause, and returned to prediapause levels after diapause termination. The response of hsp90 to heat shock and cold shock remained intact during diapause: both shocks evoked elevated expression. The results indicate differential regulation of hsps during diapause and in response to thermal injury inflicted on diapausing pupae.

Fever and the heat shock response: distinct, partially overlapping processes

The heat shock response is an ancient and highly conserved process that is essential for surviving environmental stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms temporarily subject themselves to thermal stress in the face of infections. We review studies showing that fever is beneficial in the infected host. We show that core temperatures achieved during fever can activate the heat shock response and discuss some of the biochemical consequences of such an effect. We present data suggesting 4 possible mechanisms by which fever might confer protection: (1) directly killing or inhibiting growth of pathogens; (2) inducing cytoprotective heat shock proteins (Hsps) in host cells; (3) inducing expression of pathogen Hsps, an activator of host defenses; and (4) modifying and orchestrating host defenses. Two of these mechanisms directly involve the heat shock response. We describe how heat shock factor-1, the predominant heat-induced transcriptional enhancer not only activates transcription of Hsps but also regulates expression of pivotal cytokines and early response genes. The relationship between fever and the heat shock response is an illuminating example of how a more recently evolved response might exploit preexisting biochemical pathways for a new function.

Leishmania infantum: gene cloning of the GRP94 homologue, its expression as recombinant protein, and analysis of antigenicity

The complete nucleotide sequence for the Leishmania infantum homologue to the glucose-regulated protein 94 (GRP94) gene was determined from the isolation and characterization of a genomic clone. Like the mammalian and plant GRP94s, the L. infantum GRP94 sequence possesses both an N-terminal signal peptide and a putative endoplasmic reticulum retention signal, consisting of the C-terminal tetrapeptide EDDL. Thus, L. infantum is the first protozoan organism in which GRP94 has been identified. Southern blot analysis has indicated that this protein is encoded by a single-copy gene. The L. infantum GRP94 gene was expressed in Escherichia coli and the recombinant protein used to evaluate its antigenicity and immunogenicity. Eighty-four percent of sera from dogs with visceral leishmaniasis reacted with the protein, indicating that GRP94 is a potent immunogen during Leishmania infection. Given the immunogenic and antigenic properties shown by the L. infantum GRP94, we think that this protein constitutes a valuable molecule for diagnostic purposes and a potential candidate for studies of protective immunogenicity.

Body temperatures of house mice artificially selected for high voluntary wheel-running behavior: repeatability and effect of genetic selection

We studied rectal body temperatures of house mice (Mus domesticus) that had been artificially selected for high voluntary wheel running.1. At generation 17, mice from the four replicate selected lines ran, on average, 2.5-times as many revolutions/day as did mice from the four random-bred control lines.2. During the day, repeatability of individual differences in body temperature measured 4 days apart was low; at night, repeatability was statistically significant across three time scales (1 day, 1 week, 2 weeks).3. During the day, body temperatures of selected and control animals did not differ; at night, mice from selected lines had higher body temperatures. However, when amount of wheel running immediately prior to measurement was included as a covariate, the difference was no longer statistically significant.Higher body temperatures, associated with increased activity, might enhance locomotor abilities through Q10 effects, increase metabolic rate and food requirements, affect sleep patterns, and alter expression of heat-shock proteins.

Thermal resistance, developmental rate and heat shock proteins in Artemia franciscana, from San Francisco Bay and southern Vietnam

Cysts (encysted gastrula embryos) of Artemia franciscana collected from salterns in San Francisco Bay, California, USA (SF) were inoculated into much warmer growth ponds in the Mekong Delta region of Vietnam (V) in 1996. V adults arising directly from these cysts during 17 April to 15 May produced their own cysts, which were collected, processed and stored until shipped to the USA for study. Adults grown in the laboratory from SF cysts (those used for the inoculation) were less resistant to high temperature than adults cultured from V cysts. V cysts produced heat-resistant adults, even though cultured under the same laboratory conditions as SF animals, at much lower temperatures than they ever experienced in Vietnam. Differences in thermal performance between SF and V adults were retained in the second generation, cultured from cysts produced in the laboratory by first generation adults, suggesting a genetic basis for the better heat resistance of V adults. We propose that the operation of natural selection in the Vietnam growth ponds produced adults with improved thermal tolerance, and that the basis for this tolerance was incorporated into the developmental program of their cysts. Surprisingly, differences in heat resistance of laboratory reared animals were not reflected in constitutive levels of the hsp70 family which were similar in first generation SF and V adults. A conditioning heat shock (HS, 37 degrees C, 30 min) led to the same level of induced thermotolerance in SF and V first generation adults when evaluated 24 h post-HS. Levels of hsp70 were also up-regulated at that time, but to about the same extent in SF and V adults. Developmental rates of SF cysts used for the inoculation were faster than those of cysts produced in Vietnam when both were incubated at 21+/-1 degrees C, suggesting that V cysts have become adapted to develop at higher temperatures.

Modulating cellular aging in vitro: hormetic effects of repeated mild heat stress on protein oxidation and glycation

Intracellular and extracellular proteins are subject to a variety of spontaneous non-enzymatic modifications which affect their structure, function and stability. Protein oxidation and glycation are tightly linked and are implicated in the development of many pathological consequences of aging. Although multiple endogenous pathways in the cell can prevent the formation of oxidized and glycated proteins, and repair and degrade abnormal proteins, such abnormal proteins do accumulate during aging. The heat shock response involving the family of stress-proteins or the so-called heat shock proteins (HSP), represents the quickest and highly conserved response to proteotoxic insults. Since repeated mild heat stress is able to prevent the onset of various age-related changes during cellular aging in vitro, we suggest that treatments which increase HSP expression should reduce the extent of accumulation of abnormal proteins during aging. Such modulation of aging is an example of hormesis, which is characterized by the beneficial effects resulting from the cellular responses to mild repeated stress.

Functional and physiological consequences of genetic variation at phosphoglucose isomerase: heat shock protein expression is related to enzyme genotype in a montane beetle

Allele frequency variation at the phosphoglucose isomerase (PGI) locus in Californian populations of the beetle Chrysomela aeneicollis suggests that PGI may be undergoing natural selection. We quantified (i) apparent Michaelis-Menten constant (K(m)) of fructose 6-phosphate at different temperatures and (ii) thermal stability for three common PGI genotypes (1-1, 1-4, and 4-4). We also measured air temperature (T(a)) and beetle body temperature (T(b)) in three montane drainages in the Sierra Nevada, California. Finally, we measured 70-kDa heat shock protein (Hsp70) expression in field-collected and laboratory-acclimated beetles. We found that PGI allele 1 predominated in the northernmost drainage, Rock Creek (RC), which was also significantly cooler than the southernmost drainage, Big Pine Creek (BPC), where PGI allele 4 predominated. Allele frequencies and air temperatures were intermediate in the middle drainage, Bishop Creek (BC). Differences among genotypes in K(m) (1-1 > 1-4 > 4-4) and thermal stability (4-4 > 1-4 > 1-1) followed a pattern consistent with temperature adaptation. In nature, T(b) was closely related to T(a). Hsp70 expression in adult beetles decreased with elevation and differed among drainages (BPC > BC > RC). After laboratory acclimation (8 days, 20 degrees C day, 4 degrees C night) and heat shock (4 h, 28-36 degrees C), Hsp70 expression was greater for RC than BPC beetles. In RC, field-collected beetles homozygous for PGI 1-1 had higher Hsp70 levels than heterozygotes or a 4-4 homozygote. These results reveal functional and physiological differences among PGI genotypes, which suggest that montane populations of this beetle are locally adapted to temperature.

Heat-shock protein expression is absent in the antarctic fish Trematomus bernacchii (family Nototheniidae)

The heat-shock response, the enhanced expression of one or more classes of molecular chaperones termed heat-shock proteins (hsps) in response to stress induced by high temperatures, is commonly viewed as a ‘universal’ characteristic of organisms. We examined the occurrence of the heat-shock response in a highly cold-adapted, stenothermal Antarctic teleost fish, Trematomus bernacchii, to determine whether this response has persisted in a lineage that has encountered very low and stable temperatures for at least the past 14–25 million years. The patterns of protein synthesis observed in in vivo metabolic labelling experiments that involved injection of (35)S-labelled methionine and cysteine into whole fish previously subjected to a heat stress of 10 degrees C yielded no evidence for synthesis of any size class of heat-shock protein. Parallel in vivo labelling experiments with isolated hepatocytes similarly showed significant amounts of protein synthesis, but no indication of enhanced expression of any class of hsp. The heavy metal cadmium, which is known to induce synthesis of hsps, also failed to alter the pattern of proteins synthesized in hepatocytes. Although stress-induced chaperones could not be detected under any of the experimental condition used, solid-phase antibody (western) analysis revealed that a constitutively expressed 70 kDa chaperone was present in this species, as predicted on the basis of requirements for chaperoning during protein synthesis. Amounts of the constitutively expressed 70 kDa chaperone increased in brain, but not in gill, during 22 days of acclimation to 5 degrees C. The apparent absence of a heat-shock response in this highly stenothermal species is interpreted as an indication that a physiological capacity observed in almost all other organisms has been lost as a result of the absence of positive selection during evolution at stable sub-zero temperatures. Whether the loss of the heat-shock response is due to dysfunctional genes for inducible hsps (loss of open reading frames or functional regulatory regions), unstable messenger RNAs, the absence of a functional heat-shock factor or some other lesion remains to be determined.

Colocalization of chaperone Cpn60, proinsulin and convertase PC1 within immature secretory granules of insulin-secreting cells suggests a role for Cpn60 in insulin processing

Many of the mechanisms that control insulin processing and packaging by interaction with different elements along the secretory pathway remain poorly understood. We have investigated the possibility that Cpn60, a member of the heat shock protein family, may be present in rat insulin-secreting cells, participating in the proinsulin-insulin maturation process. Immunofluorescence and high resolution immunocytochemical studies revealed the presence of the Cpn60 protein all along the insulin secretory pathway, being particularly abundant over the proinsulin-containing immature secretory granules. Double-labeling experiments showed associations between Cpn60 and proinsulin, as well as between Cpn60 and PC1 convertase, with a preferential binding to proinsulin. These findings paralleled those of coimmunoprecipitation studies showing the Cpn60 chaperone and the mature form of the PC1 convertase in proinsulin immunoprecipitates, as well as the PC1 in Cpn60 immunoprecipitates from total islet cell extracts. In vitro binding of Cpn60 to proinsulin, insulin and glucagon was also documented. Cpn60, significantly abundant in proinsulin-containing secretory granules where conversion of proinsulin to insulin takes place, and the colocalization of the chaperone with proinsulin and PC1 convertase suggest that the Cpn60 protein may play a role directing precise molecular interactions during insulin processing and/or packaging.

Transgenic organisms in evolutionary ecology

Evolutionary ecology aims to understand how phenotypes are designed for reproductive success and survival. Perhaps the most powerful approach towards this goal is to alter a character genetically and observe the resulting change in reproduction, survival, growth, defense or competitive ability. Until recently, this strategy was not practical. Transgenic manipulation now offers a solution - novel genes are introduced into the germ line and are then expressed in the developing organism. This technique is already available in model and agricultural organisms. The challenge for molecular evolutionary ecologists is to find ways to adopt these powerful systems to understand the mechanisms underlying adaptive traits and their evolution.

Thermal tolerance, climatic variability and latitude

The greater latitudinal extents of occurrence of species towards higher latitudes has been attributed to the broadening of physiological tolerances with latitude as a result of increases in climatic variation. While there is some support for such patterns in climate, the physiological tolerances of species across large latitudinal gradients have seldom been assessed. Here we report findings for insects based on published upper and lower lethal temperature data. The upper thermal limits show little geographical variation. In contrast, the lower bounds of supercooling points and lower lethal temperatures do indeed decline with latitude. However, this is not the case for the upper bounds, leading to an increase in the variation in lower lethal limits with latitude. These results provide some support for the physiological tolerance assumption associated with Rapoport's rule, but highlight the need for coupled data on species tolerances and range size.

Tissue-specific variations in the induction of Hsp70 and Hsp64 by heat shock in insects

The patterns of heat-induced synthesis (37 degrees C to 45 degrees C) of heat shock proteins (Hsps) in different tissues of grasshoppers and cockroaches from natural populations and in laboratory-reared gram-pest (Heliothis armigera) were examined by 35S-methionine labeling and sodium dodecyl sulfate-polyacrylamide gel electrophoresis fluorography. Whereas 45 degrees C was lethal in most cases, optimal induction of Hsp synthesis was seen between 37 degrees C and 42 degrees C. The ongoing protein synthesis was not much affected at these temperatures, except in the tissues of adult H. armigera exposed to 42 degrees C. The profiles of the Hsps induced in the tissues of the insects, however, were different. From the relative abundance of the synthesis of 70-kDa (Hsp70) and 64-kDa (Hsp64) polypeptides, three categories of heat shock response were identified: (1) induction of abundant Hsp70 but little Hsp64 (malpighian tubules, male accessory glands, and ovaries of adult grasshoppers), (2) abundant Hsp64 but little Hsp70 (testes of adult grasshoppers, testes and malpighian tubules of adult cockroaches, and testes, malpighian tubules, and fat bodies of H. armigera larvae), and (3) induction of both Hsp70 and Hsp64 in more or less equal abundance (ovaries of adult cockroaches, salivary glands of H. armigera larvae, and malpighian tubules, male accessory glands, testes, and ovaries of adult H. armigera). Cockroaches collected from storerooms showed detectable synthesis of Hsp64 and/or Hsp70 only after heat shock, but those collected from drains showed detectable synthesis of both Hsp70 and Hsp64 in different tissues without heat stress. Western blotting showed that the 64-kDa polypeptide in these insects is a member of the Hsp60 family. Grasshopper testes, which synthesized negligible Hsp70 but abundant Hsp64 after heat shock, developed thermotolerance. Thus, heat shock response is modulated by developmental and environmental factors in different tissues of insects.

Thermotolerant desert lizards characteristically differ in terms of heat-shock system regulation

We compare the properties and activation of heat-shock transcription factor (HSF1) and the synthesis of a major family of heat-shock proteins (HSP70) in lizard species inhabiting ecological niches with strikingly different thermal parameters. Under normal non-heat-shock conditions, all desert-dwelling lizard species studied so far differ from a northern, non-desert species (Lacerta vivipara) in the electrophoretic mobility and content of proteins constitutively bound to the regulatory heat-shock elements in the heat-shock gene promoter. Under these conditions, levels of activated HSF1 and of both HSP70 mRNA and protein are higher in the desert species than in the non-desert species. Upon heat shock, HSF1 aggregates in all species studied, although in desert species HSF1 subsequently disaggregates more rapidly. Cells of the northern species have a lower thermal threshold for HSP expression than those of the desert species, which correlates with the relatively low constitutive level of HSPs and high basal content of HSF1 in their cells.

Heat-shock-induced thermoprotection of hindleg motor control in the locust

Functional neuromuscular connections are critical for appropriate behavioural responses, but can be negatively affected by increases in temperature. We investigated the effects of heat shock on the thermosensitivity of a neuromuscular pathway to the hindleg tibial extensor muscle of Locusta migratoria. We found that exposure to heat shock induced thermoprotection of both neuromuscular transmission and extensor muscle contraction by (i) increasing the upper temperature limit for failure, (ii) improving recovery following heat-induced failure and (iii) stabilizing excitatory junction potential amplitude and duration and extensor muscle contraction force at high temperatures. Furthermore, the heat-shock-induced thermoprotection of extensor muscle contraction was not attributable to a protective effect on intrinsic components of muscle contraction. Finally, the use of jumping as a locomotor strategy to avoid capture, a behavioural response dependent upon functionally competent neuromuscular connections at the hindleg tibial extensor muscle, became less sensitive to temperature following heat shock. We conclude that the natural stress response of the locust stabilizes neuromuscular signalling during temperature stress, and that this can underlie a thermoprotection of muscle contraction force and thus alter the thermosensitivity of an escape behaviour critical for survival.

Adaptive responses of the endothelium to stress

It is now established that endothelial cells acquire several functional properties in response to a diverse array of extracellular stimuli. This expression of an altered phenotype is referred to as endothelial cell activation, and it includes several activities that promote inflammation and coagulation. While it is recognized that endothelial cell activation has a principal role in host defense, recent studies also demonstrate that endothelial cells are capable of complex molecular responses that protect the endothelium against various forms of stress including heat shock, hypoxia, oxidative stress, shock, ischemia-reperfusion injury, toxins, wounds, and mechanical stress. In this review, we examine endothelial cell genotypic and phenotypic responses to stress. Also, we highlight important cellular stress responses that, although not yet demonstrated directly in endothelial cells, likely exist as part of the repertoire of stress responses in endothelium. A detailed understanding of the molecular mechanisms mediating the adaptive responses of endothelial cells to stress should facilitate the development of novel therapeutics to aid in the management of diverse surgical diseases and their complications.

Time course and magnitude of synthesis of heat-shock proteins in congeneric marine snails (Genus tegula) from different tidal heights

The time course and magnitude of the heat-shock response in relation to severity of thermal stress are important, yet poorly understood, aspects of thermotolerance. We examined patterns of protein synthesis in congeneric marine snails (genus Tegula) that occur at different heights along the subtidal to intertidal gradient after a thermal exposure (30 degrees C for 2.5 h, followed by 50 h recovery at 13 degrees C) that induced the heat-shock response. We monitored the kinetics and magnitudes of protein synthesis by quantifying incorporation of 35S-labeled methionine and cysteine into newly synthesized proteins and observed synthesis of putative heat-shock proteins (hsp's) of size classes 90, 77, 70, and 38 kDa. In the low- to mid-intertidal species, Tegula funebralis, whose body temperature frequently exceeds 30 degrees C during emersion, synthesis of hsp's commenced immediately after heat stress, reached maximal levels 1-3 h into recovery, and returned to prestress levels by 6 h, except for hsp90 (14 h). In contrast, in the low-intertidal to subtidal species, Tegula brunnea, for which 2.5 h at 30 degrees C represents a near lethal heat stress, synthesis of hsp's commenced 2-14 h after heat stress; reached maximal levels after 15-30 h, which exceeded magnitudes of synthesis in T. funebralis; and returned to prestress levels in the case of hsp90 (50 h) and hsp77 (30 h) but not in the case of hsp70 and hsp38. Exposures to 30 degrees C under aerial (emersion) and aquatic (immersion) conditions resulted in differences in hsp synthesis in T. brunnea but not in T. funebralis. The different time courses and magnitudes of hsp synthesis in these congeners suggest that the vertical limits of their distributions may be set in part by thermal stress.

Expression of 70 kDa heat shock proteins in antarctic and New Zealand notothenioid fish

The cold and constant water temperature of the Southern Ocean surrounding Antarctica provides a natural laboratory to address questions of temperature adaptation in marine organisms. In this study, endogenous levels and the number of isoforms of the 70 kDa heat shock protein multigene family (hsp70) of Antarctic and cold temperate notothenioid fishes were determined by SDS-polyacrylamide gel electrophoresis and Western blotting. Tissues from three Antarctic Trematomus congeners had significantly lower levels of 70 kDa Hsp isoforms than their temperate confamilial from New Zealand waters. However, these two thermally disparate sets of fish did not differ in number or pattern of 70 kDa Hsp isoforms expressed under normal physiological conditions. Additionally, levels of 70 kDa Hsp isoforms in specimens of one Antarctic species, Trematomus bernacchii, acclimated to 4 degrees C were significantly higher than non-acclimated conspecifics, indicating a direct effect of temperature on Hsp expression in this species. This study shows that constitutive expression of some members of the 70 kDa Hsp multigene family have been maintained, despite the absence of environmental heat stress for at least 2.5 million years.

What makes desiccation tolerable?

A comparison of drought tolerance in plants at extreme ends of the evolutionary spectrum is beginning to show the mechanisms involved.

Desiccation and starvation resistance in Drosophila: patterns of variation at the species, population and intrapopulation levels

A substantial number of Drosophila studies have investigated variation in desiccation and starvation resistance, providing an opportunity to test for consistent patterns of direct and correlated responses across studies and across the species and population levels. In general, responses to laboratory selection for these traits in D. melanogaster are rapid and indicate abundant genetic variation in populations. However, slower responses to selection for desiccation resistance occur in other species including D. simulans. Clines suggest adaptive divergence although specific selection pressures have not been documented empirically. Drosophila species differ markedly in desiccation and starvation resistance and there is also marked variation within species for desiccation resistance that may be linked to local climatic conditions. Laboratory selection experiments on starvation resistance in D. melanogaster suggest that changes in lipid content are largely responsible for resistance variation but this factor may be less important in explaining variation among species. For desiccation, lines with increased resistance show reduced rates of water loss but no changes in the minimum water content that flies can tolerate. Changes in life history traits are sometimes associated with altered levels of stress resistance. Increased starvation resistance is associated with longer development time and reduced early age reproduction in different studies. However, other associations are inconsistent between studies as in the case of stress resistance changing following selection for longevity. Multiple mechanisms may underlie genetic variation in stress resistance and future studies should address the evolutionary importance of the different mechanisms at the population and species levels.

Evolutionary and acclimation-induced variation in the heat-shock responses of congeneric marine snails (genus Tegula) from different thermal habitats: implications for limits of thermotolerance and biogeography

Heat stress sufficient to cause cellular damage triggers the heat-shock response, the enhanced expression of a group of molecular chaperones called heat-shock proteins (hsps). We compared the heat-shock responses of four species of marine snails of the genus Tegula that occupy thermal niches differing in absolute temperature and range of temperature. We examined the effects of short-term heat stress and thermal acclimation on the synthesis of hsps of size classes 90, 77, 70 and 38 kDa by measuring incorporation of (35)S-labeled methionine and cysteine into newly synthesized proteins in gill tissue. Temperatures at which enhanced synthesis of hsps first occurred (T(on)), temperatures of maximal induction of hsp synthesis (T(peak)) and temperatures at which hsp synthesis was heat-inactivated (T(off)) were lowest in two low-intertidal to subtidal species from the temperate zone, T. brunnea and T. montereyi, intermediate in a mid- to low-intertidal species of the temperate zone, T. funebralis, and highest in a subtropical intertidal species from the Gulf of California, T. rugosa. Synthesis of hsps and other classes of protein by T. brunnea and T. montereyi was heat-inactivated at temperatures commonly encountered by T. funebralis during low tides on warm days. In turn, protein synthesis by T. funebralis was blocked at the upper temperatures of the habitat of T. rugosa. Acclimation of snails to 13 degrees C, 18 degrees C and 23 degrees C shifted T(on) and T(peak) for certain hsps, but did not affect T(off). The heat-shock responses of field-acclimatized snails were generally reduced in comparison with those of laboratory-acclimated snails. Overall, despite the occurrence of acclimatory plasticity in their heat-shock responses, genetically fixed differences in T(on), T(peak) and T(off) appear to exist that reflect the separate evolutionary histories of these species and may play important roles in setting their thermal tolerance limits and, thereby, their biogeographic distribution patterns.

Stress resistance and longevity in selected lines of Drosophila melanogaster

Five independent populations (lines) of Drosophila melanogaster were selected for female starvation resistance. Females and males from the selected lines were relatively starvation resistant when compared to flies from five control lines. Moreover, flies from selected lines were resistant to other stresses: desiccation, acetone fumes, ethanol fumes, and paraquat (a source of oxygen radicals). Data from a variety of previous studies indicate an association between stress resistance and longevity. In this context, the present study addressed the question of whether flies from the stress-resistant lines were relatively long-lived. Replicate population cages from each selected and control line were used to assess longevity. Neither females nor males from the selected lines were relatively long-lived. In at least some cases, stress resistance may be necessary, but not sufficient, for longevity.

Molecular characterization of the first heat shock protein 70 from a reef coral

The branching coral Stylophora pistillata, one of the most abundant hermatypic corals along the coasts of the Red Sea, has been used for many years as a model species for coral biological studies. Here we characterize the first coral heat shock protein 70 gene (SP-HSP70), cloned from S. pistillata, to be used as a tool for studying coral stress response. The cloning was carried out by a combination of PCR methods using heterologous, degenerate HSP70-based primers, followed by plaque-lift screening of a genomic library. The sequenced clone (5212 bp), contains a complete 1953 bp, intronless open reading frame, and 5' and 3' flanking regions of 1,935 and 1,324 bp, respectively. TATA, CAAT, and ATF boxes as well as 11 putative heat shock elements were identified in the SP-HSP70 5' flanking region. A polyadenylation site was identified in the 3' flanking region. SP-HSP70 protein sequence resembles the cytosolic/nuclear HSP70 cluster. RT-PCR studies confirmed SP-HSP70 mRNA expression in corals grown within their normal physiological conditions. Furthermore, SP-HSP70 has been shown to belong to the coral genome and not to its symbiotic algae one, as revealed by SP-HSP70 PCR amplification, using purified algal and coral DNA templates.