Genetic variation in the expression of the six hsp genes in the presence of heat shock in Drosophila melanogaster

Topoisomerase 1 Activity Is Reduced in Response to Thermal Stress in Fruit Flies and in Human HeLa Cells

In the modern world with climate changes and increasing pollution, different types of stress are becoming an increasing challenge. Hence, the identification of reliable biomarkers of stress and accessible sensors to measure such biomarkers are attracting increasing attention. In the current study, we demonstrate that the activity, but not the expression, of the ubiquitous enzyme topoisomerase 1 (TOP1), as measured in crude cell extracts by the REEAD sensor system, is markedly reduced in response to thermal stress in both fruit flies (Drosophila melanogaster) and cultivated human cells. This effect was observed in response to both mild-to-moderate long-term heat stress and more severe short-term heat stress in D. melanogaster. In cultivated HeLa cells a reduced TOP1 activity was observed in response to both cold and heat stress. The reduced TOP1 activity appeared dependent on one or more cellular pathways since the activity of purified TOP1 was unaffected by the utilized stress temperatures. We demonstrate successful quantitative measurement of TOP1 activity using an easily accessible chemiluminescence readout for REEAD pointing towards a sensor system suitable for point-of-care assessment of stress responses based on TOP1 as a biomarker.

Heritable variation in heat shock gene expression: a potential mechanism for adaptation to thermal stress in embryos of sea turtles

The capacity of species to respond adaptively to warming temperatures will be key to their survival in the Anthropocene. The embryos of egg-laying species such as sea turtles have limited behavioural means for avoiding high nest temperatures, and responses at the physiological level may be critical to coping with predicted global temperature increases. Using the loggerhead sea turtle (Caretta caretta) as a model, we used quantitative PCR to characterise variation in the expression response of heat-shock genes (hsp60, hsp70 and hsp90; molecular chaperones involved in cellular stress response) to an acute non-lethal heat shock. We show significant variation in gene expression at the clutch and population levels for some, but not all hsp genes. Using pedigree information, we estimated heritabilities of the expression response of hsp genes to heat shock and demonstrated both maternal and additive genetic effects. This is the first evidence that the heat-shock response is heritable in sea turtles and operates at the embryonic stage in any reptile. The presence of heritable variation in the expression of key thermotolerance genes is necessary for sea turtles to adapt at a molecular level to warming incubation environments.

Diurnal temperature variations affect development of a herbivorous arthropod pest and its predators

The impact of daily temperature variations on arthropod life history remains woefully understudied compared to the large body of research that has been carried out on the effects of constant temperatures. However, diurnal varying temperature regimes more commonly represent the environment in which most organisms thrive. Such varying temperature regimes have been demonstrated to substantially affect development and reproduction of ectothermic organisms, generally in accordance with Jensen’s inequality. In the present study we evaluated the impact of temperature alternations at 4 amplitudes (DTR0, +5, +10 and +15°C) on the developmental rate of the predatory mites Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus McGregor (Acari: Phytoseiidae) and their natural prey, the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae). We have modelled their developmental rates as a function of temperature using both linear and nonlinear models. Diurnally alternating temperatures resulted in a faster development in the lower temperature range as compared to their corresponding mean constant temperatures, whereas the opposite was observed in the higher temperature range. Our results indicate that Jensen’s inequality does not suffice to fully explain the differences in developmental rates at constant and alternating temperatures, suggesting additional physiological responses play a role. It is concluded that diurnal temperature range should not be ignored and should be incorporated in predictive models on the phenology of arthropod pests and their natural enemies and their performance in biological control programmes.

Nucleotide diversity in the Hsp90 gene in natural populations of Drosophila melanogaster from Australia

Hsp90 is regarded as one of the best candidates for an evolved mechanism that regulates the expression of genetic and phenotypic variability. We examined nucleotide diversity in both the promoter and coding regions of Hsp90, the gene which encodes Hsp90 in Drosophila, in natural populations of Drosophila melanogaster from eastern Australia. We found that Hsp90 is polymorphic for only two nonsynonymous changes in the coding region, both of which are deletions of a lysine residue. One of these lysine deletions was in complete linkage disequilibrium with the inversion In(3L)P, and showed a significant association with latitude. The other lysine deletion reported here for the first time varied from 0 to 15% in natural populations, but did not show a clinal pattern. The regulatory and coding regions of Hsp90 showed very low nucleotide diversity compared to other nuclear genes, and chromosomes containing In(3L)P had lower levels of nucleotide diversity than the standard arrangements. Non-neutral evolution of Hsp90 was not supported by analyses of either the regulatory or coding regions of the gene. These results are discussed within the context of Hsp90 variation being involved in thermotolerance as well as the expression of genetic and phenotypic variability.

Heat shock protein 101 effects in A. thaliana: genetic variation, fitness and pleiotropy in controlled temperature conditions

The Hsp100/ClpB heat shock protein family is ancient and required for high temperature survival, but natural variation in expression and its phenotypic effects is unexplored in plants. In controlled environment experiments, we examined the effects of variation in the Arabidopsis cytosolic AtHsp101 (hereafter Hsp101). Ten wild-collected ecotypes differed in Hsp101 expression responses across a 22 to 40 degrees C gradient. Genotypes from low latitudes expressed the least Hsp101. We tested fitness and pleiotropic consequences of varying Hsp101 expression in 'control' vs. mild thermal stress treatments (15/25 degrees C D/N vs. 15/25 degrees D/N plus 3 h at 35 degrees C 3 days/week). Comparing wild type and null mutants, wt Columbia (Col) produced approximately 33% more fruits compared to its Hsp101 homozygous null mutant. There was no difference between Landsberg erecta null mutant NIL (Ler) and wt Ler; wt Ler showed very low Hsp101 expression. In an assay of six genotypes, fecundity was a saturating function of Hsp101 content, in both experimental treatments. Thus, in addition to its essential role in acquired thermal tolerance, Hsp101 provides a substantial fitness benefit under normal growth conditions. Knocking out Hsp101 decreased fruit production, days to germination and days to bolting, total dry mass, and number of inflorescences; it increased transpiration rate and allocation to root mass. Root : total mass ratio decayed exponentially with Hsp101 content. This study shows that Hsp101 expression is evolvable in natural populations. Our results further suggest that Hsp101 is primarily an emergency high-temperature tolerance mechanism, since expression levels are lower in low-latitude populations from warmer climates. Hsp101 expression appears to carry an important trade-off in reduced root growth. This trade-off may select for suppressed expression under chronically high temperatures.

The role of fertility restoration in the maintenance of the inversion In(2L)t polymorphism in drosophila melanogaster

In order to explain the worldwide latitudinal distribution and seasonal fluctuations in In(2L)t frequencies in Drosophila melanogaster, fitness differences among In(2L)t and Standard (ST ) homo- and heterokaryotypes under high-temperature conditions were determined. Viabilities were measured for high-temperature treatment started at different juvenile stages. The capacity to restore fertility after high-temperature treatment was measured for adults and juveniles. Furthermore, genetic adaptation for increased temperature resistance for these traits was determined for strains which were reared at 33 degrees C for 10 generations. Whereas larva-pupa survival rates were high, highest juvenile mortalities and strongest karyotypic effects were observed during the pupal stage when preceding larval stages were reared at 33 degrees C. ST karyotypes showed lowest viabilities. Although mating rate was hardly influenced, sterility was induced for females and males after high-temperature treatment of adults as well as juveniles. Subsequent transfer to 25 degrees C, however, resulted in restored fertility in some of the individuals, depending on the length of the recovery period. Fertility restoration was significantly higher for heterokaryotype males and females. Heterokaryotype superiority for restored fertility as well as for viability was positively correlated with severity of the treatment. Ten generations of selection at 33 degrees C resulted in significant improvement of juvenile survival and fertility restoration for all karyotypes. These fitness components were positively correlated (r=0.91; P < 0.001), which might suggest pleiotropic effects. It is concluded that the capacity to restore fertility after heat stress is an important fitness component, especially with respect to the In(2L)t polymorphism. The observed heterokaryotypic superiority fits with the idea that the latitudinal distribution of In(2L)t frequencies is maintained by balancing selection, with equilibrium values decreasing with latitude.

Drosophila melanogaster is polymorphic for a specific repeated (CATA) sequence in the regulatory region of hsp23

To identify sequence variation associated with a selection response for heat tolerance in Drosophila melanogaster, we sequenced 1400bp of the heat shock protein 23 gene (hsp23) promoter region in four heat-selected and two control lines. The region was found to be variable for a specific (CATA) repeated sequence, and the sequence CTT seems to be a hot spot for mutation. The repeated tetranucleotide sequence was located in several short repeats scattered throughout the entire region. Similar variable repeats are also located downstream the of hsp23 gene in the intergenic region between hsp23 and hsp27. We detected nine different hsp23 alleles. Their frequencies in the selection and control lines seemed to be mainly determined by genetic drift. The function of the CATA repeats is not yet known, though these regions have homology to SAR elements located in the intergenic region between two hsp70 genes, suggesting a similar function.

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

Molecular chaperones, including the heat-shock proteins (Hsps), are a ubiquitous feature of cells in which these proteins cope with stress-induced denaturation of other proteins. Hsps have received the most attention in model organisms undergoing experimental stress in the laboratory, and the function of Hsps at the molecular and cellular level is becoming well understood in this context. A complementary focus is now emerging on the Hsps of both model and nonmodel organisms undergoing stress in nature, on the roles of Hsps in the stress physiology of whole multicellular eukaryotes and the tissues and organs they comprise, and on the ecological and evolutionary correlates of variation in Hsps and the genes that encode them. This focus discloses that (a) expression of Hsps can occur in nature, (b) all species have hsp genes but they vary in the patterns of their expression, (c) Hsp expression can be correlated with resistance to stress, and (d) species' thresholds for Hsp expression are correlated with levels of stress that they naturally undergo. These conclusions are now well established and may require little additional confirmation; many significant questions remain unanswered concerning both the mechanisms of Hsp-mediated stress tolerance at the organismal level and the evolutionary mechanisms that have diversified the hsp genes.