Hypomorphic mutation of the <Emphasis Type="Italic">dilp6</Emphasis> gene increases DILP3 expression in insulin-producing cells of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

The effect of strong hypomorphic mutation of the insulin-like protein DILP6 (dilp6), synthesized in the fat body, on the expression intensity of insulin-like protein DILP3 synthesized in median neurosecretory cells (MNCs) of D. melanogaster brain was examined. The intensity of DILP3 expression in the MNCs of the larvae was evaluated immunohistochemically using antibodies against DILP3 and confocal microscopy. For the first time, it was demonstrated that, in dilp6 ⁴¹ mutants, there was a sharp increase in DILP3 expression level. The data obtained indicate the existence of negative feedback coordinating the expression of insulin-like proteins synthesized in MNCs and peripheral tissues of Drosophila.     

The Effects of Stress-Related Hormones on the Stress Resistance in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> Carrying Mutation in the <Emphasis Type="Italic">Dilp6</Emphasis> Gene

The heat stress resistance of Drosophila melanogaster females carrying a hypomorphic mutation of the DILP6 insulin-like protein gene (dilp6 ⁴¹ ) under a change in the level of stress-related hormones (juvenile hormone and octopamine) is studied. It is revealed that the dilp6 ⁴¹ mutation decreases the heat stress resistance of mature D. melanogaster females. An experimental decrease in the level of juvenile hormone is shown to restore the stress resistance of mutant females to the level of stress resistance observed in wild type Canton S females. These data suggest that the effects of the dilp6 ⁴¹ mutation on the stress resistance of females are mediated by an increased level of juvenile hormone. An experimental increase in the octopamine level that causes an increase in juvenile hormone level supports this hypothesis: the resistance to heat stress decreases in females of both lines and this decrease is more significant in mutant females than in the control line. Thus, it is established for the first time that the effect of the hypomorphic dilp6 gene mutation on the heat stress resistance of D. melanogaster females is mediated by juvenile hormone.     

Gene <Emphasis Type="Italic">dilp6</Emphasis> regulates octopamine metabolism in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

The effect of strong hypomorphic mutation of the insulin-like protein gene (dilp6) on metabolism of octopamine (one of the main biogenic amines in insects) was studied in Drosophila melanogaster males and females. The activity of tyrosine decarboxylase (the key enzyme of octopamine synthesis) and the activity of octopamine-dependent N-acetyltransferase (the enzyme of its degradation) were measured. It was demonstrated that the activity of both studied enzymes is decreased under normal conditions in the dilp6⁴¹ mutants (as we previously demonstrated, this is correlated with an increased level of octopamine). It was also found that hypomorphic mutation of the dilp6 gene decreases the intensity of tyrosine decarboxylase response to heat stress. Thus, it was demonstrated for the first time that insulin-like DILP6 protein in drosophila influences the level of octopamine (regulating the activity of the enzyme degrading octopamine).     

The insulin-like receptor gene expression in the tissues synthesizing gonadotropic hormones at sexual maturation of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> females

The insulin/insulin-like growth factor signaling pathway is involved in the regulation of the synthesis of insect gonadotropic hormones, juvenile (JH) and 20-hydroxyecdysone (20E). We carried out the immunohistochemical analysis of the insulin receptor (InR) expression in the corpus allatum (the JH-producing gland) and in the ovarian follicular cells (a site for the synthesis of 20E precursor, ecdysone) in the process of sexual maturation of D. melanogaster females and examined the influence of exogenous JH on the InR expression in these tissues. For the first time, it was demonstrated that InR was expressed in follicular cells and that its expression in corpus allatum and follicular cells of Drosophila females was stage-specific, i.e., the expression intensity in young females greatly exceeded that in mature individuals. We also found a negative feedback loop in the regulation of JH levels by the insulin signaling pathway in Drosophila adults: the experimental increase in the JH titers in young females dramatically reduced the InR expression intensity in corpus allatum and follicular cells.     

The Toll pathway underlies host sexual dimorphism in resistance to both Gram-negative and Gram-positive bacteria in mated <Emphasis Type="Italic">Drosophila</Emphasis>

Background

Host sexual dimorphism is being increasingly recognized to generate strong differences in the outcome of infectious disease, but the mechanisms underlying immunological differences between males and females remain poorly characterized. Here, we used Drosophila melanogaster to assess and dissect sexual dimorphism in the innate response to systemic bacterial infection.

Results

We demonstrated sexual dimorphism in susceptibility to infection by a broad spectrum of Gram-positive and Gram-negative bacteria. We found that both virgin and mated females are more susceptible than mated males to most, but not all, infections. We investigated in more detail the lower resistance of females to infection with Providencia rettgeri, a Gram-negative bacterium that naturally infects D. melanogaster. We found that females have a higher number of phagocytes than males and that ablation of hemocytes does not eliminate the dimorphism in resistance to P. rettgeri, so the observed dimorphism does not stem from differences in the cellular response. The Imd pathway is critical for the production of antimicrobial peptides in response to Gram-negative bacteria, but mutants for Imd signaling continued to exhibit dimorphism even though both sexes showed strongly reduced resistance. Instead, we found that the Toll pathway is responsible for the dimorphism in resistance. The Toll pathway is dimorphic in genome-wide constitutive gene expression and in induced response to infection. Toll signaling is dimorphic in both constitutive signaling and in induced activation in response to P. rettgeri infection. The dimorphism in pathway activation can be specifically attributed to Persephone-mediated immune stimulation, by which the Toll pathway is triggered in response to pathogen-derived virulence factors. We additionally found that, in absence of Toll signaling, males become more susceptible than females to the Gram-positive Enterococcus faecalis. This reversal in susceptibility between male and female Toll pathway mutants compared to wildtype hosts highlights the key role of the Toll pathway in D. melanogaster sexual dimorphism in resistance to infection.

Conclusion

Altogether, our data demonstrate that Toll pathway activity differs between male and female D. melanogaster in response to bacterial infection, thus identifying innate immune signaling as a determinant of sexual immune dimorphism.

     

Body size regulation by maturation steroid hormones: a <Emphasis Type="Italic">Drosophila</Emphasis> perspective

The mechanism that determines the specific body size of an animal is a fundamental biological question that remains largely unanswered. This aspect is now beginning to be understood in insect models, particularly in Drosophila melanogaster, with studies highlighting the importance of nutrient-responsive growth signaling pathways involving insulin/insulin-like growth factor signaling (IIS) and target of rapamycin (TOR) (IIS/TOR). These pathways operate in animals, from insects to mammals, adjusting the growth rate in response to the nutritional condition of the organism. Organismal growth is closely coupled with the process of developmental maturation mediated by maturation steroid hormones, which is influenced greatly by environmental and nutritional conditions. Recent Drosophila studies have been revealing the mechanisms responsible for this phenomenon. In this review, I summarize some important findings about the steroid hormone regulation of Drosophila body growth, calling attention to the influence of developmental nutritional conditions on animal size determination.     

Characterization of a maize ERF gene, <Emphasis Type="Italic">ZmERF1,</Emphasis> in hormone and stress responses

ERFs are downstream component in ethylene signaling pathway and involved in plant’s abiotic stress response. The specific role of ERFs under stress and the molecular mechanism underlying the signaling cross talk still need to be elucidated. This study describes the isolation and characterization of ZmERF1 promoter. There were many cis-regulatory elements related to stress responses in the ZmERF1 promoter sequence. ZmERF1 could be highly induced by ABA and ethylene treatment in maize, suggesting that it might be at the crossroads of multiple hormone signaling pathways. Furthermore, ZmERF1 transgenic Arabidopsis lines (35S::ZmERF1) showed higher salt-tolerant, drought- and heat resistance. Consistently, tolerance-related genes were up-regulated in 35S::ZmERF1 lines compared with the WT plants in Arabidopsis. Overall, ZmERF1 might play an important role in plant resistance to a coercive environment by mediating various physiological processes via ethylene and ABA signaling pathways.     

Effect of Gonadotropic Hormones on Stress Resistance of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> Females Infected with Different <Emphasis Type="Italic">Wolbachia pipientis</Emphasis> Genotypes

The effect of gonadotropic hormones (juvenile (JH) and 20-hydroxyecdysone (20E)) on heat stress resistance was for the first time studied in wild type D. melanogaster line females infected with different genotypes of the Wolbachia pipientis alpha-proteobacterium. It was found that an experimental increase in JH level induces a decrease in the heat stress resistance, while an increase in 20E level induces its increase in sixday females both uninfected with the Wolbachia and infected with different bacterium strains (wMelCS, wMelPop, and wMel). However, the intensity of response differs: a decrease in the survival with an increase in JH level and its increase with an increase in 20E level are more pronounced in females infected with pathogenic wMelPop strain and less pronounced in females infected with the wMelCS genotype than in uninfected females and females infected with the wMel genotype. Data obtained suggest that the wMelCS genotype induces a decrease and wMelPop induces an increase in the level of stress hormone (dopamine), since previously we demonstrated that an increase in the JH level in mature females increases the dopamine level, an increase in the 20E level decreases it, and an increase/decrease in the dopamine level, in turn, leads to a decrease/increase of the Drosophila female resistance to heat stress.     

Calcium chloride improves photosynthesis and water status in the C<Subscript>4</Subscript> succulent xerophyte <Emphasis Type="Italic">Haloxylon ammodendron</Emphasis> under water deficit

It is important to reveal the mechanism of plants coping with heat stress, which results in a severe retardation in crop growth and development. Although Synaptotagmin A (SYTA) regulates the cell endocytosis and the plasma membrane reparation of Arabidopsis, its roles in heat resistance are not well understood. In this study, we obtained the new finding that SYTA is related to the heat resistance of Arabidopsis. In the SYTA overexpression strains, the germination rate of the seeds and the survival rate of the seedlings improved after heat shock treatment, and their degree of membrane peroxidation was reduced. However, syta mutant showed the opposite results. Meanwhile, the expressions of some heat stress signal pathway genes were higher in SYTA overexpression strains than that in wild-type strains, and were lower in syta mutant strains. These results suggested that SYTA responded positively to heat shock and was involved in the heat stress signal pathway.     

Signaling pathway of insulin and insulin-like growth factor 1 (IGF-1) as a potential regulator of lifespan

The experimental material accumulated for two decades allows concluding that regulation of lifespan has hormonal control based on the evolutionary conservative insulin/IGF-1 receptor signaling pathway. Data obtained on the commonly accepted models of longevity — nematode Caenorhabditis elegans, fruit fly Drosophila melanogaster, and rodents — demonstrate that reduction of the insulin/IGF-1 signaling pathway results in an increase of the lifespan. There is shown involvement in the longevity mechanism of a large group of genes whose products perform control of metabolism, feeding behavior, reproduction, and resistance to oxidative stress. Discussed in this review are current concepts of the insulin/IGF-1 signaling system as a regulatory “longevity module” and of its possible role in prolongation of life in the higher vertebrates, including human.     

Contribution of olfactory and gustatory sensations of octanoic acid in the oviposition behavior of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> (Diptera: Drosophilidae)

Selection of oviposition sites in insects represents an important part of their ecological adaptation. In Drosophila fruit flies, adult preference for a particular oviposition site determines larval food, affecting fitness throughout the entire life cycle. Two odorant-binding proteins (OBPs) OBP57d and OBP57e were identified to be involved in the evolution of specific preference for the toxic plant Morinda citrifolia L. in D. sechellia Tsacas &; Bächli. D. melanogaster Meigen mutants for Obp57d and Obp57e showed enhanced preference for octanoic acid, but still not as much as D. sechellia does, indicating that other genes are also involved in the behavioral evolution of D. sechellia. Here, by using an improved method for behavioral assay, we found that the ablation of antenna enhanced the preference for octanoic acid in the Obp57d and Obp57e mutants to a level comparable with D. sechellia, suggesting that both olfactory and gustatory sensations are involved in oviposition site selection in response to octanoic acid. Behavioral analysis of gene-knockout strains revealed that Odorant receptor co-receptor (Orco) has little contribution compared with the effect of antennal ablation. These data suggest that in addition to Obp57d and Obp57e, the evolution of D. sechellia involves genetic changes in olfactory genes that function independently from Orco.     

Pattern Formation in the Longevity-Related Expression of Heat Shock Protein-16.2 in <Emphasis Type="Italic">Caenorhabditis elegans</Emphasis>

Aging in Caenorhabditis elegans is controlled, in part, by the insulin-like signaling and heat shock response pathways. Following thermal stress, expression levels of small heat shock protein-16.2 show a spatial patterning across the 20 intestinal cells that reside along the length of the worm. Here, we present a hypothesized mechanism that could lead to this patterned response and develop a mathematical model of this system to test our hypothesis. We propose that the patterned expression of heat shock protein is caused by a diffusion-driven instability within the pseudocoelom, or fluid-filled cavity, that borders the intestinal cells in C. elegans. This instability is due to the interactions between two classes of insulin-like peptides that serve antagonistic roles. We examine output from the developed model and compare it to experimental data on heat shock protein expression. Given biologically bounded parameters, the model presented is capable of producing patterns similar to what is observed experimentally and provides a first step in mathematically modeling aging-related mechanisms in C. elegans.     

The endosymbiotic bacterium <Emphasis Type="Italic">Wolbachia</Emphasis> enhances the nonspecific resistance to insect pathogens and alters behavior of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

To determine biologically important effects of the cytoplasmic endosymbiont Wolbachia, two substrains of the same Drosophila melanogaster strain have been studied, one of them infected with Wolbachia and the other treated with tetracycline to eliminate the bacterium. Females of D. melanogaster infected with Wolbachia are more resistant to the fungus Blauveria bassiana (an insect pathogen) than uninfected females; infected females also exhibited changes in oviposition substrate preference. Males infected with the bacterium are more competitive than uninfected males. The possible role of Wolbachia in the formation of alternative ecological strategies of D. melanogaster is discussed.     

Over-Expression of <Emphasis Type="Italic">PmHSP17.9</Emphasis> in Transgenic <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> Confers Thermotolerance

Small heat shock proteins (sHSPs) have been shown to be involved in stress tolerance. However, their functions in Prunus mume under heat treatment are poorly characterized. To improve our understanding of sHSPs, we cloned a sHSP gene, PmHSP17.9, from P. mume. Sequence alignment and phylogenetic analysis indicated that PmHSP17.9 was a member of plant cytosolic class III sHSPs. Besides heat stress, PmHSP17.9 was also upregulated by salt, dehydration, oxidative stresses and ABA treatment. Leaves of transgenic Arabidopsis thaliana that ectopically express PmHSP17.9 accumulated less O₂ ^? and H₂O₂ compared with wild type (WT) after 42 °C treatment for 6 h. Over-expression of PmHSP17.9 in transgenic Arabidopsis enhanced seedling thermotolerance by decreased relative electrolyte leakage and MDA content under heat stress treatment when compared to WT plants. In addition, the induced expression of HSP101, HSFA2, and delta 1-pyrroline-5-carboxylate synthase (P5CS) under heat stress was more pronounced in transgenic plants than in WT plants. These results support the positive role of PmHSP17.9 in response to heat stress treatment.     

Gene up-regulation in response to predator kairomones in the water flea, <Emphasis Type="Italic">Daphnia pulex</Emphasis>

Background

Numerous cases of predator-induced polyphenisms, in which alternate phenotypes are produced in response to extrinsic stimuli, have been reported in aquatic taxa to date. The genus Daphnia (Branchiopoda, Cladocera) provides a model experimental system for the study of the developmental mechanisms and evolutionary processes associated with predator-induced polyphenisms. In D. pulex, juveniles form neckteeth in response to predatory kairomones released by Chaoborus larvae (Insecta, Diptera).

Results

Previous studies suggest that the timing of the sensitivity to kairomones in D. pulex can generally be divided into the embryonic and postembryonic developmental periods. We therefore examined which of the genes in the embryonic and first-instar juvenile stages exhibit different expression levels in the presence or absence of predator kairomones. Employing a candidate gene approach and identifying differentially-expressed genes revealed that the morphogenetic factors, Hox3, extradenticle and escargot, were up-regulated by kairomones in the postembryonic stage and may potentially be responsible for defense morph formation. In addition, the juvenile hormone pathway genes, JHAMT and Met, and the insulin signaling pathway genes, InR and IRS-1, were up-regulated in the first-instar stage. It is well known that these hormonal pathways are involved in physiological regulation following morphogenesis in many insect species. During the embryonic stage when morphotypes were determined, one of the novel genes identified by differential display was up-regulated, suggesting that this gene may be related to morphotype determination. Biological functions of the up-regulated genes are discussed in the context of defense morph formation.

Conclusions

It is suggested that, following the reception of kairomone signals, the identified genes are involved in a series of defensive phenotypic alterations and the production of a defensive phenotype.