The effect of dietary ethanol on the composition of lipids of Drosophila melanogaster larvae

Dodecanol, metabolite of entomopathogenic fungus Conidiobolus coronatus, affects fatty acid composition and cellular immunity of Galleria mellonella and Calliphora vicina

One group of promising pest control agents are the entomopathogenic fungi; one such example is Conidiobolus coronatus, which produces a range of metabolites. Our present findings reveal for the first time that C. coronatus also produces dodecanol, a compound widely used to make surfactants and pharmaceuticals, and enhance flavors in food. The main aim of the study was to determine the influence of dodecanol on insect defense systems, i.e. cuticular lipid composition and the condition of insect immunocompetent cells; hence, its effect was examined in detail on two species differing in susceptibility to fungal infection: Galleria mellonella and Calliphora vicina. Dodecanol treatment elicited significant quantitative and qualitative differences in cuticular free fatty acid (FFA) profiles between the species, based on gas chromatography analysis with mass spectrometry (GC/MS), and had a negative effect on G. mellonella and C. vicina hemocytes and a Sf9 cell line in vitro: after 48 h, almost all the cells were completely disintegrated. The metabolite had a negative effect on the insect defense system, suggesting that it could play an important role during C. coronatus infection. Its high insecticidal activity and lack of toxicity towards vertebrates suggest it could be an effective insecticide.

Alpha-ketoglutarate reduces ethanol toxicity in Drosophila melanogaster by enhancing alcohol dehydrogenase activity and antioxidant capacity

Ethanol at low concentrations (<4%) can serve as a food source for fruit fly Drosophila melanogaster, whereas at higher concentrations it may be toxic. In this work, protective effects of dietary alpha-ketoglutarate (AKG) against ethanol toxicity were studied. Food supplementation with 10-mM AKG alleviated toxic effects of 8% ethanol added to food, and improved fly development. Two-day-old adult flies, reared on diet containing both AKG and ethanol, possessed higher alcohol dehydrogenase (ADH) activity as compared with those reared on control diet or diet with ethanol only. Native gel electrophoresis data suggested that this combination diet might promote post-translational modifications of ADH protein with the formation of a highly active ADH form. The ethanol-containing diet led to significantly higher levels of triacylglycerides stored in adult flies, and this parameter was not altered by AKG supplement. The influence of diet on antioxidant defenses was also assessed. In ethanol-fed flies, catalase activity was higher in males and the levels of low molecular mass thiols were unchanged in both sexes compared to control values. Feeding on a mixture of AKG and ethanol did not affect catalase activity but caused a higher level of low molecular mass thiols compared to ethanol-fed flies. It can be concluded that both a stimulation of some components of antioxidant defense and the increase in ADH activity may be responsible for the protective effects of AKG diet supplementation in combination with ethanol. The results suggest that AKG might be useful as a treatment option to neutralize toxic effects of excessive ethanol intake and to improve the physiological state of D. melanogaster and other animals, potentially including humans.

Proteomic evaluation of cadmium toxicity on the midgeChironomus riparius Meigen larvae

Heavy-metal pollution of aquatic ecosystems is a widespread phenomenon after industrial consumption. Whether aquatic organisms are adapted to the heavy-metal pollutants or not, such environmental stress causes changes in physiological responses. In this study, the aquatic midge, Chironomus riparius Meigen, was used to find changes of expression of proteins in relation to cadmium exposure. Dose-response relationships between cadmium concentrations and mortality of 3rd instar midge larvae were observed and the protein levels were compared using PD-Quest after 2-DE. Comparing the intensity of protein spots, 21 proteins decreased and 18 proteins increased in response to cadmium treatment. With increased proteins, three enzymes such as S-adenosylmethionine decarboxylase, O-methyltransferase, and aspartokinase were involved in the glutathione biosynthesis and a key enzyme regulating fatty acid biosynthesis, oleyl-acyl carrier protein thioesterase was also identified. According to the functional classification of decreased levels of proteins, they were involved in energy production, protein fate, nucleotide biosynthesis, cell division, transport and binding, signal transduction, and fatty acid and phospholipid metabolism in the cell. In addition, phenol hydroxylase, thioesterase, zinc metalloprotease, and aspartate kinase were newly expressed after cadmium exposure at the concentration of the LC(10 )value. Therefore, these proteins seem to be potential biomarkers for cadmium exposure in the aquatic ecosystems.

Functional constraints of alcohol dehydrogenase (ADH) of tephritidae and relationships with other Dipteran species

Alcohol dehydrogenase is considered a very important enzyme in insect metabolism because it is involved (in its homodimeric form) in the catalysis of the reversible conversion of various alcohols in larval feeding sites to their corresponding aldehydes and ketones, thus contributing to detoxification and metabolic purposes. Using 14 amino acid ADH sequences recently determined in our laboratory, we constructed a three-dimensional (3D) model of olive fruit fly Bactrocera oleae ADH1 and ADH2, based on the known homologous Drosophila lebanonensis ADH structure, and the amino acid residues that have been proposed as being responsible for catalysis were located on it. Moreover, in a comparative study of the ADH sequences, the residues occupying characteristic positions in the ADH of species of the Bactrocera and Ceratitis genera (called genus-specific) as well as residues appearing only in ADH1 or ADH2 (called isozymic-specific) were defined and localized on the 3D model. All regions important for catalytic activity, such as those forming the substrate- and coenzyme-binding sites, are highly conserved in all tephritid species examined. Genus-specific amino acids are located on the outside of the protein, on loops and regions predicted to be antigenic. The higher percentage of genus-specific amino acid variation seems to be centered in the NAD adenine-binding site, located near the surface of the protein molecule. Nine of 12 isozymic-specific positions are lined along an "arc" on the surface of the protein, thus linking the two "monomer bases" of the dimer via the C-terminal interacting loops. Furthermore, the distribution of isozymic- and genus-specific amino acids on the monomer-monomer interface may have some evolutionary significance. Most amino acids predicted to be antigenic are positioned in peripheral regions of nonfunctional importance, but surprisingly, an additional antigenic region is contained within the (highly conserved in tephritids) C-terminal tail.

Drosophila melanogaster, a genetic model system for alcohol research

In its natural environment, which consists of fermenting plant materials, the fruit fly Drosophila melanogaster encounters high levels of ethanol. Flies are well equipped to deal with the toxic effects of ethanol; they use it as an energy source and for lipid biosynthesis. The primary ethanol-metabolizing pathway in flies involves the enzymes alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH); their role in adaptation to ethanol-rich environments has been studied extensively. The similarity between Drosophila and mammals is not restricted to the manner in which they metabolize ethanol; behaviors elicited by ethanol exposure are also remarkably similar in these organisms. Flies show signs of acute intoxication, which range from locomotor stimulation at low doses to complete sedation at higher doses, they develop tolerance upon intermittent ethanol exposure, and they appear to like ethanol, showing preference for ethanol-containing media. Molecular genetic analysis of ethanol-induced behaviors in Drosophila, while still in its early stages, has already revealed some surprising parallels with mammals. The availability of powerful tools for genetic manipulation in Drosophila, together with the high degree of conservation at the genomic level, make Drosophila a promising model organism to study the mechanism by which ethanol regulates behavior and the mechanisms underlying the organism's adaptation to long-term ethanol exposure.

Heat shock response of warm-incubated barley aleurone layers

Heat shock suppresses secretory protein synthesis in GA(3)-stimulated barley (Hordeum vulgare cv. Himalaya) aleurone layers by selectively destabilizing their mRNAs and dissociating the stacked rough endoplasmic reticulum (ER) lamellae upon which they are translated. Heat shock also increases phosphatidylcholine (PC) synthesis, and these PC molecules have increased levels of fatty acid saturation. This appears to be adaptive, for aleurone layers maintained at heat shock temperatures for 18 h resynthesize secretory protein mRNAs, rebuild stacked ER lamellae, and resume secretory protein synthesis. In the present study aleurone layers were incubated at warmer than normal pre-heat shock temperatures to determine whether this would favor the formation of heat-resistant ER lamellae that could continue secretory protein synthesis during heat shock. Western blot and SDS-PAGE analyses showed that such treatment did not induce heat shock protein (HSP) synthesis, but it preserved significant secretory protein synthesis during heat shock. Northern hybridizations revealed that levels of mRNAs encoding secretory proteins were several-fold elevated as compared to 25°C preincubated controls, and transmission electron microscopic observations revealed stacked ER lamellae. Thin layer and gas chromatography showed that PC molecules in warm-incubated barley aleurone layers had more fatty acid saturation than did controls. These observations indicate that previous incubation temperature influences both the induction of HSP synthesis and the suppression of normal protein synthesis in the heat shock response. However, we found that it does not affect the temperature at which heat shock becomes lethal.

A highly conserved sequence in the 3'-untranslated region of the drosophila Adh gene plays a functional role in Adh expression

Phylogenetic analysis identified a highly conserved eight-base sequence (AAGGCTGA) within the 3'-untranslated region (UTR) of the Drosophila alcohol dehydrogenase gene, Adh. To examine the functional significance of this conserved motif, we performed in vitro deletion mutagenesis on the D. melanogaster Adh gene followed by P-element-mediated germline transformation. Deletion of all or part of the eight-base sequence leads to a twofold increase in in vivo ADH enzymatic activity. The increase in activity is temporally and spatially general and is the result of an underlying increase in Adh transcript. These results indicate that the conserved 3'-UTR motif plays a functional role in the negative regulation of Adh gene expression. The evolutionary significance of our results may be understood in the context of the amino acid change that produces the ADH-F allele and also leads to a twofold increase in ADH activity. While there is compelling evidence that the amino acid replacement has been a target of positive selection, the conservation of the 3'-UTR sequence suggests that it is under strong purifying selection. The selective difference between these two sequence changes, which have similar effects on ADH activity, may be explained by different metabolic costs associated with the increase in activity.

Dietary ethanol stimulates the activity of phosphatidylcholine-specific phospholipase D and the formation of phosphatidylethanol in Drosophila melanogaster larvae

When administered in the diet to third instar Drosophila melanogaster larvae, short chain primary alcohols reduce phosphatidylcholine (PC) levels. The ethanol-induced reductions in larval PC may be in part due to an increase in the activity of PC-specific phospholipase D (PC-specific PLD, EC 3.1.4.4). PC-specific PLD not only hydrolyzes PC, but it also apparently catalyzes the formation of phosphatidylethanol. PC-specific PLD activity was also stimulated by 200 mM ethanol, methanol, isopropanol, n-butanol, and n-propanol. In vitro studies indicated that Drosophila PC-specific PLD activities were enhanced by submicromolar concentrations of Ca2+ and by GTP-gamma S. In vivo studies utilizing [14C]lyso-palmitoyl phosphatidylcholine indicated that dietary ethanol promoted the flux of label into triacylglycerol, 1,2 diacylglycerol, and fatty acid ethyl esters, while the label in PC decreased.

Long-chain fatty acids and ethanol affect the properties of membranes in Drosophila melanogaster larvae

The larval fatty acid composition of neutral lipids and membrane lipids was determined in three ethanol-tolerant strains of Drosophila melanogaster. Dietary ethanol promoted a decrease in long-chain fatty acids in neutral lipids along with enhanced alcohol dehydrogenase (EC 1.1.1.1) activity in all of the strains. Dietary ethanol also increased the incorporation of 14C-ethanol into fatty acid ethyl esters (FAEE) by two- to threefold and decreased the incorporation of 14C-ethanol into free fatty acids (FFA). When cultured on sterile, defined media with stearic acid at 0 to 5 mM, stearic acid decreased ADH activity up to 33%. In strains not selected for superior tolerance to ethanol, dietary ethanol promoted a loss of long-chain fatty acids in membrane lipids. The loss of long-chain fatty acids in membranes was strongly correlated with increased fluidity in hydrophobic domains of mitochondrial membranes as determined by electron spin resonance and correlated with a loss of ethanol tolerance. In the ethanol-tolerant E2 strain, which had been exposed to ethanol for many generations, dietary ethanol failed to promote a loss of long-chain fatty acids in membrane lipids.

Dietary ethanol reduces phosphatidylcholine levels and inhibits the uptake of dietary choline in Drosophila melanogaster larvae

1. Low to moderate concentrations of dietary ethanol (200 mM to 600 mM) significantly increased the level of phosphatidylethanolamine (PE), while phosphatidylcholine (PC) levels decreased in third instar larvae. This was seen in both ethanol tolerant and intolerant strains of Drosophila melanogaster, indicating that the reduction of PC is not associated with a high level of ethanol tolerance. 2. The phospholipid changes were not ethanol-specific. Larvae fed ethanol, n-butanol, isopropanol, methanol, and n-propanol exhibited similar changes. 3. At 200 mM concentrations, dietary ethanol acted as a competitive inhibitor for the larval uptake of dietary choline. At higher concentrations, dietary ethanol acted as a noncompetitive inhibitor. This ethanol-induced inhibition of dietary choline uptake can only partially explain the ethanol-induced reductions in larval PC.

ADH activity and ethanol tolerance in third chromosome substitution lines in Drosophila melanogaster

In vitro ADH activity and ethanol tolerance were studied in males of a series of third chromosome substitution lines in Drosophila melanogaster. The lines were divided into those with a random third chromosome from a vineyard population (VO lines) and those with a selected third chromosome from males obtained after an egg-to-adult ethanol survival test on the F4 of the previous population (VE lines). Both ADH activity and ethanol tolerance varied significantly among the lines, but the characters showed no significant correlation. Ethanol tolerance (at the higher ethanol concentrations) was higher in the selected lines (VE lines) but ADH activity was not. In our lines, the in vitro ADH activity variability, linked to the regulatory genes (located on the third chromosome) and unrelated to the polymorphism of the Adh locus (located on the second chromosome), is not involved in the ethanol tolerance variability. The data suggest that in this population ethanol tolerance was acquired in nature, at least partially, by means other than increasing ADH activity.

Functional and biochemical features of alcohol dehydrogenase in four species of the obscura group of Drosophila

The biochemical features of ADH of four Drosophila species of the obscura group have been studied. The relationship between ethanol tolerance and ADH activity has been investigated. Propan-2-ol and acetone concentrations have been determined in propan-2-ol treated flies and ADH activity has been followed during 96 h of propan-2-ol treatment. Data on the ADH system confirm constructed phylogenies based on electrophoretic variation and chromosome homologies.

The effects of a choline deficiency on the lipid composition and ethanol tolerance of Drosophila melanogaster

1. A reduction in the dietary concentration of choline, an essential nutrient for Drosophila melanogaster, from the optimal concentration of 80 micrograms/ml of defined medium to 8 micrograms/ml diminished the level of tissue phosphatidylcholine to less than one-third the normal level in third instar larvae without significantly altering the amount of phosphatidylethanolamine. 2. The rates of synthesis of phospholipids, triglycerides, diglycerides and monoglycerides were reduced by the choline-deficiency, and the chain length of fatty acids in lipids was shortened. 3. The activity of succinic dehydrogenase, a mitochondrial enzyme, was decreased by the deficiency, but the activities of fumarase, sn-glycerol-3-phosphate dehydrogenase, alcohol dehydrogenase, sn-glycerol-3-phosphate oxidase and fatty acid synthetase were unaffected. A choline-deficiency did not alter the ultrastructure of mitochondria of larval fat body cells. 4. Choline-deficient individuals were more susceptible to the toxic effects of ethanol during larval and pupal development, and less adept at utilizing ethanol as a substrate for adult tissue synthesis.

Selection affecting enzyme polymorphisms in enclosed Drosophila populations maintained in a natural environment

Allele frequencies for the Adh, Gpdh, and Est6 enzyme polymorphisms of Drosophila melanogaster show large-scale latitudinal clines, whereas those for Pgm do not vary systematically with latitude. To elucidate possible mechanisms of selection underlying these distributions, large collections of the species were made from five Australasian localities spanning 24 degrees of latitude. Two replicate experimental populations were established from each collection, and each replicate was then released into an enclosure surrounding a natural habitat at a central-latitude locality. Genotype frequencies at the four loci were monitored for 15 months, covering 12 discrete generations, and selection coefficients on each polymorphism were then estimated by maximum likelihood procedures. For Est6 no coefficients were found to be significantly different from zero. For Pgm some nonzero coefficients were estimated, but these were heterogeneous across experimental populations of different geographic origins. For both Adh and Gpdh, nonzero selection coefficients were estimated that were homogeneous across populations and indicated heterozygote advantage. Predicted Adh and Gpdh equilibrium allele frequencies were consistent with those found in adjacent free-living populations. It is concluded that, at such intermediate latitudes at least, selection operates on the Adh and Gpdh polymorphisms to the advantage of heterozygotes.