Ethanol sensitivity and tolerance in long-term memory mutants of Drosophila melanogaster

APOE and Alzheimer's disease: Pathologic clues from transgenic Drosophila melanogaster

Alzheimer's disease (AD) is one of the most common forms of neurodegenerative diseases. Apolipoprotein E4 (ApoE4) is the main genetic risk factor in the development of late-onset AD. However, the exact mechanism underlying ApoE4-mediated neurodegeneration remains unclear. We utilized Drosophila melanogaster to examine the neurotoxic effects of various human APOE isoforms when expressed specifically in glial and neural cells. We assessed impacts on mitochondrial dynamics, ER stress, lipid metabolism, and bio-metal ion concentrations in the central nervous system (CNS) of the transgenic flies. Dachshund antibody staining revealed a reduction in the number of Kenyon cells. Behavioral investigations including ethanol tolerance and learning and memory performance demonstrated neuronal dysfunction in APOE4-expressing larvae and adult flies. Transcription level of marf and drp-1 were found to be elevated in APOE4 flies, while atf4, atf6, and xbp-1 s showed down regulation. Enhanced concentrations of triglyceride and cholesterol in the CNS were observed in APOE4 transgenic flies, with especially pronounced effects upon glial-specific expression of the gene. Spectrophotometry of brain homogenate revealed enhanced Fe++ and Zn++ ion levels in conjunction with diminished Cu++ levels upon APOE4 expression. To explore therapeutic strategies, we subjected the flies to heat-shock treatment, aiming to activate heat-shock proteins (HSPs) and assess their potential to mitigate the neurotoxic effects of APOE isoforms. The results showed potential therapeutic benefits for APOE4-expressing flies, hinting at an ability to attenuate memory deterioration. Overall, our findings suggest that APOE4 can alter lipid metabolism, bio metal ion homeostasis, and disrupt the harmonious fission-fusion balance of neuronal and glial mitochondria, ultimately inducing ER stress. These alterations mirror the main clinical manifestations of AD in patients. Therefore, our work underscores the suitability of Drosophila as a fertile model for probing the pathological roles of APOE and furthering our understanding of diverse isoform-specific functions.

Synaptic Mechanisms of Ethanol Tolerance and Neuroplasticity: Insights from Invertebrate Models

Alcohol tolerance is a neuroadaptive response that leads to a reduction in the effects of alcohol caused by previous exposure. Tolerance plays a critical role in the development of alcohol use disorder (AUD) because it leads to the escalation of drinking and dependence. Understanding the molecular mechanisms underlying alcohol tolerance is therefore important for the development of effective therapeutics and for understanding addiction in general. This review explores the molecular basis of alcohol tolerance in invertebrate models, Drosophila and C. elegans, focusing on synaptic transmission. Both organisms exhibit biphasic responses to ethanol and develop tolerance similar to that of mammals. Furthermore, the availability of several genetic tools makes them a great candidate to study the molecular basis of ethanol response. Studies in invertebrate models show that tolerance involves conserved changes in the neurotransmitter systems, ion channels, and synaptic proteins. These neuroadaptive changes lead to a change in neuronal excitability, most likely to compensate for the enhanced inhibition by ethanol.

Drosophila learning and memory centers and the actions of drugs of abuse

Drug addiction and the circuitry for learning and memory are intimately intertwined. Drugs of abuse create strong, inappropriate, and lasting memories that contribute to many of their destructive properties, such as continued use despite negative consequences and exceptionally high rates of relapse. Studies in Drosophila melanogaster are helping us understand how drugs of abuse, especially alcohol, create memories at the level of individual neurons and in the circuits where they function. Drosophila is a premier organism for identifying the mechanisms of learning and memory. Drosophila also respond to drugs of abuse in ways that remarkably parallel humans and rodent models. An emerging consensus is that, for alcohol, the mushroom bodies participate in the circuits that control acute drug sensitivity, not explicitly associative forms of plasticity such as tolerance, and classical associative memories of their rewarding and aversive properties. Moreover, it is becoming clear that drugs of abuse use the mushroom body circuitry differently from other behaviors, potentially providing a basis for their addictive properties.

Maria JP, Tablante KIG, Tiam-Lee JGA, Sison MCC, Medina PMB. Effect of Garcinia binucao Crude Leaf Extract Supplementation on Lifespan of Drosophila melanogaster Chronically Exposed to Alcohol

Background

Consumption and abuse of alcohol remains a significant cause of concern worldwide. Furthermore, there is evidence of the association between chronic alcohol use and reduced life expectancy.

Objectives

To study the effects of Garcinia binucao extract (GBE) supplementation on lifespan of Drosophila melanogaster, in the presence or absence of chronic alcohol exposure.

Methods

D. melanogaster was mass cultured and given GBE supplementation in high (1 mg/mL) and low (200 µg/mL) sublethal doses. D. melanogaster flies were divided into groups - with and without chronic alcohol exposure, and their respective lifespans were monitored.

Results

In D. melanogaster without alcohol exposure, mean lifespan was highest in the control flies (38.15 days), followed by high-dose GBE (34.42 days), low-dose GBE (33.24 days), and DMSO (22.29 days). In D. melanogaster chronically exposed to alcohol, the longest mean lifespan was observed in flies treated with high-dose GBE (33.80 days), followed by low-dose GBE (33.63 days), the DMSO group (30.30), and the control group (29.65 days), but the differences were not statistically significant. Comparing groups with and without chronic alcohol exposure, the mean lifespan of the control group chronically exposed to alcohol significantly decreased by 9.51 days (p < 0.05). In GBE treatment groups, mean lifespan significantly decreased by 0.82 days in high-dose set-up (p < 0.05), and significantly increased by 0.39 days in the low-dose set-up (p < 0.05) upon chronic alcohol exposure.

Conclusion

Garcinia binucao extract supplementation ameliorated the observed reduction in lifespan of Drosophila melanogaster chronically exposed to alcohol.

Curcumin improves the ability of donepezil to ameliorate memory impairment in Drosophila melanogaster: involvement of cholinergic and cnc/Nrf2-redox systems

One of the well-established models for examining neurodegeneration and neurotoxicity is the Drosophila melanogaster model of aluminum-induced toxicity. Anti-cholinesterase drugs have been combined with other neuroprotective agents to improve Alzheimer's disease management, but there is not much information on the combination of anti-cholinesterases with dietary polyphenols to combat memory impairment. Here, we assess how curcumin influences some of the critical therapeutic effects of donepezil (a cholinesterase inhibitor) in AlCl3-treated Drosophila melanogaster. Harwich strain flies were exposed to 40 mM AlCl3 - alone or in combination with curcumin (1 mg/g) and/or donepezil (12.5 µg/g and 25 µg/g) - for seven days. The flies' behavioral evaluations (memory index and locomotor performance) were analyzed. Thereafter, the flies were processed into homogenates for the quantification of acetylcholinesterase (AChE), catalase, total thiol, and rate of lipid peroxidation, as well as the mRNA levels of acetylcholinesterase (ACE1) and cnc/NRF2. Results showed that AlCl3-treated flies presented impaired memory and increased activities of acetylcholinesterase and lipid peroxidation, while there were decrease in total thiol levels and catalase activity when compared to the control. Also, the expression of ACE1 was significantly increased while that of cnc/NRF2 was significantly decreased. However, combinations of curcumin and donepezil, especially at lower dose of donepezil, significantly improved the memory index and biochemical parameters compared to donepezil alone. Thus, curcumin plus donepezil offers unique therapeutic effects during memory impairment in the D. melanogaster model of neurotoxicity.

The Stage-Based Model of Addiction-Using Drosophila to Investigate Alcohol and Psychostimulant Responses

Addiction is a progressive and complex disease that encompasses a wide range of disorders and symptoms, including substance use disorder (SUD), for which there are few therapeutic treatments. SUD is the uncontrolled and chronic use of substances despite the negative consequences resulting from this use. The progressive nature of addiction is organized into a testable framework, the neurobiological stage-based model, that includes three behavioral stages: (1) binge/intoxication, (2) withdrawal/negative affect, and (3) preoccupation/anticipation. Human studies offer limited opportunities for mechanistic insights into these; therefore, model organisms, like Drosophila melanogaster, are necessary for understanding SUD. Drosophila is a powerful model organism that displays a variety of SUD-like behaviors consistent with human and mammalian substance use, making flies a great candidate to study mechanisms of behavior. Additionally, there are an abundance of genetic tools like the GAL4/UAS and CRISPR/Cas9 systems that can be used to gain insight into the molecular mechanisms underlying the endophenotypes of the three-stage model. This review uses the three-stage framework and discusses how easily testable endophenotypes have been examined with experiments using Drosophila, and it outlines their potential for investigating other endophenotypes.

Rapid and Chronic Ethanol Tolerance Are Composed of Distinct Memory-Like States in Drosophila

Ethanol tolerance is the first type of behavioral plasticity and neural plasticity that is induced by ethanol intake, and yet its molecular and circuit bases remain largely unexplored. Here, we characterize the following three distinct forms of ethanol tolerance in male Drosophila: rapid, chronic, and repeated. Rapid tolerance is composed of two short-lived memory-like states, one that is labile and one that is consolidated. Chronic tolerance, induced by continuous exposure, lasts for 2 d, induces ethanol preference, and hinders the development of rapid tolerance through the activity of histone deacetylases (HDACs). Unlike rapid tolerance, chronic tolerance is independent of the immediate early gene Hr38/Nr4a Chronic tolerance is suppressed by the sirtuin HDAC Sirt1, whereas rapid tolerance is enhanced by Sirt1 Moreover, rapid and chronic tolerance map to anatomically distinct regions of the mushroom body learning and memory centers. Chronic tolerance, like long-term memory, is dependent on new protein synthesis and it induces the kayak/c-fos immediate early gene, but it depends on CREB signaling outside the mushroom bodies, and it does not require the Radish GTPase. Thus, chronic ethanol exposure creates an ethanol-specific memory-like state that is molecularly and anatomically different from other forms of ethanol tolerance.SIGNIFICANCE STATEMENT The pattern and concentration of initial ethanol exposure causes operationally distinct types of ethanol tolerance to form. We identify separate molecular and neural circuit mechanisms for two forms of ethanol tolerance, rapid and chronic. We also discover that chronic tolerance forms an ethanol-specific long-term memory-like state that localizes to learning and memory circuits, but it is different from appetitive and aversive long-term memories. By contrast, rapid tolerance is composed of labile and consolidated short-term memory-like states. The multiple forms of ethanol memory-like states are genetically tractable for understanding how initial forms of ethanol-induced neural plasticity form a substrate for the longer-term brain changes associated with alcohol use disorder.

Long-Term Memory Formation in Drosophila Depends on the 3'UTR of CPEB Gene orb2

Activation of local translation in neurites in response to stimulation is an important step in the formation of long-term memory (LTM). CPEB proteins are a family of translation factors involved in LTM formation. The Drosophila CPEB protein Orb2 plays an important role in the development and function of the nervous system. Mutations of the coding region of the orb2 gene have previously been shown to impair LTM formation. We found that a deletion of the 3'UTR of the orb2 gene similarly results in loss of LTM in Drosophila. As a result of the deletion, the content of the Orb2 protein remained the same in the neuron soma, but significantly decreased in synapses. Using RNA immunoprecipitation followed by high-throughput sequencing, we detected more than 6000 potential Orb2 mRNA targets expressed in the Drosophila brain. Importantly, deletion of the 3'UTR of orb2 mRNA also affected the localization of the Csp, Pyd, and Eya proteins, which are encoded by putative mRNA targets of Orb2. Therefore, the 3'UTR of the orb2 mRNA is important for the proper localization of Orb2 and other proteins in synapses of neurons and the brain as a whole, providing a molecular basis for LTM formation.

Huntingtin Plays a Role in the Physiological Response to Ethanol in Drosophila

BACKGROUND

Huntingtin (htt) protein is an essential regulator of nervous system function through its various neuroprotective and pro-survival functions, and loss of wild-type htt function is implicated in the etiology of Huntington's disease. While its pathological role is typically understood as a toxic gain-of-function, some neuronal phenotypes also result from htt loss. Therefore, it is important to understand possible roles for htt in other physiological circumstances.

OBJECTIVE

To elucidate the role of htt in the context of ethanol exposure, we investigated how loss of htt impacts behavioral and physiological responses to ethanol in Drosophila.

METHODS

We tested flies lacking htt for ethanol sensitivity and tolerance, preference for ethanol using capillary feeder assays, and recovery of mobility after intoxication. Levels of dopamine neurotransmitter and numbers of dopaminergic cells in brains lacking dhtt were also measured.

RESULTS

We found that dhtt-null flies are both less sensitive and more tolerant to ethanol exposure in adulthood. Moreover, flies lacking dhtt are more averse to alcohol than controls, and they recover mobility faster following acute ethanol intoxication. We showed that dhtt mediates these effects at least in part through the dopaminergic system, as dhtt is required to maintain normal levels of dopamine in the brain and normal numbers of dopaminergic cells in the adult protocerebrum.

CONCLUSIONS

Our results demonstrate that htt regulates the physiological response to ethanol and indicate a novel neuroprotective role for htt in the dopaminergic system, raising the possibility that it may be involved more generally in the response to toxic stimuli.

The foraging gene affects alcohol sensitivity, metabolism and memory in Drosophila

The genetic basis of alcohol use disorder (AUD) is complex. Understanding how natural genetic variation contributes to alcohol phenotypes can help us identify and understand the genetic basis of AUD. Recently, a single nucleotide polymorphism in the human foraging (for) gene ortholog, Protein Kinase cGMP-Dependent 1 (PRKG1), was found to be associated with stress-induced risk for alcohol abuse. However, the mechanistic role that PRKG1 plays in AUD is not well understood. We use natural variation in the Drosophila for gene to describe how variation of cGMP-dependent protein kinase (PKG) activity modifies ethanol-induced phenotypes. We found that variation in for affects ethanol-induced increases in locomotion and memory of the appetitive properties of ethanol intoxication. Further, these differences may stem from the ability to metabolize ethanol. Together, this data suggests that natural variation in PKG modulates cue reactivity for alcohol, and thus could influence alcohol cravings by differentially modulating metabolic and behavioral sensitivities to alcohol.

Repeated ethanol intoxications of Drosophila melanogaster adults increases the resistance to ethanol of their progeny

BACKGROUND

For decades, Drosophila melanogaster has been used as a model organism to understand the genetics and neurobiology of ethanol intoxication and tolerance. Previous research has shown that acute and chronic pre-exposures to ethanol can trigger the development of functional ethanol tolerance in flies and has unveiled some of the genetic pathways involved in the process. To our knowledge, however, no previous work has systematically explored whether repeated intoxications of adult flies can affect the ethanol tolerance of their progeny.

METHODS

Adult flies were intoxicated several times (once daily, over several days), and their F1 and F2 progeny were subjected to a functional tolerance test in which flies are exposed to ethanol and video recorded twice within 5 hr. Their behavior was subsequently analyzed to determine how long it took them to become sedated during the first and second exposures. One- and 2-way ANOVAs were used to determine whether parental treatment had an effect on their progeny's baseline resistance and/or acquired functional tolerance to ethanol.

RESULTS

Parental flies that were intoxicated several times produced F1 and F2 progeny with a significantly higher resistance to ethanol than progeny from unexposed controls. Further, parental intoxications inconsistently increased the progeny's capacity to develop rapid functional tolerance upon re-exposure to ethanol. The transmission of increased ethanol resistance to progeny lasted several days after the last parental intoxication.

CONCLUSION

To our knowledge, this is the first demonstration that repeated parental daily intoxications affect the progeny's response to ethanol in fruit flies. Our findings support the use of D. melanogaster to explore conserved pathways underlying the transmission of ethanol tolerance and can help in the identificaton of novel strategies for managing alcohol use disorder.

Receptors and Channels Associated with Alcohol Use: Contributions from Drosophila

Alcohol Use Disorder (AUD) is a debilitating disorder that manifests as problematic patterns of alcohol use. At the core of AUD's behavioral manifestations are the profound structural, physiological, cellular, and molecular effects of alcohol on the brain. While the field has made considerable progress in understanding the neuromolecular targets of alcohol we still lack a comprehensive understanding of alcohol's actions and effective treatment strategies. Drosophila melanogaster is a powerful model for investigating the neuromolecular targets of alcohol because flies model many of the core behavioral elements of AUD and offer a rich genetic toolkit to precisely reveal the in vivo molecular actions of alcohol. In this review, we focus on receptors and channels that are often targeted by alcohol within the brain. We discuss the general roles of these proteins, their role in alcohol-associated behaviors across species, and propose ways in which Drosophila models can help advance the field.

DNT1 Downregulation and Increased Ethanol Sensitivity in Transgenic Drosophila Models of Alzheimer's Disease

Two major pathological hallmarks of Alzheimer's disease (AD) are amyloid plaques and neurofibrillary tangles of hyperphosphorylated tau. Aggregation of amyloid-β (Aβ) is considered as the primary insult in AD. However, failure in treatments based on targetingAβ without considering the pathologic tau and close correlation between pathological tau and cognitive decline highlighted the crucial role of tau in AD. Loss of synaptic plasticity and cognitive decline, partly due to decrease in Brain Derived Neurotrophic Factor (BDNF), are other hallmarks of AD. Aβ and tau downregulate BDNF at both transcriptional and translational levels. The aim of this research was to study the expression levels of Drosophila Neuroteophin 1 (DNT1), as an orthologue of BDNF, in flies expressing Aβ₄₂ or tau^R406W. Levels of DNT1 were determined using quantitative real time PCR. Behavioral and Biochemical investigations were also performed in parallel. Our results showed that there is a significant decrease in the levels of DNT1 expression in Aβ₄₂ or tau^R406W expressing flies. Interestingly, a significant increase was observed in sensitivity to ethanol in both transgenic flies. Rise in Reactive Oxygen Species (ROS) levels was also detected. We concluded that both Aβ and pathological tau exert their toxic effect on DNT1 expression, ROS production, and response to ethanol, independently. Interestingly, pathological tau showed higher impact on the ROS production compared to Aβ. It seems that Aβ₄₂ and tau^R406W transgenic flies are proper models to investigate the interplay between BDNF and oxidative stress, and also to assess the mechanism underlying behavioral response to ethanol.

Normal Ethanol Sensitivity and Rapid Tolerance Require the G Protein Receptor Kinase 2 in Ellipsoid Body Neurons in Drosophila

BACKGROUND

G protein signaling pathways are key neuromodulatory mechanisms for behaviors and neurological functions that affect the impact of ethanol (EtOH) on locomotion, arousal, and synaptic plasticity. Here, we report a novel role for the Drosophila G protein-coupled receptor kinase 2 (GPRK2) as a member of the GRK4/5/6 subfamily in modulating EtOH-induced behaviors.

METHODS

We studied the requirement of Drosophila Gprk2 for naïve sensitivity to EtOH sedation and ability of the fly to develop rapid tolerance after a single exposure to EtOH, using the loss of righting reflex (LORR) and fly group activity monitor (FlyGrAM) assays.

RESULTS

Loss-of-function Gprk2 mutants demonstrate an increase in alcohol-induced hyperactivity, reduced sensitivity to the sedative effects of EtOH, and diminished rapid tolerance after a single intoxicating exposure. The requirement for Gprk2 in EtOH sedation and rapid tolerance maps to ellipsoid body neurons within the Drosophila brain, suggesting that wild-type Gprk2 is required for modulation of locomotion and alertness. However, even though Gprk2 loss of function leads to decreased and fragmented sleep, this change in the sleep state does not depend on Gprk2 expression in the ellipsoid body.

CONCLUSION

Our work on GPRK2 has established a role for this GRK4/5/6 subfamily member in EtOH sensitivity and rapid tolerance.

Solanum vegetable-based diets improve impairments in memory, redox imbalance, and altered critical enzyme activities in Drosophila melanogaster model of neurodegeneration

The effects of two Solanum vegetables, S. macrocarpon L. (African eggplant), and S. nigrum L. (black nightshade) on aluminum model of neurodegeneration in Drosophila melanogaster was investigated. Flies were treated with AlCl₃ alone or in combination with the leaves from both samples in their diets for 7 days. Thereafter, locomotor performance and aversive phototaxic suppression test for learning and memory were carried out. This was followed by assay for reactive oxygen species, antioxidant properties, and enzyme (monoamine oxidase and cholinesterase) activities. Also, the in vitro antioxidant properties and chromatographic phenolic and alkaloid characterization of the samples were determined. Results showed that impaired behavioral physiology, antioxidant status, and enzyme activities observed in Al-treated flies were ameliorated in flies treated with both samples. In addition, both samples exhibited in vitro antioxidant effects. The protective effects from these samples against Al-induced toxicity can be associated with their antioxidant, antimonoaminergic, and anticholinergic properties. PRACTICAL APPLICATIONS: In the quest for a holistic prevention/management approach to neurodegenerative diseases, functional foods are becoming prominent. The use of Drosophila melanogaster to study human diseases is gaining huge recognition due to the high homologue between disease-causing genes between the two organisms. Consequently, this study presents African eggplant and black nightshade leafy vegetables as sources of polyphenols and alkaloids which are able to ameliorate impaired learning and memory, redox status, and enzyme activities in Al-induced D. melanogaster model of neurodegeneration.

Insights from intoxicated Drosophila

Our understanding of alcohol use disorder (AUD), particularly alcohol's effects on the nervous system, has unquestionably benefited from the use of model systems such as Drosophila melanogaster. Here, we briefly introduce the use of flies in alcohol research, and highlight the genetic accessibility and neurobiological contribution that flies have made to our understanding of AUD. Future fly research offers unique opportunities for addressing unresolved questions in the alcohol field, such as the neuromolecular and circuit basis for cravings and alcohol-induced neuroimmune dysfunction. This review strongly advocates for interdisciplinary approaches and translational collaborations with the united goal of confronting the major health problems associated with alcohol abuse and addiction.

Honey Bees (Apis mellifera) Show a Preference for the Consumption of Ethanol

BACKGROUND

Alcohol abuse and alcoholism are significant global issues. Honey bees are excellent models for learning and other complex behaviors; furthermore, they share many behavioral responses to ethanol (EtOH) with humans and animal models. We develop a 2-feeder choice assay to determine whether honey bees will self-administer and preferentially consume solutions containing EtOH.

METHODS

Gustatory responsiveness to EtOH is determined using the proboscis extension reflex and consumption assays. A 2-feeder choice assay is used to examine preference for the consumption of EtOH. Survival assays assess the metabolic and toxic effects of EtOH consumption.

RESULTS

Honey bees find the taste of EtOH to be aversive when in water, but addition of sucrose masks the aversive taste. Even though the taste of EtOH is not appetitive, honey bees preferentially consume sucrose solutions containing 1.25 to 2.5% EtOH in a dose-dependent manner. Based on survival assays, honey bees may not be able to derive caloric value from EtOH, and EtOH concentrations of 2.5% or higher lead to significant increases in mortality.

CONCLUSIONS

Honey bees will self-administer EtOH and show a preference for consuming solutions containing EtOH. Bees may not be able to efficiently utilize EtOH as an energy source, but EtOH-dependent increases in mortality complicate separating the effects of caloric value and toxicity.

Dynamic changes in gene expression and alternative splicing mediate the response to acute alcohol exposure in Drosophila melanogaster

Environmental changes typically cause rapid gene expression responses in the exposed organisms, including changes in the representation of gene isoforms with different functions or properties. Identifying the genes that respond to environmental change, including in genotype-specific ways, is an important step in treating the undesirable physiological effects of stress, such as exposure to toxins or ethanol. Ethanol is a unique environmental stress in that chronic exposure results in permanent physiological changes and the development of alcohol use disorders. Drosophila is a classic model for deciphering the mechanisms of the response to alcohol exposure, as it meets the criteria for the development of alcohol use disorders, and has similar physiological underpinnings with vertebrates. Because many studies on the response to ethanol have relied on a priori candidate genes, broad surveys of gene expression and splicing are required and have been investigated here. Further, we expose Drosophila to ethanol in an environment that is genetically, socially, and ecologically relevant. Both expression and splicing differences, inasmuch as they can be decomposed, contribute to the response to ethanol in Drosophila melanogaster. However, we find that while D. melanogaster responds to ethanol, there is very little genetic variation in how it responds to ethanol. In addition, the response to alcohol over time is dynamic, suggesting that incorporating time into studies on the response to the environment is important.

Mechanisms Underlying the Risk to Develop Drug Addiction, Insights From Studies in Drosophila melanogaster

The ability to adapt to environmental changes is an essential feature of biological systems, achieved in animals by a coordinated crosstalk between neuronal and hormonal programs that allow rapid and integrated organismal responses. Reward systems play a key role in mediating this adaptation by reinforcing behaviors that enhance immediate survival, such as eating or drinking, or those that ensure long-term survival, such as sexual behavior or caring for offspring. Drugs of abuse co-opt neuronal and molecular pathways that mediate natural rewards, which under certain circumstances can lead to addiction. Many factors can contribute to the transition from drug use to drug addiction, highlighting the need to discover mechanisms underlying the progression from initial drug use to drug addiction. Since similar responses to natural and drug rewards are present in very different animals, it is likely that the central systems that process reward stimuli originated early in evolution, and that common ancient biological principles and genes are involved in these processes. Thus, the neurobiology of natural and drug rewards can be studied using simpler model organisms that have their systems stripped of some of the immense complexity that exists in mammalian brains. In this paper we review studies in Drosophila melanogaster that model different aspects of natural and drug rewards, with an emphasis on how motivational states shape the value of the rewarding experience, as an entry point to understanding the mechanisms that contribute to the vulnerability of drug addiction.

FcRav2, a gene with a ROGDI domain involved in Fusarium head blight and crown rot on durum wheat caused by Fusarium culmorum

Fusarium culmorum is a soil-borne fungal pathogen which causes foot and root rot and Fusarium head blight on small-grain cereals, in particular wheat and barley. It causes significant yield and quality losses and results in the contamination of kernels with type B trichothecene mycotoxins. Our knowledge of the pathogenicity factors of this fungus is still limited. A transposon tagging approach based on the mimp1/impala double-component system has allowed us to select a mutant altered in multiple metabolic and morphological processes, trichothecene production and virulence. The flanking regions of mimp1 were used to seek homologies in the F. culmorum genome, and revealed that mimp1 had reinserted within the last exon of a gene encoding a hypothetical protein of 318 amino acids which contains a ROGDI-like leucine zipper domain, supposedly playing a protein-protein interaction or regulatory role. By functional complementation and bioinformatic analysis, we characterized the gene as the yeast Rav2 homologue, confirming the high level of divergence in multicellular fungi. Deletion of FcRav2 or its orthologous gene in F. graminearum highlighted its ability to influence a number of functions, including virulence, trichothecene type B biosynthesis, resistance to azoles and resistance to osmotic and oxidative stress. Our results indicate that the FcRav2 protein (and possibly the RAVE complex as a whole) may become a suitable target for new antifungal drug development or the plant-mediated resistance response in filamentous fungi of agricultural interest.

Drosophila: An Emergent Model for Delineating Interactions between the Circadian Clock and Drugs of Abuse

Endogenous circadian oscillators orchestrate rhythms at the cellular, physiological, and behavioral levels across species to coordinate activity, for example, sleep/wake cycles, metabolism, and learning and memory, with predictable environmental cycles. The 21st century has seen a dramatic rise in the incidence of circadian and sleep disorders with globalization, technological advances, and the use of personal electronics. The circadian clock modulates alcohol- and drug-induced behaviors with circadian misalignment contributing to increased substance use and abuse. Invertebrate models, such as Drosophila melanogaster, have proven invaluable for the identification of genetic and molecular mechanisms underlying highly conserved processes including the circadian clock, drug tolerance, and reward systems. In this review, we highlight the contributions of Drosophila as a model system for understanding the bidirectional interactions between the circadian system and the drugs of abuse, alcohol and cocaine, and illustrate the highly conserved nature of these interactions between Drosophila and mammalian systems. Research in Drosophila provides mechanistic insights into the corresponding behaviors in higher organisms and can be used as a guide for targeted inquiries in mammals.

A screen for E3 ubiquitination ligases that genetically interact with the adaptor protein Cindr during Drosophila eye patterning

Ubiquitination is a crucial post-translational modification that can target proteins for degradation. The E3 ubiquitin ligases are responsible for recognizing substrate proteins for ubiquitination, hence providing specificity to the process of protein degradation. Here, we describe a genetic modifier screen that identified E3 ligases that modified the rough-eye phenotype generated by expression of cindr^RNAi transgenes during Drosophila eye development. In total, we identified 36 E3 ligases, as well as 4 Cullins, that modified the mild cindr^RNA mis-patterning phenotype. This indicates possible roles for these E3s/Cullins in processes that require Cindr function, including cytoskeletal regulation, cell adhesion, cell signaling and cell survival. Three E3 ligases identified in our screen had previously been linked to regulating JNK signaling.

Genetics of alcohol consumption in Drosophila melanogaster

Individual variation in alcohol consumption in human populations is determined by genetic, environmental, social and cultural factors. In contrast to humans, genetic contributions to complex behavioral phenotypes can be readily dissected in Drosophila, where both the genetic background and environment can be controlled and behaviors quantified through simple high-throughput assays. Here, we measured voluntary consumption of ethanol in ∼3000 individuals of each sex from an advanced intercross population derived from 37 lines of the Drosophila melanogaster Genetic Reference Panel. Extreme quantitative trait loci mapping identified 385 differentially segregating allelic variants located in or near 291 genes at P < 10-8 . The effects of single nucleotide polymorphisms associated with voluntary ethanol consumption are sex-specific, as found for other alcohol-related phenotypes. To assess causality, we used RNA interference knockdown or P{MiET1} mutants and their corresponding controls and functionally validated 86% of candidate genes in at least one sex. We constructed a genetic network comprised of 23 genes along with a separate trio and a pair of connected genes. Gene ontology analyses showed enrichment of developmental genes, including development of the nervous system. Furthermore, a network of human orthologs showed enrichment for signal transduction processes, protein metabolism and developmental processes, including nervous system development. Our results show that the genetic architecture that underlies variation in voluntary ethanol consumption is sexually dimorphic and partially overlaps with genetic factors that control variation in feeding behavior and alcohol sensitivity. This integrative genetic architecture is rooted in evolutionarily conserved features that can be extrapolated to human genetic interaction networks.

Genetics and genomics of alcohol responses in Drosophila

Drosophila melanogaster has become a significant model organism for alcohol research. In flies, a rich variety of behaviors can be leveraged for identifying genes affecting alcohol responses and adaptations. Furthermore, almost all genes can be easily genetically manipulated. Despite the great evolutionary distance between flies and mammals, many of the same genes have been implicated in strikingly similar alcohol-induced behaviors. A major problem in medical research today is that it is difficult to extrapolate from any single model system to humans. Strong evolutionary conservation of a mechanistic response between distantly related organisms, such as flies and mammals, is a powerful predictor that conservation will continue all the way to humans. This review describes the state of the Drosophila alcohol research field. It describes common alcohol behavioral assays, the independent origins of resistance and tolerance, the results of classical genetic screens and candidate gene analysis, and the outcomes of recent genomics studies employing GWAS, transcriptome, miRNA, and genome-wide histone acetylation surveys. This article is part of the Special Issue entitled "Alcoholism".

Immediate-early alcohol-responsive miRNA expression in Drosophila

At the core of the changes characteristic of alcoholism are alterations in gene expression in the brain of the addicted individual. These changes are believed to underlie some of the neuroadaptations that promote compulsive drinking. Unfortunately, the mechanisms by which alcohol consumption produces changes in gene expression remain poorly understood. MicroRNAs (miRNAs) have emerged as important regulators of gene expression because they can coordinately modulate the translation efficiency of large sets of specific mRNAs. Here, we investigate the early miRNA responses elicited by an acute sedating dose of alcohol in the Drosophila model organism. In our analysis, we combine the power of next-generation sequencing with Drosophila genetics to identify alcohol-sensitive miRNAs and to functionally test them for a role in modulating alcohol sensitivity. We identified 14 known Drosophila miRNAs, and 13 putative novel miRNAs that respond to an acute sedative exposure to alcohol. Using the GeneSwitch Gal4/UAS system, a subset of these ethanol-responsive miRNAs was functionally tested to determine their individual contribution in modulating ethanol sensitivity. We identified two microRNAs that when overexpressed significantly increased ethanol sensitivity: miR-6 and miR-310. MicroRNA target prediction analysis revealed that the different alcohol-responsive miRNAs target-overlapping sets of mRNAs. Alcoholism is the product of accumulated cellular changes produced by chronic ethanol consumption. Although all of the changes described herein are extremely rapid responses evoked by a single ethanol exposure, understanding the gene expression changes that occur in the first few minutes after ethanol exposure will help us to categorize ethanol responses into those that are near instantaneous and those that are emergent responses produced only by repeated ethanol exposure.

From Learning to Memory: What Flies Can Tell Us about Intellectual Disability Treatment

Intellectual disability (ID), previously known as mental retardation, affects 3% of the population and remains without pharmacological treatment. ID is characterized by impaired general mental abilities associated with defects in adaptive function in which onset occurs before 18 years of age. Genetic factors are increasing and being recognized as the causes of severe ID due to increased use of genome-wide screening tools. Unfortunately drug discovery for treatment of ID has not followed the same pace as gene discovery, leaving clinicians, patients, and families without the ability to ameliorate symptoms. Despite this, several model organisms have proven valuable in developing and screening candidate drugs. One such model organism is the fruit fly Drosophila. First, we review the current understanding of memory in human and its model in Drosophila. Second, we describe key signaling pathways involved in ID and memory such as the cyclic adenosine 3',5'-monophosphate (cAMP)-cAMP response element binding protein (CREB) pathway, the regulation of protein synthesis, the role of receptors and anchoring proteins, the role of neuronal proliferation, and finally the role of neurotransmitters. Third, we characterize the types of memory defects found in patients with ID. Finally, we discuss how important insights gained from Drosophila learning and memory could be translated in clinical research to lead to better treatment development.

The FlyBar: administering alcohol to flies

Fruit flies (Drosophila melanogaster) are an established model for both alcohol research and circadian biology. Recently, we showed that the circadian clock modulates alcohol sensitivity, but not the formation of tolerance. Here, we describe our protocol in detail. Alcohol is administered to the flies using the FlyBar. In this setup, saturated alcohol vapor is mixed with humidified air in set proportions, and administered to the flies in four tubes simultaneously. Flies are reared under standardized conditions in order to minimize variation between the replicates. Three-day old flies of different genotypes or treatments are used for the experiments, preferably by matching flies of two different time points (e.g., CT 5 and CT 17) making direct comparisons possible. During the experiment, flies are exposed for 1 hr to the pre-determined percentage of alcohol vapor and the number of flies that exhibit the Loss of Righting reflex (LoRR) or sedation are counted every 5 min. The data can be analyzed using three different statistical approaches. The first is to determine the time at which 50% of the flies have lost their righting reflex and use an Analysis of the Variance (ANOVA) to determine whether significant differences exist between time points. The second is to determine the percentage flies that show LoRR after a specified number of minutes, followed by an ANOVA analysis. The last method is to analyze the whole times series using multivariate statistics. The protocol can also be used for non-circadian experiments or comparisons between genotypes.

Long-lasting, experience-dependent alcohol preference in Drosophila

To understand the molecular and neural mechanisms underlying alcohol addiction, many models ranging from vertebrates to invertebrates have been developed. In Drosophila melanogaster, behavioral paradigms from assaying acute responses to alcohol and to behaviors more closely modeling addiction have emerged in recent years. However, both the CAFÉ assay, similar to a two-bottle choice consumption assay, as well as conditioned odor preference, where ethanol is used as the reinforcer, are labor intensive and have low throughput. To address this limitation, we have established a novel ethanol consumption preference assay, called FRAPPÉ, which allows for fast, high throughput measurement of consumption in individual flies, using a fluorescence plate reader. We show that naïve flies do not prefer to consume ethanol, but various pre-exposures, such as ethanol vapor or voluntary ethanol consumption, induce ethanol preference. This ethanol-primed preference is long lasting and is not driven by calories contained in ethanol during the consumption choice. Our novel experience-dependent model of ethanol preference in Drosophila-a highly genetically tractable organism-therefore recapitulates salient features of human alcohol abuse and will facilitate the molecular understanding of the development of alcohol preference.

The role of the actin cytoskeleton in regulating Drosophila behavior

Over the past decade, the function of the cytoskeleton has been studied extensively in developing and mature neurons. Actin, a major cytoskeletal protein, is indispensable for the structural integrity and plasticity of neurons and their synapses. Disruption of actin dynamics has significant consequence for neurons, neuronal circuits, and the functions they govern. In particular, cell adhesion molecules, members of the Rho family of GTPases, and actin-binding proteins are important modulators of actin dynamics and neuronal as well as behavioral plasticity. In this review, we discuss recent advances in Drosophila that highlight the importance of actin regulatory proteins in mediating fly behaviors such as circadian rhythm, courtship behavior, learning and memory, and the development of drug addiction.

Alcohol-induced histone acetylation reveals a gene network involved in alcohol tolerance

Sustained or repeated exposure to sedating drugs, such as alcohol, triggers homeostatic adaptations in the brain that lead to the development of drug tolerance and dependence. These adaptations involve long-term changes in the transcription of drug-responsive genes as well as an epigenetic restructuring of chromosomal regions that is thought to signal and maintain the altered transcriptional state. Alcohol-induced epigenetic changes have been shown to be important in the long-term adaptation that leads to alcohol tolerance and dependence endophenotypes. A major constraint impeding progress is that alcohol produces a surfeit of changes in gene expression, most of which may not make any meaningful contribution to the ethanol response under study. Here we used a novel genomic epigenetic approach to find genes relevant for functional alcohol tolerance by exploiting the commonalities of two chemically distinct alcohols. In Drosophila melanogaster, ethanol and benzyl alcohol induce mutual cross-tolerance, indicating that they share a common mechanism for producing tolerance. We surveyed the genome-wide changes in histone acetylation that occur in response to these drugs. Each drug induces modifications in a large number of genes. The genes that respond similarly to either treatment, however, represent a subgroup enriched for genes important for the common tolerance response. Genes were functionally tested for behavioral tolerance to the sedative effects of ethanol and benzyl alcohol using mutant and inducible RNAi stocks. We identified a network of genes that are essential for the development of tolerance to sedation by alcohol.

The evolution of Drosophila melanogaster as a model for alcohol research

Animal models have been widely used to gain insight into the mechanisms underlying the acute and long-term effects of alcohol exposure. The fruit fly Drosophila melanogaster encounters ethanol in its natural habitat and possesses many adaptations that allow it to survive and thrive in ethanol-rich environments. Several assays to study ethanol-related behaviors in flies, ranging from acute intoxication to self-administration and reward, have been developed in the past 20 years. These assays have provided the basis for studying the physiological and behavioral effects of ethanol and for identifying genes mediating these effects. In this review we describe the ecological relationship between flies and ethanol, the effects of ethanol on fly development and behavior, the use of flies as a model for alcohol addiction, and the interaction between ethanol and social behavior. We discuss these advances in the context of their utility to help decipher the mechanisms underlying the diverse effects of ethanol, including those that mediate ethanol dependence and addiction in humans.

Is alcoholism learned? Insights from the fruit fly

Alcohol addiction is a complex, unique human disease. Breaking addiction down into contributing endophenotypes enables its study in a variety of model systems. The Drosophila model system has been most often used to study alcohol sensitivity, tolerance, and physiological dependence. However, none of these endophenotypes can account for the near-permanent quality of the addicted state. It has been recently discussed that addictive drugs may hijack the learning-and-memory machinery to produce persistent behavioral changes. Learning and memory is amenable to experimental study, and provides us with a window into how alcohol affects higher-order mental functions that are likely to contribute compulsive drug use. Here, we review the Drosophila literature that links alcohol-related behaviors to learning and memory.

DlgS97/SAP97, a neuronal isoform of discs large, regulates ethanol tolerance

From a genetic screen for Drosophila melanogaster mutants with altered ethanol tolerance, we identified intolerant (intol), a novel allele of discs large 1 (dlg1). Dlg1 encodes Discs Large 1, a MAGUK (Membrane Associated Guanylate Kinase) family member that is the highly conserved homolog of mammalian PSD-95 and SAP97. The intol mutation disrupted specifically the expression of DlgS97, a SAP97 homolog, and one of two major protein isoforms encoded by dlg1 via alternative splicing. Expression of the major isoform, DlgA, a PSD-95 homolog, appeared unaffected. Ethanol tolerance in the intol mutant could be partially restored by transgenic expression of DlgS97, but not DlgA, in specific neurons of the fly's brain. Based on co-immunoprecipitation, DlgS97 forms a complex with N-methyl-D-aspartate (NMDA) receptors, a known target of ethanol. Consistent with these observations, flies expressing reduced levels of the essential NMDA receptor subunit dNR1 also showed reduced ethanol tolerance, as did mutants in the gene calcium/calmodulin-dependent protein kinase (caki), encoding the fly homolog of mammalian CASK, a known binding partner of DlgS97. Lastly, mice in which SAP97, the mammalian homolog of DlgS97, was conditionally deleted in adults failed to develop rapid tolerance to ethanol's sedative/hypnotic effects. We propose that DlgS97/SAP97 plays an important and conserved role in the development of tolerance to ethanol via NMDA receptor-mediated synaptic plasticity.

Drosophila melanogaster as a model to study drug addiction

Animal studies have been instrumental in providing knowledge about the molecular and neural mechanisms underlying drug addiction. Recently, the fruit fly Drosophilamelanogaster has become a valuable system to model not only the acute stimulating and sedating effects of drugs but also their more complex rewarding properties. In this review, we describe the advantages of using the fly to study drug-related behavior, provide a brief overview of the behavioral assays used, and review the molecular mechanisms and neural circuits underlying drug-induced behavior in flies. Many of these mechanisms have been validated in mammals, suggesting that the fly is a useful model to understand the mechanisms underlying addiction.

The arouser EPS8L3 gene is critical for normal memory in Drosophila

The genetic mechanisms that influence memory formation and sensitivity to the effects of ethanol on behavior in Drosophila have some common elements. So far, these have centered on the cAMP/PKA signaling pathway, synapsin and fas2-dependent processes, pumilio-dependent regulators of translation, and a few other genes. However, there are several genes that are important for one or the other behaviors, suggesting that there is an incomplete overlap in the mechanisms that support memory and ethanol sensitive behaviors. The basis for this overlap is far from understood. We therefore examined memory in arouser (aru) mutant flies, which have recently been identified as having ethanol sensitivity deficits. The aru mutant flies showed memory deficits in both short-term place memory and olfactory memory tests. Flies with a revertant aru allele had wild-type levels of memory performance, arguing that the aru gene, encoding an EPS8L3 product, has a role in Drosophila memory formation. Furthermore, and interestingly, flies with the aru^8–128 insertion allele had deficits in only one of two genetic backgrounds in place and olfactory memory tests. Flies with an aru imprecise excision allele had deficits in tests of olfactory memory. Quantitative measurements of aru EPS8L3 mRNA expression levels correlate decreased expression with deficits in olfactory memory while over expression is correlated with place memory deficits. Thus, mutations of the aru EPS8L3 gene interact with the alleles of a particular genetic background to regulate arouser expression and reveals a role of this gene in memory.

The genetic relationships between ethanol preference, acute ethanol sensitivity, and ethanol tolerance in Drosophila melanogaster

The relationship between alcohol consumption, sensitivity, and tolerance is an important question that has been addressed in humans and rodent models. Studies have shown that alcohol consumption and risk of abuse may correlate with (1) increased sensitivity to the stimulant effects of alcohol, (2) decreased sensitivity to the depressant effects of alcohol, and (3) increased alcohol tolerance. However, many conflicting results have been observed. To complement these studies, we utilized a different organism and approach to analyze the relationship between ethanol consumption and other ethanol responses. Using a set of 20 Drosophila melanogaster mutants that were isolated for altered ethanol sensitivity, we measured ethanol-induced hyperactivity, ethanol sedation, sedation tolerance, and ethanol consumption preference. Ethanol preference showed a strong positive correlation with ethanol tolerance, consistent with some rodent and human studies, but not with ethanol hyperactivity or sedation. No pairwise correlations were observed between ethanol hyperactivity, sedation, and tolerance. The evolutionary conservation of the relationship between tolerance and ethanol consumption in flies, rodents, and humans indicates that there are fundamental biological mechanisms linking specific ethanol responses.

The long-term memory trace formed in the Drosophila α/β mushroom body neurons is abolished in long-term memory mutants

A prior screen identified dozens of Drosophila melanogaster mutants that possess defective long-term memory (LTM). Using spaced olfactory conditioning, we trained 26 of these mutant lines to associate an odor cue with electric shock and then examined the memory of this conditioning 24 h later. All of the mutants tested revealed a deficit in LTM compared to the robust LTM observed in control flies. We used in vivo functional optical imaging to measure the magnitude of a previously characterized LTM trace, which is manifested as increased calcium influx into the axons of α/β mushroom body neurons in response to the conditioned odor. This memory trace was defective in all 26 of the LTM mutants. These observations elevate the significance of this LTM trace given that 26 independent mutants all exhibit a defect in the trace, and further suggest that the calcium trace is a fundamental mechanism underlying Drosophila LTM.

A Drosophila model for alcohol reward

The rewarding properties of drugs contribute to the development of abuse and addiction. We developed a new assay for investigating the motivational properties of ethanol in the genetically tractable model Drosophila melanogaster. Flies learned to associate cues with ethanol intoxication and, although transiently aversive, the experience led to a long-lasting attraction for the ethanol-paired cue, implying that intoxication is rewarding. Temporally blocking transmission in dopaminergic neurons revealed that flies require activation of these neurons to express, but not develop, conditioned preference for ethanol-associated cues. Moreover, flies acquired, consolidated and retrieved these rewarding memories using distinct sets of neurons in the mushroom body. Finally, mutations in scabrous, encoding a fibrinogen-related peptide that regulates Notch signaling, disrupted the formation of memories for ethanol reward. Our results thus establish that Drosophila can be useful for understanding the molecular, genetic and neural mechanisms underling the rewarding properties of ethanol.

The Heat Shock Protein 26 Gene is Required for Ethanol Tolerance in Drosophila

Stress plays an important role in drug- and addiction-related behaviours. However, the mechanisms underlying these behavioural responses are still poorly understood. In the light of recent reports that show consistent regulation of many genes encoding stress proteins including heat shock proteins following ethanol exposure in Drosophila, it was hypothesised that transition to alcohol dependence may involve the dysregulation of the circuits that mediate behavioural responses to stressors. Thus, behavioural genetic methodologies were used to investigate the role of the Drosophila hsp26 gene, a small heat shock protein coding gene which is induced in response to various stresses, in the development of rapid tolerance to ethanol sedation. Rapid tolerance was quantified as the percentage difference in the mean sedation times between the second and first ethanol exposure. Two independently isolated P-element mutations near the hsp26 gene eliminated the capacity for tolerance. In addition, RNAi-mediated functional knockdown of hsp26 expression in the glial cells and the whole nervous system also caused a defect in tolerance development. The rapid tolerance phenotype of the hsp26 mutants was rescued by the expression of the wild-type hsp26 gene in the nervous system. None of these manipulations of the hsp26 gene caused changes in the rate of ethanol absorption. Hsp26 genes are evolutionary conserved, thus the role of hsp26 in ethanol tolerance may present a new direction for research into alcohol dependency.

Tolerance to anesthesia depends on synaptic proteins

The hypnotic effects of anesthetics are caused by their interactions with neuronal components vital for proper signaling. An understanding of the adaptive mechanisms that lead to the development of anesthetic tolerance can offer insight into the regulation of neuroexcitability and plasticity that alter behavioral output. Here we use genetic and pharmacological manipulation of Drosophila to investigate the mechanisms of tolerance to benzyl alcohol. The mutants tested were temperature-sensitive paralytics that interfere with neuronal signaling: two mutations in dynamin that affect vesicle recycling, shi (ts1) and shi (ts2), and one that affects the voltage-activated Na(+) channel, para (ts1). We also used N-ethylmaleimide (NEM) to pharmacologically interfere with synaptic function. We found that blocking the generation of action potentials using a temperature-sensitive paralytic mutation does not induce nor prevent the development of functional tolerance to benzyl alcohol, but that disruption of synaptic signaling using mutations in the dynamin gene or by NEM treatment inhibits the induction of tolerance.

A Drosophila model for fetal alcohol syndrome disorders: role for the insulin pathway

Prenatal exposure to ethanol in humans results in a wide range of developmental abnormalities, including growth deficiency, developmental delay, reduced brain size, permanent neurobehavioral abnormalities and fetal death. Here we describe the use of Drosophila melanogaster as a model for exploring the effects of ethanol exposure on development and behavior. We show that developmental ethanol exposure causes reduced viability, developmental delay and reduced adult body size. We find that flies reared on ethanol-containing food have smaller brains and imaginal discs, which is due to reduced cell division rather than increased apoptosis. Additionally, we show that, as in mammals, flies reared on ethanol have altered responses to ethanol vapor exposure as adults, including increased locomotor activation, resistance to the sedating effects of the drug and reduced tolerance development upon repeated ethanol exposure. We have found that the developmental and behavioral defects are largely due to the effects of ethanol on insulin signaling; specifically, a reduction in Drosophila insulin-like peptide (Dilp) and insulin receptor expression. Transgenic expression of Dilp proteins in the larval brain suppressed both the developmental and behavioral abnormalities displayed by ethanol-reared adult flies. Our results thus establish Drosophila as a useful model system to uncover the complex etiology of fetal alcohol syndrome.

Genetic approaches to alcohol addiction: gene expression studies and recent candidates from Drosophila

Ethanol intake causes gene expression changes resulting in cellular and molecular adaptations that could be associated with a predisposition to alcohol dependence. Recently, several research groups have used high-throughput gene expression profiling to search for alcohol-responsive genes in Drosophila melanogaster. Comparison of data from these studies highlights the functional similarities in their results despite differences in their experimental approach and selection cases. Notably, alcohol-responsive gene sets associated with stress response, olfaction, metabolism, proteases, transcriptional regulation, regulation of signal transduction, nucleic acid binding and cytoskeletal organisation were markedly common to these studies. These data support the view that changes in gene expression in alcoholics are associated with widespread cellular functions.

Short-term memories in Drosophila are governed by general and specific genetic systems

In a dynamic environment, there is an adaptive value in the ability of animals to acquire and express memories. That both simple and complex animals can learn is therefore not surprising. How animals have solved this problem genetically and anatomically probably lies somewhere in a range between a single molecular/anatomical mechanism that applies to all situations and a specialized mechanism for each learning situation. With an intermediate level of nervous system complexity, the fruit fly Drosophila has both general and specific resources to support different short-term memories. Some biochemical/cellular mechanisms are common between learning situations, indicating that flies do not have a dedicated system for each learning context. The opposite possible extreme does not apply to Drosophila either. Specialization in some biochemical and anatomical terms suggests that there is not a single learning mechanism that applies to all conditions. The distributed basis of learning in Drosophila implies that these systems were independently selected.

Individual carboxypeptidase D domains have both redundant and unique functions in Drosophila development and behavior

Metallocarboxypeptidase D (CPD) functions in protein and peptide processing. The Drosophila CPD svr gene undergoes alternative splicing, producing forms containing 1-3 active or inactive CP domains. To investigate the function of the various CP domains, we created transgenic flies expressing specific forms of CPD in the embryonic-lethal svr (PG33) mutant. All constructs containing an active CP domain rescued the lethality with varying degrees, and full viability required inactive CP domain-3. Transgenic flies overexpressing active CP domain-1 or -2 were similar to each other and to the viable svr mutants, with pointed wing shape, enhanced ethanol sensitivity, and decreased cold sensitivity. The transgenes fully compensated for a long-term memory deficit observed in the viable svr mutants. Overexpression of CP domain-1 or -2 reduced the levels of Lys/Arg-extended adipokinetic hormone intermediates. These findings suggest that CPD domains-1 and -2 have largely redundant functions in the processing of growth factors, hormones, and neuropeptides.

The genetics of behavioral alcohol responses in Drosophila

Drosophila melanogaster is commonly found near rotting or fermenting fruit, reflected in its name pomace, or vinegar fly. In such environments, flies often encounter significant levels of ethanol. Three observations have made Drosophila a very promising model organism to understand the genetic contributions to the behavioral responses to alcohol. First, similar to higher vertebrates, flies show hyperactivation upon exposure to a low to medium dose of alcohol, while high doses can lead to sedation. In addition, when given a choice, flies will actually prefer alcohol-containing food over regular food. Second, the genes and biochemical pathways implicated in controlling these behavioral responses in flies are also participating in determining alcohol responses, and drinking behavior in mammals. Third, the fact that flies have been studied genetically for over one hundred years means that an exceptional repertoire of genetic tools are at our disposal. Here, we will review some of these tools and experimental approaches, survey the methods for, and measures after Drosophila ethanol exposure, and discuss the different molecular components and functional pathways involved in these behavioral responses to alcohol.