Conditioned responses in courtship behavior of normal and mutant Drosophila

Sleep induced by mechanosensory stimulation provides cognitive and health benefits in Drosophila

Study Objectives

Sleep is a complex phenomenon regulated by various factors, including sensory input. Anecdotal observations have suggested that gentle rocking helps babies fall asleep, and experimental studies have verified that rocking promotes sleep in both humans and mice. Recent studies have expanded this understanding, demonstrating that gentle vibration also induces sleep in Drosophila. Natural sleep serves multiple functions, including learning and memory, synaptic downscaling, and clearance of harmful substances associated with neurodegenerative diseases. Here, we investigated whether vibration-induced sleep provides similar cognitive and health benefits in Drosophila.

Methods

We administered gentle vibration to flies that slept very little due to a forced activation of wake-promoting neurons and investigated how the vibration influenced learning and memory in the courtship conditioning paradigm. Additionally, we examined the effects of VIS on synaptic downscaling by counting synapse numbers of select neurons. Finally, we determined whether vibration could induce sleep in Drosophila models of Alzheimer's disease (AD) and promote the clearance of Amyloid b (Ab) and Tubulin Associated Unit (TAU).

Results

Vibration-induced sleep enhanced performance in a courtship conditioning paradigm and reduced the number of synapses in select neurons. Moreover, vibration improved sleep in Drosophila models of AD, promoting the clearance of Ab and TAU.

Conclusions

Mechanosensory stimulation offers a promising non-invasive avenue for enhancing sleep, potentially providing associated cognitive and health benefits.

Fruit ripening retardant Daminozide induces cognitive impairment, cell specific neurotoxicity, and genotoxicity in Drosophila melanogaster

BACKGROUND

We explored neurotoxic and genotoxic effects of Daminozide, a fruit ripening retardant, on the brain of Drosophila melanogaster, based on our previous finding of DNA fragmentation in larval brain cell in the flies experimentally exposed to this chemicals.

METHODS

Adult flies were subjected to two distinct concentrations of daminozide (200 mg/L and 400 mg/L) mixed in culture medium, followed by an examination of specific behaviors such as courtship conditioning and aversive phototaxis, which serve as indicators of cognitive functions. We investigated brain histology and histochemistry to assess the overall toxicity of daminozide, focusing on neuron type-specific effects. Additionally, we conducted studies on gene expression specific to neuronal function. Statistical comparisons were then made between the exposed and control flies across all tested attributes.

RESULTS

The outcome of behavioral assays suggested deleterious effects of Daminozide on learning, short term and long term memory function. Histological examination of brain sections revealed cellular degeneration, within Kenyon cell neuropiles in Daminozide-exposed flies. Neurone specific Immuno-histochemistry study revealed significant reduction of dopaminergic and glutaminergic neurones with discernible reduction in cellular counts, alteration in cell and nuclear morphology among daminozide exposed flies. Gene expression analyses demonstrated upregulation of rutabaga (rut), hb9 and down regulation of PKa- C1, CrebB, Ace and nAchRbeta-1 in exposed flies which suggest dysregulation of gene functions involved in motor neuron activity, learning, and memory.

CONCLUSION

Taken together, our findings suggests that Daminozide induces multifaceted harmful impacts on the neural terrain of Drosophila melanogaster, posing a threat to its cognitive abilities.

Diverse memory paradigms in Drosophila reveal diverse neural mechanisms

In this review, we aggregated the different types of learning and memory paradigms developed in adult Drosophila and attempted to assess the similarities and differences in the neural mechanisms supporting diverse types of memory. The simplest association memory assays are conditioning paradigms (olfactory, visual, and gustatory). A great deal of work has been done on these memories, revealing hundreds of genes and neural circuits supporting this memory. Variations of conditioning assays (reversal learning, trace conditioning, latent inhibition, and extinction) also reveal interesting memory mechanisms, whereas mechanisms supporting spatial memory (thermal maze, orientation memory, and heat box) and the conditioned suppression of innate behaviors (phototaxis, negative geotaxis, anemotaxis, and locomotion) remain largely unexplored. In recent years, there has been an increased interest in multisensory and multicomponent memories (context-dependent and cross-modal memory) and higher-order memory (sensory preconditioning and second-order conditioning). Some of this work has revealed how the intricate mushroom body (MB) neural circuitry can support more complex memories. Finally, the most complex memories are arguably those involving social memory: courtship conditioning and social learning (mate-copying and egg-laying behaviors). Currently, very little is known about the mechanisms supporting social memories. Overall, the MBs are important for association memories of multiple sensory modalities and multisensory integration, whereas the central complex is important for place, orientation, and navigation memories. Interestingly, several different types of memory appear to use similar or variants of the olfactory conditioning neural circuitry, which are repurposed in different ways.

Sexual conflict and social networks in bed bugs: effects of social experience

Living in groups can provide essential experience that improves sexual performance and reproductive success. While the effects of social experience have drawn considerable scientific interest, commonly used behavioral assays often do not capture the dynamic nature of interactions within a social group. Here, we conducted 3 experiments using a social network framework to test whether social experience during early adulthood improves the sexual competence of bed bugs (Cimex lectularius) when placed in a complex and competitive group environment. In each experiment, we observed replicate groups of bed bugs comprising previously socialized and previously isolated individuals of the same sex, along with an equal number of standardized individuals of the opposite sex. Regardless of whether we controlled for their insemination history, previously isolated males mounted and inseminated females at significantly higher rates than previously socialized males. However, we found no evidence of social experience influencing our other measures of sexual competence: proportion of mounts directed at females, ability to overcome female resistance, and strength of opposite-sex social associations. We similarly did not detect effects of social experience on our female sexual competence metrics: propensity to avoid mounts, rate of successfully avoiding mounts, opposite-sex social association strength, and rate of receiving inseminations. Our findings indicate that early social experience does not improve sexual competence in male and female bed bugs.

Roles of feedback and feed-forward networks of dopamine subsystems: insights from Drosophila studies

Across animal species, dopamine-operated memory systems comprise anatomically segregated, functionally diverse subsystems. Although individual subsystems could operate independently to support distinct types of memory, the logical interplay between subsystems is expected to enable more complex memory processing by allowing existing memory to influence future learning. Recent comprehensive ultrastructural analysis of the Drosophila mushroom body revealed intricate networks interconnecting the dopamine subsystems-the mushroom body compartments. Here, we review the functions of some of these connections that are beginning to be understood. Memory consolidation is mediated by two different forms of network: A recurrent feedback loop within a compartment maintains sustained dopamine activity required for consolidation, whereas feed-forward connections across compartments allow short-term memory formation in one compartment to open the gate for long-term memory formation in another compartment. Extinction and reversal of aversive memory rely on a similar feed-forward circuit motif that signals omission of punishment as a reward, which triggers plasticity that counteracts the original aversive memory trace. Finally, indirect feed-forward connections from a long-term memory compartment to short-term memory compartments mediate higher-order conditioning. Collectively, these emerging studies indicate that feedback control and hierarchical connectivity allow the dopamine subsystems to work cooperatively to support diverse and complex forms of learning.

The Neurotranscriptome of Monochamus alternatus

The Japanese pine sawyer Monochamus alternatus serves as the primary vector for pine wilt disease, a devastating pine disease that poses a significant threat to the sustainable development of forestry in the Eurasian region. Currently, trap devices based on informational compounds have played a crucial role in monitoring and controlling the M. alternatus population. However, the specific proteins within M. alternatus involved in recognizing the aforementioned informational compounds remain largely unclear. To elucidate the spatiotemporal distribution of M. alternatus chemosensory-related genes, this study conducted neural transcriptome analyses to investigate gene expression patterns in different body parts during the feeding and mating stages of both male and female beetles. The results revealed that 15 genes in the gustatory receptor (GR) gene family exhibited high expression in the mouthparts, most genes in the odorant binding protein (OBP) gene family exhibited high expression across all body parts, 22 genes in the odorant receptor (OR) gene family exhibited high expression in the antennae, a significant number of genes in the chemosensory protein (CSP) and sensory neuron membrane protein (SNMP) gene families exhibited high expression in both the mouthparts and antennae, and 30 genes in the ionotropic receptors (IR) gene family were expressed in the antennae. Through co-expression analyses, it was observed that 34 genes in the IR gene family were co-expressed across the four developmental stages. The Antenna IR subfamily and IR8a/Ir25a subfamily exhibited relatively high expression levels in the antennae, while the Kainate subfamily, NMDA subfamily, and Divergent subfamily exhibited predominantly high expression in the facial region. MalIR33 is expressed only during the feeding stage of M. alternatus, the MalIR37 gene exhibits specific expression in male beetles, the MalIR34 gene exhibits specific expression during the feeding stage in male beetles, the MalIR8 and MalIR39 genes exhibit specific expression during the feeding stage in female beetles, and MalIR8 is expressed only during two developmental stages in male beetles and during the mating stage in female beetles. The IR gene family exhibits gene-specific expression in different spatiotemporal contexts, laying the foundation for the subsequent selection of functional genes and facilitating the full utilization of host plant volatiles and insect sex pheromones, thereby enabling the development of more efficient attractants.

Biological aging of two innate behaviors of Drosophila melanogaster: Escape climbing versus courtship learning and memory

Motor and cognitive aging can severely affect life quality of elderly people and burden health care systems. In search for diagnostic behavioral biomarkers, it has been suggested that walking speed can predict forms of cognitive decline, but in humans, it remains challenging to separate the effects of biological aging and lifestyle. We examined a possible association of motor and cognitive decline in Drosophila, a genetic model organism of healthy aging. Long term courtship memory is present in young male flies but absent already during mid life (4-8 weeks). By contrast, courtship learning index and short term memory (STM) are surprisingly robust and remain stable through mid (4-8 weeks) and healthy late life (>8 weeks), until courtship performance collapses suddenly at ~4.5 days prior to death. By contrast, climbing speed declines gradually during late life (>8 weeks). The collapse of courtship performance and short term memory close to the end of life occur later and progress with a different time course than the gradual late life decline in climbing speed. Thus, during healthy aging in male Drosophila, climbing and courtship motor behaviors decline differentially. Moreover, cognitive and motor performances decline at different time courses. Differential behavioral decline during aging may indicate different underlying causes, or alternatively, a common cause but different thresholds for defects in different behaviors.

Overexpression of the limk1 Gene in Drosophila melanogaster Can Lead to Suppression of Courtship Memory in Males

Courtship suppression is a behavioral adaptation of the fruit fly. When majority of the females in a fly population are fertilized and non-receptive for mating, a male, after a series of failed attempts, decreases its courtship activity towards all females, saving its energy and reproductive resources. The time of courtship decrease depends on both duration of unsuccessful courtship and genetically determined features of the male nervous system. Thereby, courtship suppression paradigm can be used for studying molecular mechanisms of learning and memory. p-Cofilin, a component of the actin remodeling signaling cascade and product of LIM-kinase 1 (LIMK1), regulates Drosophila melanogaster forgetting in olfactory learning paradigm. Previously, we have shown that limk1 suppression in the specific types of nervous cells differently affects fly courtship memory. Here, we used Gal4 > UAS system to induce limk1 overexpression in the same types of neurons. limk1 activation in the mushroom body, glia, and fruitless neurons decreased learning index compared to the control strain or the strain with limk1 knockdown. In cholinergic and dopaminergic/serotoninergic neurons, both overexpression and knockdown of limk1 impaired Drosophila short-term memory. Thus, proper balance of the limk1 activity is crucial for normal cognitive activity of the fruit fly.

Nested neural circuits generate distinct acoustic signals during Drosophila courtship

Many motor control systems generate multiple movements using a common set of muscles. How are premotor circuits able to flexibly generate diverse movement patterns? Here, we characterize the neuronal circuits that drive the distinct courtship songs of Drosophila melanogaster. Male flies vibrate their wings toward females to produce two different song modes-pulse and sine song-which signal species identity and male quality. Using cell-type-specific genetic reagents and the connectome, we provide a cellular and synaptic map of the circuits in the male ventral nerve cord that generate these songs and examine how activating or inhibiting each cell type within these circuits affects the song. Our data reveal that the song circuit is organized into two nested feedforward pathways with extensive reciprocal and feedback connections. The larger network produces pulse song, the more complex and ancestral song form. A subset of this network produces sine song, the simpler and more recent form. Such nested organization may be a common feature of motor control circuits in which evolution has layered increasing flexibility onto a basic movement pattern.

Regulation of long-term memory by a few clock neurons in Drosophila

Identification of the neural circuits in the brain regulating animal behavior and physiology is critical for understanding brain functions and is one of the most challenging goals in neuroscience research. The fruitfly Drosophila melanogaster has often been used to identify the neural circuits involved in the regulation of specific behaviors because of the many neurogenetic tools available to express target genes in particular neurons. Neurons controlling sexual behavior, feeding behavior, and circadian rhythms have been identified, and the number of neurons responsible for controlling these phenomena is small. The search for a few neurons controlling a specific behavior is an important first step to clarify the overall picture of the neural circuits regulating that behavior. We previously found that the clock gene period (per), which is essential for circadian rhythms in Drosophila, is also essential for long-term memory (LTM). We have also found that a very limited number of per-expressing clock neurons in the adult brain are required for the consolidation and maintenance of LTM. In this review, we focus on LTM in Drosophila, introduce the concept of LTM regulation by a few clock neurons that we have recently discovered, and discuss how a few clock neurons regulate Drosophila LTM.

Failure to mate enhances investment in behaviors that may promote mating reward and impairs the ability to cope with stressors via a subpopulation of Neuropeptide F receptor neurons

Living in dynamic environments such as the social domain, where interaction with others determines the reproductive success of individuals, requires the ability to recognize opportunities to obtain natural rewards and cope with challenges that are associated with achieving them. As such, actions that promote survival and reproduction are reinforced by the brain reward system, whereas coping with the challenges associated with obtaining these rewards is mediated by stress-response pathways, the activation of which can impair health and shorten lifespan. While much research has been devoted to understanding mechanisms underlying the way by which natural rewards are processed by the reward system, less attention has been given to the consequences of failure to obtain a desirable reward. As a model system to study the impact of failure to obtain a natural reward, we used the well-established courtship suppression paradigm in Drosophila melanogaster as means to induce repeated failures to obtain sexual reward in male flies. We discovered that beyond the known reduction in courtship actions caused by interaction with non-receptive females, repeated failures to mate induce a stress response characterized by persistent motivation to obtain the sexual reward, reduced male-male social interaction, and enhanced aggression. This frustrative-like state caused by the conflict between high motivation to obtain sexual reward and the inability to fulfill their mating drive impairs the capacity of rejected males to tolerate stressors such as starvation and oxidative stress. We further show that sensitivity to starvation and enhanced social arousal is mediated by the disinhibition of a small population of neurons that express receptors for the fly homologue of neuropeptide Y. Our findings demonstrate for the first time the existence of social stress in flies and offers a framework to study mechanisms underlying the crosstalk between reward, stress, and reproduction in a simple nervous system that is highly amenable to genetic manipulation.

Molecular and cellular origins of behavioral sex differences: a tiny little fly tells a lot

Behavioral sex differences primarily derive from the sexually dimorphic organization of neural circuits that direct the behavior. In Drosophila melanogaster, the sex-determination genes fruitless (fru) and doublesex (dsx) play pivotal roles in producing the sexual dimorphism of neural circuits for behavior. Here we examine three neural groups expressing fru and/or dsx, i.e., the P1 cluster, aSP-f and aSP-g cluster pairs and aDN cluster, in which causal relationships between the dimorphic behavior and dimorphic neural characteristics are best illustrated. aSP-f, aSP-g and aDN clusters represent examples where fru or dsx switches cell-autonomously their neurite structures between the female-type and male-type. Processed sensory inputs impinging on these neurons may result in outputs that encode different valences, which culminate in the execution of distinct behavior according to the sex. In contrast, the P1 cluster is male-specific as its female counterpart undergoes dsx-driven cell death, which lowers the threshold for the induction of male-specific behaviors. We propose that the products of fru and dsx genes, as terminal selectors in sexually dimorphic neuronal wiring, induce and maintain the sex-typical chromatin state at postembryonic stages, orchestrating the transcription of effector genes that shape single neuron structures and govern cell survival and death.

Courtship suppression in Drosophila melanogaster: The role of mating failure

Drosophila melanogaster is a popular model organism in the study of memory due to a wide arsenal of methods used to analyze neuronal activity. The most commonly used tests in research of behavioral plasticity are shock avoidance associated with chemosensory cues and courtship suppression after mating failure. Many authors emphasize the value of courtship suppression as a model of behavior most appropriate to natural conditions. However, researchers often investigate courtship suppression using immobilized and decapitated females as targets of courtship by males, which makes the data obtained from such flies less valuable. In our study, we evaluate courtship suppression towards immature mobile non-receptive females after training with mated or immature females combined with an aversive stimulus (quinine). We have shown that the previously described mechanisms of courtship suppression, as a result of the association of the courtship object with the repellent, as well as due to increased sensitivity to the anti-aphrodisiac cVA after mating failure, are not confirmed when immature mobile females are used. We discuss the reasons for the discrepancies between our results and literature data, define the conditions to be met in the courtship suppression test if the aim is to analyze the natural forms of behavioral plasticity, and present data on the test modifications to approximate conditions to natural ones.

The clinical and molecular spectrum of the KDM6B-related neurodevelopmental disorder

De novo variants are a leading cause of neurodevelopmental disorders (NDDs), but because every monogenic NDD is different and usually extremely rare, it remains a major challenge to understand the complete phenotype and genotype spectrum of any morbid gene. According to OMIM, heterozygous variants in KDM6B cause "neurodevelopmental disorder with coarse facies and mild distal skeletal abnormalities." Here, by examining the molecular and clinical spectrum of 85 reported individuals with mostly de novo (likely) pathogenic KDM6B variants, we demonstrate that this description is inaccurate and potentially misleading. Cognitive deficits are seen consistently in all individuals, but the overall phenotype is highly variable. Notably, coarse facies and distal skeletal anomalies, as defined by OMIM, are rare in this expanded cohort while other features are unexpectedly common (e.g., hypotonia, psychosis, etc.). Using 3D protein structure analysis and an innovative dual Drosophila gain-of-function assay, we demonstrated a disruptive effect of 11 missense/in-frame indels located in or near the enzymatic JmJC or Zn-containing domain of KDM6B. Consistent with the role of KDM6B in human cognition, we demonstrated a role for the Drosophila KDM6B ortholog in memory and behavior. Taken together, we accurately define the broad clinical spectrum of the KDM6B-related NDD, introduce an innovative functional testing paradigm for the assessment of KDM6B variants, and demonstrate a conserved role for KDM6B in cognition and behavior. Our study demonstrates the critical importance of international collaboration, sharing of clinical data, and rigorous functional analysis of genetic variants to ensure correct disease diagnosis for rare disorders.

LIM-kinase 1 effects on memory abilities and male courtship song in Drosophila depend on the neuronal type

The signal pathway of actin remodeling, including LIM-kinase 1 (LIMK1) and its substrate cofilin, regulates multiple processes in neurons of vertebrates and invertebrates. Drosophila melanogaster is widely used as a model object for studying mechanisms of memory formation, storage, retrieval and forgetting. Previously, active forgetting in Drosophila was investigated in the standard Pavlovian olfactory conditioning paradigm. The role of specific dopaminergic neurons (DAN) and components of the actin remodeling pathway in different forms of forgetting was shown. In our research, we investigated the role of LIMK1 in Drosophila memory and forgetting in the conditioned courtship suppression paradigm (CCSP). In the Drosophila brain, LIMK1 and p-cofilin levels appeared to be low in specific neuropil structures, including the mushroom body (MB) lobes and the central complex. At the same time, LIMK1 was observed in cell bodies, such as DAN clusters regulating memory formation in CCSP. We applied GAL4 × UAS binary system to induce limk1 RNA interference in different types of neurons. The hybrid strain with limk1 interference in MB lobes and glia showed an increase in 3-h short-term memory (STM), without significant effects on long-term memory. limk1 interference in cholinergic neurons (CHN) impaired STM, while its interference in DAN and serotoninergic neurons (SRN) also dramatically impaired the flies' learning ability. By contrast, limk1 interference in fruitless neurons (FRN) resulted in increased 15-60 min STM, indicating a possible LIMK1 role in active forgetting. Males with limk1 interference in CHN and FRN also showed the opposite trends of courtship song parameters changes. Thus, LIMK1 effects on the Drosophila male memory and courtship song appeared to depend on the neuronal type or brain structure.

Depletion of ESCRT ameliorates APP-induced AD-like symptoms in Drosophila

The amyloid-β (Aβ) peptide, produced from amyloid precursor protein (APP) by β and γ-secretases, has been implicated in the etiology of Alzheimer's disease (AD). However, the precise intracellular trafficking pathway of APP and its subcellular locations to produce Aβ have remained unclear. To address these issues, we established fly AD models that recapitulated multiple AD-like symptoms by expressing human APP in the Drosophila nerve system. The ESCRT (endosomal sorting complexes required for transport) machinery regulates the sorting and trafficking of endocytosed proteins, yet its role in AD pathogenesis has not been explored in vivo. We found that knockdown of distinct ESCRT components ameliorated APP-induced morphological and behavioral defects, including impaired wing expansion, eye degeneration, dopamine neuron loss, locomotor disability, lifespan shortening, and cognitive deficits. Mechanistically, we showed that impaired ESCRT impeded APP's intracellular transportation from early endosomes to late endosomes, resulting in reduced Aβ production and amyloid deposit load. These data suggest that APP undergoes ESCRT-mediated endocytic trafficking, and Aβ is generated mainly in late endosomes. Our data provide the first in vivo evidence to support a physiological role of ESCRT in AD pathogenesis, suggesting that interfering with ESCRT machinery might be an alternative therapeutic strategy for AD.

Neural circuit mechanisms linking courtship and reward in Drosophila males

Courtship has evolved to achieve reproductive success in animal species. However, whether courtship itself has a positive value remains unclear. In the present work, we report that courtship is innately rewarding and can induce the expression of appetitive short-term memory (STM) and long-term memory (LTM) in Drosophila melanogaster males. Activation of male-specific P1 neurons is sufficient to mimic courtship-induced preference and memory performance. Surprisingly, P1 neurons functionally connect to a large proportion of dopaminergic neurons (DANs) in the protocerebral anterior medial (PAM) cluster. The acquisition of STM and LTM depends on two distinct subsets of PAM DANs that convey the courtship-reward signal to the restricted regions of the mushroom body (MB) γ and α/β lobes through two dopamine receptors, D1-like Dop1R1 and D2-like Dop2R. Furthermore, the retrieval of STM stored in the MB α'/β' lobes and LTM stored in the MB α/β lobe relies on two distinct MB output neurons. Finally, LTM consolidation requires two subsets of PAM DANs projecting to the MB α/β lobe and corresponding MB output neurons. Taken together, our findings demonstrate that courtship is a potent rewarding stimulus and reveal the underlying neural circuit mechanisms linking courtship and reward in Drosophila males.

C. elegans males optimize mate-choice decisions via sex-specific responses to multimodal sensory cues

For sexually reproducing animals, selecting optimal mates is essential for maximizing reproductive fitness. Because the nematode C. elegans reproduces mostly by self-fertilization, little is known about its mate-choice behaviors. While several sensory cues have been implicated in males' ability to recognize hermaphrodites, achieving an integrated understanding of the ways males use these cues to assess relevant characteristics of potential mates has proven challenging. Here, we use a choice-based social-interaction assay to explore the ability of C. elegans males to make and optimize mate choices. We find that males use a combination of volatile sex pheromones (VSPs), ascaroside pheromones, surface-bound chemical cues, and other signals to robustly assess a variety of features of potential mates. Specific aspects of mate choice are communicated by distinct signals: the presence of a sperm-depleted, receptive hermaphrodite is likely signaled by VSPs, while developmental stage and sex are redundantly specified by ascaroside pheromones and surface-associated cues. Ascarosides also signal nutritional information, allowing males to choose well-fed over starved mates, while both ascarosides and surface-associated cues cause males to prefer virgin over previously mated hermaphrodites. The male-specificity of these behavioral responses is determined by both male-specific neurons and the male state of sex-shared circuits, and we reveal an unexpected role for the sex-shared ASH sensory neurons in male attraction to endogenously produced hermaphrodite ascarosides. Together, our findings lead to an integrated view of the signaling and behavioral mechanisms by which males use diverse sensory cues to assess multiple features of potential mates and optimize mate choice.

A simplified courtship conditioning protocol to test learning and memory in Drosophila

In Drosophila, a male that has previously been sexually rejected reduces its courtship behavior when confronted again with an unreceptive female. This reduced courting time reflects a memory formation process. Here, we describe a simplified protocol to perform the courtship conditioning assay for assessing the reduced courting time, using regular lab equipment and handmade tools. Every step of the procedure, from raising flies and training to testing and quantification of this memory-related behavior, can be implemented in any practice laboratory.

Aging and memory are altered by genetically manipulating lactate dehydrogenase in the neurons or glia of flies

The astrocyte-neuron lactate shuttle hypothesis posits that glial-generated lactate is transported to neurons to fuel metabolic processes required for long-term memory. Although studies in vertebrates have revealed that lactate shuttling is important for cognitive function, it is uncertain if this form of metabolic coupling is conserved in invertebrates or is influenced by age. Lactate dehydrogenase (Ldh) is a rate limiting enzyme that interconverts lactate and pyruvate. Here we genetically manipulated expression of Drosophila melanogaster lactate dehydrogenase (dLdh) in neurons or glia to assess the impact of altered lactate metabolism on invertebrate aging and long-term courtship memory at different ages. We also assessed survival, negative geotaxis, brain neutral lipids (the core component of lipid droplets) and brain metabolites. Both upregulation and downregulation of dLdh in neurons resulted in decreased survival and memory impairment with age. Glial downregulation of dLdh expression caused age-related memory impairment without altering survival, while upregulated glial dLdh expression lowered survival without disrupting memory. Both neuronal and glial dLdh upregulation increased neutral lipid accumulation. We provide evidence that altered lactate metabolism with age affects the tricarboxylic acid (TCA) cycle, 2-hydroxyglutarate (2HG), and neutral lipid accumulation. Collectively, our findings indicate that the direct alteration of lactate metabolism in either glia or neurons affects memory and survival but only in an age-dependent manner.

Many faces of sleep regulation: beyond the time of day and prior wake time

The two-process model of sleep regulation posits two main processes regulating sleep: the circadian process controlled by the circadian clock and the homeostatic process that depends on the history of sleep and wakefulness. The model has provided a dominant conceptual framework for sleep research since its publication ~ 40 years ago. The time of day and prior wake time are the primary factors affecting the circadian and homeostatic processes, respectively. However, it is critical to consider other factors influencing sleep. Since sleep is incompatible with other behaviors, it is affected by the need for essential behaviors such as eating, foraging, mating, caring for offspring, and avoiding predators. Sleep is also affected by sensory inputs, sickness, increased need for memory consolidation after learning, and other factors. Here, we review multiple factors influencing sleep and discuss recent insights into the mechanisms balancing competing needs.

Sleep benefits different stages of memory in Drosophila

Understanding the physiological mechanisms that modulate memory acquisition and consolidation remains among the most ambitious questions in neuroscience. Massive efforts have been dedicated to deciphering how experience affects behavior, and how different physiological and sensory phenomena modulate memory. Our ability to encode, consolidate and retrieve memories depends on internal drives, and sleep stands out among the physiological processes that affect memory: one of the most relatable benefits of sleep is the aiding of memory that occurs in order to both prepare the brain to learn new information, and after a learning task, to consolidate those new memories. Drosophila lends itself to the study of the interactions between memory and sleep. The fruit fly provides incomparable genetic resources, a mapped connectome, and an existing framework of knowledge on the molecular, cellular, and circuit mechanisms of memory and sleep, making the fruit fly a remarkable model to decipher the sophisticated regulation of learning and memory by the quantity and quality of sleep. Research in Drosophila has stablished not only that sleep facilitates learning in wild-type and memory-impaired animals, but that sleep deprivation interferes with the acquisition of new memories. In addition, it is well-accepted that sleep is paramount in memory consolidation processes. Finally, studies in Drosophila have shown that that learning itself can promote sleep drive. Nevertheless, the molecular and network mechanisms underlying this intertwined relationship are still evasive. Recent remarkable work has shed light on the neural substrates that mediate sleep-dependent memory consolidation. In a similar way, the mechanistic insights of the neural switch control between sleep-dependent and sleep-independent consolidation strategies were recently described. This review will discuss the regulation of memory by sleep in Drosophila, focusing on the most recent advances in the field and pointing out questions awaiting to be investigated.

Circadian disruption of memory consolidation in Drosophila

The role of the circadian system in memory formation is an important question in neurobiology. Despite this hypothesis being intuitively appealing, the existing data is confusing. Recent work in Drosophila has helped to clarify certain aspects of the problem, but the emerging sense is that the likely mechanisms are more complex than originally conceptualized. In this report, we identify a post-training window of time (during consolidation) when the circadian clock and its components are involved in memory formation. In the broader context, our data suggest that circadian biology might have multiple roles during memory formation. Testing for its roles at multiple timepoints, and in different cells, will be necessary to resolve some of the conflicting data.

Flexibility of neural circuits regulating mating behaviors in mice and flies

Mating is essential for the reproduction of animal species. As mating behaviors are high-risk and energy-consuming processes, it is critical for animals to make adaptive mating decisions. This includes not only finding a suitable mate, but also adapting mating behaviors to the animal's needs and environmental conditions. Internal needs include physical states (e.g., hunger) and emotional states (e.g., fear), while external conditions include both social cues (e.g., the existence of predators or rivals) and non-social factors (e.g., food availability). With recent advances in behavioral neuroscience, we are now beginning to understand the neural basis of mating behaviors, particularly in genetic model organisms such as mice and flies. However, how internal and external factors are integrated by the nervous system to enable adaptive mating-related decision-making in a state- and context-dependent manner is less well understood. In this article, we review recent knowledge regarding the neural basis of flexible mating behaviors from studies of flies and mice. By contrasting the knowledge derived from these two evolutionarily distant model organisms, we discuss potential conserved and divergent neural mechanisms involved in the control of flexible mating behaviors in invertebrate and vertebrate brains.

cd1 Mutation in Drosophila Affects Phenoxazinone Synthase Catalytic Site and Impairs Long-Term Memory

Being involved in development of Huntington's, Parkinson's and Alzheimer's diseases, kynurenine pathway (KP) of tryptophan metabolism plays a significant role in modulation of neuropathology. Accumulation of a prooxidant 3-hydroxykynurenine (3-HOK) leads to oxidative stress and neuronal cell apoptosis. Drosophila mutant cardinal (cd¹) with 3-HOK excess shows age-dependent neurodegeneration and short-term memory impairments, thereby presenting a model for senile dementia. Although cd gene for phenoxazinone synthase (PHS) catalyzing 3-HOK dimerization has been presumed to harbor the cd¹ mutation, its molecular nature remained obscure. Using next generation sequencing, we have shown that the cd gene in cd¹ carries a long deletion leading to PHS active site destruction. Contrary to the wild type Canton-S (CS), cd¹ males showed defective long-term memory (LTM) in conditioned courtship suppression paradigm (CCSP) at days 5-29 after eclosion. The number of dopaminergic neurons (DAN) regulating fly locomotor activity showed an age-dependent tendency to decrease in cd¹ relative to CS. Thus, in accordance with the concept "from the gene to behavior" proclaimed by S. Benzer, we have shown that the aberrant PHS sequence in cd¹ provokes drastic LTM impairments and DAN alterations.

Evaluating Learning and Memory in Drosophila melanogaster to Study the Neurodevelopmental Impacts of Toxicants

Neurodevelopmental disorders are a heterogeneous group of behaviorally defined disorders with both genetic and environmental risk factors. Given that many neurodevelopmental disorders are characterized by impaired learning and/or intellectual abilities, behavioral paradigms that assess cognition in animal models have been effective tools in delineating underlying genetic variants that impact disease pathophysiology. For example, learning and memory paradigms in the common fruit fly Drosophila melanogaster have been successfully used to study risk genes and biological pathways associated with several neurodevelopmental disorders, including fragile X syndrome, autism spectrum disorder, and CHARGE syndrome. While these established Drosophila behavioral paradigms have historically been used to investigate genetic risk factors, they also have many other applications, including use in developmental neurotoxicology studies to determine environmental risk factors for neurodevelopmental disorders. There is, however, a deficit of step-by-step protocols that describe how to apply learning and memory assays in fruit flies to developmental neurotoxicology studies. Here, we describe two quantitative behavioral paradigms for Drosophila-predator-induced oviposition and courtship conditioning-that can be used to measure different forms of learning and memory in the context of a developmental neurotoxicology study. Non-associative learning and memory are measured here by examining female Drosophila oviposition behavior in response to endoparasitoid wasps, while associative learning and memory are measured in males using courtship conditioning. Our protocols outline procedures for oral toxicant exposure of developing fruit flies, culturing of endoparasitoid wasps, measuring Drosophila oviposition activity, and assessing conditioned courtship in order to identify the impact of toxicants on learning and memory in both females and males. As an example, we present the protocols using bisphenol A, a chemical utilized in the synthesis of polycarbonate plastics, to determine its impacts on learning and memory. These protocols are inexpensive and relatively simple to perform, and can be used by labs that are new to Drosophila behavioral research to evaluate how toxicant exposure influences learning and memory in male and female flies. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Preparation of toxicant-containing food and developmental exposure Basic Protocol 2: Predator-induced oviposition assay Support Protocol: Culture of Leptopilina heterotoma Basic Protocol 3: Conditioned courtship assay.

A dopamine-gated learning circuit underpins reproductive state-dependent odor preference in Drosophila females

Motherhood induces a drastic, sometimes long-lasting, change in internal state and behavior in many female animals. How a change in reproductive state or the discrete event of mating modulates specific female behaviors is still incompletely understood. Using calcium imaging of the whole brain of Drosophila females, we find that mating does not induce a global change in brain activity. Instead, mating modulates the pheromone response of dopaminergic neurons innervating the fly's learning and memory center, the mushroom body (MB). Using the mating-induced increased attraction to the odor of important nutrients, polyamines, we show that disruption of the female fly's ability to smell, for instance the pheromone cVA, during mating leads to a reduction in polyamine preference for days later indicating that the odor environment at mating lastingly influences female perception and choice behavior. Moreover, dopaminergic neurons including innervation of the β'1 compartment are sufficient to induce the lasting behavioral increase in polyamine preference. We further show that MB output neurons (MBON) of the β'1 compartment are activated by pheromone odor and their activity during mating bidirectionally modulates preference behavior in mated and virgin females. Their activity is not required, however, for the expression of polyamine attraction. Instead, inhibition of another type of MBON innervating the β'2 compartment enables expression of high odor attraction. In addition, the response of a lateral horn (LH) neuron, AD1b2, which output is required for the expression of polyamine attraction, shows a modulated polyamine response after mating. Taken together, our data in the fly suggests that mating-related sensory experience regulates female odor perception and expression of choice behavior through a dopamine-gated learning circuit.

Circadian photoreceptors are required for light-dependent maintenance of long-term memory in Drosophila

In the fruit fly Drosophila melanogaster, environmental light is required for maintaining long-term memory (LTM). Furthermore, the Pigment dispersing factor (Pdf), which is a circadian neuropeptide, and the neuronal activity of Pdf neurons are essential for light-dependent maintenance of courtship LTM. Since Pdf neurons can sense light directly via circadian photoreceptors [Rhodopsin 7 (Rh7) and Cryptochrome (Cry)], it is possible that Rh7 and Cry in Pdf neurons are involved in the maintenance of LTM. In this study, using a courtship conditioning assay, we demonstrated that circadian photoreceptors in Pdf neurons are required for maintaining courtship LTM.

Mutation in Drosophila concentrative nucleoside transporter 1 alters spermatid maturation and mating behavior

Concentrative nucleoside transporters (Cnts) are unidirectional carriers that mediate the energy-costly influx of nucleosides driven by the transmembrane sodium gradient. Cnts are transmembrane proteins that share a common structural organization and are found in all phyla. Although there have been studies on Cnts from a biochemical perspective, no deep research has examined their role at the organismal level. Here, we investigated the role of the Drosophila melanogaster cnt1 gene, which is specifically expressed in the testes. We used the CRISPR/Cas9 system to generate a mutation in the cnt1 gene. The cnt1 mutants exhibited defects in the duration of copulation and spermatid maturation, which significantly impaired male fertility. The most striking effect of the cnt1 mutation in spermatid maturation was an abnormal structure of the sperm tail, in which the formation of major and minor mitochondrial derivatives was disrupted. Our results demonstrate the importance of cnt1 in male fertility and suggest that the observed defects in mating behavior and spermatogenesis are due to alterations in nucleoside transport and associated metabolic pathways.

Circadian Neuropeptide-Expressing Clock Neurons as Regulators of Long-Term Memory: Molecular and Cellular Perspectives

The neuropeptide pigment-dispersing factor (Pdf) is critically involved in the regulation of circadian rhythms in various insects. The function of Pdf in circadian rhythms has been best studied in the fruitfly, i.e., Drosophila melanogaster. Drosophila Pdf is produced in a small subset of circadian clock neurons in the adult brain and functions as a circadian output signal. Recently, however, Pdf has been shown to play important roles not only in regulating circadian rhythms but also in innate and learned behaviors in Drosophila. In this mini-review, we will focus on the current findings that Pdf signaling and Pdf-producing neurons are essential for consolidating and maintaining long-term memory induced by the courtship conditioning in Drosophila and discuss the mechanisms of courtship memory processing through Pdf-producing neurons.

Factors affecting the biosynthesis and emission of a Drosophila pheromone

The most studied pheromone in Drosophila melanogaster, cis-vaccenyl acetate (cVA), is synthesized in the male ejaculatory bulb and transferred to the female during copulation. Combined with other chemicals, cVA can modulate fly aggregation, courtship, mating and fighting. We explored the mechanisms underlying both cVA biosynthesis and emission in males of two wild types and a pheromonal mutant line. The effects of ageing, adult social interaction, and maternally transmitted cVA and microbes - both associated with the egg chorion - on cVA biosynthesis and emission were measured. While ageing and genotype changed both biosynthesis and emission in similar ways, early developmental exposure to maternally transmitted cVA and microbes strongly decreased cVA emission but not the biosynthesis of this molecule. This indicates that the release - but not the biosynthesis - of this sex pheromone strongly depends on early developmental context. The mechanism by which the preimaginal effects occur is unknown, but reinforces the significance of development in determining adult physiology and behaviour.

Drosophila Model for Studying Gut Microbiota in Behaviors and Neurodegenerative Diseases

Mounting evidence indicates that the gut microbiota is linked to several physiological processes and disease development in mammals; however, the underlying mechanisms remained unexplored mostly due to the complexity of the mammalian gut microbiome. The fruit fly, Drosophila melanogaster, is a valuable animal model for studying host-gut microbiota interactions in translational aspects. The availability of powerful genetic tools and resources in Drosophila allowed the scientists to unravel the mechanisms by which the gut microbes affect fitness, health, and behavior of their hosts. Drosophila models have been extensively used not only to study animal behaviors (i.e., courtship, aggression, sleep, and learning & memory), but also some human related neurodegenerative diseases (i.e., Alzheimer's disease and Parkinson's disease) in the past. This review comprehensively summarizes the current understanding of the gut microbiota of Drosophila and its impact on fly behavior, physiology, and neurodegenerative diseases.

Bisphenol A affects neurodevelopmental gene expression, cognitive function, and neuromuscular synaptic morphology in Drosophila melanogaster

Bisphenol A (BPA) is an environmentally prevalent endocrine disrupting chemical that can impact human health and may be an environmental risk factor for neurodevelopmental disorders. BPA has been associated with behavioral impairment in children and a variety of neurodevelopmental phenotypes in model organisms. We used Drosophila melanogaster to explore the consequences of developmental BPA exposure on gene expression, cognitive function, and synapse development. Our transcriptome analysis indicated neurodevelopmentally relevant genes were predominantly downregulated by BPA. Among the misregulated genes were those with roles in learning, memory, and synapse development, as well as orthologs of human genes associated with neurodevelopmental and neuropsychiatric disorders. To examine how gene expression data corresponded to behavioral and cellular phenotypes, we first used a predator-response behavioral paradigm and found that BPA disrupts visual perception. Further analysis using conditioned courtship suppression showed that BPA impairs associative learning. Finally, we examined synapse morphology within the larval neuromuscular junction and found that BPA significantly increased the number of axonal branches. Given that our findings align with studies of BPA in mammalian model organisms, this data indicates that BPA impairs neurodevelopmental pathways that are functionally conserved from invertebrates to mammals. Further, because Drosophila do not possess classic estrogen receptors or estrogen, this research suggests that BPA can impact neurodevelopment by molecular mechanisms distinct from its role as an estrogen mimic.

3-Hydroxykynurenine as a Potential Ligand for Hsp70 Proteins and Its Effects on Drosophila Memory After Heat Shock

Kynurenine products of tryptophan metabolism are modifiers of the nervous activity and oxidative processes in mammals and invertebrates. 3-Hydroxykynurenine (3HOK) in moderate concentrations is a lipid peroxidation inhibitor. However, its accumulation and oxidative auto-dimerization lead to oxidative stress development manifested in age-related neurodegenerative diseases (NDD) and neurological disorders provoked by acute stress. Different forms of stress, the mostly studied being heat shock response, rely on functioning of heat shock proteins of the Hsp70 superfamily. Since kynurenines are called "kids of stress," we performed computational estimation of affinity of 3HOK and other kynurenines binding to predicted ATP site of Drosophila melanogaster Hsp cognate 71 protein (Dhsp71) using AutoDock Vina. The binding energy of 3HOK dimer is - 9.4 kcal/mol; its orientation within the active site is close to that of ATP. This might be a new mechanism of producing a competitive inhibitor of Hsp70 chaperones that decreases organism ability to adapt to heat shock. We also showed that the Drosophila cardinal (cd¹) mutant with 3HOK excess, serving as a model for Huntington's disease (HD), manifests severe defects of short-term memory after heat shock applied either in adults or at the prepupal stage.

Consolidation and maintenance of long-term memory involve dual functions of the developmental regulator Apterous in clock neurons and mushroom bodies in the Drosophila brain

Memory is initially labile but can be consolidated into stable long-term memory (LTM) that is stored in the brain for extended periods. Despite recent progress, the molecular and cellular mechanisms underlying the intriguing neurobiological processes of LTM remain incompletely understood. Using the Drosophila courtship conditioning assay as a memory paradigm, here, we show that the LIM homeodomain (LIM-HD) transcription factor Apterous (Ap), which is known to regulate various developmental events, is required for both the consolidation and maintenance of LTM. Interestingly, Ap is involved in these 2 memory processes through distinct mechanisms in different neuronal subsets in the adult brain. Ap and its cofactor Chip (Chi) are indispensable for LTM maintenance in the Drosophila memory center, the mushroom bodies (MBs). On the other hand, Ap plays a crucial role in memory consolidation in a Chi-independent manner in pigment dispersing factor (Pdf)-containing large ventral–lateral clock neurons (l-LNvs) that modulate behavioral arousal and sleep. Since disrupted neurotransmission and electrical silencing in clock neurons impair memory consolidation, Ap is suggested to contribute to the stabilization of memory by ensuring the excitability of l-LNvs. Indeed, ex vivo imaging revealed that a reduced function of Ap, but not Chi, results in exaggerated Cl⁻ responses to the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in l-LNvs, indicating that wild-type (WT) Ap maintains high l-LNv excitability by suppressing the GABA response. Consistently, enhancing the excitability of l-LNvs by knocking down GABA_A receptors compensates for the impaired memory consolidation in ap null mutants. Overall, our results revealed unique dual functions of the developmental regulator Ap for LTM consolidation in clock neurons and LTM maintenance in MBs.

A neurogenetic study using Drosophila reveals that the centrally expressed LIM-homeodomain transcription factor Apterous plays a crucial neuron-type-dependent role in two different memory processes - consolidation and maintenance of long-term memory.

Does sexual experience affect the strength of male mate choice for high-quality females in Drosophila melanogaster?

Although females are traditionally thought of as the choosy sex, there is increasing evidence in many species that males will preferentially court or mate with certain females over others when given a choice. In the fruit fly, Drosophila melanogaster, males discriminate between potential mating partners based on a number of female traits, including species, mating history, age, and condition. Interestingly, many of these male preferences are affected by the male's previous sexual experiences, such that males increase courtship toward types of females that they have previously mated with and decrease courtship toward types of females that have previously rejected them. D. melanogaster males also show courtship and mating preferences for larger females over smaller females, likely because larger females have higher fecundity. It is unknown, however, whether this preference shows behavioral plasticity based on the male's sexual history as we see for other male preferences. Here, we manipulate the sexual experience of D. melanogaster males and test whether this manipulation has any effect on the strength of male mate choice for large females. We find that sexually inexperienced males have a robust courtship preference for large females that is unaffected by previous experience mating with, or being rejected by, females of differing sizes. Given that female body size is one of the most common targets of male mate choice across insect species, our experiments with D. melanogaster may provide insight into how these preferences develop and evolve.

Genetic and functional analysis reveals TENM4 contributes to schizophrenia

TENM4, encoding a member of the teneurin protein family, is a risk gene shared by many types of mental diseases and is implicated in neuronal plasticity and signaling. However, the role and the mechanisms of TENM4 in schizophrenia (SCZ) remain unclear. We identified possible pathogenic mutations in the TENM4 gene through target sequencing of TENM4 in 68 SCZ families. We further demonstrated that aberrant expression of Ten-m leads to lower learning ability, sleep reduction, and increased aggressiveness in animal models. RNA sequencing showed that aberrant expression of Ten-m was related to stimulus perception and metabolic process, and Gene Ontology enrichment terms were neurogenesis and ATPase activity. This study provides strong evidence that TENM4 contributes to SCZ, and its functional mutations might be responsible for the impaired neural circuits and behaviors observed in SCZ.

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Possible pathogenic rare missense mutations in TENM4 gene contribute to SCZ

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Aberrant expression of Ten-m leads to behavioral disturbances related to SCZ symptoms

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Ten-m affects stimulation, metabolic process, neurogenesis, and ATPase activity

Characterization of SETD1A haploinsufficiency in humans and Drosophila defines a novel neurodevelopmental syndrome

Defects in histone methyltransferases (HMTs) are major contributing factors in neurodevelopmental disorders (NDDs). Heterozygous variants of SETD1A involved in histone H3 lysine 4 (H3K4) methylation were previously identified in individuals with schizophrenia. Here, we define the clinical features of the Mendelian syndrome associated with haploinsufficiency of SETD1A by investigating 15 predominantly pediatric individuals who all have de novo SETD1A variants. These individuals present with a core set of symptoms comprising global developmental delay and/or intellectual disability, subtle facial dysmorphisms, behavioral and psychiatric problems. We examined cellular phenotypes in three patient-derived lymphoblastoid cell lines with three variants: p.Gly535Alafs*12, c.4582-2_4582delAG, and p.Tyr1499Asp. These patient cell lines displayed DNA damage repair defects that were comparable to previously observed RNAi-mediated depletion of SETD1A. This suggested that these variants, including the p.Tyr1499Asp in the catalytic SET domain, behave as loss-of-function (LoF) alleles. Previous studies demonstrated a role for SETD1A in cell cycle control and differentiation. However, individuals with SETD1A variants do not show major structural brain defects or severe microcephaly, suggesting that defective proliferation and differentiation of neural progenitors is unlikely the single underlying cause of the disorder. We show here that the Drosophila melanogaster SETD1A orthologue is required in postmitotic neurons of the fly brain for normal memory, suggesting a role in post development neuronal function. Together, this study defines a neurodevelopmental disorder caused by dominant de novo LoF variants in SETD1A and further supports a role for H3K4 methyltransferases in the regulation of neuronal processes underlying normal cognitive functioning.

A conserved role for sleep in supporting Spatial Learning in Drosophila

Sleep loss and aging impair hippocampus-dependent Spatial Learning in mammalian systems. Here we use the fly Drosophila melanogaster to investigate the relationship between sleep and Spatial Learning in healthy and impaired flies. The Spatial Learning assay is modeled after the Morris Water Maze. The assay uses a "thermal maze" consisting of a 5 × 5 grid of Peltier plates maintained at 36-37°C and a visual panorama. The first trial begins when a single tile that is associated with a specific visual cue is cooled to 25°C. For subsequent trials, the cold tile is heated, the visual panorama is rotated and the flies must find the new cold tile by remembering its association with the visual cue. Significant learning was observed with two different wild-type strains-Cs and 2U, validating our design. Sleep deprivation prior to training impaired Spatial Learning. Learning was also impaired in the classic learning mutant rutabaga (rut); enhancing sleep restored learning to rut mutants. Further, we found that flies exhibited a dramatic age-dependent cognitive decline in Spatial Learning starting at 20-24 days of age. These impairments could be reversed by enhancing sleep. Finally, we find that Spatial Learning requires dopaminergic signaling and that enhancing dopaminergic signaling in aged flies restored learning. Our results are consistent with the impairments seen in rodents and humans. These results thus demonstrate a critical conserved role for sleep in supporting Spatial Learning, and suggest potential avenues for therapeutic intervention during aging.

Regulation of Drosophila Long-Term Courtship Memory by Ecdysis Triggering Hormone

Endocrine state is an important determinant of learning and memory in animals. In Drosophila, rejection of male courtship overtures by mated females leads to an aversive response manifested as courtship memory. Here we report that ecdysis triggering hormone (ETH) is an obligatory enabler of long-term courtship memory (LTM). ETH deficiency suppresses LTM, whereas augmented ETH release reduces the minimum training period required for LTM induction. ETH receptor knockdown either in the mushroom body (MB) γ lobe or in octopaminergic dorsal-anterior-lateral (DAL) neurons impairs memory performance, indicating its direct action in these brain areas. Consistent with these findings, brain exposure to ETH mobilizes calcium in MB γ lobe neuropils and DAL neurons. ETH receptor (ETHR) knockdown in the corpus allatum (CA) to create juvenile hormone (JH) deficiency also suppresses LTM, as does knockdown of the JH receptor Met in the MB γ lobe, indicating a convergence of ETH and JH signaling in this region of the brain. Our findings identify endocrine-enabled neural circuit components in the brain that are critical for persistent behavioral changes resulting from aversive social experience.

The chromatin remodeler ISWI acts during Drosophila development to regulate adult sleep

Sleep disruptions are among the most commonly reported symptoms across neurodevelopmental disorders (NDDs), but mechanisms linking brain development to normal sleep are largely unknown. From a Drosophila screen of human NDD-associated risk genes, we identified the chromatin remodeler Imitation SWItch/SNF (ISWI) to be required for adult fly sleep. Loss of ISWI also results in disrupted circadian rhythms, memory, and social behavior, but ISWI acts in different cells and during distinct developmental times to affect each of these adult behaviors. Specifically, ISWI expression in type I neuroblasts is required for both adult sleep and formation of a learning-associated brain region. Expression in flies of the human ISWI homologs SMARCA1 and SMARCA5 differentially rescues adult phenotypes, while de novo SMARCA5 patient variants fail to rescue sleep. We propose that sleep deficits are a primary phenotype of early developmental origin in NDDs and point toward chromatin remodeling machinery as critical for sleep circuit formation.

Conditioned courtship suppression in Drosophila melanogaster

Drosophila melanogaster males reduce courtship behaviour after mating failure. In the lab, such conditioned courtship suppression, aka 'courtship conditioning', serves as a complex learning and memory assay. Interestingly, variations in the courtship conditioning assay can establish different types of memory. Here, we review research investigating the underlying cellular and molecular mechanisms that allow male flies to form memories of previous mating failures.

Studying the Contribution of Serotonin to Neurodevelopmental Disorders. Can This Fly?

Serotonin is a biogenic amine that acts as neurotransmitter in different brain regions and is involved in complex behaviors, such as aggression or mood regulation. Thus, this amine is found in defined circuits and activates specific receptors in different target regions. Serotonin actions depend on extracellular levels of this amine, which are regulated by its synthetic enzymes and the plasma membrane transporter, SERT. Serotonin acts also as a neurotrophic signal in ontogeny and in the mature brain, controlling cell proliferation, differentiation, neurogenesis, and neural plasticity. Interestingly, early alterations in serotonergic signaling have been linked to a diversity of neurodevelopmental disorders, including autism spectrum disorder (ASD), attention deficit/hyperactivity disorder (ADHD), or mental illnesses like schizophrenia or depression. It has been proposed that given the complex and numerous actions of serotonin, animal models could better serve to study the complexity of serotonin actions, while providing insights on how hindering serotonergic signaling could contribute to brain disorders. In this mini-review, it will be examined what the general properties of serotonin acting as a neurotransmitter in animals are, and furthermore, whether it is possible that Drosophila could be used to study the contribution of this amine to neurodevelopmental and mental disorders.

Angiotensin Converting Enzyme Inhibitors and Angiotensin Receptor Blockers Rescue Memory Defects in Drosophila-Expressing Alzheimer's Disease-Related Transgenes Independently of the Canonical Renin Angiotensin System

Alzheimer's disease (AD) is a degenerative disorder that causes progressive memory and cognitive decline. Recently, studies have reported that inhibitors of the mammalian renin angiotensin system (RAS) result in a significant reduction in the incidence and progression of AD by unknown mechanisms. Here, we used a genetic and pharmacological approach to evaluate the beneficial effects of angiotensin converting enzyme inhibitors (ACE-Is) and angiotensin receptor blockers (ARBs) in Drosophila expressing AD-related transgenes. Importantly, while ACE orthologs have been identified in Drosophila, other RAS components are not conserved. We show that captopril, an ACE-I, and losartan, an ARB, can suppress a rough eye phenotype and brain cell death in flies expressing a mutant human C99 transgene. Captopril also significantly rescues memory defects in these flies. Similarly, both drugs reduce cell death in Drosophila expressing human Aβ42 and losartan significantly rescues memory deficits. However, neither drug affects production, accumulation or clearance of Aβ42 Importantly, neither drug rescued brain cell death in Drosophila expressing human Tau, suggesting that RAS inhibitors specifically target the amyloid pathway. Of note, we also observed reduced cell death and a complete rescue of memory deficits when we crossed a null mutation in Drosophila Acer into each transgenic line demonstrating that the target of captopril in Drosophila is Acer. Together, these studies demonstrate that captopril and losartan are able to modulate AD related phenotypes in the absence of the canonical RAS pathway and suggest that both drugs have additional targets that can be identified in Drosophila.

Arginine kinase interacts with 2MIT and is involved in Drosophila melanogaster short-term memory

Mushroom bodies are a higher order center for sensory integration, learning and memory of the insect brain. Memory is generally subdivided into different phases. In the model organism Drosophila melanogaster, mushroom bodies have been shown to play a central role in both short- and long-term memory. In D. melanogaster, the gene 2mit codes a transmembrane protein carrying an extracellular Leucin-rich-repeat domain, which is highly transcribed in the mushroom and ellipsoid bodies of the adult fly brain and has a role in the early phase of memory. Utilizing coimmunoprecipitation experiments and mass spectrometry analyses, we have shown that 2MIT interacts with Arginine kinase in adult fly heads. Arginine kinase belongs to the family of Phosphagen kinases and plays a fundamental role in energy homeostasis. Using the GAL4/UAS binary system, we demonstrated that a downregulation of Arginine kinase mainly driven in the mushroom bodies affects short-term memory of Drosophila adult flies, in a courtship conditioning paradigm. As 2mit ^c03963 hypomorphic mutants showed comparable results when analyzed with the same assay, these data suggest that 2MIT and Arginine kinase are both involved in the same memory phenotype, likely interacting at the level of mushroom bodies. 2MIT and Arginine kinase are conserved among insects, the implications of which, along with their potential roles in other insect taxa are also discussed.

Variants in SCAF4 Cause a Neurodevelopmental Disorder and Are Associated with Impaired mRNA Processing

RNA polymerase II interacts with various other complexes and factors to ensure correct initiation, elongation, and termination of mRNA transcription. One of these proteins is SR-related CTD-associated factor 4 (SCAF4), which is important for correct usage of polyA sites for mRNA termination. Using exome sequencing and international matchmaking, we identified nine likely pathogenic germline variants in SCAF4 including two splice-site and seven truncating variants, all residing in the N-terminal two thirds of the protein. Eight of these variants occurred de novo, and one was inherited. Affected individuals demonstrated a variable neurodevelopmental disorder characterized by mild intellectual disability, seizures, behavioral abnormalities, and various skeletal and structural anomalies. Paired-end RNA sequencing on blood lymphocytes of SCAF4-deficient individuals revealed a broad deregulation of more than 9,000 genes and significant differential splicing of more than 2,900 genes, indicating an important role of SCAF4 in mRNA processing. Knockdown of the SCAF4 ortholog CG4266 in the model organism Drosophila melanogaster resulted in impaired locomotor function, learning, and short-term memory. Furthermore, we observed an increased number of active zones in larval neuromuscular junctions, representing large glutamatergic synapses. These observations indicate a role of CG4266 in nervous system development and function and support the implication of SCAF4 in neurodevelopmental phenotypes. In summary, our data show that heterozygous, likely gene-disrupting variants in SCAF4 are causative for a variable neurodevelopmental disorder associated with impaired mRNA processing.

Modelling Learning and Memory in Drosophila to Understand Intellectual Disabilities

Neurodevelopmental disorders (NDDs) include a large number of conditions such as Fragile  X  syndrome, autism spectrum disorders and Down syndrome, among others. They are characterized by limitations in adaptive and social behaviors, as well as intellectual disability (ID). Whole-exome and whole-genome sequencing studies have highlighted a large number of NDD/ID risk genes. To dissect the genetic causes and underlying biological pathways, in vivo experimental validation of the effects of these mutations is needed. The fruit fly, Drosophila melanogaster, is an ideal model to study NDDs, with highly tractable genetics, combined with simple behavioral and circuit assays, permitting rapid medium-throughput screening of NDD/ID risk genes. Here, we review studies where the use of well-established assays to study mechanisms of learning and memory in Drosophila has permitted insights into molecular mechanisms underlying IDs. We discuss how technologies in the fly model, combined with a high degree of molecular and physiological conservation between flies and mammals, highlight the Drosophila system as an ideal model to study neurodevelopmental disorders, from genetics to behavior.

Dynamic neural and glial responses of a head-specific model for traumatic brain injury in Drosophila

Traumatic brain injury (TBI) is the strongest environmental risk factor for the accelerated development of neurodegenerative diseases. There are currently no therapeutics to address this due to lack of insight into mechanisms of injury progression, which are challenging to study in mammalian models. Here, we have developed and extensively characterized a head-specific approach to TBI in Drosophila, a powerful genetic system that shares many conserved genes and pathways with humans. The Drosophila TBI (dTBI) device inflicts mild, moderate, or severe brain trauma by precise compression of the head using a piezoelectric actuator. Head-injured animals display features characteristic of mammalian TBI, including severity-dependent ataxia, life span reduction, and brain degeneration. Severe dTBI is associated with cognitive decline and transient glial dysfunction, and stimulates antioxidant, proteasome, and chaperone activity. Moreover, genetic or environmental augmentation of the stress response protects from severe dTBI-induced brain degeneration and life span deficits. Together, these findings present a tunable, head-specific approach for TBI in Drosophila that recapitulates mammalian injury phenotypes and underscores the ability of the stress response to mitigate TBI-induced brain degeneration.

Anti-instinctive Learning Behavior Revealed by Locomotion-Triggered Mild Heat Stress in Drosophila

Anti-instinctive learning, an ability to modify an animal's innate behaviors in ways that go against one's innate tendency, can confer great evolutionary advantages to animals and enable them to better adapt to the changing environment. Yet, our understanding of anti-instinctive learning and its underlying mechanisms is still limited. In this work, we describe a new anti-instinctive learning behavior of fruit flies. This learning paradigm requires the fruit fly to respond to a recurring, aversive, mild heat stress by modifying its innate locomotion behavior. We found that experiencing movement-triggered mild heat stress repeatedly significantly reduced walking activity in wild type fruit flies, indicating that fruit flies are capable of anti-instinctive learning. We also report that such learning ability is reduced in dopamine 1-like receptor 1 (Dop1R1) null mutant and dopamine 2-like receptor (Dop2R) null mutant flies, suggesting that these two dopamine receptors are involved in mediating anti-instinctive learning in flies.