Recent Advances in the Genetic Dissection of Neural Circuits in Drosophila

Inhibitory control of locomotor statistics in walking Drosophila

In order to forage for food, many animals regulate not only specific limb movements but the statistics of locomotor behavior over time, for example switching between long-range dispersal behaviors and more localized search depending on the availability of resources. How pre-motor circuits regulate such locomotor statistics is not clear. Here we took advantage of the robust changes in locomotor statistics evoked by attractive odors in walking Drosophila to investigate their neural control. We began by analyzing the statistics of ground speed and angular velocity during three well-defined motor regimes: baseline walking, upwind running during odor, and search behavior following odor offset. We find that during search behavior, flies adopt higher angular velocities and slower ground speeds, and tend to turn for longer periods of time in one direction. We further find that flies spontaneously adopt periods of different mean ground speed, and that these changes in state influence the length of odor-evoked runs. We next developed a simple physiologically-inspired computational model of locomotor control that can recapitulate these statistical features of fly locomotion. Our model suggests that contralateral inhibition plays a key role both in regulating the difference between baseline and search behavior, and in modulating the response to odor with ground speed. As the fly connectome predicts decussating inhibitory neurons in the lateral accessory lobe (LAL), a pre-motor structure, we generated genetic tools to target these neurons and test their role in behavior. Consistent with our model, we found that activation of neurons labeled in one line increased curvature. In a second line labeling distinct neurons, activation and inactivation strongly and reciprocally regulated ground speed and altered the length of the odor-evoked run. Additional targeted light activation experiments argue that these effects arise from the brain rather than from neurons in the ventral nerve cord, while sparse activation experiments argue that speed control in the second line arises from both LAL neurons and a population of neurons in the dorsal superior medial protocerebrum (SMP). Together, our work develops a biologically plausible computational architecture that captures the statistical features of fly locomotion across behavioral states and identifies potential neural substrates of these computations.

Single-cell transcriptomics dissecting the development and evolution of nervous system in insects

Insects can display a vast repertoire of complex and adaptive behaviors crucial for survival and reproduction. Yet, how the neural circuits underlying insect behaviors are assembled throughout development and remodeled during evolution remains largely obscure. The advent of single-cell transcriptomics has opened new paths to illuminate these historically intractable questions. Insect behavior is governed by its brain, whose functional complexity is realized through operations across multiple levels, from the molecular and cellular to the circuit and organ. Single-cell transcriptomics enables dissecting brain functions across all these levels and allows tracking regulatory dynamics throughout development and under perturbation. In this review, we mainly focus on the achievements of single-cell transcriptomics in dissecting the molecular and cellular architectures of nervous systems in representative insects, then discuss its applications in tracking the developmental trajectory and functional evolution of insect brains.

Comparative exploration of mammalian deafness gene homologues in the Drosophila auditory organ shows genetic correlation between insect and vertebrate hearing

Johnston's organ, the Drosophila auditory organ, is anatomically very different from the mammalian organ of Corti. However, recent evidence indicates significant cellular and molecular similarities exist between vertebrate and invertebrate hearing, suggesting that Drosophila may be a useful platform to determine the function of the many mammalian deafness genes whose underlying biological mechanisms are poorly characterized. Our goal was a comprehensive screen of all known orthologues of mammalian deafness genes in the fruit fly to better understand conservation of hearing mechanisms between the insect and the fly and ultimately gain insight into human hereditary deafness. We used bioinformatic comparisons to screen previously reported human and mouse deafness genes and found that 156 of them have orthologues in Drosophila melanogaster. We used fluorescent imaging of T2A-GAL4 gene trap and GFP or YFP fluorescent protein trap lines for 54 of the Drosophila genes and found 38 to be expressed in different cell types in Johnston's organ. We phenotypically characterized the function of strong loss-of-function mutants in three genes expressed in Johnston's organ (Cad99C, Msp-300, and Koi) using a courtship assay and electrophysiological recordings of sound-evoked potentials. Cad99C and Koi were found to have significant courtship defects. However, when we tested these genes for electrophysiological defects in hearing response, we did not see a significant difference suggesting the courtship defects were not caused by hearing deficiencies. Furthermore, we used a UAS/RNAi approach to test the function of seven genes and found two additional genes, CG5921 and Myo10a, that gave a statistically significant delay in courtship but not in sound-evoked potentials. Our results suggest that many mammalian deafness genes have Drosophila homologues expressed in the Johnston's organ, but that their requirement for hearing may not necessarily be the same as in mammals.

Ancestral neural circuits potentiate the origin of a female sexual behavior

Courtship interactions are remarkably diverse in form and complexity among species. How neural circuits evolve to encode new behaviors that are functionally integrated into these dynamic social interactions is unknown. Here we report a recently originated female sexual behavior in the island endemic Drosophila species D. santomea, where females signal receptivity to male courtship songs by spreading their wings, which in turn promotes prolonged songs in courting males. Copulation success depends on this female signal and correlates with males' ability to adjust his singing in such a social feedback loop. Functional comparison of sexual circuitry across species suggests that a pair of descending neurons, which integrates male song stimuli and female internal state to control a conserved female abdominal behavior, drives wing spreading in D. santomea. This co-option occurred through the refinement of a pre-existing, plastic circuit that can be optogenetically activated in an outgroup species. Combined, our results show that the ancestral potential of a socially-tuned key circuit node to engage the wing motor program facilitates the expression of a new female behavior in appropriate sensory and motivational contexts. More broadly, our work provides insights into the evolution of social behaviors, particularly female behaviors, and the underlying neural mechanisms.

A Neural Circuit Controlling Virgin Female Aggression Induced by Mating-related Cues in Drosophila

Females increase aggression for mating opportunities and for acquiring reproductive resources. Although the close relationship between female aggression and mating status is widely appreciated, whether and how female aggression is regulated by mating-related cues remains poorly understood. Here we report an interesting observation that Drosophila virgin females initiate high-frequency attacks toward mated females. We identify 11-cis-vaccenyl acetate (cVA), a male-derived pheromone transferred to females during mating, which promotes virgin female aggression. We subsequently reveal a cVA-responsive neural circuit consisting of four orders of neurons, including Or67d, DA1, aSP-g, and pC1 neurons, that mediate cVA-induced virgin female aggression. We also determine that aSP-g neurons release acetylcholine (ACh) to excite pC1 neurons via the nicotinic ACh receptor nAChRα7. Together, beyond revealing cVA as a mating-related inducer of virgin female aggression, our results identify a neural circuit linking the chemosensory perception of mating-related cues to aggressive behavior in Drosophila females.

Olfactory navigation in arthropods

Using odors to find food and mates is one of the most ancient and highly conserved behaviors. Arthropods from flies to moths to crabs use broadly similar strategies to navigate toward odor sources-such as integrating flow information with odor information, comparing odor concentration across sensors, and integrating odor information over time. Because arthropods share many homologous brain structures-antennal lobes for processing olfactory information, mechanosensors for processing flow, mushroom bodies (or hemi-ellipsoid bodies) for associative learning, and central complexes for navigation, it is likely that these closely related behaviors are mediated by conserved neural circuits. However, differences in the types of odors they seek, the physics of odor dispersal, and the physics of locomotion in water, air, and on substrates mean that these circuits must have adapted to generate a wide diversity of odor-seeking behaviors. In this review, we discuss common strategies and specializations observed in olfactory navigation behavior across arthropods, and review our current knowledge about the neural circuits subserving this behavior. We propose that a comparative study of arthropod nervous systems may provide insight into how a set of basic circuit structures has diversified to generate behavior adapted to different environments.

Direction Selectivity of TmY Neurites in Drosophila

The perception of motion is an important function of vision. Neural wiring diagrams for extracting directional information have been obtained by connectome reconstruction. Direction selectivity in Drosophila is thought to originate in T4/T5 neurons through integrating inputs with different temporal filtering properties. Through genetic screening based on synaptic distribution, we isolated a new type of TmY neuron, termed TmY-ds, that form reciprocal synaptic connections with T4/T5 neurons. Its neurites responded to grating motion along the four cardinal directions and showed a variety of direction selectivity. Intriguingly, its direction selectivity originated from temporal filtering neurons rather than T4/T5. Genetic silencing and activation experiments showed that TmY-ds neurons are functionally upstream of T4/T5. Our results suggest that direction selectivity is generated in a tripartite circuit formed among these three neurons-temporal filtering, TmY-ds, and T4/T5 neurons, in which TmY-ds plays a role in the enhancement of direction selectivity in T4/T5 neurons.

On body-environment continuities from a laboratory commensalism

The article attends to everyday practices in a laboratory of neural genetics that studies olfaction, with the fruit fly as its model organism. Practices in neural genetics exhibit one of the 'post' aspects in post-genomic science - a turn to the environment. To get at how laboratory members engage body-environment continuities, I pay attention to an occasion of designing experimental chambers for an optogenetics study. As practitioners deal with the body's continuities with the world by engaging the spatial character of olfaction, their accounts exhibit qualities of feelings of immediate experience, relatable to C.S. Peirce's phenomenological category of Firstness. While these traces of Firstness inevitably manifest themselves in mixtures with the other two of Peirce's categories - namely, Secondness and Thirdness - noticing them allows for an engagement of the environment that goes beyond action and meaning. I reflect on that environment by considering the involvement of scientists' bodies in life with flies, while not forgetting my inhabitation of the laboratory space. Rather than relying on a cross-mapping of attributes known from the human sphere (intentional states or features of the human body) while managing a measurable space observed from the outside, this is an environment lived from within and with others. I conclude the article by proposing its noticing as an orientation toward ecological preoccupations.

A searchable image resource of Drosophila GAL4 driver expression patterns with single neuron resolution

Precise, repeatable genetic access to specific neurons via GAL4/UAS and related methods is a key advantage of Drosophila neuroscience. Neuronal targeting is typically documented using light microscopy of full GAL4 expression patterns, which generally lack the single-cell resolution required for reliable cell type identification. Here, we use stochastic GAL4 labeling with the MultiColor FlpOut approach to generate cellular resolution confocal images at large scale. We are releasing aligned images of 74,000 such adult central nervous systems. An anticipated use of this resource is to bridge the gap between neurons identified by electron or light microscopy. Identifying individual neurons that make up each GAL4 expression pattern improves the prediction of split-GAL4 combinations targeting particular neurons. To this end, we have made the images searchable on the NeuronBridge website. We demonstrate the potential of NeuronBridge to rapidly and effectively identify neuron matches based on morphology across imaging modalities and datasets.

The doublesex gene regulates dimorphic sexual and aggressive behaviors in Drosophila

Most animal species display dimorphic sexual behaviors and male-biased aggressiveness. Current models have focused on the male-specific product from the fruitless (fru^M) gene, which controls male courtship and male-specific aggression patterns in fruit flies, and describe a male-specific mechanism underlying sexually dimorphic behaviors. Here we show that the doublesex (dsx) gene, which expresses male-specific Dsx^M and female-specific Dsx^F transcription factors, functions in the nervous system to control both male and female sexual and aggressive behaviors. We find that Dsx is not only required in central brain neurons for male and female sexual behaviors, but also functions in approximately eight pairs of male-specific neurons to promote male aggressiveness and approximately two pairs of female-specific neurons to inhibit female aggressiveness. Dsx^F knockdown females fight more frequently, even with males. Our findings reveal crucial roles of dsx, which is broadly conserved from worms to humans, in a small number of neurons in both sexes to establish dimorphic sexual and aggressive behaviors.

Neural Control of Action Selection Among Innate Behaviors

Nervous systems must not only generate specific adaptive behaviors, such as reproduction, aggression, feeding, and sleep, but also select a single behavior for execution at any given time, depending on both internal states and external environmental conditions. Despite their tremendous biological importance, the neural mechanisms of action selection remain poorly understood. In the past decade, studies in the model animal Drosophila melanogaster have demonstrated valuable neural mechanisms underlying action selection of innate behaviors. In this review, we summarize circuit mechanisms with a particular focus on a small number of sexually dimorphic neurons in controlling action selection among sex, fight, feeding, and sleep behaviors in both sexes of flies. We also discuss potentially conserved circuit configurations and neuromodulation of action selection in both the fly and mouse models, aiming to provide insights into action selection and the sexually dimorphic prioritization of innate behaviors.

Neural mechanisms to exploit positional geometry for collision avoidance

Visual motion provides rich geometrical cues about the three-dimensional configuration of the world. However, how brains decode the spatial information carried by motion signals remains poorly understood. Here, we study a collision-avoidance behavior in Drosophila as a simple model of motion-based spatial vision. With simulations and psychophysics, we demonstrate that walking Drosophila exhibit a pattern of slowing to avoid collisions by exploiting the geometry of positional changes of objects on near-collision courses. This behavior requires the visual neuron LPLC1, whose tuning mirrors the behavior and whose activity drives slowing. LPLC1 pools inputs from object and motion detectors, and spatially biased inhibition tunes it to the geometry of collisions. Connectomic analyses identified circuitry downstream of LPLC1 that faithfully inherits its response properties. Overall, our results reveal how a small neural circuit solves a specific spatial vision task by combining distinct visual features to exploit universal geometrical constraints of the visual world.

The sex determination gene doublesex regulates expression and secretion of the basement membrane protein Collagen IV

The highly conserved doublesex (dsx) and doublesex/mab-3 related (Dmrt) genes control sexually dimorphic traits across animals. The dsx gene encodes sex-specific transcription factors, Dsx^M in males and Dsx^F in females, which function differentially and often oppositely to establish sexual dimorphism. Here, we report that mutations in dsx, or overexpression of dsx, result in abnormal distribution of the basement membrane (BM) protein Collagen IV in the fat body. We find that Dsx isoforms regulate the expression of Collagen IV in the fat body and its secretion into the BM of other tissues. We identify the procollagen lysyl hydroxylase (dPlod) gene, which is involved in the biosynthesis of Collagen IV, as a direct target of Dsx. We further show that Dsx regulates Collagen IV through dPlod-dependent and independent pathways. These findings reveal how Dsx isoforms function in the secretory fat body to regulate Collagen IV and remotely establish sexual dimorphism.

Building on a Solid Foundation: Adding Relevance and Reproducibility to Neurological Modeling Using Human Pluripotent Stem Cells

The brain is our most complex and least understood organ. Animal models have long been the most versatile tools available to dissect brain form and function; however, the human brain is highly distinct from that of standard model organisms. In addition to existing models, access to human brain cells and tissues is essential to reach new frontiers in our understanding of the human brain and how to intervene therapeutically in the face of disease or injury. In this review, we discuss current and developing culture models of human neural tissue, outlining advantages over animal models and key challenges that remain to be overcome. Our principal focus is on advances in engineering neural cells and tissue constructs from human pluripotent stem cells (PSCs), though primary human cell and slice culture are also discussed. By highlighting studies that combine animal models and human neural cell culture techniques, we endeavor to demonstrate that clever use of these orthogonal model systems produces more reproducible, physiological, and clinically relevant data than either approach alone. We provide examples across a range of topics in neuroscience research including brain development, injury, and cancer, neurodegenerative diseases, and psychiatric conditions. Finally, as testing of PSC-derived neurons for cell replacement therapy progresses, we touch on the advancements that are needed to make this a clinical mainstay.

Molecular Tools for Targeted Control of Nerve Cell Electrical Activity. Part II

In modern life sciences, the issue of a specific, exogenously directed manipulation of a cell's biochemistry is a highly topical one. In the case of electrically excitable cells, the aim of the manipulation is to control the cells' electrical activity, with the result being either excitation with subsequent generation of an action potential or inhibition and suppression of the excitatory currents. The techniques of electrical activity stimulation are of particular significance in tackling the most challenging basic problem: figuring out how the nervous system of higher multicellular organisms functions. At this juncture, when neuroscience is gradually abandoning the reductionist approach in favor of the direct investigation of complex neuronal systems, minimally invasive methods for brain tissue stimulation are becoming the basic element in the toolbox of those involved in the field. In this review, we describe three approaches that are based on the delivery of exogenous, genetically encoded molecules sensitive to external stimuli into the nervous tissue. These approaches include optogenetics (overviewed in Part I), as well as chemogenetics and thermogenetics (described here, in Part II), which is significantly different not only in the nature of the stimuli and structure of the appropriate effector proteins, but also in the details of experimental applications. The latter circumstance is an indication that these are rather complementary than competing techniques.

The Role of Dopamine in Associative Learning in Drosophila: An Updated Unified Model

Learning to associate a positive or negative experience with an unrelated cue after the presentation of a reward or a punishment defines associative learning. The ability to form associative memories has been reported in animal species as complex as humans and as simple as insects and sea slugs. Associative memory has even been reported in tardigrades [1], species that diverged from other animal phyla 500 million years ago. Understanding the mechanisms of memory formation is a fundamental goal of neuroscience research. In this article, we work on resolving the current contradictions between different Drosophila associative memory circuit models and propose an updated version of the circuit model that predicts known memory behaviors that current models do not. Finally, we propose a model for how dopamine may function as a reward prediction error signal in Drosophila, a dopamine function that is well-established in mammals but not in insects [2, 3].

A subset of DN1p neurons integrates thermosensory inputs to promote wakefulness via CNMa signaling

Sleep is an essential and evolutionarily conserved behavior that is modulated by many environmental factors. Ambient temperature shifting usually occurs during climatic or seasonal change or travel from high-latitude area to low-latitude area that affects animal physiology. Increasing ambient temperature modulates sleep in both humans and Drosophila. Although several thermosensory molecules and neurons have been identified, the neural mechanisms that integrate temperature sensation into the sleep neural circuit remain poorly understood. Here, we reveal that prolonged increasing of ambient temperature induces a reversible sleep reduction and impaired sleep consolidation in Drosophila via activating the internal thermosensory anterior cells (ACs). ACs form synaptic contacts with a subset of posterior dorsal neuron 1 (DN1p) neurons and release acetylcholine to promote wakefulness. Furthermore, we identify that this subset of DN1ps promotes wakefulness by releasing CNMamide (CNMa) neuropeptides to inhibit the Dh44-positive pars intercerebralis (PI) neurons through CNMa receptors. Our study demonstrates that the AC-DN1p-PI neural circuit is responsible for integrating thermosensory inputs into the sleep neural circuit. Moreover, we identify the CNMa signaling pathway as a newly recognized wakefulness-promoting DN1 pathway.

Gut microbiome modulates Drosophila aggression through octopamine signaling

Gut microbiome profoundly affects many aspects of host physiology and behaviors. Here we report that gut microbiome modulates aggressive behaviors in Drosophila. We found that germ-free males showed substantial decrease in inter-male aggression, which could be rescued by microbial re-colonization. These germ-free males are not as competitive as wild-type males for mating with females, although they displayed regular levels of locomotor and courtship behaviors. We further found that Drosophila microbiome interacted with diet during a critical developmental period for the proper expression of octopamine and manifestation of aggression in adult males. These findings provide insights into how gut microbiome modulates specific host behaviors through interaction with diet during development.

The gut microbiome regulates behaviour in a number of species. Here the authors show that depletion of the gut microbiome in Drosophila reduced aggressive behaviour, in an octopamine-dependent manner.

Dysregulated CRMP Mediates Circadian Deficits in a Drosophila Model of Fragile X Syndrome

Fragile X syndrome (FXS) is the leading inherited cause of intellectual disability, resulting from the lack of functional fragile X mental retardation protein (FMRP), an mRNA binding protein mainly serving as a translational regulator. Loss of FMRP leads to dysregulation of target mRNAs. The Drosophila model of FXS show an abnormal circadian rhythm with disruption of the output pathway downstream of the clock network. Yet the FMRP targets involved in circadian regulation have not been identified. Here, we identified collapsing response mediator protein (CRMP) mRNA as a target of FMRP. Knockdown of pan-neuronal CRMP expression ameliorated the circadian defects and abnormal axonal structures of clock neurons (ventral lateral neurons) in dfmr1 mutant flies. Furthermore, specific reduction of CRMP in the downstream output insulin-producing cells attenuated the aberrant circadian behaviors. Molecular analyses revealed that FMRP binds with CRMP mRNA and negatively regulates its translation. Our results indicate that CRMP is an FMRP target and establish an essential role for CRMP in the circadian output in FXS Drosophila.

Parallel Synaptic Acetylcholine Signals Facilitate Large Monopolar Cell Repolarization and Modulate Visual Behavior in Drosophila

Appropriate termination of the photoresponse in image-forming photoreceptors and downstream neurons is critical for an animal to achieve high temporal resolution. Although the cellular and molecular mechanisms of termination in image-forming photoreceptors have been extensively studied in Drosophila, the underlying mechanism of termination in their downstream large monopolar cells remains less explored. Here, we show that synaptic ACh signaling, from both amacrine cells (ACs) and L4 neurons, facilitates the rapid repolarization of L1 and L2 neurons. Intracellular recordings in female flies show that blocking synaptic ACh output from either ACs or L4 neurons leads to slow repolarization of L1 and L2 neurons. Genetic and electrophysiological studies in both male and female flies determine that L2 neurons express ACh receptors and directly receive ACh signaling. Moreover, our results demonstrate that synaptic ACh signaling from both ACs and L4 neurons simultaneously facilitates ERG termination. Finally, visual behavior studies in both male and female flies show that synaptic ACh signaling, from either ACs or L4 neurons to L2 neurons, is essential for the optomotor response of the flies in high-frequency light stimulation. Our study identifies parallel synaptic ACh signaling for repolarization of L1 and L2 neurons and demonstrates that synaptic ACh signaling facilitates L1 and L2 neuron repolarization to maintain the optomotor response of the fly on high-frequency light stimulation.SIGNIFICANCE STATEMENT The image-forming photoreceptor downstream neurons receive multiple synaptic inputs from image-forming photoreceptors and various types of interneurons. It remains largely unknown how these synaptic inputs modulate the neural activity and function of image-forming photoreceptor downstream neurons. We show that parallel synaptic ACh signaling from both amacrine cells and L4 neurons facilitates rapid repolarization of large monopolar cells in Drosophila and maintains the optomotor response of the fly on high-frequency light stimulation. This work is one of the first reports showing how parallel synaptic signaling modulates the activity of large monopolar cells and motion vision simultaneously.

Genetic Transsynaptic Techniques for Mapping Neural Circuits in Drosophila

A neural circuit is composed of a population of neurons that are interconnected by synapses and carry out a specific function when activated. It is the structural framework for all brain functions. Its impairments often cause diseases in the nervous system. To understand computations and functions in a brain circuit, it is of crucial importance to identify how neurons in this circuit are connected. Genetic transsynaptic techniques provide opportunities to efficiently answer this question. These techniques label synapses or across synapses to unbiasedly label synaptic partners. They allow for mapping neural circuits with high reproducibility and throughput, as well as provide genetic access to synaptically connected neurons that enables visualization and manipulation of these neurons simultaneously. This review focuses on three recently developed Drosophila genetic transsynaptic tools for detecting chemical synapses, highlights their advantages and potential pitfalls, and discusses the future development needs of these techniques.

Sex and Death: Identification of Feedback Neuromodulation Balancing Reproduction and Survival

Some semelparous organisms in nature mate as many times as they can in a single reproductive episode before death, while most iteroparous species including humans avoid such suicidal reproductive behavior. Animals naturally pursue more sex and the possible fatal consequence of excessive sex must be orchestrated by negative feedback signals in iteroparous species, yet very little is known about the regulatory mechanisms. Here we used Drosophila male sexual behavior as a model system to study how excessive sex may kill males and how the nervous system reacts to prevent death by sex. We found that continuous sexual activity by activating the fruitless-expressing neurons induced a fixed multi-step behavioral pattern ending with male death. We further found negative feedback in the fly brain to prevent suicidal sexual behavior by expression changes of the neurotransmitters acetylcholine and gamma-aminobutyric acid, and neuropeptide F. These findings are crucial to understand the molecular underpinnings of how different organisms choose reproductive strategies and balance reproduction and survival.

Gαq splice variants mediate phototransduction, rhodopsin synthesis, and retinal integrity in Drosophila

Heterotrimeric G proteins mediate a variety of signaling processes by coupling G protein-coupled receptors to intracellular effector molecules. In Drosophila, the Gαq gene encodes several Gαq splice variants, with the Gαq1 isoform protein playing a major role in fly phototransduction. However, Gαq1 null mutant flies still exhibit a residual light response, indicating that other Gαq splice variants or additional Gq α subunits are involved in phototransduction. Here, we isolated a mutant fly with no detectable light responses, decreased rhodopsin (Rh) levels, and rapid retinal degeneration. Using electrophysiological and genetic studies, biochemical assays, immunoblotting, real-time RT-PCR, and EM analysis, we found that mutations in the Gαq gene disrupt light responses and demonstrate that the Gαq3 isoform protein is responsible for the residual light response in Gαq1 null mutants. Moreover, we report that Gαq3 mediates rhodopsin synthesis. Depletion of all Gαq splice variants led to rapid light-dependent retinal degeneration, due to the formation stable Rh1-arrestin 2 (Arr2) complexes. Our findings clarify essential roles of several different Gαq splice variants in phototransduction and retinal integrity in Drosophila and reveal that Gαq3 functions in rhodopsin synthesis.