Drosophila nicotinic acetylcholine receptor subunits and their native interactions with insecticidal peptide toxins

Molecular organization of central cholinergic synapses

Synapses have undergone significant diversification and adaptation, contributing to the complexity of the central nervous system. Understanding their molecular architecture is essential for deciphering the brain's functional evolution. While nicotinic acetylcholine receptors (nAchRs) are widely distributed across metazoan brains, their associated protein networks remain poorly characterized. Using in vivo proximity labeling, we generated proteomic maps of subunit-specific nAchR interactomes in developing and mature Drosophila brains. Our findings reveal a developmental expansion and reconfiguration of the nAchR interactome. Proteome profiling with genetic perturbations showed that removing individual nAchR subunits consistently triggers compensatory shifts in receptor subtypes, highlighting mechanisms of synaptic plasticity. We also identified the Rho-GTPase regulator Still life (Sif) as a key organizer of cholinergic synapses, with loss of Sif disrupting their molecular composition and structural integrity. These results provide molecular insights into the development and plasticity of central cholinergic synapses, advancing our understanding of synaptic identity conservation and divergence.

Columnar cholinergic neurotransmission onto T5 cells of Drosophila

Several nicotinic and muscarinic acetylcholine receptors (AChRs) are expressed in the brain of Drosophila melanogaster. However, the contribution of different AChRs to visual information processing remains poorly understood. T5 cells are the primary motion-sensing neurons in the OFF pathway and receive input from four different columnar cholinergic neurons, Tm1, Tm2, Tm4, and Tm9. We reasoned that different AChRs in T5 postsynaptic sites might contribute to direction selectivity, a central feature of motion detection. We show that the nicotinic nAChRα1, nAChRα3, nAChRα4, nAChRα5, nAChRα7, and nAChβ1 subunits localize on T5 dendrites. By targeting synaptic markers specifically to each cholinergic input neuron, we find a prevalence of the nAChRα5 in Tm1, Tm2, and Tm4-to-T5 synapses and of nAChRα7 in Tm9-to-T5 synapses. Knockdown of nAChRα4, nAChRα5, nAChRα7, or mAChR-B individually in T5 cells alters the optomotor response and reduces T5 directional selectivity. Our findings indicate the contribution of a consortium of postsynaptic receptors to input visual processing and, thus, to the computation of motion direction in T5 cells.

Alcohol induces long-lasting sleep deficits in Drosophila via subsets of cholinergic neurons

Alcohol consumption causes short- and long-term sleep impairments, which persist into recovery from alcohol use disorder (AUD). In humans, sleep quantity and quality are disturbed even after 2 weeks of alcohol abstinence in as many as 72% of AUD patients. These sleep deficits are strong predictors of relapse to drinking, but their underlying biological mechanisms are poorly understood, making them difficult to treat in a targeted manner. Here, we took advantage of Drosophila melanogaster's translational relevance for human sleep and alcohol responses to model human alcohol-induced sleep deficits and determine mechanisms of these effects. While low doses of alcohol stimulate the central nervous system (CNS) in flies and in humans, high doses depress the CNS, leading to sedation. After a single, sedating alcohol exposure, flies experienced loss of nighttime sleep, increased time to fall asleep, and reduced sleep quality. These effects lasted for days but eventually recovered. Hyperactivating ethanol exposures failed to induce sleep deficits, even when repeated, suggesting that CNS-depressant effects of sedating ethanol exposures are required for long-lasting sleep deficits. By manipulating activity in neurons producing different neurotransmitters, we determined that reduced cholinergic activity synergized with a sub-sedating ethanol exposure to cause sleep deficits. We then identified subsets of cholinergic neurons mediating these effects, which included mushroom body neurons previously implicated in sleep and alcohol responses. When those neurons were excluded, sleep effects were abrogated. These data suggest that ethanol-induced suppression of cholinergic neurons induces long-lasting sleep deficits, which are conserved from Drosophila to humans.

The inhibitory effect of nicotine on Lumbriculus variegatus stereotypical movements and locomotor activity

Nicotine has been shown to induce profound physiological and behavioural responses in invertebrate model organisms such as Caenorhabditis elegans and Drosophila melanogaster. Lumbriculus variegatus is an aquatic oligochaete worm which we have previously demonstrated has application within pharmacological research. Herein, we demonstrate the presence of endogenous acetylcholine and cholinesterase activity within L. variegatus and show the time-dependent effects on the sensitivity of L. variegatus to nicotine. We describe the effects of a broad range of concentrations of nicotine (1 μM - 1 mM) on L. variegatus response to tactile stimulation and locomotor activity following acute (10-min) and chronic (24-h) exposure. Here, we show that 10 min of exposure to ≥0.1 mM nicotine reversibly reduces the ability of tactile stimulation to elicit stereotypical movements of body reversal and helical swimming, and locomotor activity in L. variegatus. We also demonstrate that exposure to ≥0.1 mM nicotine for 24 h was toxic to L. variegatus. Chronic low-dose nicotine ≥25 μM similarly inhibits L. variegatus behaviours with 50 μM causing irreversible inhibition of movement. Thus, L. variegatus presents a model for studying the effects of nicotine and further demonstrates the application of the in vivo model L. variegatus for behavioural pharmacology research.

Advances in spatial proteomics: Mapping proteome architecture from protein complexes to subcellular localizations

Proteins are responsible for most intracellular functions, which they perform as part of higher-order molecular complexes, located within defined subcellular niches. Localization is both dynamic and context specific and mislocalization underlies a multitude of diseases. It is thus vital to be able to measure the components of higher-order protein complexes and their subcellular location dynamically in order to fully understand cell biological processes. Here, we review the current range of highly complementary approaches that determine the subcellular organization of the proteome. We discuss the scale and resolution at which these approaches are best employed and the caveats that should be taken into consideration when applying them. We also look to the future and emerging technologies that are paving the way for a more comprehensive understanding of the functional roles of protein isoforms, which is essential for unraveling the complexities of cell biology and the development of disease treatments.

A tailed mirtron promotes longevity in Drosophila

Thousands of atypical microRNAs (miRNAs) have been described in the genomes of animals; however, it is unclear if many of these non-canonical miRNAs can measurably influence phenotypes. Mirtrons are the largest class of non-canonical miRNAs that are produced from hairpins excised by splicing, which after debranching become substrates for Dicer and load into RISC. Most mirtrons require additional processing after splicing to remove 'tail' residues interposed between one of the host intron splice sites and base of the hairpin precursor structure. Despite most mirtrons requiring tail removal no function has been elucidated for a tailed species, indeed for all mirtrons identified function has only been assigned to a single species. Here we study miR-1017, a mirtron with a 3' tail, which is well expressed and conserved in Drosophila species. We found that miR-1017 can extend lifespan when ectopically expressed in the neurons, which seems partly due to this miRNA targeting its host transcript, acetylcholine receptor Dα2. Unexpectedly we found that not only did miR-1017 function in trans but also in cis by affecting splicing of Dα2. This suggests a mechanism for mirtron evolution where initial roles of structural elements in splicing lead to secondary acquisition of trans-regulatory function.

Enrichment of Membrane Proteins for Downstream Analysis Using Styrene Maleic Acid Lipid Particles (SMALPs) Extraction

Integral membrane proteins are an important class of cellular proteins. These take part in key cellular processes such as signaling transducing receptors to transporters, many operating within the plasma membrane. More than half of the FDA-approved protein-targeting drugs operate via interaction with proteins that contain at least one membrane-spanning region, yet the characterization and study of their native interactions with therapeutic agents remains a significant challenge. This challenge is due in part to such proteins often being present in small quantities within a cell. Effective solubilization of membrane proteins is also problematic, with the detergents typically employed in solubilizing membranes leading to a loss of functional activity and key interacting partners. In recent years, alternative methods to extract membrane proteins within their native lipid environment have been investigated, with the aim of producing functional nanodiscs, maintaining protein-protein and protein-lipid interactions. A promising approach involves extracting membrane proteins in the form of styrene maleic acid lipid particles (SMALPs) that allow the retention of their native conformation. This extraction method offers many advantages for further protein analysis and allows the study of the protein interactions with other molecules, such as drugs. Here, we describe a protocol for efficient SMALP extraction of functionally active membrane protein complexes within nanodiscs. We showcase the method on the isolation of a low copy number plasma membrane receptor complex, the nicotinic acetylcholine receptor (nAChR), from adult Drosophila melanogaster heads. We demonstrate that these nanodiscs can be used to study native receptor-ligand interactions. This protocol can be applied across many biological scenarios to extract the native conformations of low copy number integral membrane proteins.

Controlled expression of nicotinic acetylcholine receptor-encoding genes in insects uncovers distinct mechanisms of action of the neonicotinoid insecticide dinotefuran

Dinotefuran, a neonicotinoid, is a unique insecticide owing to its structure and action. We took two approaches that employed insects with controlled expression of nicotinic acetylcholine receptor (nAChR)-encoding genes to gain insight into the uniqueness of dinotefuran. First, we examined the insecticidal activity of dinotefuran and imidacloprid against brown planthoppers (Nilaparvata lugens), in which the expression of eight (of 13) individual subunit-encoding genes was specifically reduced using RNA interference. Knockdown of the tested gene, except one, resulted in a decrease in sensitivity to imidacloprid, whereas the sensitivity of N. lugens to dinotefuran decreased only when two of the eight genes were knocked down. These findings imply that a major dinotefuran-targeted nAChR subtype may contain specific subunits although imidacloprid acts on a broad range of receptor subtypes. Next, we examined the effects of knockout of Drosophila α1 subunit-encoding gene (Dα1) on the insecticidal effects of dinotefuran and imidacloprid. Dα1-deficient flies (Dα1^KO) demonstrated the same sensitivity to dinotefuran as control flies, but a decreased sensitivity to imidacloprid. This difference was attributed to a reduction in imidacloprid-binding sites in Dα1^KO flies, whereas the binding of dinotefuran remained unchanged. RNA sequencing analysis indicated that Dα2 expression was specifically enhanced in Dα1^KO flies. These findings suggest that changes in Dα1 and Dα2 expression contribute to the differences in the insecticidal activity of dinotefuran and imidacloprid in Dα1^KO flies. Overall, our findings suggest that dinotefuran acts on distinct nAChR subtypes.

Detergent-Free Isolation of Membrane Proteins and Strategies to Study Them in a Near-Native Membrane Environment

Atomic-resolution structural studies of membrane-associated proteins and peptides in a membrane environment are important to fully understand their biological function and the roles played by them in the pathology of many diseases. However, the complexity of the cell membrane has severely limited the application of commonly used biophysical and biochemical techniques. Recent advancements in NMR spectroscopy and cryoEM approaches and the development of novel membrane mimetics have overcome some of the major challenges in this area. For example, the development of a variety of lipid-nanodiscs has enabled stable reconstitution and structural and functional studies of membrane proteins. In particular, the ability of synthetic amphipathic polymers to isolate membrane proteins directly from the cell membrane, along with the associated membrane components such as lipids, without the use of a detergent, has opened new avenues to study the structure and function of membrane proteins using a variety of biophysical and biological approaches. This review article is focused on covering the various polymers and approaches developed and their applications for the functional reconstitution and structural investigation of membrane proteins. The unique advantages and limitations of the use of synthetic polymers are also discussed.