Tissue-specific O-GlcNAcylation profiling identifies substrates in translational machinery in Drosophila mushroom body contributing to olfactory learning.

O-GlcNAcylation is a dynamic post-translational modification that diversifies the proteome. Its dysregulation is associated with neurological disorders that impair cognitive function, and yet identification of phenotype-relevant candidate substrates in a brain-region specific manner remains unfeasible. By combining an O-GlcNAc binding activity derived from Clostridium perfringens OGA (CpOGA) with TurboID proximity labeling in Drosophila, we developed an O-GlcNAcylation profiling tool that translates O-GlcNAc modification into biotin conjugation for tissue-specific candidate substrates enrichment. We mapped the O-GlcNAc interactome in major brain regions of Drosophila and found that components of the translational machinery, particularly ribosomal subunits, were abundantly O-GlcNAcylated in the mushroom body of Drosophila brain. Hypo-O-GlcNAcylation induced by ectopic expression of active CpOGA in the mushroom body decreased local translational activity, leading to olfactory learning deficits that could be rescued by dMyc overexpression-induced increase of protein synthesis. Our study provides a useful tool for future dissection of tissue-specific functions of O-GlcNAcylation in Drosophila, and suggests a possibility that O-GlcNAcylation impacts cognitive function via regulating regional translational activity in the brain.

Newly synthesized proteins often receive further chemical modifications that change their structure and role in the cell. O-GlcNAcylation, for instance, consists in a certain type of sugar molecule being added onto dedicated protein segments. It is required for the central nervous system to develop and work properly; in fact, several neurological disorders such as Alzheimer's, Parkinson's or Huntington's disease are linked to disruptions in O-GlcNAcylation. However, scientists are currently lacking approaches that would allow them to reliably identify which proteins require O-GlcNAcylation in specific regions of the brain to ensure proper cognitive health. To address this gap, Yu et al. developed a profiling tool that allowed them to probe O-GlcNAcylation protein targets in different tissues of fruit flies. Their approach relies on genetically manipulating the animals so that a certain brain area overproduces two enzymes that work in tandem; the first binds specifically to O-GlcNAcylated proteins, which allows the second to add a small 'biotin' tag to them. Tagged proteins can then be captured and identified. Using this tool helped Yu et al. map out which proteins go through O-GlcNAcylation in various brain regions. This revealed, for example, that in the mushroom body ­ the 'learning center' of the fly brain ­ O-GlcNAcylation occurred predominantly in the protein-building machinery. To investigate the role of O-GlcNAcylation in protein synthesis and learning, Yu et al. used an approach that allowed them to decrease the levels of O-GlcNAcylation in the mushroom body. This resulted in reduced local protein production and the flies performing poorly in olfactory learning tasks. However, artificially increasing protein synthesis reversed these deficits. Overall, the work by Yu et al. provides a useful tool for studying the tissue-specific effects of O-GlcNAcylation in fruit flies, and its role in learning. Further studies should explore how this process may be linked to cognitive function by altering protein synthesis in the brain.

The Drosophila NPY-like system protects against chronic stress-induced learning deficit by preventing the disruption of autophagic flux.

Chronic stress may induce learning and memory deficits that are associated with a depression-like state in Drosophila melanogaster. The molecular and neural mechanisms underlying the etiology of chronic stress-induced learning deficit (CSLD) remain elusive. Here, we show that the autophagy-lysosomal pathway, a conserved cellular signaling mechanism, is associated with chronic stress in Drosophila, as indicated by time-series transcriptome profiling. Our findings demonstrate that chronic stress induces the disruption of autophagic flux, and chronic disruption of autophagic flux could lead to a learning deficit. Remarkably, preventing the disruption of autophagic flux by up-regulating the basal autophagy level is sufficient to protect against CSLD. Consistent with the essential role of the dopaminergic system in modulating susceptibility to CSLD, dopamine neuronal activity is also indispensable for chronic stress to induce the disruption of autophagic flux. By screening knockout mutants, we found that neuropeptide F, the Drosophila homolog of neuropeptide Y, is necessary for normal autophagic flux and promotes resilience to CSLD. Moreover, neuropeptide F signaling during chronic stress treatment promotes resilience to CSLD by preventing the disruption of autophagic flux. Importantly, neuropeptide F receptor activity in dopamine neurons also promotes resilience to CSLD. Together, our data elucidate a mechanism by which stress-induced excessive dopaminergic activity precipitates the disruption of autophagic flux, and chronic disruption of autophagic flux leads to CSLD, while inhibitory neuropeptide F signaling to dopamine neurons promotes resilience to CSLD by preventing the disruption of autophagic flux.

Preoperative prediction of Lauren classification in gastric cancer: a radiomics model based on dual-energy CT iodine map.

OBJECTIVE: To investigate the value of a radiomics model based on dual-energy computed tomography (DECT) venous-phase iodine map (IM) and 120 kVp equivalent mixed images (MIX) in predicting the Lauren classification of gastric cancer. METHODS: A retrospective analysis of 240 patients undergoing preoperative DECT and postoperative pathologically confirmed gastric cancer was done. Training sets (n = 168) and testing sets (n = 72) were randomly assigned with a ratio of 7:3. Patients are divided into intestinal and non-intestinal groups. Traditional features were analyzed by two radiologists, using logistic regression to determine independent predictors for building clinical models. Using the Radiomics software, radiomics features were extracted from the IM and MIX images. ICC and Boruta algorithm were used for dimensionality reduction, and a random forest algorithm was applied to construct the radiomics model. ROC and DCA were used to evaluate the model performance. RESULTS: Gender and maximum tumor thickness were independent predictors of Lauren classification and were used to build a clinical model. Separately establish IM-radiomics (R-IM), mixed radiomics (R-MIX), and combined IM + MIX image radiomics (R-COMB) models. In the training set, each radiomics model performed better than the clinical model, and the R-COMB model showed the best prediction performance (AUC: 0.855). In the testing set also, the R-COMB model had better prediction performance than the clinical model (AUC: 0.802). CONCLUSION: The R-COMB radiomics model based on DECT-IM and 120 kVp equivalent MIX images can effectively be used for preoperative noninvasive prediction of the Lauren classification of gastric cancer. CRITICAL RELEVANCE STATEMENT: The radiomics model based on dual-energy CT can be used for Lauren classification prediction of preoperative gastric cancer and help clinicians formulate individualized treatment plans and assess prognosis.

Protein O-GlcNAcylation homeostasis regulates facultative heterochromatin to fine-tune sog-Dpp signaling during Drosophila early embryogenesis.

Protein O-GlcNAcylation is a monosaccharide post-translational modification maintained by two evolutionarily conserved enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Mutations in human OGT have recently been associated with neurodevelopmental disorders, although the mechanisms linking O-GlcNAc homeostasis to neurodevelopment are not understood. Here, we investigate the effects of perturbing protein O-GlcNAcylation using transgenic Drosophila lines that overexpress a highly active OGA. We reveal that temporal reduction of protein O-GlcNAcylation in early embryos leads to reduced brain size and olfactory learning in adult Drosophila. Downregulation of O-GlcNAcylation induced by the exogenous OGA activity promotes nuclear foci formation of Polycomb-group protein Polyhomeotic and the accumulation of excess K27 trimethylation of histone H3 (H3K27me3) at the mid-blastula transition. These changes interfere with the zygotic expression of several neurodevelopmental genes, particularly shortgastrulation (sog), a component of an evolutionarily conserved sog-Decapentaplegic (Dpp) signaling system required for neuroectoderm specification. Our findings highlight the importance of early embryonic O-GlcNAcylation homeostasis for the fidelity of facultative heterochromatin redeployment and initial cell fate commitment of neuronal lineages, suggesting a possible mechanism underpinning OGT-associated intellectual disability.

Fatty Acid Biosynthesis Pathways Are Downregulated during Stigma Development and Are Critical during Self-Incompatible Responses in Ornamental Kale.

In Brassicaceae, the papillary cells of the stigma are the primary site of the self-incompatibility (SI) responses. SI preserves the genetic diversity by selectively rejecting irrelevant or incompatible pollen, thus promoting cross fertilization and species fitness. Mechanisms that regulate SI responses in Brassica have been studied mainly on the mature stigma that often undermines how stigma papillary cells attain the state of SI during development. To understand this, we integrated PacBio SMRT-seq with Illumina RNA-seq to construct a de novo full-length transcriptomic database for different stages of stigma development in ornamental kale. A total of 48,800 non-redundant transcripts, 31,269 novel transcripts, 24,015 genes, 13,390 alternative splicing, 22,389 simple sequence repeats, 21,816 complete ORF sequences, and 4591 lncRNAs were identified and analyzed using PacBio SMRT-seq. The Illumina RNA-seq revealed 15,712 differentially expressed genes (DEGs) and 8619 transcription factors. The KEGG enrichment analysis of 4038 DEGs in the "incompatibility" group revealed that the flavonoid and fatty acid biosynthesis pathways were significantly enriched. The cluster and qRT-PCR analysis indicated that 11 and 14 candidate genes for the flavonoid and fatty acid biosynthesis pathways have the lowest expression levels at stigma maturation, respectively. To understand the physiological relevance of the downregulation of fatty acid biosynthesis pathways, we performed inhibitor feeding assays on the mature stigma. The compatible pollination response was drastically reduced when mature stigmas were pre-treated with a fatty acid synthase inhibitor. This finding suggested that fatty acid accumulation in the stigmas may be essential for compatible pollination and its downregulation during maturity must have evolved as a support module to discourage the mounting of self-incompatible pollen.

Novel study on the prevalence of Trichinella spiralis in farmed American minks (Neovison vison) associated with exposure to wild rats (Rattus norvegicus) in China.

Minks and brown rats are reservoir hosts for many endoparasites including those of the genus Trichinella, a group of parasite nematodes with a worldwide distribution. However, little is known about the prevalence of Trichinella sp. infection in the American mink (Neovison vison) and rats (Rattus norvegicus) in China. Therefore, we aimed to examine the prevalence of Trichinella sp. infection in farmed minks in Weihai city, Shandong province, China and infer the possible route for Trichinella transmission to farmed American minks. In total, 289 muscle samples from minks and 102 carcasses of rats were collected from Weihai City. The appearance of Trichinella sp. was examined using the pooled artificial HCl-pepsin digestion method. The results showed that muscle larvae were detected in 20 of 289 minks (6.92%) and 2 of 102 synanthropic rats (1.96%). The larval density of Trichinella sp. in mink samples ranged from 0.025 to 0.815 larvae per gram (lpg), while the average larval burden in rats was 0.17 lpg. The isolates derived from minks and rats were identified at the species level using multiplex polymerase chain reaction (PCR), which revealed that the size of the two PCR products matched that of T. spiralis at 173 bp. Furthermore, sequence analysis showed 100% identity of the 5S rDNA inter-gene spacer regions of the two isolates to that of T. spiralis. This study presents a novel report of T. spiralis-mediated infection in minks and synanthropic rats in China. We highlight the vulnerability of farmed minks to Trichinella infection through exposure to synanthropic rats, which may raise a public health concern of potential zoonotic risks for domestic animals.

Euonymine inhibits in-stent restenosis through enhancing contractile phenotype of vascular smooth muscle cells via modulating the PTEN/AKT/mTOR signaling pathway.

BACKGROUND: Percutaneous coronary intervention (PCI) is an effective treatment for acute myocardial infarction, but the postoperative in-stent re-stenosis (ISR) remains a major risk factor that affects the prognosis of PCI. Clinically, drug-eluting stents (DES) are widely applied to prevent and treat ISR. However, only a few stent coating drugs are currently available for clinical use, including paclitaxel and rapamycin (sirolimus) and their derivatives. These stent-coated drugs have led to a decrease in restenosis rates, but the major adverse outcomes, such as delayed endothelial healing and increased in-stent thrombosis, seriously reduce their therapeutic effects. PURPOSE: Herein, we explored the potential efficacy of Euonymine (Euo), an alkaloid extracted from Tripterygium Hypoglaucum (Levl) Hutch (THH, Lei gong Teng), for the prevention against ISR after PCI. STUDY DESIGN: Our study depicts the potential efficacy of Euo in treating ISR and explores its mechanism with in vitro and in vivo models. METHODS: Primary vascular smooth muscle cells (VSMCs) from the rabbit thoracic aorta were cultured, and the proliferation and migration of VSMCs were monitored. Apoptosis was measured by Transmission Electron Microscopy and TUNEL staining assay. Protein and gene levels were measured to explore the underlying molecular mechanisms. In vivo models of porcine coronary implantation and rabbit carotid balloon injury are used to validate the efficacy of Euo in inhibiting ISR after PCI. RESULTS: With an ox-LDL-injured cell model, we showed that Euo suppressed the proliferation and migration of the rabbit thoracic aorta primary VSMCs, while inducing their apoptosis. We next established a rabbit carotid balloon injury model in which the phosphorylation levels of PI3K and AKT1 (Ser473) as well as mTOR activity were significantly elevated compared to the sham-operated control. These activities were significantly attenuated by the Euo intervention. Additionally, the balloon angioplasty significantly increased the expression of Bcl-2, while decreased the expression of Bax and caspase-3. Euo intervention significantly increased the ratio of Bax/Bcl-2 and the level of caspase-3. Taken together, Euo may enhance the VSMCs contractile phenotype by modulating the PTEN/AKT/mTOR signaling pathway. Furthermore, with two in vivo models, the porcine coronary artery implantation model, and the rabbit carotid balloon injury model, we demonstrated that Euo-eluting stents indeed inhibited ISR after PCI. CONCLUSION: For the first time, this study delineates the potential efficacy of Euo, derived from Tripterygium Hypoglaucum (Levl) Hutch, in ameliorating ISR after PCI with two in vivo models. The phytochemical targets PTEN/AKT/mTOR signaling pathway to increase the contractile phenotype of VSMCs and exerts anti-proliferative, anti-migratory as well as pro-apoptotic effects, thereby inhibiting the ISR.

A pair of dopamine neurons mediate chronic stress signals to induce learning deficit in Drosophila melanogaster.

Chronic stress could induce severe cognitive impairments. Despite extensive investigations in mammalian models, the underlying mechanisms remain obscure. Here, we show that chronic stress could induce dramatic learning and memory deficits in Drosophila melanogaster The chronic stress-induced learning deficit (CSLD) is long lasting and associated with other depression-like behaviors. We demonstrated that excessive dopaminergic activity provokes susceptibility to CSLD. Remarkably, a pair of PPL1-γ1pedc dopaminergic neurons that project to the mushroom body (MB) γ1pedc compartment play a key role in regulating susceptibility to CSLD so that stress-induced PPL1-γ1pedc hyperactivity facilitates the development of CSLD. Consistently, the mushroom body output neurons (MBON) of the γ1pedc compartment, MBON-γ1pedc>α/ß neurons, are important for modulating susceptibility to CSLD. Imaging studies showed that dopaminergic activity is necessary to provoke the development of chronic stress-induced maladaptations in the MB network. Together, our data support that PPL1-γ1pedc mediates chronic stress signals to drive allostatic maladaptations in the MB network that lead to CSLD.

Trichinella spiralis Thioredoxin Peroxidase 2 Regulates Protective Th2 Immune Response in Mice by Directly Inducing Alternatively Activated Macrophages.

Trichinella infection can induce macrophages into the alternatively activated phenotype, which is primarily associated with the development of a polarized Th2 immune response. In the present study, we examined the immunomodulatory effect of T. spiralis thioredoxin peroxidase-2 (TsTPX2), a protein derived from T. spiralis ES products, in the regulation of Th2 response through direct activation of macrophages. The location of TsTPX2 was detected by immunohistochemistry and immunofluorescence analyses. The immune response in vivo induced by rTsTPX2 was characterized by analyzing the Th2 cytokines and Th1 cytokines in the peripheral blood. The rTsTPX2-activated macrophages (MrTsTPX2) were tested for polarization, their ability to evoke naïve CD4+ T cells, and resistance to the larval infection after adoptive transfer in BALB/c mice. The immunolocalization analysis showed TsTPX2 in cuticles and stichosome of T. spiralis ML. The immunostaining was detected in cuticles and stichosome of T. spiralis Ad3 and ML, as well as in tissue-dwellings around ML after the intestines and muscle tissues of infected mice were incubated with anti-rTsTPX2 antibody. Immunization of BALB/c mice with rTsTPX2 could induce a Th1-suppressing mixed immune response given the increased levels of Th2 cytokines (IL-4 and IL-10) production along with the decreased levels of Th1 cytokines (IFN-γ, IL-12, and TNF-α). In vitro studies showed that rTsTPX2 could directly drive RAW264.7 and peritoneal macrophages to the M2 phenotype. Moreover, MrTsTPX2 could promote CD4+ T cells polarized into Th2 type in vitro. Adoptive transfer of MrTsTPX2 into mice suppressed Th1 responses by enhancing Th2 responses and exhibited a 44.7% reduction in adult worm burden following challenge with T. spiralis infective larval, suggesting that the TsTPX2 is a potential vaccine candidate against trichinosis. Our study showed that TsTPX2 would be at least one of the molecules to switch macrophages into the M2 phenotype during T. spiralis infection, which provides a new therapeutic approach to various inflammatory disorders like allergies or autoimmune diseases.

Analysis of miRNAs Targeted Storage Regulatory Genes during Soybean Seed Development Based on Transcriptome Sequencing.

Soybeans are an important cash crop and are widely used as a source of vegetable protein and edible oil. MicroRNAs (miRNA) are endogenous small RNA that play an important regulatory role in the evolutionarily conserved system of gene expression. In this study, we selected four lines with extreme phenotypes, as well as high or low protein and oil content, from the chromosome segment substitution line (CSSL) constructed from suinong (SN14) and ZYD00006, and planted and sampled at three stages of grain development for small RNA sequencing and expression analysis. The sequencing results revealed the expression pattern of miRNA in the materials, and predicted miRNA-targeted regulatory genes, including 1967 pairs of corresponding relationships between known-miRNA and their target genes, as well as 597 pairs of corresponding relationships between novel-miRNA and their target genes. After screening and annotating genes that were targeted for regulation, five specific genes were identified to be differentially expressed during seed development and subsequently analyzed for their regulatory relationship with miRNAs. The expression pattern of the targeted gene was verified by Real-time Quantitative PCR (RT-qPCR). Our research provides more information about the miRNA regulatory network in soybeans and further identifies useful genes that regulate storage during soy grain development, providing a theoretical basis for the regulation of soybean quality traits.

Identification of Soybean Genes Related to Soybean Seed Protein Content Based on Quantitative Trait Loci Collinearity Analysis.

Increasing the protein content of soybean seeds through a higher ratio of glycinin is important for soybean breeding and food processing; therefore, the integration of different quantitative trait loci (QTLs) is of great significance. In this study, we investigated the collinearity of seed protein QTLs. We identified 192 collinear protein QTLs that formed six hotspot regions. The two most important regions had seed protein 36-10 and seed protein 36-20 as hub nodes. We used a chromosome segment substitution line (CSSL) population for QTL validation and identified six CSSL materials with collinear QTLs. Five materials with higher protein and glycinin contents in comparison to the recurrent parent were analyzed. A total of 13 candidate genes related to seed protein from the QTL hotspot intervals were detected, 8 of which had high expression in mature soybean seeds. These results offer a new analysis method for molecular-assisted selection (MAS) and improvement of soybean product quality.

Identification of Major QTLs Associated With First Pod Height and Candidate Gene Mining in Soybean.

First pod height (FPH) is a quantitative trait in soybean [Glycine max (L.) Merr.] that affects mechanized harvesting. A compatible combination of the FPH and the mechanized harvester is required to ensure that the soybean is efficiently harvested. In this study, 147 recombinant inbred lines, which were derived from a cross between 'Dongnong594' and 'Charleston' over 8 years, were used to identify the major quantitative trait loci (QTLs) associated with FPH. Using a composite interval mapping method with WinQTLCart (version 2.5), 11 major QTLs were identified. They were distributed on five soybean chromosomes, and 90 pairs of QTLs showed significant epistatic associates with FPH. Of these, 3 were main QTL × main QTL interactions, and 12 were main QTL × non-main QTL interactions. A KEGG gene annotation of the 11 major QTL intervals revealed 8 candidate genes related to plant growth, appearing in the pathways K14486 (auxin response factor 9), K14498 (serine/threonine-protein kinase), and K13946 (transmembrane amino acid transporter family protein), and 7 candidate genes had high expression levels in the soybean stems. These results will aid in building a foundation for the fine mapping of the QTLs related to FPH and marker-assisted selection for breeding in soybean.

Meta-analysis and transcriptome profiling reveal hub genes for soybean seed storage composition during seed development.

Soybean is an important crop providing edible oil and protein source. Soybean oil and protein contents are quantitatively inherited and significantly affected by environmental factors. In this study, meta-analysis was conducted based on soybean physical maps to integrate quantitative trait loci (QTLs) from multiple experiments in different environments. Meta-QTLs for seed oil, fatty acid composition, and protein were identified. Of them, 11 meta-QTLs were located on hot regions for both seed oil and protein. Next, we selected 4 chromosome segment substitution lines with different seed oil and protein contents to characterize their 3 years of phenotype selection in the field. Using strand-specific RNA-sequencing analysis, we profile the time-course transcriptome patterns of soybean seeds at early maturity, middle maturity, and dry seed stages. Pairwise comparison and K-means clustering analysis revealed 7,482 differentially expressed genes and 45 expression patterns clusters. Weighted gene coexpression network analysis uncovered 46 modules of gene expression patterns. The 2 most significant coexpression networks were visualized, and 7 hub genes were identified that were involved in soybean oil and seed storage protein accumulation processes. Our results provided a transcriptome dataset for soybean seed development, and the candidate hub genes represent a foundation for further research.

Label-free DNAsensor with PCR-like sensitivity based on background reduction and target-triggered polymerization amplification.

In this work, we have developed a highly sensitive and label-free DNAsensor for nucleic acid detection based on background noise reduction by exonuclease I (Exo I) and target-triggered cycled polymerization amplification. This DNAsensor consists of a long-tail probe, a short primer and polymerase. In the absence of the target, the long-tail probe and short primer are digested by Exo I, which minimizes the intercalation of fluorescence dye and reduces the background noise. In the presence of the target, the specific binding between the long-tail probe and the target triggers cycled polymerization reactions to form long dsDNA products. These long dsDNA products prevent effectively them from degrading by Exo I and amplify the fluorescence signals. In our sensing approach, the combination of the ExoI-assisted background reduction with the cycled polymerization amplification allows us to achieve a PCR-like sensitivity without labeling, washing separation and temperature cycles in a homogenous solution. Using total RNA samples extracted from hepatitis C virus (HCV) as targets, we further demonstrate the detection capability of the DNAsensor for complex nucleic acid samples, indicating its potential applicability for clinic molecular diagnostic assays.

Imaging a population code for odor identity in the Drosophila mushroom body.

The brain represents sensory information in the coordinated activity of neuronal ensembles. Although the microcircuits underlying olfactory processing are well characterized in Drosophila, no studies to date have examined the encoding of odor identity by populations of neurons and related it to the odor specificity of olfactory behavior. Here we used two-photon Ca(2+) imaging to record odor-evoked responses from >100 neurons simultaneously in the Drosophila mushroom body (MB). For the first time, we demonstrate quantitatively that MB population responses contain substantial information on odor identity. Using a series of increasingly similar odor blends, we identified conditions in which odor discrimination is difficult behaviorally. We found that MB ensemble responses accounted well for olfactory acuity in this task. Kenyon cell ensembles with as few as 25 cells were sufficient to match behavioral discrimination accuracy. Using a generalization task, we demonstrated that the MB population code could predict the flies' responses to novel odors. The degree to which flies generalized a learned aversive association to unfamiliar test odors depended upon the relative similarity between the odors' evoked MB activity patterns. Discrimination and generalization place different demands on the animal, yet the flies' choices in these tasks were reliably predicted based on the amount of overlap between MB activity patterns. Therefore, these different behaviors can be understood in the context of a single physiological framework.

MicroRNA-276a functions in ellipsoid body and mushroom body neurons for naive and conditioned olfactory avoidance in Drosophila.

MicroRNA (miRNA)-mediated gene regulation plays a key role in brain development and function. But there are few cases in which the roles of individual miRNAs have been elucidated in behaving animals. We report a miR-276a::DopR regulatory module in Drosophila that functions in distinct circuits for naive odor responses and conditioned odor memory. Drosophila olfactory aversive memory involves convergence of the odors (conditioned stimulus) and the electric shock (unconditioned stimulus) in mushroom body (MB) neurons. Dopamine receptor DopR mediates the unconditioned stimulus inputs onto MB. Distinct dopaminergic neurons also innervate ellipsoid body (EB), where DopR function modulates arousal to external stimuli. We demonstrate that miR-276a is required in MB neurons for memory formation and in EB for naive responses to odors. Both roles of miR-276a are mediated by tuning DopR expression. The dual role of this miR-276a::DopR genetic module in these two neural circuits highlights the importance of miRNA-mediated gene regulation within distinct circuits underlying both naive behavioral responses and memory.

Gamma neurons mediate dopaminergic input during aversive olfactory memory formation in Drosophila.

Mushroom body (MB)-dependent olfactory learning in Drosophila provides a powerful model to investigate memory mechanisms. MBs integrate olfactory conditioned stimulus (CS) inputs with neuromodulatory reinforcement (unconditioned stimuli, US), which for aversive learning is thought to rely on dopaminergic (DA) signaling to DopR, a D1-like dopamine receptor expressed in MBs. A wealth of evidence suggests the conclusion that parallel and independent signaling occurs downstream of DopR within two MB neuron cell types, with each supporting half of memory performance. For instance, expression of the Rutabaga (Rut) adenylyl cyclase in γ neurons is sufficient to restore normal learning to rut mutants, whereas expression of Neurofibromatosis 1 (NF1) in α/ß neurons is sufficient to rescue NF1 mutants. DopR mutations are the only case where memory performance is fully eliminated, consistent with the hypothesis that DopR receives the US inputs for both γ and α/ß lobe traces. We demonstrate, however, that DopR expression in γ neurons is sufficient to fully support short- and long-term memory. We argue that DA-mediated CS-US association is formed in γ neurons followed by communication between γ and α/ß neurons to drive consolidation.

Distinct molecular underpinnings of Drosophila olfactory trace conditioning.

Trace conditioning is valued as a simple experimental model to assess how the brain associates events that are discrete in time. Here, we adapted an olfactory trace conditioning procedure in Drosophila melanogaster by training fruit flies to avoid an odor that is followed by foot shock many seconds later. The molecular underpinnings of the learning are distinct from the well-characterized simultaneous conditioning, where odor and punishment temporally overlap. First, Rutabaga adenylyl cyclase (Rut-AC), a putative molecular coincidence detector vital for simultaneous conditioning, is dispensable in trace conditioning. Second, dominant-negative Rac expression, thought to sustain early labile memory, significantly enhances learning of trace conditioning, but leaves simultaneous conditioning unaffected. We further show that targeting Rac inhibition to the mushroom body (MB) but not the antennal lobe (AL) suffices to achieve the enhancement effect. Moreover, the absence of trace conditioning learning in D1 dopamine receptor mutants is rescued by restoration of expression specifically in the adult MB. These results suggest the MB as a crucial neuroanatomical locus for trace conditioning, which may harbor a Rac activity-sensitive olfactory "sensory buffer" that later converges with the punishment signal carried by dopamine signaling. The distinct molecular signature of trace conditioning revealed here shall contribute to the understanding of how the brain overcomes a temporal gap in potentially related events.

The Caenorhabditis elegans AHR-1 transcription complex controls expression of soluble guanylate cyclase genes in the URX neurons and regulates aggregation behavior.

C. elegans ahr-1 is orthologous to the mammalian aryl hydrocarbon receptor, and it functions as a transcription factor to regulate the development of certain neurons. Here, we describe the role of ahr-1 in a specific behavior: the aggregation of C. elegans on lawns of bacterial food. This behavior is modulated by nutritional cues and ambient oxygen levels, and aggregation is inhibited by the npr-1 G protein-coupled neuropeptide receptor gene. Loss-of-function mutations in ahr-1 or its transcription partner aha-1 (ARNT) suppress aggregation behavior in npr-1-deficient animals. This behavioral defect is not irreparable. Aggregation behavior can be restored to ahr-1-deficient animals by heat-shock induction of ahr-1 transcription several hours after ahr-1-expressing neurons have normally differentiated. We show that ahr-1 and aha-1 promote cell-type-specific expression of soluble guanylate cyclase genes that have key roles in aggregation behavior and hyperoxia avoidance. Aggregation behavior can be partially restored to ahr-1 mutant animals by expression of ahr-1 in only 4 neurons, including URXR and URXL. We conclude that the AHR-1:AHA-1 transcription complex regulates the expression of soluble guanylate cyclase genes and other unidentified genes that are essential for acute regulation of aggregation behavior.

The Caenorhabditis elegans aryl hydrocarbon receptor, AHR-1, regulates neuronal development.

The mammalian aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the toxic effects of dioxins and related compounds. Dioxins have been shown to cause a range of neurological defects, but the role of AHR during normal neuronal development is not known. Here we investigate the developmental functions of ahr-1, the Caenorhabditis elegans aryl hydrocarbon receptor homolog. We show that ahr-1:GFP is expressed in a subset of neurons, and we demonstrate that animals lacking ahr-1 function have specific defects in neuronal differentiation, as evidenced by changes in gene expression, aberrant cell migration, axon branching, or supernumerary neuronal processes. In ahr-1-deficient animals, the touch receptor neuron AVM and its sister cell, the interneuron SDQR, exhibit cell and axonal migration defects. We show that dorsal migration of SDQR is mediated by UNC-6/Netrin, SAX-3/Robo, and UNC-129/TGFbeta, and this process requires the functions of both ahr-1 and its transcription factor dimerization partner aha-1. We also document a role for ahr-1 during the differentiation of the neurons that contact the pseudocoelomic fluid. In ahr-1-deficient animals, these neurons are born but they do not express the cell-type-specific markers gcy-32:GFP and npr-1:GFP at appropriate levels. Additionally, we show that ahr-1 expression is regulated by the UNC-86 transcription factor. We propose that the AHR-1 transcriptional complex acts in combination with other intrinsic and extracellular factors to direct the differentiation of distinct neuronal subtypes. These data, when considered with the neurotoxic effects of AHR-activating pollutants, support the hypothesis that AHR has an evolutionarily conserved role in neuronal development.