Serum Response Factor-Mediated Gene Regulation in a Drosophila Visual Working Memory

Targeting XPO6 inhibits prostate cancer progression and enhances the suppressive efficacy of docetaxel

BACKGROUND

Although XPO6, one of the Exportin family members, functions in malignant progression of certain types of cancer, its role in prostate cancer (PCa) has not been elucidated. Herein, we investigated the oncogenic effect and clarified the downstream mechanism of XPO6 in PCa cells.

METHODS

We detected the expression level of XPO6 in PCa tissues by immunohistochemistry (IHC) and analyzed the correlation between clinicopathological characteristics and XPO6 level based on TCGA database. The effects of XPO6 in the proliferation and migration or resistance to docetaxel (DTX) in PCa cells were assessed using CCK8, colony formation, wound-healing and Transwell assays. Mice experiments were performed to investigate the role of XPO6 in tumor progression and DTX effect in vivo. Further, functional analysis of DEGs revealed the correlation of XPO6 with Hippo pathway and XPO6 could promote the expression and nuclear translocation of YAP1 protein. Furthermore, blocking Hippo pathway with YAP1 inhibitor leads to the loss of XPO6-mediated regulation of biological functions.

RESULTS

XPO6 was highly expressed and positively correlated with the clinicopathological characteristics of PCa. Functional experiments indicated that XPO6 could promote tumor development and DTX resistance in PCa. Mechanistically, we further confirmed that XPO6 could regulate Hippo pathway via mediating YAP1 protein expression and nuclear translocation thereby promoting PCa progression and chemotherapeutic resistance.

CONCLUSION

In conclusion, our research reveals that XPO6 potentially function as an oncogene and promotes DTX resistance of PCa, suggesting that XPO6 could be both a potential prognostic marker as well as a therapeutic target to effectively overcome DTX resistance.

Key role of exportin 6 in exosome-mediated viral transmission from insect vectors to plants

Exosomes play a key role in virus exocytosis and transmission. The exportin family is usually responsible for cargo nucleocytoplasmic trafficking, and they are frequently found in exosomes. However, the function of exportins sorted in exosomes remains unknown. Here, we successfully isolated "cup holder"-like exosomes from the saliva of ∼30,000 small brown planthoppers, which are vectors of rice stripe virus (RSV). RSV virions were packed in comparatively large exosomes. Four viral genomic RNAs at a certain ratio were identified in the saliva exosomes. The virions contained in the saliva exosomes were capable of replicating and causing disease in rice plants. Interference with each phase of the insect exosome system affected the transmission of RSV from the insect vectors to rice plants. Fragmented exportin 6 was coimmunoprecipitated with viral nucleocapsid protein in saliva and sorted to exosomes via interactions with the cargo sorting protein VPS37a. When the expression of exportin 6 was knocked down, the amounts of RSV secreted in saliva and rice plants were reduced by 60% and 74%, respectively. These results showed that exportin 6 acted as a vehicle for transporting RSV into exosomes to overcome the barrier of insect salivary glands for horizontal transmission. Exportin 6 would represent an ideal target that could be manipulated to control the outbreak of insect-borne viruses in the future.

MRTF-A-mediated protection against amyloid-β-induced neuronal injury correlates with restoring autophagy via miR-1273g-3p/mTOR axis in Alzheimer models

Myocardia-Related Transcription Factors-A (MRTF-A), which is enriched in the hippocampus and cerebral cortex, has been shown to have a protective function against ischemia hypoxia-induced neuronal apoptosis. However, the function of MRTF-A on β-amyloid peptide (Aβ)-induced neurotoxicity and autophagy dysfunction in Alzheimer's disease is still unclear. This study shows that the expression of MRTF-A in the hippocampus of Tg2576 transgenic mice is reduced, and the overexpression of MRTF-A mediated by lentiviral vectors carrying MRTF-A significantly reduces the accumulation of hippocampal β-amyloid peptide and reduces cognition defect. Overexpression of MRTF-A inhibits neuronal apoptosis, increases the protein levels of microtubule-associated protein 1 light chain 3-II (MAP1LC3/LC3-II) and Beclin1, reduces the accumulation of SQSTM1/p62 protein, and promotes autophagosomes-Lysosomal fusion in vivo and in vitro. Microarray analysis and bioinformatics analysis show that MRTF-A reverses Aβ-induced autophagy impairment by up-regulating miR-1273g-3p level leading to negative regulation of the mammalian target of rapamycin (mTOR), which is confirmed in Aβ1-42-treated SH-SY5Y cells. Further, overexpression of MRTF-A reduces Aβ1-42-induced neuronal apoptosis. And the effect was abolished by miR-1273g-3p inhibitor or MHY1485 (mTOR agonist), indicating that the protection of MRTF-A on neuronal damage is through targeting miR-1273g-3p/mTOR axis. Targeting this signaling may be a promising approach to protect against Aβ-induced neuronal injury.

bsAS, an antisense long non-coding RNA, essential for correct wing development through regulation of blistered/DSRF isoform usage

Natural Antisense Transcripts (NATs) are long non-coding RNAs (lncRNAs) that overlap coding genes in the opposite strand. NATs roles have been related to gene regulation through different mechanisms, including post-transcriptional RNA processing. With the aim to identify NATs with potential regulatory function during fly development, we generated RNA-Seq data in Drosophila developing tissues and found bsAS, one of the most highly expressed lncRNAs in the fly wing. bsAS is antisense to bs/DSRF, a gene involved in wing development and neural processes. bsAS plays a crucial role in the tissue specific regulation of the expression of the bs/DSRF isoforms. This regulation is essential for the correct determination of cell fate during Drosophila development, as bsAS knockouts show highly aberrant phenotypes. Regulation of bs isoform usage by bsAS is mediated by specific physical interactions between the promoters of these two genes, which suggests a regulatory mechanism involving the collision of RNA polymerases transcribing in opposite directions. Evolutionary analysis suggests that bsAS NAT emerged simultaneously to the long-short isoform structure of bs, preceding the emergence of wings in insects.

Integrating GWAS and Transcriptomics to Identify the Molecular Underpinnings of Thermal Stress Responses in Drosophila melanogaster

Thermal tolerance of an organism depends on both the ability to dynamically adjust to a thermal stress and preparatory developmental processes that enhance thermal resistance. However, the extent to which standing genetic variation in thermal tolerance alleles influence dynamic stress responses vs. preparatory processes is unknown. Here, using the model species Drosophila melanogaster, we used a combination of Genome Wide Association mapping (GWAS) and transcriptomic profiling to characterize whether genes associated with thermal tolerance are primarily involved in dynamic stress responses or preparatory processes that influence physiological condition at the time of thermal stress. To test our hypotheses, we measured the critical thermal minimum (CTmin) and critical thermal maximum (CTmax) of 100 lines of the Drosophila Genetic Reference Panel (DGRP) and used GWAS to identify loci that explain variation in thermal limits. We observed greater variation in lower thermal limits, with CTmin ranging from 1.81 to 8.60°C, while CTmax ranged from 38.74 to 40.64°C. We identified 151 and 99 distinct genes associated with CTmin and CTmax, respectively, and there was strong support that these genes are involved in both dynamic responses to thermal stress and preparatory processes that increase thermal resistance. Many of the genes identified by GWAS were involved in the direct transcriptional response to thermal stress (72/151 for cold; 59/99 for heat), and overall GWAS candidates were more likely to be differentially expressed than other genes. Further, several GWAS candidates were regulatory genes that may participate in the regulation of stress responses, and gene ontologies related to development and morphogenesis were enriched, suggesting many of these genes influence thermal tolerance through effects on development and physiological status. Overall, our results suggest that thermal tolerance alleles can influence both dynamic plastic responses to thermal stress and preparatory processes that improve thermal resistance. These results also have utility for directly comparing GWAS and transcriptomic approaches for identifying candidate genes associated with thermal tolerance.

Importin-α2 mediates brain development, learning and memory consolidation in Drosophila

Neuronal development and memory consolidation are conserved processes that rely on nuclear-cytoplasmic transport of signaling molecules to regulate gene activity and initiate cascades of downstream cellular events. Surprisingly, few reports address and validate this widely accepted perspective. Here we show that Importin-α2 (Imp-α2), a soluble nuclear transporter that shuttles cargoes between the cytoplasm and nucleus, is vital for brain development, learning and persistent memory in Drosophila melanogaster. Mutations in importin-α2 (imp-α2, known as Pendulin or Pen and homologous with human KPNA2) are alleles of mushroom body miniature B (mbmB), a gene known to regulate aspects of brain development and influence adult behavior in flies. Mushroom bodies (MBs), paired associative centers in the brain, are smaller than normal due to defective proliferation of specific intrinsic Kenyon cell (KC) neurons in mbmB mutants. Extant KCs projecting to the MB β-lobe terminate abnormally on the contralateral side of the brain. mbmB adults have impaired olfactory learning but normal memory decay in most respects, except that protein synthesis-dependent long-term memory (LTM) is abolished. This observation supports an alternative mechanism of persistent memory in which mutually exclusive protein-synthesis-dependent and -independent forms rely on opposing cellular mechanisms or circuits. We propose a testable model of Imp-α2 and nuclear transport roles in brain development and conditioned behavior. Based on our molecular characterization, we suggest that mbmB is hereafter referred to as imp-α2^mbmB.

Implications of the Sap47 null mutation for synapsin phosphorylation, longevity, climbing proficiency and behavioural plasticity in adult Drosophila

The Sap47 gene of Drosophila melanogaster encodes a highly abundant 47 kDa synaptic vesicle-associated protein. Sap47 null mutants show defects in synaptic plasticity and larval olfactory associative learning but the molecular function of Sap47 at the synapse is unknown. We demonstrate that Sap47 modulates the phosphorylation of another highly abundant conserved presynaptic protein, synapsin. Site-specific phosphorylation of Drosophila synapsin has repeatedly been shown to be important for behavioural plasticity but it was not known where these phospho-synapsin isoforms are localized in the brain. Here, we report the distribution of serine-6-phosphorylated synapsin in the adult brain and show that it is highly enriched in rings of synapses in the ellipsoid body and in large synapses near the lateral triangle. The effects of knockout of Sap47 or synapsin on olfactory associative learning/memory support the hypothesis that both proteins operate in the same molecular pathway. We therefore asked if this might also be true for other aspects of their function. We show that knockout of Sap47 but not synapsin reduces lifespan, whereas knockout of Sap47 and synapsin, either individually or together, affects climbing proficiency, as well as plasticity in circadian rhythms and sleep. Furthermore, electrophysiological assessment of synaptic properties at the larval neuromuscular junction (NMJ) reveals increased spontaneous synaptic vesicle fusion and reduced paired pulse facilitation in Sap47 and synapsin single and double mutants. Our results imply that Sap47 and synapsin cooperate non-uniformly in the control of synaptic properties in different behaviourally relevant neuronal networks of the fruitfly.

Working Memory: It's a Gas, Gas, Gas

The ellipsoid body, a doughnut-shaped part of the fly brain, is essential for visual working memory. Gaseous second messengers establish a functional ellipsoid body and act as a short-term aid in orientation behavior.

Intellectual disability and autism spectrum disorders 'on the fly': insights from Drosophila

Intellectual disability (ID) and autism spectrum disorders (ASD) are frequently co-occurring neurodevelopmental disorders and affect 2-3% of the population. Rapid advances in exome and genome sequencing have increased the number of known implicated genes by threefold, to more than a thousand. The main challenges in the field are now to understand the various pathomechanisms associated with this bewildering number of genetic disorders, to identify new genes and to establish causality of variants in still-undiagnosed cases, and to work towards causal treatment options that so far are available only for a few metabolic conditions. To meet these challenges, the research community needs highly efficient model systems. With an increasing number of relevant assays and rapidly developing novel methodologies, the fruit fly Drosophila melanogaster is ideally positioned to change gear in ID and ASD research. The aim of this Review is to summarize some of the exciting work that already has drawn attention to Drosophila as a model for these disorders. We highlight well-established ID- and ASD-relevant fly phenotypes at the (sub)cellular, brain and behavioral levels, and discuss strategies of how this extraordinarily efficient and versatile model can contribute to 'next generation' medical genomics and to a better understanding of these disorders.

Automated real-time quantification of group locomotor activity in Drosophila melanogaster

Recent advances in neurogenetics have highlighted Drosophila melanogaster as an exciting model to study neural circuit dynamics and complex behavior. Automated tracking methods have facilitated the study of complex behaviors via high throughput behavioral screening. Here we describe a newly developed low-cost assay capable of real-time monitoring and quantifying Drosophila group activity. This platform offers reliable real-time quantification with open source software and a user-friendly interface for data acquisition and analysis. We demonstrate the utility of this platform by characterizing ethanol-induced locomotor activity in a dose-dependent manner as well as the effects of thermo and optogenetic manipulation of ellipsoid body neurons important for ethanol-induced locomotor activity. As expected, low doses of ethanol induced an initial startle and slow ramping of group activity, whereas high doses of ethanol induced sustained group activity followed by sedation. Advanced offline processing revealed discrete behavioral features characteristic of intoxication. Thermogenetic inactivation of ellipsoid body ring neurons reduced group activity whereas optogenetic activation increased activity. Together, these data establish the fly Group Activity Monitor (flyGrAM) platform as a robust means of obtaining an online read out of group activity in response to manipulations to the environment or neural activity, with an opportunity for more advanced post-processing offline.

Neuronal Constituents and Putative Interactions Within the Drosophila Ellipsoid Body Neuropil

The central complex (CX) is a midline-situated collection of neuropil compartments in the arthropod central brain, implicated in higher-order processes such as goal-directed navigation. Here, we provide a systematic genetic-neuroanatomical analysis of the ellipsoid body (EB), a compartment which represents a major afferent portal of the Drosophila CX. The neuropil volume of the EB, along with its prominent input compartment, called the bulb, is subdivided into precisely tessellated domains, distinguishable based on intensity of the global marker DN-cadherin. EB tangential elements (so-called ring neurons), most of which are derived from the DALv2 neuroblast lineage, predominantly interconnect the bulb and EB domains in a topographically organized fashion. Using the DN-cadherin domains as a framework, we first characterized this connectivity by Gal4 driver lines expressed in different DALv2 ring neuron (R-neuron) subclasses. We identified 11 subclasses, 6 of which correspond to previously described projection patterns, and 5 novel patterns. These subclasses both spatially (based on EB innervation pattern) and numerically (cell counts) summate to the total EB volume and R-neuron cell number, suggesting that our compilation of R-neuron subclasses approaches completion. EB columnar elements, as well as non-DALv2 derived extrinsic ring neurons (ExR-neurons), were also incorporated into this anatomical framework. Finally, we addressed the connectivity between R-neurons and their targets, using the anterograde trans-synaptic labeling method, trans-Tango. This study demonstrates putative interactions of R-neuron subclasses and reveals general principles of information flow within the EB network. Our work will facilitate the generation and testing of hypotheses regarding circuit interactions within the EB and the rest of the CX.

Development of the anterior visual input pathway to the Drosophila central complex

The anterior visual pathway (AVP) conducts visual information from the medulla of the optic lobe via the anterior optic tubercle (AOTU) and bulb (BU) to the ellipsoid body (EB) of the central complex. The anatomically defined neuron classes connecting the AOTU, BU, and EB represent discrete lineages, genetically and developmentally specified sets of cells derived from common progenitors (Omoto et al., Current Biology, 27, 1098-1110, 2017). In this article, we have analyzed the formation of the AVP from early larval to adult stages. The immature fiber tracts of the AVP, formed by secondary neurons of lineages DALcl1/2 and DALv2, assemble into structurally distinct primordia of the AOTU, BU, and EB within the late larval brain. During the early pupal period (P6-P48) these primordia grow in size and differentiate into the definitive subcompartments of the AOTU, BU, and EB. The primordium of the EB has a complex composition. DALv2 neurons form the anterior EB primordium, which starts out as a bilateral structure, then crosses the midline between P6 and P12, and subsequently bends to adopt the ring shape of the mature EB. Columnar neurons of the central complex, generated by the type II lineages DM1-4, form the posterior EB primordium. Starting out as an integral part of the fan-shaped body primordium, the posterior EB primordium moves forward and merges with the anterior EB primordium. We document the extension of neuropil glia around the nascent EB and BU, and analyze the relationship of primary and secondary neurons of the AVP lineages.

Crucial roles of Pox neuro in the developing ellipsoid body and antennal lobes of the Drosophila brain

The paired box gene Pox neuro (Poxn) is expressed in two bilaterally symmetric neuronal clusters of the developing adult Drosophila brain, a protocerebral dorsal cluster (DC) and a deutocerebral ventral cluster (VC). We show that all cells that express Poxn in the developing brain are postmitotic neurons. During embryogenesis, the DC and VC consist of only 20 and 12 neurons that express Poxn, designated embryonic Poxn-neurons. The number of Poxn-neurons increases only during the third larval instar, when the DC and VC increase dramatically to about 242 and 109 Poxn-neurons, respectively, virtually all of which survive to the adult stage, while no new Poxn-neurons are added during metamorphosis. Although the vast majority of Poxn-neurons express Poxn only during third instar, about half of them are born by the end of embryogenesis, as demonstrated by the absence of BrdU incorporation during larval stages. At late third instar, embryonic Poxn-neurons, which begin to express Poxn during embryogenesis, can be easily distinguished from embryonic-born and larval-born Poxn-neurons, which begin to express Poxn only during third instar, (i) by the absence of Pros, (ii) their overt differentiation of axons and neurites, and (iii) the strikingly larger diameter of their cell bodies still apparent in the adult brain. The embryonic Poxn-neurons are primary neurons that lay out the pioneering tracts for the secondary Poxn-neurons, which differentiate projections and axons that follow those of the primary neurons during metamorphosis. The DC and the VC participate only in two neuropils of the adult brain. The DC forms most, if not all, of the neurons that connect the bulb (lateral triangle) with the ellipsoid body, a prominent neuropil of the central complex, while the VC forms most of the ventral projection neurons of the antennal lobe, which connect it ipsilaterally to the lateral horn, bypassing the mushroom bodies. In addition, Poxn-neurons of the VC are ventral local interneurons of the antennal lobe. In the absence of Poxn protein in the developing brain, embryonic Poxn-neurons stall their projections and cannot find their proper target neuropils, the bulb and ellipsoid body in the case of the DC, or the antennal lobe and lateral horn in the case of the VC, whereby the absence of the ellipsoid body neuropil is particularly striking. Poxn is thus crucial for pathfinding both in the DC and VC. Additional implications of our results are discussed.

MRL proteins cooperate with activated Ras in glia to drive distinct oncogenic outcomes

The Mig10/RIAM/Lpd (MRL) adapter protein Lpd regulates actin dynamics through interactions with Scar/WAVE and Ena/VASP proteins to promote the formation of cellular protrusions and to stimulate invasive migration. However, the ability of MRL proteins to interact with multiple actin regulators and to promote serum response factor (SRF) signalling has raised the question of whether MRL proteins employ alternative downstream mechanisms to drive oncogenic processes in a context-dependent manner. Here, using a Drosophila model, we show that overexpression of either human Lpd or its Drosophila orthologue Pico can promote growth and invasion of Ras^V12-induced cell tumours in the brain. Notably, effects were restricted to two populations of Repo-positive glial cells: an invasive population, characterized by JNK-dependent elevation of Mmp1 expression, and a hyperproliferative population lacking elevated JNK signalling. JNK activation was not triggered by reactive immune cell signalling, implicating the involvement of an intrinsic stress response. The ability to promote dissemination of Ras^V12-induced tumours was shared by a subset of actin regulators, including, most prominently, Chicadee/Profilin, which directly interacts with Pico, and, Mal, a cofactor for serum response factor that responds to changes in G:F actin dynamics. Suppression of Mal activity partially abrogated the ability of pico to promote invasion of Ras^V12 tumours. Furthermore, we found that larval glia are enriched for serum response factor expression, explaining the apparent sensitivity of glial cells to Pico/Ras^V12 overexpression. Taken together, our findings indicate that MRL proteins cooperate with oncogenic Ras to promote formation of glial tumours, and that, in this context, Mal/serum response factor activation is rate-limiting for tumour dissemination.

Visual Working Memory Requires Permissive and Instructive NO/cGMP Signaling at Presynapses in the Drosophila Central Brain

The gaseous second messenger nitric oxide (NO) has been shown to regulate memory formation by activating retrograde signaling cascades from post- to presynapse that involve cyclic guanosine monophosphate (cGMP) production to induce synaptic plasticity and transcriptional changes. In this study, we analyzed the role of NO in the formation of a visual working memory that lasts only a few seconds. This memory is encoded in a subset of ring neurons that form the ellipsoid body in the Drosophila brain. Using genetic and pharmacological manipulations, we show that NO signaling is required for cGMP-mediated CREB activation, leading to the expression of competence factors like the synaptic homer protein. Interestingly, this cell-autonomous function can also be fulfilled by hydrogen sulfide (H₂S) through a converging pathway, revealing for the first time that endogenously produced H₂S has a role in memory processes. Notably, the NO synthase is strictly localized to the axonal output branches of the ring neurons, and this localization seems to be necessary for a second, phasic role of NO signaling. We provide evidence for a model where NO modulates the opening of cGMP-regulated cation channels to encode a short-term memory trace. Local production of NO/cGMP in restricted branches of ring neurons seems to represent the engram for objects, and comparing signal levels between individual ring neurons is used to orient the fly during search behavior. Due to its short half-life, NO seems to be a uniquely suited second messenger to encode working memories that have to be restricted in their duration.

A decision underlies phototaxis in an insect

Like a moth into the flame-phototaxis is an iconic example for innate preferences. Such preferences probably reflect evolutionary adaptations to predictable situations and have traditionally been conceptualized as hard-wired stimulus-response links. Perhaps for that reason, the century-old discovery of flexibility in Drosophila phototaxis has received little attention. Here, we report that across several different behavioural tests, light/dark preference tested in walking is dependent on various aspects of flight. If we temporarily compromise flying ability, walking photopreference reverses concomitantly. Neuronal activity in circuits expressing dopamine and octopamine, respectively, plays a differential role in photopreference, suggesting a potential involvement of these biogenic amines in this case of behavioural flexibility. We conclude that flies monitor their ability to fly, and that flying ability exerts a fundamental effect on action selection in Drosophila This work suggests that even behaviours which appear simple and hard-wired comprise a value-driven decision-making stage, negotiating the external situation with the animal's internal state, before an action is selected.

Behavioral responses to a repetitive visual threat stimulus express a persistent state of defensive arousal in Drosophila

The neural circuit mechanisms underlying emotion states remain poorly understood. Drosophila offers powerful genetic approaches for dissecting neural circuit function, but whether flies exhibit emotion-like behaviors has not been clear. We recently proposed that model organisms may express internal states displaying "emotion primitives," which are general characteristics common to different emotions, rather than specific anthropomorphic emotions such as "fear" or "anxiety." These emotion primitives include scalability, persistence, valence, and generalization to multiple contexts. Here, we have applied this approach to determine whether flies' defensive responses to moving overhead translational stimuli ("shadows") are purely reflexive or may express underlying emotion states. We describe a new behavioral assay in which flies confined in an enclosed arena are repeatedly exposed to an overhead translational stimulus. Repetitive stimuli promoted graded (scalable) and persistent increases in locomotor velocity and hopping, and occasional freezing. The stimulus also dispersed feeding flies from a food resource, suggesting both negative valence and context generalization. Strikingly, there was a significant delay before the flies returned to the food following stimulus-induced dispersal, suggestive of a slowly decaying internal defensive state. The length of this delay was increased when more stimuli were delivered for initial dispersal. These responses can be mathematically modeled by assuming an internal state that behaves as a leaky integrator of stimulus exposure. Our results suggest that flies' responses to repetitive visual threat stimuli express an internal state exhibiting canonical emotion primitives, possibly analogous to fear in mammals. The mechanistic basis of this state can now be investigated in a genetically tractable insect species.

Central complex and mushroom bodies mediate novelty choice behavior in Drosophila

Novelty choice, a visual paired-comparison task, for the fly Drosophila melanogaster is studied with severely restrained single animals in a flight simulator. The virtual environment simulates free flight for rotation in the horizontal plane. The behavior has three functional components: visual azimuth orientation, working memory, and pattern discrimination (perception). Here we study novelty choice in relation to its neural substrate in the brain and show that it requires the central complex and, in particular, the ring neurons of the ellipsoid body. Surprisingly, it also involves the mushroom bodies which are needed specifically in the comparison of patterns of different sizes.