Nitric oxide mediates activity-dependent change to synaptic excitation during a critical period in Drosophila

From Springer Nature via Jisc Publications RouterHistory: received 2021-07-29, accepted 2021-09-17, registration 2021-10-05, online 2021-10-13, pub-electronic 2021-10-13, collection 2021-12Publication status: PublishedFunder: Biotechnology and Biological Sciences Research Council; doi: http://dx.doi.org/10.13039/501100000268; Grant(s): BB/N/014561/1, BB/R016666/1Funder: Wellcome Trust; doi: http://dx.doi.org/10.13039/100010269; Grant(s): 217099/Z/19/ZAbstract: The emergence of coordinated network function during nervous system development is often associated with critical periods. These phases are sensitive to activity perturbations during, but not outside, of the critical period, that can lead to permanently altered network function for reasons that are not well understood. In particular, the mechanisms that transduce neuronal activity to regulating changes in neuronal physiology or structure are not known. Here, we take advantage of a recently identified invertebrate model for studying critical periods, the Drosophila larval locomotor system. Manipulation of neuronal activity during this critical period is sufficient to increase synaptic excitation and to permanently leave the locomotor network prone to induced seizures. Using genetics and pharmacological manipulations, we identify nitric oxide (NO)-signaling as a key mediator of activity. Transiently increasing or decreasing NO-signaling during the critical period mimics the effects of activity manipulations, causing the same lasting changes in synaptic transmission and susceptibility to seizure induction. Moreover, the effects of increased activity on the developing network are suppressed by concomitant reduction in NO-signaling and enhanced by additional NO-signaling. These data identify NO signaling as a downstream effector, providing new mechanistic insight into how activity during a critical period tunes a developing network

High flavonoid accompanied with high starch accumulation triggered by nutrient starvation in bioenergy crop duckweed (Landoltia punctata)

Background: As the fastest growing plant, duckweed can thrive on anthropogenic wastewater. The purple-backed duckweed, Landoltia punctata, is rich in starch and flavonoids. However, the molecular biological basis of high flavonoid and low lignin content remains largely unknown, as does the best method to combine nutrients removed from sewage and the utilization value improvement of duckweed biomass. Results: A combined omics study was performed to investigate the biosynthesis of flavonoid and the metabolic flux changes in L. punctata grown in different culture medium. Phenylalanine metabolism related transcripts were identified and carefully analyzed. Expression quantification results showed that most of the flavonoid biosynthetic transcripts were relatively highly expressed, while most lignin-related transcripts were poorly expressed or failed to be detected by iTRAQ based proteomic analyses. This explains why duckweed has a much lower lignin percentage and higher flavonoid content than most other plants. Growing in distilled water, expression of most flavonoid-related transcripts were increased, while most were decreased in uniconazole treated L. punctata (1/6 x Hoagland + 800 mg center dot L-1 uniconazole). When L. punctata was cultivated in full nutrient medium (1/6 x Hoagland), more than half of these transcripts were increased, however others were suppressed. Metabolome results showed that a total of 20 flavonoid compounds were separated by HPLC in L. punctata grown in uniconazole and full nutrient medium. The quantities of all 20 compounds were decreased by uniconazole, while 11 were increased and 6 decreased when grown in full nutrient medium. Nutrient starvation resulted in an obvious purple accumulation on the underside of each frond. Conclusions: The high flavonoid and low lignin content of L. punctata appears to be predominantly caused by the flavonoid-directed metabolic flux. Nutrient starvation is the best option to obtain high starch and flavonoid accumulation simultaneously in a short time for biofuels fermentation and natural products isolation

Inappropriate Neural Activity during a Sensitive Period in Embryogenesis Results in Persistent Seizure-like Behavior.

SummaryMaturation of neural circuits requires activity-dependent processes that underpin the emergence of appropriate behavior in the adult. It has been proposed that disruption of these events, during specific critical periods when they exert maximal influence, may lead to neurodevelopmental diseases, including epilepsy [1–3]. However, complexity of neurocircuitry, coupled with the lack of information on network formation in mammals, makes it difficult to directly investigate this hypothesis. Alternative models, including the fruit fly Drosophila melanogaster, show remarkable similarities between experimental seizure-like activity and clinical phenotypes [4–6]. In particular, a group of flies, termed bang-sensitive (bs) mutants have been extensively used to investigate the pathophysiological mechanisms underlying seizure [7–12]. Seizure phenotype can be measured in larval stages using an electroshock assay, and this behavior in bs mutants is dramatically reduced following ingestion of typical anti-epileptic drugs (AEDs; [13]). In this study we describe a critical period of embryonic development in Drosophila during which manipulation of neural activity is sufficient to significantly influence seizure behavior at postembryonic stages. We show that inhibition of elevated activity, characteristic of bs seizure models, during the critical period is sufficient to suppress seizure. By contrast, increasing neuronal excitation during the same period in wild-type (WT) is sufficient to permanently induce a seizure behavior. Further, we show that induction of seizure in WT correlates with functional alteration of motoneuron inputs that is a characteristic of bs mutants. Induction of seizure is rescued by prior administration of AEDs, opening a new perspective for early drug intervention in the treatment of genetic epilepsy

Seizure control through genetic and pharmacological manipulation of Pumilio in Drosophila:A key component of neuronal homeostasis

Epilepsy is a significant disorder for which approximately one-third of patients do not respond to drug treatments. Next-generation drugs, which interact with novel targets, are required to provide a better clinical outcome for these individuals. To identify potential novel targets for antiepileptic drug (AED) design, we used RNA sequencing to identify changes in gene transcription in two seizure models of the fruit fly Drosophila melanogaster. The first model compared gene transcription between wild type (WT) and bangsenseless1 (parabss), a gain-of-function mutant in the sole fly voltage-gated sodium channel (paralytic). The second model compared WT with WT fed the proconvulsant picrotoxin (PTX). We identified 743 genes (FDR≤1%) with significant altered expression levels that are common to both seizure models. Of these, 339 are consistently upregulated and 397 downregulated. We identify pumilio (pum) to be downregulated in both seizure models. Pum is a known homeostatic regulator of action potential firing in both flies and mammals, achieving control of neuronal firing through binding to, and regulating translation of, the mRNA transcripts of voltage-gated sodium channels (Nav). We show that maintaining expression of pum in the CNS of parabss flies is potently anticonvulsive, whereas its reduction through RNAi-mediated knockdown is proconvulsive. Using a cell-based luciferase reporter screen, we screened a repurposed chemical library and identified 12 compounds sufficient to increase activity of pum. Of these compounds, we focus on avobenzone, which significantly rescues seizure behaviour in parabss flies. The mode of action of avobenzone includes potentiation of pum expression and mirrors the ability of this homeostatic regulator to reduce the persistent voltage-gated Na+ current (INaP) in an identified neuron. This study reports a novel approach to suppress seizure and highlights the mechanisms of neuronal homeostasis as potential targets for next-generation AEDs

Cryptochrome-dependent magnetic field effect on seizure response in Drosophila larvae

The mechanisms that facilitate animal magnetoreception have both fascinated and confounded scientists for decades, and its precise biophysical origin remains unclear. Among the proposed primary magnetic sensors is the flavoprotein, cryptochrome, which is thought to provide geomagnetic information via a quantum effect in a light-initiated radical pair reaction. Despite recent advances in the radical pair model of magnetoreception from theoretical, molecular and animal behaviour studies, very little is known of a possible signal transduction mechanism. We report a substantial effect of magnetic field exposure on seizure response in Drosophila larvae. The effect is dependent on cryptochrome, the presence and wavelength of light and is blocked by prior ingestion of typical antiepileptic drugs. These data are consistent with a magnetically-sensitive, photochemical radical pair reaction in cryptochrome that alters levels of neuronal excitation, and represent a vital step forward in our understanding of the signal transduction mechanism involved in animal magnetoreception

Reactive oxygen species regulate activity-dependent neuronal plasticity in <i>Drosophila</i>

Reactive oxygen species (ROS) have been extensively studied as damaging agents associated with ageing and neurodegenerative conditions. Their role in the nervous system under non-pathological conditions has remained poorly understood. Working with the Drosophila larval locomotor network, we show that in neurons ROS act as obligate signals required for neuronal activity-dependent structural plasticity, of both pre- and postsynaptic terminals. ROS signaling is also necessary for maintaining evoked synaptic transmission at the neuromuscular junction, and for activity-regulated homeostatic adjustment of motor network output, as measured by larval crawling behavior. We identified the highly conserved Parkinson's disease-linked protein DJ-1β as a redox sensor in neurons where it regulates structural plasticity, in part via modulation of the PTEN-PI3Kinase pathway. This study provides a new conceptual framework of neuronal ROS as second messengers required for neuronal plasticity and for network tuning, whose dysregulation in the ageing brain and under neurodegenerative conditions may contribute to synaptic dysfunction.</p