Genetic analysis of Eclosion hormone action during Drosophila larval ecdysis

Identification and characterization of ecdysis-related neuropeptides in the lone star tick Amblyomma americanum

Introduction

The lone star tick, Amblyomma americanum, is an important ectoparasite known for transmitting diseases to humans and animals. Ecdysis-related neuropeptides (ERNs) control behaviors crucial for arthropods to shed exoskeletons. However, ERN identification and characterization in A. americanum remain incomplete.

Methods

We investigated ERNs in A. americanum, assessing their evolutionary relationships, protein properties, and functions. Phylogeny, sequence alignment, and domain structures of ERNs were analyzed. ERN functionality was explored using enrichment analysis, and developmental and tissue-specific ERN expression profiles were examined using qPCR and RNAi experiments.

Results and discussion

The study shows that ERN catalogs (i.e., eclosion hormone, corazonin, and bursicon) are found in most arachnids, and these ERNs in A. americanum have high evolutionary relatedness with other tick species. Protein modeling analysis indicates that ERNs primarily consist of secondary structures and protein stabilizing forces (i.e., hydrophobic clusters, hydrogen bond networks, and salt bridges). Gene functional analysis shows that ENRs are involved in many ecdysis-related functions, including ecdysis-triggering hormone activity, neuropeptide signaling pathway, and corazonin receptor binding. Bursicon proteins have functions in chitin binding and G protein-coupled receptor activity and strong interactions with leucine-rich repeat-containing G-protein coupled receptor 5. ERNs were expressed in higher levels in newly molted adults and synganglia. RNAi-mediated knockdown of burs α and burs β expression led to a significant decrease in the expression of an antimicrobial peptide, defensin, suggesting they might act in signaling or regulatory pathways that control the expression of immune-related genes. Arthropods are vulnerable immediately after molting because new cuticles are soft and susceptible to injury and pathogen infections. Bursicon homodimers act in prophylactic immunity during this vulnerable period by increasing the synthesis of transcripts encoding antimicrobial peptides to protect them from microbial invasion. Collectively, the expression pattern and characterization of ERNs in this study contribute to a deeper understanding of the physiological processes in A. americanum.

Comparative transcriptomics of the irradiated melon fly (Zeugodacus cucurbitae) reveal key developmental genes

Irradiation can be used as an insect pest management technique to reduce post-harvest yield losses. It causes major physiological changes, impairing insect development and leading to mortality. This technique is used to control the melon fly Zeugodacus cucurbitae, a major pest of Cucurbitaceae in Asia. Here, we applied irradiation to melon fly eggs, and the larvae emerged from irradiated eggs were used to conduct comparative transcriptomics and thereby identify key genes involved in the development and survival. We found 561 upregulated and 532 downregulated genes in irradiated flies compared to non-irradiated flies. We also observed abnormal small-body phenotypes in irradiated flies. By screening the 532 downregulated genes, we selected eight candidate genes putatively involved in development based in described functions in public databases and in the literature. We first established the expression profile of each candidate gene. Using RNA interference (RNAi), we individually knocked down each gene in third instar larvae and measured the effects on development. The knockdown of ImpE2 ecdysone-inducible gene controlling life stage transitions-led to major body size reductions in both pupae and adults. The knockdown of the tyrosine-protein kinase-like tok (Tpk-tok) caused severe body damage to larvae, characterized by swollen and black body parts. Adults subject to knockdown of the eclosion hormone (Eh_1) failed to shed their old cuticle which remained attached to their bodies. However, no obvious developmental defects were observed following the knockdown of the heat shock protein 67B1-like (Hsp67), the insulin receptor (Insr), the serine/threonine-protein kinase Nek4 (Nek4), the tyrosine-protein kinase transmembrane receptor Ror (Ror_1) and the probable insulin-like peptide 1 (Insp_1). We argue that irradiation can be successfully used not only as a pest management technique but also for the screening of essential developmental genes in insects via comparative transcriptomics. Our results demonstrate that ImpE2 and Eh_1 are essential for the development of melon fly and could therefore be promising candidates for the development of RNAi-based pest control strategies.

The role of neuropeptides in regulating ecdysis and reproduction in the hemimetabolous insect Rhodnius prolixus

In ecdysozoan animals, moulting entails the production of a new exoskeleton and shedding the old one during ecdysis. It is induced by a pulse of ecdysone that regulates the expression of different hormonal receptors and activates a peptide-mediated signalling cascade. In Holometabola, the peptidergic cascade regulating ecdysis has been well described. However, very little functional information regarding the neuroendocrine regulation of ecdysis is available for Hemimetabola, which displays an incomplete metamorphosis. We use Rhodnius prolixus as a convenient experimental model to test two hypotheses: (a) the role of neuropeptides that regulate ecdysis in Holometabola is conserved in hemimetabolous insects; (b) the neuropeptides regulating ecdysis play a role in the regulation of female reproduction during the adult stage. The RNA interference-mediated reduction of ETH expression in fourth-instar nymphs resulted in lethality at the expected time of ecdysis. Unlike in holometabolous insects, the knockdown of ETH and OKA did not affect oviposition in adult females, pointing to a different endocrine regulation of ovary maturation. However, ETH knockdown prevented egg hatching. The blockage of egg hatching appears to be a consequence of embryonic ecdysis failure. Most of the first-instar nymphs hatched from the eggs laid by females injected with dsEH, dsCCAP and dsOKA died at the expected time of ecdysis, indicating the crucial involvement of these genes in post-embryonic development. No phenotypes were observed upon CZ knockdown in nymphs or adult females. The results are relevant for evolutionary entomology and could reveal targets for neuropeptide-based pest control tools.

Drosophila Populations Reared Under Tropical Semi-natural Conditions Evolve Season-dependent Differences in Timing of Eclosion

Circadian clocks are considered an evolutionary adaptation to environmental cycles, helping organisms to adapt to daily and seasonal changes. However, most studies on the evolution of circadian rhythms have been carried out in controlled laboratory conditions; hence evolution of circadian clocks and rhythms in organisms reared under the influence of naturally varying time cues is not well understood. To address this, we reared large outbred fly populations in an outdoor enclosure on our institutional grounds in Bengaluru, southern India for about 150 generations, at the same time maintaining their ancestral control populations under standard laboratory conditions. Studying their rhythms in eclosion, a vital behavior for Drosophila, in the laboratory and semi-natural environments revealed that flies reared under semi-natural conditions differed in the timing of eclosion under semi-natural conditions in a season-dependent manner from their laboratory-reared counterparts. These differences were manifested under harsh semi-natural environments but not under mild ones or in standard laboratory conditions. Further analysis revealed that this phenotype might be responsive to seasonal changes in temperature cycles which was confirmed in the laboratory with simulated light and temperature cycles that approximated semi-natural conditions. Our results highlight key intricacies on the relative impact of intensity and timing of environmental cues for predicting the timing of Drosophila eclosion under tropical naturalistic conditions. Overall, our research uncovers previously unexplored aspects of adaptive circadian timekeeping in complex natural conditions, offering valuable insight into the evolution of clocks.

A large chromosomal inversion shapes gene expression in seaweed flies (Coelopa frigida)

Inversions often underlie complex adaptive traits, but the genic targets inside them are largely unknown. Gene expression profiling provides a powerful way to link inversions with their phenotypic consequences. We examined the effects of the Cf-Inv(1) inversion in the seaweed fly Coelopa frigida on gene expression variation across sexes and life stages. Our analyses revealed that Cf-Inv(1) shapes global expression patterns, most likely via linked variation, but the extent of this effect is variable, with much stronger effects in adults than larvae. Furthermore, within adults, both common as well as sex-specific patterns were found. The vast majority of these differentially expressed genes mapped to Cf-Inv(1). However, genes that were differentially expressed in a single context (i.e., in males, females, or larvae) were more likely to be located outside of Cf-Inv(1). By combining our findings with genomic scans for environmentally associated SNPs, we were able to pinpoint candidate variants in the inversion that may underlie mechanistic pathways that determine phenotypes. Together the results of this study, combined with previous findings, support the notion that the polymorphic Cf-Inv(1) inversion in this species is a major factor shaping both coding and regulatory variation resulting in highly complex adaptive effects.

Transcriptome dynamics during metamorphosis of imaginal discs into wings and thoracic dorsum in Apis mellifera castes

BACKGROUND

Much of the complex anatomy of a holometabolous insect is built from disc-shaped epithelial structures found inside the larva, i.e., the imaginal discs, which undergo a rapid differentiation during metamorphosis. Imaginal discs-derived structures, like wings, are built through the action of genes under precise regulation.

RESULTS

We analyzed 30 honeybee transcriptomes in the search for the gene expression needed for wings and thoracic dorsum construction from the larval wing discs primordia. Analyses were carried out before, during, and after the metamorphic molt and using worker and queen castes. Our RNA-seq libraries revealed 13,202 genes, representing 86.2% of the honeybee annotated genes. Gene Ontology analysis revealed functional terms that were caste-specific or shared by workers and queens. Genes expressed in wing discs and descendant structures showed differential expression profiles dynamics in premetamorphic, metamorphic and postmetamorphic developmental phases, and also between castes. At the metamorphic molt, when ecdysteroids peak, the wing buds of workers showed maximal gene upregulation comparatively to queens, thus underscoring differences in gene expression between castes at the height of the larval-pupal transition. Analysis of small RNA libraries of wing buds allowed us to build miRNA-mRNA interaction networks to predict the regulation of genes expressed during wing discs development.

CONCLUSION

Together, these data reveal gene expression dynamics leading to wings and thoracic dorsum formation from the wing discs, besides highlighting caste-specific differences during wing discs metamorphosis.

Expression Patterns of Three Important Hormone Genes and Respiratory Metabolism in Antheraea pernyi during Pupal Diapause under a Long Photoperiod

Simple Summary

In insects, the precise timing of metamorphosis and diapause is regulated by hormones. The Chinese oak silkworm, Antheraea pernyi, is a typical pupal diapause insect. Bivoltine species enter diapause in winter and terminate it under suitable environmental conditions in the following year; they produce 70% of total cocoons, whereas univoltine species in lower-latitude areas enter diapause in summer and contribute just one generation a year. A long photoperiod can trigger termination of pupal diapause. It is not clear how photoperiod influences hormone gene expression. Here, hormone-related genes were cloned, and their expression patterns were studied under different photoperiod treatments. The results will help us to understand the molecular changes during diapause termination under long photoperiods and improve breeding of multi-generation tussah pupae in areas where they are naturally univoltine.

Abstract

The Chinese oak silkworm is commonly used in pupal diapause research. In this study, a long photoperiod was used to trigger pupal diapause termination. Genes encoding three hormones, namely prothoracicotropic hormone (PTTH), ecdysis triggering hormone (ETH), and eclosion hormone (EH), were studied. Additionally, ecdysteroids (mainly 20-hydroxyecdysone, 20E) were quantified by HPLC. Pupal diapause stage was determined by measuring respiratory intensity. The pupae enter a low metabolic rate, which starts approximately 1 month after pupal emergence. ApPTTH expression showed a small increase at 14 days and then a larger increase from 35 days under the long photoperiod treatment. A similar pattern was observed for the titer of 20E in the hemolymph. However, ApETH expression later increased under the long photoperiod treatment (42 days) just before eclosion. Moreover, ApEH expression increased from 21 to 35 days, and then decreased before ecdysis. These results suggest that hormone-related gene expression is closely related to pupal development. Our study lays a foundation for future diapause studies in A. pernyi.

The steroid-hormone ecdysone coordinates parallel pupariation neuromotor and morphogenetic subprograms via epidermis-to-neuron Dilp8-Lgr3 signal induction

Innate behaviors consist of a succession of genetically-hardwired motor and physiological subprograms that can be coupled to drastic morphogenetic changes. How these integrative responses are orchestrated is not completely understood. Here, we provide insight into these mechanisms by studying pupariation, a multi-step innate behavior of Drosophila larvae that is critical for survival during metamorphosis. We find that the steroid-hormone ecdysone triggers parallel pupariation neuromotor and morphogenetic subprograms, which include the induction of the relaxin-peptide hormone, Dilp8, in the epidermis. Dilp8 acts on six Lgr3-positive thoracic interneurons to couple both subprograms in time and to instruct neuromotor subprogram switching during behavior. Our work reveals that interorgan feedback gates progression between subunits of an innate behavior and points to an ancestral neuromodulatory function of relaxin signaling.

Unveiling the sensory and interneuronal pathways of the neuroendocrine connectome in Drosophila

Neuroendocrine systems in animals maintain organismal homeostasis and regulate stress response. Although a great deal of work has been done on the neuropeptides and hormones that are released and act on target organs in the periphery, the synaptic inputs onto these neuroendocrine outputs in the brain are less well understood. Here, we use the transmission electron microscopy reconstruction of a whole central nervous system in the Drosophila larva to elucidate the sensory pathways and the interneurons that provide synaptic input to the neurosecretory cells projecting to the endocrine organs. Predicted by network modeling, we also identify a new carbon dioxide-responsive network that acts on a specific set of neurosecretory cells and that includes those expressing corazonin (Crz) and diuretic hormone 44 (Dh44) neuropeptides. Our analysis reveals a neuronal network architecture for combinatorial action based on sensory and interneuronal pathways that converge onto distinct combinations of neuroendocrine outputs.

Identification and function of ETH receptor networks in the silkworm Bombyx mori

Insect ecdysis triggering hormones (ETHs) released from endocrine Inka cells act on specific neurons in the central nervous system (CNS) to activate the ecdysis sequence. These primary target neurons express distinct splicing variants of ETH receptor (ETHR-A or ETHR-B). Here, we characterized both ETHR subtypes in the moth Bombyx mori in vitro and mapped spatial and temporal distribution of their expression within the CNS and peripheral organs. In the CNS, we detected non-overlapping expression patterns of each receptor isoform which showed dramatic changes during metamorphosis. Most ETHR-A and a few ETHR-B neurons produce multiple neuropeptides which are downstream signals for the initiation or termination of various phases during the ecdysis sequence. We also described novel roles of different neuropeptides during these processes. Careful examination of peripheral organs revealed ETHRs expression in specific cells of the frontal ganglion (FG), corpora allata (CA), H-organ and Malpighian tubules prior to each ecdysis. These data indicate that PETH and ETH are multifunctional hormones that act via ETHR-A and ETHR-B to control various functions during the entire development—the ecdysis sequence and associated behaviors by the CNS and FG, JH synthesis by the CA, and possible activity of the H-organ and Malpighian tubules.

The Drosophila foraging gene plays a vital role at the start of metamorphosis for subsequent adult emergence

The foraging (for) gene has been extensively studied in many species for its functions in development, physiology, and behavior. It is common for genes that influence behavior and development to be essential genes, and for has been found to be an essential gene in both fruit flies and mammals, with for mutants dying before reaching the adult stage. However, the biological process underlying the lethality associated with this gene is not known. Here, we show that in Drosophila melanogaster, some but not all gene products of for are essential for survival. Specifically, we show that promoter 3 of for, but not promoters 1, 2, and 4 are required for survival past pupal stage. We use full and partial genetic deletions of for, and temperature-restricted knock-down of the gene to further investigate the stage of lethality. While deletion analysis shows that flies lacking for die at the end of pupal development, as pharate adults, temperature-restricted knock-down shows that for is only required at the start of pupal development, for normal adult emergence (AE) and viability. We further show that the inability of these mutants to emerge from their pupal cases is linked to deficiencies in emergence behaviors, caused by a possible energy deficiency, and finally, that the lethality of for mutants seems to be linked to protein isoform P3, transcribed from for promoter 3.

Evidence for Co-Evolution of Masking With Circadian Phase in Drosophila Melanogaster

Heritable variation in the timing of rhythmic events with respect to daily time cues gives rise to chronotypes. Despite its importance, the mechanisms (clock or non-clock) regulating chronotypes remain elusive. Using artificial laboratory selection for divergent phasing of emergence of adults from pupae, our group has derived populations of Drosophila melanogaster which are early and late chronotypes for eclosion rhythm. Several circadian rhythm characteristics of these populations have since been described. We hypothesized that our selection protocol has inadvertently resulted in selection for masking, a non-clock phenomenon, in the early chronotype due to the placement of our selection window (which includes the lights-ON transition). We designed experiments to discriminate between enhanced masking to light versus circadian clock mediated changes in determining enhanced emergence in the morning window in our early chronotypes. Using a series of phase-shift protocols, LD-DD transition, and T-cycle experiments, we find that our early chronotypes have evolved positive masking, and their apparent entrained phases are largely contributed by masking. Through skeleton T-cycle experiments, we find that in addition to the evolution of greater masking, our early chronotypes have also evolved advanced phase of entrainment. Furthermore, our study systematically outlines experimental approaches to examine relative contributions of clock versus non-clock control of an entrained behavior. Although it has previously been suggested that masking may confer an adaptive advantage to organisms, here we provide experimental evidence for the evolution of masking as a means of phasing that can complement clock control of an entrained behavior.

Two Splice Isoforms of Leptinotarsa Ecdysis Triggering Hormone Receptor Have Distinct Roles in Larva-Pupa Transition

Insect ecdysis triggering hormone (ETH) receptors (ETHRs) are rhodopsin-like G protein-coupled receptors. Upon binding its ligand ETH, ETHR initiates a precisely programed ecdysis behavior series and physiological events. In Drosophila melanogaster, the ethr gene produces two functionally distinct splicing isoforms, ethra and ethrb. ETH/ETHRA activates eclosion hormone (EH), kinin, crustacean cardioactive peptide (CCAP), and bursicon (burs and pburs) neurons, among others, in a rigid order, to elicit the behavioral sequences and physiological actions for ecdysis at all developmental stages, whereas ETH/ETHRB is required at both pupal and adult ecdysis. However, the role of ETHRB in regulation of molting has not been clarified in any non-drosophila insects. In the present paper, we found that 20-hydroxyecdysone (20E) signaling triggers the expression of both ethra and ethrb in a Coleopteran insect pest, the Colorado potato beetle Leptinotarsa decemlineata. RNA interference (RNAi) was performed using double-stranded RNAs (dsRNAs) targeting the common (dsethr) or isoform-specific (dsethra, dsethrb) regions of ethr. RNAi of dsethr, dsethra, or dsethrb by the final-instar larvae arrested larva development. The arrest was not rescued by feeding 20E. All the ethra depleted larvae stopped development at prepupae stage; the body cavity was expanded by a large amount of liquid. Comparably, more than 80% of the ethrb RNAi larvae developmentally halted at the prepupae stage. The remaining Ldethrb hypomorphs became pupae, with blackened wings and highly-expressed burs, pburs and four melanin biosynthesis genes. Therefore, ETHRA and ETHRB play isoform-specific roles in regulation of ecdysis during larva-pupa transition in L. decemlineata.

RNA interference of eclosion hormone gene reveals its roles in the control of ecdysis behavior in Heortia vitessoides Moore

Eclosion hormone (EH) is an important neuropeptide that regulates growth and development. This study predicted the EH gene (HvEH) of Heortia vitessoides Moore (Lepidoptera: Crambidae) from the transcriptome database and its expression patterns were determined using quantitative real-time polymerase chain reaction. HvEH was expressed in all developmental stages and especially in the head area. RNA interference-mediated silencing of HvEH (2 μg/individual) with double-stranded HvEH RNA (dsHvEH) was achieved within 48 hr. Abnormal phenotypes appeared in the pupa and adult stages. dsHvEH injection suppressed pupation and eclosion rates. HvEH expression increased upon treatment with 20-hydroxyecdysone but decreased at extreme temperatures. These results suggest that HvEH plays an essential role in ecdysis and wing formation in H. vitessoides.

Chromosome-level assembly of the horseshoe crab genome provides insights into its genome evolution

The evolutionary history of horseshoe crabs, spanning approximately 500 million years, is characterized by remarkable morphological stasis and a low species diversity with only four extant species. Here we report a chromosome-level genome assembly for the mangrove horseshoe crab (Carcinoscorpius rotundicauda) using PacBio reads and Hi-C data. The assembly spans 1.67 Gb with contig N50 of 7.8 Mb and 98% of the genome assigned to 16 chromosomes. The genome contains five Hox clusters with 34 Hox genes, the highest number reported in any invertebrate. Detailed analysis of the genome provides evidence that suggests three rounds of whole-genome duplication (WGD), raising questions about the relationship between WGD and species radiation. Several gene families, particularly those involved in innate immunity, have undergone extensive tandem duplication. These expanded gene families may be important components of the innate immune system of horseshoe crabs, whose amebocyte lysate is a sensitive agent for detecting endotoxin contamination.

Horseshoe crabs have been morphologically stable across evolutionary time. Here, the authors generate a chromosome-level assembly for the mangrove horseshoe crab, with implications for innate immunity, and challenging assumptions about the role of genome duplication in adaptive radiation.

Non-canonical Eclosion Hormone-Expressing Cells Regulate Drosophila Ecdysis

Eclosion hormone (EH) was originally identified as a brain-derived hormone capable of inducing the behavioral sequences required for molting across insect species. However, its role in this process (called ecdysis) has since been confounded by discrepancies in the effects of genetic and cellular manipulations of EH function in Drosophila. Although knock-out of the Eh gene results in severe ecdysis-associated deficits accompanied by nearly complete larval lethality, ablation of the only neurons known to express EH (i.e. V_m neurons) is only partially lethal and surviving adults emerge, albeit abnormally. Using new tools for sensitively detecting Eh gene expression, we show that EH is more widely expressed than previously thought, both within the nervous system and in somatic tissues, including trachea. Ablating all Eh-expressing cells has effects that closely match those of Eh gene knock-out; developmentally suppressing them severely disrupts eclosion. Our results thus clarify and extend the scope of EH action.

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Eh is expressed in non-neuronal peripheral tissues including trachea

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Eh expression is found in neurons other than the V_m neurons in pharate adults

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Non-V_m expression is essential for eclosion

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Non-neuronal Eh expression is required for normal larval ecdysis

Ancient origins of arthropod moulting pathway components

Ecdysis (moulting) is the defining character of Ecdysoza (arthropods, nematodes and related phyla). Despite superficial similarities, the signalling cascade underlying moulting differs between Panarthropoda and the remaining ecdysozoans. Here, we reconstruct the evolution of major components of the ecdysis pathway. Its key elements evolved much earlier than previously thought and are present in non-moulting lophotrochozoans and deuterostomes. Eclosion hormone (EH) and bursicon originated prior to the cnidarian-bilaterian split, whereas ecdysis-triggering hormone (ETH) and crustacean cardioactive peptide (CCAP) evolved in the bilaterian last common ancestor (LCA). Identification of EH, CCAP and bursicon in Onychophora and EH, ETH and CCAP in Tardigrada suggests that the pathway was present in the panarthropod LCA. Trunk, an ancient extracellular signalling molecule and a well-established paralog of the insect peptide prothoracicotropic hormone (PTTH), is present in the non-bilaterian ctenophore Mnemiopsis leidyi. This constitutes the first case of a ctenophore signalling peptide with homology to a neuropeptide.

Animals such as insects, crabs and spiders belong to one of the most species-rich animal groups, called the arthropods. These animals have exoskeletons, which are hard, external coverings that support their bodies. Arthropods shed their exoskeletons as they grow, a process called ecdysis or moulting, and this behaviour is controlled by a set of hormones and small protein-like molecules called neuropeptides that allow communication between neurons.

Other animals, such as roundworms, also moult; and together with arthropods they are classified into a group called the Ecdysozoa. Since moulting is a common behaviour in ecdysozoans, it was previously assumed that its signalling components had evolved in the common ancestor of roundworms and arthropods, although differences in the moulting machinery between both groups exist.

Here, De Oliveira et al. investigate the evolutionary origins of the arthropod moulting machinery and find that some of the hormones and neuropeptides involved appeared long before the arthropods themselves.

Database searches showed that important hormones and neuropeptides involved in arthropod moulting can be found in diverse animal groups, such as jellyfish, molluscs and starfish, confirming that these molecules evolved before the last common ancestor of roundworms and arthropods. These animals must therefore use the hormones and neuropeptides in many processes unrelated to moulting. De Oliveira et al. also found that roundworms have lost most of these molecules, and that moulting in these animals must be driven by a different complement of hormones and neuropeptides.

These results invite research into the role of moulting hormones and neuropeptides in animals outside the Ecdysozoa. They also show that signalling pathways and the processes they regulate are highly adaptable: two animals can use the same hormone in entirely different processes, but conversely, the same behaviour may be regulated by different molecules depending on the animal. This means that the evolution of a process and the evolution of its regulation can be decoupled, a finding that has important implications for the study of signalling pathways and their evolution.

Recent advances in neuropeptide signaling in Drosophila, from genes to physiology and behavior

This review focuses on neuropeptides and peptide hormones, the largest and most diverse class of neuroactive substances, known in Drosophila and other animals to play roles in almost all aspects of daily life, as w;1;ell as in developmental processes. We provide an update on novel neuropeptides and receptors identified in the last decade, and highlight progress in analysis of neuropeptide signaling in Drosophila. Especially exciting is the huge amount of work published on novel functions of neuropeptides and peptide hormones in Drosophila, largely due to the rapid developments of powerful genetic methods, imaging techniques and innovative assays. We critically discuss the roles of peptides in olfaction, taste, foraging, feeding, clock function/sleep, aggression, mating/reproduction, learning and other behaviors, as well as in regulation of development, growth, metabolic and water homeostasis, stress responses, fecundity, and lifespan. We furthermore provide novel information on neuropeptide distribution and organization of peptidergic systems, as well as the phylogenetic relations between Drosophila neuropeptides and those of other phyla, including mammals. As will be shown, neuropeptide signaling is phylogenetically ancient, and not only are the structures of the peptides, precursors and receptors conserved over evolution, but also many functions of neuropeptide signaling in physiology and behavior.

A cell surface protein controls endocrine ring gland morphogenesis and steroid production

Identification of signals for systemic adaption of hormonal regulation would help to understand the crosstalk between cells and environmental cues contributing to growth, metabolic homeostasis and development. Physiological states are controlled by precise pulsatile hormonal release, including endocrine steroids in human and ecdysteroids in insects. We show in Drosophila that regulation of genes that control biosynthesis and signaling of the steroid hormone ecdysone, a central regulator of developmental progress, depends on the extracellular matrix protein Obstructor-A (Obst-A). Ecdysone is produced by the prothoracic gland (PG), where sensory neurons projecting axons from the brain integrate stimuli for endocrine control. By defining the extracellular surface, Obst-A promotes morphogenesis and axonal growth in the PG. This process requires Obst-A-matrix reorganization by Clathrin/Wurst-mediated endocytosis. Our data identifies the extracellular matrix as essential for endocrine ring gland function, which coordinates physiology, axon morphogenesis, and developmental programs. As Obst-A and Wurst homologs are found among all arthropods, we propose that this mechanism is evolutionary conserved.

Transcriptomic analysis of crustacean neuropeptide signaling during the moult cycle in the green shore crab, Carcinus maenas

Background

Ecdysis is an innate behaviour programme by which all arthropods moult their exoskeletons. The complex suite of interacting neuropeptides that orchestrate ecdysis is well studied in insects, but details of the crustacean ecdysis cassette are fragmented and our understanding of this process is comparatively crude, preventing a meaningful evolutionary comparison. To begin to address this issue we identified transcripts coding for neuropeptides and their putative receptors in the central nervous system (CNS) and Y-organs (YO) within the crab, Carcinus maenas, and mapped their expression profiles across accurately defined stages of the moult cycle using RNA-sequencing. We also studied gene expression within the epidermally-derived YO, the only defined role for which is the synthesis of ecdysteroid moulting hormones, to elucidate peptides and G protein-coupled receptors (GPCRs) that might have a function in ecdysis.

Results

Transcriptome mining of the CNS transcriptome yielded neuropeptide transcripts representing 47 neuropeptide families and 66 putative GPCRs. Neuropeptide transcripts that were differentially expressed across the moult cycle included carcikinin, crustacean hyperglycemic hormone-2, and crustacean cardioactive peptide, whilst a single putative neuropeptide receptor, proctolin R1, was differentially expressed. Carcikinin mRNA in particular exhibited dramatic increases in expression pre-moult, suggesting a role in ecdysis regulation. Crustacean hyperglycemic hormone-2 mRNA expression was elevated post- and pre-moult whilst that for crustacean cardioactive peptide, which regulates insect ecdysis and plays a role in stereotyped motor activity during crustacean ecdysis, was elevated in pre-moult.

In the YO, several putative neuropeptide receptor transcripts were differentially expressed across the moult cycle, as was the mRNA for the neuropeptide, neuroparsin-1. Whilst differential gene expression of putative neuropeptide receptors was expected, the discovery and differential expression of neuropeptide transcripts was surprising. Analysis of GPCR transcript expression between YO and epidermis revealed 11 to be upregulated in the YO and thus are now candidates for peptide control of ecdysis.

Conclusions

The data presented represent a comprehensive survey of the deduced C. maenas neuropeptidome and putative GPCRs. Importantly, we have described the differential expression profiles of these transcripts across accurately staged moult cycles in tissues key to the ecdysis programme. This study provides important avenues for the future exploration of functionality of receptor-ligand pairs in crustaceans.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5057-3) contains supplementary material, which is available to authorized users.

Orcokinins regulate the expression of neuropeptide precursor genes related to ecdysis in the hemimetabolous insect Rhodnius prolixus

Ecdysis is a vital process for insects, during which they shed the old cuticle in order to emerge as the following developmental stage. Given its relevance for survival and reproduction, ecdysis is tightly regulated by peptidic hormones that conform an interrelated neuromodulatory network. This network was studied in species that undergo a complete metamorphosis, but not in hemimetabola. In a recent work, we demonstrated that orcokinin neuropeptides are essential for ecdysis to occur in the kissing bug Rhodnius prolixus. Here we performed gene silencing, quantitative PCR and in vitro treatments in order to study the interrelationships between RhoprOKs and hormones such as ecdysis triggering hormone, corazonin, eclosion hormone, crustacean cardioactive peptide and ecdysone. Our results suggest that RhoprOKs directly or indirectly regulate the expression of other genes. Whereas RhoprOKA is centrally involved in the regulation of gene expression, RhoprOKB is implicated in processes related to midgut physiology. Therefore, we propose that the different transcripts encoded in RhoprOK gene could integrate signaling cues, in order to coordinate the nutritional state with development and ecdysis. Given the emerging data that point to OKs as important factors for survival and reproduction, they could be candidates in the search for new insect management strategies based on neuroendocrine targets.

Discovery of novel representatives of bilaterian neuropeptide families and reconstruction of neuropeptide precursor evolution in ophiuroid echinoderms

Neuropeptides are a diverse class of intercellular signalling molecules that mediate neuronal regulation of many physiological and behavioural processes. Recent advances in genome/transcriptome sequencing are enabling identification of neuropeptide precursor proteins in species from a growing variety of animal taxa, providing new insights into the evolution of neuropeptide signalling. Here, detailed analysis of transcriptome sequence data from three brittle star species, Ophionotus victoriae, Amphiura filiformis and Ophiopsila aranea, has enabled the first comprehensive identification of neuropeptide precursors in the class Ophiuroidea of the phylum Echinodermata. Representatives of over 30 bilaterian neuropeptide precursor families were identified, some of which occur as paralogues. Furthermore, homologues of endothelin/CCHamide, eclosion hormone, neuropeptide-F/Y and nucleobinin/nesfatin were discovered here in a deuterostome/echinoderm for the first time. The majority of ophiuroid neuropeptide precursors contain a single copy of a neuropeptide, but several precursors comprise multiple copies of identical or non-identical, but structurally related, neuropeptides. Here, we performed an unprecedented investigation of the evolution of neuropeptide copy number over a period of approximately 270 Myr by analysing sequence data from over 50 ophiuroid species, with reference to a robust phylogeny. Our analysis indicates that the composition of neuropeptide ‘cocktails’ is functionally important, but with plasticity over long evolutionary time scales.

Ecdysis-related pleiotropic neuropeptides expression during Anopheles albimanus development

OBJECTIVE

To analyze the transcription pattern of neuropeptides in the ontogeny of a malaria vector, the mosquito Anopheles albimanus.

MATERIALS AND METHODS

The transcription pattern of Crustacean CardioActive peptide (CCAP), corazonin, Ecdysis Triggering Hormone (ETH), allatostatin-A, orcokinin, Insulin Like Peptide 2 (ILP2), Insulin Like Peptide 5 (ILP5) and bursicon was evaluated using qPCR on larvae (1st - 4th instar), pupae and adult mosquitoes.

RESULTS

Unlike in other insects, transcripts of CCAP (70.8%), ETH (60.2%) and corazonin (76.5%) were expressed in 4th instar larvae, probably because these three neuropeptides are associated with the beginning of ecdysis. The neuropeptide ILP2 showed higher transcription levels in other stages and orcokinin decreased during the development of the mosquito.

CONCLUSIONS

The CCAP, corazonin and ETH neuropeptidesare potential targets for the design of control strategies aimed at disrupting An. albiamnus larval development.

A gene-specific T2A-GAL4 library for Drosophila

We generated a library of ~1000 Drosophila stocks in which we inserted a construct in the intron of genes allowing expression of GAL4 under control of endogenous promoters while arresting transcription with a polyadenylation signal 3’ of the GAL4. This allows numerous applications. First, ~90% of insertions in essential genes cause a severe loss-of-function phenotype, an effective way to mutagenize genes. Interestingly, 12/14 chromosomes engineered through CRISPR do not carry second-site lethal mutations. Second, 26/36 (70%) of lethal insertions tested are rescued with a single UAS-cDNA construct. Third, loss-of-function phenotypes associated with many GAL4 insertions can be reverted by excision with UAS-flippase. Fourth, GAL4 driven UAS-GFP/RFP reports tissue and cell-type specificity of gene expression with high sensitivity. We report the expression of hundreds of genes not previously reported. Finally, inserted cassettes can be replaced with GFP or any DNA. These stocks comprise a powerful resource for assessing gene function.

Determining what role newly discovered genes play in the body is an important part of genetics. This task requires a lot of extra information about each gene, such as the specific cells where the gene is active, or what happens when the gene is deleted. To answer these questions, researchers need tools and methods to manipulate genes within a living organism.

The fruit fly Drosophila is useful for such experiments because a toolbox of genetic techniques is already available. Gene editing in fruit flies allows small pieces of genetic information to be removed from or added to anywhere in the animal’s DNA. Another tool, known as GAL4-UAS, is a two-part system used to study gene activity. The GAL4 component is a protein that switches on genes. GAL4 alone does very little in Drosophila cells because it only recognizes a DNA sequence called UAS. However, if a GAL4-producing cell is also engineered to contain a UAS-controlled gene, GAL4 will switch the gene on.

Lee et al. used gene editing to insert a small piece of DNA, containing the GAL4 sequence followed by a ‘stop’ signal, into many different fly genes. The insertion made the cells where each gene was normally active produce GAL4, but – thanks to the stop signal – rendered the rest of the original gene non-functional. This effectively deleted the proteins encoded by each gene, giving information about the biological processes they normally control.

Lee et al. went on to use their insertion approach to make a Drosophila genetic library. This is a collection of around 1,000 different strains of fly, each carrying the GAL4/stop combination in a single gene. The library allows any gene in the collection to be studied in detail simply by combining the GAL4 with different UAS-controlled genetic tools. For example, introducing a UAS-controlled marker would pinpoint where in the body the original gene was active. Alternatively, adding UAS-controlled human versions of the gene would create humanized flies, which are a valuable tool to study potential disease-causing genes in humans.

This Drosophila library is a resource that contributes new experimental tools to fly genetics. Insights gained from flies can also be applied to more complex animals like humans, especially since around 65% of genes are similar across humans and Drosophila. As such, Lee et al. hope that this resource will help other researchers shed new light on the role of many different genes in health and disease.

Neuromodulatory connectivity defines the structure of a behavioral neural network

Neural networks are typically defined by their synaptic connectivity, yet synaptic wiring diagrams often provide limited insight into network function. This is due partly to the importance of non-synaptic communication by neuromodulators, which can dynamically reconfigure circuit activity to alter its output. Here, we systematically map the patterns of neuromodulatory connectivity in a network that governs a developmentally critical behavioral sequence in Drosophila. This sequence, which mediates pupal ecdysis, is governed by the serial release of several key factors, which act both somatically as hormones and within the brain as neuromodulators. By identifying and characterizing the functions of the neuronal targets of these factors, we find that they define hierarchically organized layers of the network controlling the pupal ecdysis sequence: a modular input layer, an intermediate central pattern generating layer, and a motor output layer. Mapping neuromodulatory connections in this system thus defines the functional architecture of the network.

Why do animals behave the way they do? Behavior occurs in response to signals from the environment, such as those indicating food or danger, or signals from the body, such as those indicating hunger or thirst. The nervous system detects these signals and triggers an appropriate response, such as seeking food or fleeing a threat. But because much of the nervous system takes part in generating these responses, it can make it difficult to understand how even simple behaviors come about.

One behavior that has been studied extensively is molting in insects. Molting enables insects to grow and develop, and involves casting off the outer skeleton of the previous developmental stage. To do this, the insect performs a series of repetitive movements, known as an ecdysis sequence. In the fruit fly, the pupal ecdysis sequence consists of three distinct patterns rhythmic abdominal movement. A hormone called ecdysis triggering hormone, or ETH for short, initiates this sequence by triggering the release of two further hormones, Bursicon and CCAP. All three hormones act on the nervous system to coordinate molting behavior, but exactly how they do so is unclear.

Diao et al. have now used genetic tools called Trojan exons to identify the neurons of fruit flies on which these hormones act. Trojan exons are short sequences of DNA that can be inserted into non-coding regions of a target gene to mark or manipulate the cells that express it. When a cell uses its copy of the target gene to make a protein, it also makes the product encoded by the Trojan exon. Using this technique, Diao et al. identified three sets of neurons that produce receptor proteins that recognize the molting hormones. Neurons with ETH receptors start the molting process by activating neurons that make Bursicon and CCAP. Neurons with Bursicon receptors then generate motor rhythms within the nervous system. Finally, neurons with CCAP receptors respond to these rhythms and produce the abdominal movements of the ecdysis sequence.

Many other animal behaviors depend on substances like ETH, Bursicon and CCAP, which act within the brain to change the activity of neurons and circuits. The work of Diao et al. suggests that identifying the sites at which such substances act can help reveal the circuits that govern complex behaviors.

Ecdysis Triggering Hormone Signaling (ETH/ETHR-A) Is Required for the Larva-Larva Ecdysis in Bactrocera dorsalis (Diptera: Tephritidae)

Insects must undergo ecdysis for successful development and growth, and the ecdysis triggering hormone (ETH), released by the Inka cells, is a master hormone in this process. In this study, we determined the sequence of the ETH precursor and receptors in an agriculturally important pest insect, the oriental fruit fly Bactrocera dorsalis (Hendel). We identified two functionally distinct splice receptor isoforms: BdETH-R-A and BdETH-R-B, and when expressed in Chinese hamster ovary (CHO-WTA11) cells, they exhibited a high sensitivity to the two mature peptides BdETH1 and BdETH2. The BdETH transcript was detected in the tracheal tissue of the larvae. Inka cells were identified with immunohistochemical antibody staining against Drosophila melanogaster ETH1, and in situ hybridization with specific DNA probes. Selective RNA silencing of BdETH or BdETH-R-A, but not of BdETH-R-B, caused developmental failure at ecdysis. The dsRNA-treated larvae displayed tracheal defects and could not shed the old cuticle followed by death. Our results demonstrated that BdETH, via activation of BdETH-R-A but not ETH-R-B, plays an essential role in regulating the process of larva-larva ecdysis in B. dorsalis.

Senecio brasiliensis impairs eclosion rate and induces apoptotic cell death in larvae of Drosophila melanogaster

Senecio brasilienis (Spreng) Less., is a species native from Brazil, popularly known as "Maria mole", and known to induce hepatotoxicity due to its high content of Pyrrolizidine alkaloids. Despite its toxicity, this plant is widely used in Brazilian folk medicine. Considering the antagonizing effects described for S. brasiliensis, we describe here molecular markers involved in the toxicity of hydroalcoholic extract from leaves of S. brasiliensis (HESB) in Drosophila melanogaster. Phytochemical analysis of HESB revealed the presence of phenolic acids and flavonoids. A significant antioxidant potential against ABTS⁺ and DPPH radical was found in parallel. Ingestion of extract did not alter the survival and locomotor activity of adult flies. However when ingested along the larval developmental phase, the eclosion rate of flies was interrupted at higher concentration of extract. To comprehend this phenomenon several analysis were conducted in larvae. HESB stimulated activity of antioxidant enzymes SOD and GST, and increased GSH/GSSG ratio and ROS production. Additionally, HESB caused a significant decrease of cell viability. The mRNA expression of Nrf2, TrxR, CAT, Drice and Dilp6 were also significantly up-regulated. HESB caused significant decrease on the phosphorylation of MAPKs and AKT. In parallel, PARP cleavage and caspases 3/7 activity were stimulated. In addition, glucose, glycogen and triglycerides levels were decreased. Taken together our study depicts a disruption in the eclosion of D. melanogaster possibly attributed to the inhibition of kinases implied in developmental process, energetic demand and induction of apoptotic cell death process.

WEclMon - A simple and robust camera-based system to monitor Drosophila eclosion under optogenetic manipulation and natural conditions

Eclosion in flies and other insects is a circadian-gated behaviour under control of a central and a peripheral clock. It is not influenced by the motivational state of an animal, and thus presents an ideal paradigm to study the relation and signalling pathways between central and peripheral clocks, and downstream peptidergic regulatory systems. Little is known, however, about eclosion rhythmicity under natural conditions, and research into this direction is hampered by the physically closed design of current eclosion monitoring systems.

We describe a novel open eclosion monitoring system (WEclMon) that allows the puparia to come into direct contact with light, temperature and humidity. We demonstrate that the system can be used both in the laboratory and outdoors, and shows a performance similar to commercial closed funnel-type monitors. Data analysis is semi-automated based on a macro toolset for the open imaging software Fiji. Due to its open design, the WEclMon is also well suited for optogenetic experiments. A small screen to identify putative neuroendocrine signals mediating time from the central clock to initiate eclosion showed that optogenetic activation of ETH-, EH and myosuppressin neurons can induce precocious eclosion. Genetic ablation of myosuppressin-expressing neurons did, however, not affect eclosion rhythmicity.

Ecdysone Receptor Agonism Leading to Lethal Molting Disruption in Arthropods: Review and Adverse Outcome Pathway Development

Molting is critical for growth, development, reproduction, and survival in arthropods. Complex neuroendocrine pathways are involved in the regulation of molting and may potentially become targets of environmental endocrine disrupting chemicals (EDCs). Based on several known ED mechanisms, a wide range of pesticides has been developed to combat unwanted organisms in food production activities such as agriculture and aquaculture. Meanwhile, these chemicals may also pose hazards to nontarget species by causing molting defects, and thus potentially affecting the health of the ecosystems. The present review summarizes the available knowledge on molting-related endocrine regulation and chemically mediated disruption in arthropods (with special focus on insects and crustaceans), to identify research gaps and develop a mechanistic model for assessing environmental hazards of these compounds. Based on the review, multiple targets of EDCs in the molting processes were identified and the link between mode of action (MoA) and adverse effects characterized to inform future studies. An adverse outcome pathway (AOP) describing ecdysone receptor agonism leading to incomplete ecdysis associated mortality was developed according to the OECD guideline and subjected to weight of evidence considerations by evolved Bradford Hill Criteria. This review proposes the first invertebrate ED AOP and may serve as a knowledge foundation for future environmental studies and AOP development.

Stereotyped responses of Drosophila peptidergic neuronal ensemble depend on downstream neuromodulators

Neuropeptides play a key role in the regulation of behaviors and physiological responses including alertness, social recognition, and hunger, yet, their mechanism of action is poorly understood. Here, we focus on the endocrine control ecdysis behavior, which is used by arthropods to shed their cuticle at the end of every molt. Ecdysis is triggered by ETH (Ecdysis triggering hormone), and we show that the response of peptidergic neurons that produce CCAP (crustacean cardioactive peptide), which are key targets of ETH and control the onset of ecdysis behavior, depends fundamentally on the actions of neuropeptides produced by other direct targets of ETH and released in a broad paracrine manner within the CNS; by autocrine influences from the CCAP neurons themselves; and by inhibitory actions mediated by GABA. Our findings provide insights into how this critical insect behavior is controlled and general principles for understanding how neuropeptides organize neuronal activity and behaviors.