Ecdysis triggering hormone receptors regulate male courtship behavior via antennal lobe interneurons in Drosophila

Knockout of ecdysis triggering hormone receptor (ETHr) gene adversely affects the nymphal molting and adult reproduction in Bemisia tabaci

Bemisia tabaci (Gennadius) is one of the most dangerous polyphagous pests in the world causing damage to various crops by sucking sap during the nymphal and adult stages. Chemical management of whiteflies is challenging because of the emergence of pesticide resistance. RNA interference has been well established in whitefly to study the functions of various genes. G-protein coupled receptors (GPCRs) are important targets for development of new generation insecticides. In this study, Ecdysis triggering hormone receptor (ETHr) gene expression was recorded in different stages of whitefly and its function has been studied through RNAi. The expression of ETHr is highest in third-instar nymphs followed by other nymphal instars, pupae and newly emerged adults. Silencing of ETHr resulted in significantly higher adult mortality (68.88%), reduced fecundity (4.46 eggs /female), reduced longevity of male and female (1.05 and 1.40 days, respectively) when adults were fed with dsETHr @ 1.0 μg/μl. Silencing of ETHr in nymphs lead to significantly higher mortality (81.35%) as compared to control. This study confirms that ETHr gene is essential for growth and development of whitefly nymphs and adults. Hence, it can be future target for developing dsRNA based insecticides for management of whitefly.

Courtship suppression in Drosophila melanogaster: The role of mating failure

Drosophila melanogaster is a popular model organism in the study of memory due to a wide arsenal of methods used to analyze neuronal activity. The most commonly used tests in research of behavioral plasticity are shock avoidance associated with chemosensory cues and courtship suppression after mating failure. Many authors emphasize the value of courtship suppression as a model of behavior most appropriate to natural conditions. However, researchers often investigate courtship suppression using immobilized and decapitated females as targets of courtship by males, which makes the data obtained from such flies less valuable. In our study, we evaluate courtship suppression towards immature mobile non-receptive females after training with mated or immature females combined with an aversive stimulus (quinine). We have shown that the previously described mechanisms of courtship suppression, as a result of the association of the courtship object with the repellent, as well as due to increased sensitivity to the anti-aphrodisiac cVA after mating failure, are not confirmed when immature mobile females are used. We discuss the reasons for the discrepancies between our results and literature data, define the conditions to be met in the courtship suppression test if the aim is to analyze the natural forms of behavioral plasticity, and present data on the test modifications to approximate conditions to natural ones.

The ecdysis triggering hormone system is essential for reproductive success in Mythimna separata (Walker)

Ecdysis triggering hormone (ETH) was originally discovered as a key hormone that regulates insect moulting via binding to its receptor, ETH receptor (ETHR). However, the precise role of ETH in moth reproduction remains to be explored in detail. ETH function was verified in vivo using Mythimna separata (Walker), an important cereal crop pest. RT-qPCR analysis revealed that transcriptional expression profiles of MsepETH showed evident sexual dimorphism in the adult stage. MsepETH expression increased in the females on day 3 and persisted thereafter till day 7, consistent with female ovarian maturation, and was merely detectable in males. Meanwhile, MsepETH expression levels were significantly higher in the trachea than in other tissues. MsepETHR-A and MsepETHR-B were expressed in both sexes and were significantly higher in the antennae than in other tissues. MsepETH and MsepETHR knockdown in females by RNA interference significantly reduced the expression of MsepETH, MsepETHR-A, MsepETHR-B, MsepJHAMT, and MsepVG, which delayed egg-laying and significantly reduced egg production. RNAi 20-hydroxyecdysone (20E) receptor (EcR) decreased MsepETH expression whereas injecting 20E restored egg production that had been disrupted by MsepETH interference. Meanwhile, RNAi juvenile hormone (JH) methoprene tolerant protein (Met) also decreased MsepETH expression and smearing JH analog methoprene (Meth) restored egg production. In conclusion, the reproduction roles of ETH, JH, and 20E were investigated in M. separata. These findings will lay the foundation for future research to develop an antagonist that reduces female reproduction and control strategies for pest insects.

Endocrine modulation of primary chemosensory neurons regulates Drosophila courtship behavior

The decision to engage in courtship depends on external cues from potential mates and internal cues related to maturation, health, and experience. Hormones allow for coordinated conveyance of such information to peripheral tissues. Here, we show Ecdysis-Triggering Hormone (ETH) is critical for courtship inhibition after completion of copulation in Drosophila melanogaster. ETH deficiency relieves post-copulation courtship inhibition (PCCI) and increases male-male courtship. ETH appears to modulate perception and attractiveness of potential mates by direct action on primary chemosensory neurons. Knockdown of ETH receptor (ETHR) expression in GR32A-expressing neurons leads to reduced ligand sensitivity and elevated male-male courtship. We find OR67D also is critical for normal levels of PCCI after mating. ETHR knockdown in OR67D-expressing neurons or GR32A-expressing neurons relieves PCCI. Finally, ETHR silencing in the corpus allatum (CA), the sole source of juvenile hormone, also relieves PCCI; treatment with the juvenile hormone analog methoprene partially restores normal post-mating behavior. We find that ETH, a stress-sensitive reproductive hormone, appears to coordinate multiple sensory modalities to guide Drosophila male courtship behaviors, especially after mating.

The decision of when to reproduce is paramount for organismal survival. In models like mice and flies, we have a comprehensive understanding of neuronal substrates for perception of mates and courtship drive, but how these substrates adapt to malleable internal and external environments remains unclear. Here, we show that post-mating refractoriness depends upon a peptide hormone, Ecdysis-Triggering Hormone (ETH). We show repression of courtship toward recently-mated females depends upon pheromone cues and that ETH deficiency impairs perception of female matedness. ETH signaling appears to promote the activity and function of pheromone-sensing primary olfactory and gustatory sensory neurons. Additionally, ETH sets internal levels of Juvenile Hormone, a hormone known to inhibit courtship drive in flies. Elimination of ETH or its receptor in primary sensory neurons or the glandular source of Juvenile Hormone reduces male post-copulation courtship inhibition (PCCI), causing continued courtship toward female counterparts after successful mating. Our data suggest ETH and its targets are critical for post-mating refractoriness in males.

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.

Transcriptome responses of RNAi-mediated ETH knockdown in Scylla paramamosain at different premolt substages

Ecdysis triggering hormone (ETH) plays an important role in molting, reproduction, and courtship behavior in insects. To investigate the potential downstream pathways and genes of ETH in Scylla paramamosain, RNA interference (RNAi) was conducted on crabs at early (D0) and late (D2) premolt substages, and the transcriptome profiles of each group were compared by RNA sequencing. Real-time quantitative polymerase chain reaction (RT-qPCR) and semiquantitative polymerase chain reaction (RT-PCR) results showed a significant knockdown of ETH at D0 stage, whereas a significant increase was shown conversely in crabs at D2 substage after the injection of dsETH. A total of 242,979 transcripts were assembled, and 44,012 unigenes were identified. Transcriptomic comparison between crabs at D2 and D0 substages showed 2,683 differentially expressed genes (DEGs); these genes were enriched in ribosome and pathways related to transcription factor complex and cell part. Twenty DEGs were identified between dsETH-injected and dsGFP-injected crabs at D0 substage; these DEGs were involved in carbohydrate metabolism, one carbon pool by folate, and chitin binding. Twenty-six DEGs were identified between dsETH-injected and dsGFP-injected crabs at D2 substage; these DEGs were involved in calcium channel inhibitor activity, fat digestion and absorption, and cardiac muscle contraction. RT-qPCR verified the differential expression of the selected genes. In conclusion, crabs at D0 substage are more active in preparing the macromolecular complex that is needed for molting. Moreover, ETH has potential roles in carbohydrate metabolism, one carbon pool by folate, and chitin binding for crabs at D0 substage, while the role of ETH turns to be involved in calcium channel inhibitor activity, fat digestion and absorption, and cardiac muscle contraction at D2 substage to facilitate the occurrence of molting. The selected DEGs provide valuable insight into the role of ETH in the regulation of crustacean molting.

Functional Characterization of Ecdysis Triggering Hormone Receptors (AgETHR-A and AgETHR-B) in the African Malaria Mosquito, Anopheles gambiae

Insect ecdysis behavior, shedding off the old cuticle, is under the control of specific neuropeptides with the top command by the ecdysis triggering hormone (ETH). We characterized the ETH receptor (ETHR) of the malaria mosquito, Anopheles gambiae, by manual annotation of the NCBI gene (AGAP002881) and functional analysis, using a heterologous expression system in a mammalian cell line. The two splicing variants of ETHRs, ecdysis triggering hormone receptors (AgETHR-A and AgETHR-B), a conserved feature among insects, included of four (552 aa) and five exons (635 aa), respectively. The main feature of manual annotation of the receptor was a correction of N-terminal and exon-intron boundaries of an annotated gene (AGAP002881). Interestingly, the functional expression of the receptor in Chinese hamster ovary cells required modification of the transcription initiation site for mammalian Kozak consensus. In the calcium mobilization assay using the heterologous expression of each receptor, AgETHR-B showed a higher sensitivity to AgETH-1 (28 times) and AgETH-2 (320 times) than AgETHR-A. The AgETHRs showed specificity only to the ETH group of peptides but not to other groups carrying the C-termini motifs as PRXamide, such as pyrokinin1/DH and pyrokinin2/PBAN. Ecdysis triggering hormone receptors (AgETHR-B) responded to different ETH variants of other insect species more promiscuously than AgETHR-A.