Juvenile hormone III skipped bisepoxide is widespread in true bugs (Hemiptera: Heteroptera)

The moulting arthropod: a complete genetic toolkit review

Exoskeletons are a defining character of all arthropods that provide physical support for their segmented bodies and appendages as well as protection from the environment and predation. This ubiquitous yet evolutionarily variable feature has been instrumental in facilitating the adoption of a variety of lifestyles and the exploitation of ecological niches across all environments. Throughout the radiation that produced the more than one million described modern species, adaptability afforded by segmentation and exoskeletons has led to a diversity that is unrivalled amongst animals. However, because of the limited extensibility of exoskeleton chitin and cuticle components, they must be periodically shed and replaced with new larger ones, notably to accommodate the growing individuals encased within. Therefore, arthropods grow discontinuously by undergoing periodic moulting events, which follow a series of steps from the preparatory pre-moult phase to ecdysis itself and post-moult maturation of new exoskeletons. Each event represents a particularly vulnerable period in an arthropod's life cycle, so processes must be tightly regulated and meticulously executed to ensure successful transitions for normal growth and development. Decades of research in representative arthropods provide a foundation of understanding of the mechanisms involved. Building on this, studies continue to develop and test hypotheses on the presence and function of molecular components, including neuropeptides, hormones, and receptors, as well as the so-called early, late, and fate genes, across arthropod diversity. Here, we review the literature to develop a comprehensive overview of the status of accumulated knowledge of the genetic toolkit governing arthropod moulting. From biosynthesis and regulation of ecdysteroid and sesquiterpenoid hormones, to factors involved in hormonal stimulation responses and exoskeleton remodelling, we identify commonalities and differences, as well as highlighting major knowledge gaps, across arthropod groups. We examine the available evidence supporting current models of how components operate together to prepare for, execute, and recover from ecdysis, comparing reports from Chelicerata, Myriapoda, Crustacea, and Hexapoda. Evidence is generally highly taxonomically imbalanced, with most reports based on insect study systems. Biases are also evident in research on different moulting phases and processes, with the early triggers and late effectors generally being the least well explored. Our synthesis contrasts knowledge based on reported observations with reasonably plausible assumptions given current taxonomic sampling, and exposes weak assumptions or major gaps that need addressing. Encouragingly, advances in genomics are driving a diversification of tractable study systems by facilitating the cataloguing of putative genetic toolkits in previously under-explored taxa. Analysis of genome and transcriptome data supported by experimental investigations have validated the presence of an "ultra-conserved" core of arthropod genes involved in moulting processes. The molecular machinery has likely evolved with elaborations on this conserved pathway backbone, but more taxonomic exploration is needed to characterise lineage-specific changes and novelties. Furthermore, linking these to transformative innovations in moulting processes across Arthropoda remains hampered by knowledge gaps and hypotheses based on untested assumptions. Promisingly however, emerging from the synthesis is a framework that highlights research avenues from the underlying genetics to the dynamic molecular biology through to the complex physiology of moulting.

Design, synthesis, and biological evaluation of insect hormone agonists

Agonists of insect hormones, namely molting hormone (MH) and juvenile hormone (JH), disrupt the normal growth of insects and can be employed as insecticides that are harmless to vertebrates. In this study, a series of experiments and computational analyses were conducted to rationally design novel insect hormone agonists. Syntheses and quantitative structure-activity relationship (QSAR) analyses of two MH agonist chemotypes, imidazothiadiazoles and tetrahydroquinolines, revealed that the structural factors important for the ligand-receptor interactions are significantly different between these chemotypes. On the other hand, a virtual screening cascade combining ligand- and structure-based methods identified a piperazine derivative as a novel JH agonist. The results obtained in this study will be useful for the future development of novel insect growth regulators.

Aphis craccivora (Hemiptera: Aphididae) synthesizes juvenile hormone III via a pathway involving epoxidation followed by esterification, potentially providing an epoxidation active site for the synthesis of juvenile hormone SB3

Juvenile hormones (JHs) play a crucial role in regulating development and reproduction in insects. Most insects predominantly synthesize JH III, which typically involves esterification followed by epoxidation, lepidopteran insects use a pathway of epoxidation followed by esterification. Although hemipteran insects have JH III and JH skipped bisepoxide III (JH SB3), the synthesis pathway and key epoxidases remain unclear. This study was conducted on Aphis craccivora, and demonstrated that corpora allata, microsomes, Ac-CYP15C1, and Ac-JHAMT catalyze JH III production in vitro, establishing the pathway of epoxidation followed by esterification. These findings were further confirmed through RNA interference and molecular docking. The presence of JH III and JH SB3 in A. craccivora was identified, and their synthesis pathway was elucidated as follows: Ac-CYP15C1 oxidizes farnesic acid to JH A, followed by methylation to JH III by Ac-JHAMT, possibly providing an epoxidation site on the second carbon for JH SB3. This alteration may significantly contribute to the differentiation and functional diversification of JH types in insects.

Simultaneous Detection and Distribution of Five Juvenile Hormones in 58 Insect Species and the Absolute Configuration in 32 Insect Species

Juvenile hormone (JH) plays an important role in regulating various insect physiological processes. Herein, a novel method (chiral and achiral) for the simultaneous detection of five JHs was established by processing a whole insect without complicated hemolymph extraction. The proposed method was used to determine the distribution of JHs in 58 insect species and the absolute configuration of JHs in 32 species. The results showed that JHSB₃ was uniquely synthesized in Hemiptera, JHB₃ was unique to Diptera, and JH I and JH II were unique to Lepidoptera. JH III was present in most insect species surveyed, with social insects having generally higher JH III titers. Interestingly, JHSB₃ and JHB₃, both double epoxidation JHs, were found in insects with sucking mouthparts. The absolute conformation of JH III and the 10C of the detected JHs were all R stereoisomers.

Neuropeptide F regulates feeding via the juvenile hormone pathway in Ostrinia furnacalis larvae

BACKGROUND

Feeding by pests is one of the most important reasons for reductions in agricultural crop yield. This study aimed to reveal how juvenile hormone (JH) participates in larval feeding regulation of the Asian corn borer Ostrinia furnacalis.

RESULTS

Larvae of O. furnacalis exhibit a daily circadian feeding rhythm, with a peak at ZT18 and a trough at ZT6 under both photoperiod (LD) and constant dark (DD) conditions, which may be eliminated by application of fenoxycarb, a JH active analogue. JH negatively regulates larval feeding as a downstream factor of neuropeptide F (NPF), in which knocking down JH increases larval feeding amount along with body weight and length. The production of JH in the brain-corpora cardiaca-corpora allata (brain-CC-CA) is regulated by brain NPF rather than gut NPF, which was demonstrated in Drosophila larvae through GAL4/UAS genetic analysis. In addition, feeding regulation of JH is closely related to energy homeostasis in the fat body by inhibiting energy storage and promoting degradation. The JH analogue fenoxycarb is an effective pesticide against O. furnacalis, controlling feeding and metabolism.

CONCLUSION

The brain NPF system regulates JH, with functions in food consumption, feeding rhythms, energy homeostasis and body size. This study provides an important basis for understanding the feeding mechanism and potential pest control of O. furnacalis. © 2022 Society of Chemical Industry.

Evolution of proteins involved in the final steps of juvenile hormone synthesis

Juvenile hormone (JH), a sesquiterpenoid produced by the insect corpus allatum gland (CA), is a key regulator of insect metamorphosis, reproduction, caste differentiation, and polyphenism. The first part of JH biosynthesis occurs via the universal eukaryotic mevalonate pathway. The final steps involve epoxidation and methylation. However, the sequence of these steps might not be conserved among all insects and Crustacea. Therefore, we used available genomic and transcriptomic data and identified JH acid methyltransferase (JHAMT), analyzed their genomic duplications in selected model organisms, and reconstructed their phylogeny. We have further reconstructed phylogeny of FAMeT proteins and show that evolution of this protein group is more complicated than originally appreciated. The analysis delineates important milestones in the evolution of several JH biosynthetic enzymes in arthropods, reviews major literature data on the last steps of JH synthesis, and defines questions and some hypotheses worth pursuing experimentally.

Crosstalk between Nutrition, Insulin, Juvenile Hormone, and Ecdysteroid Signaling in the Classical Insect Model, Rhodnius prolixus

The rigorous balance of endocrine signals that control insect reproductive physiology is crucial for the success of egg production. Rhodnius prolixus, a blood-feeding insect and main vector of Chagas disease, has been used over the last century as a model to unravel aspects of insect metabolism and physiology. Our recent work has shown that nutrition, insulin signaling, and two main types of insect lipophilic hormones, juvenile hormone (JH) and ecdysteroids, are essential for successful reproduction in R. prolixus; however, the interplay behind these endocrine signals has not been established. We used a combination of hormone treatments, gene expression analyses, hormone measurements, and ex vivo experiments using the corpus allatum or the ovary, to investigate how the interaction of these endocrine signals might define the hormone environment for egg production. The results show that after a blood meal, circulating JH levels increase, a process mainly driven through insulin and allatoregulatory neuropeptides. In turn, JH feeds back to provide some control over its own biosynthesis by regulating the expression of critical biosynthetic enzymes in the corpus allatum. Interestingly, insulin also stimulates the synthesis and release of ecdysteroids from the ovary. This study highlights the complex network of endocrine signals that, together, coordinate a successful reproductive cycle.

Toxicological effects of trace amounts of pyriproxyfen on the midgut of non-target insect silkworm

Pyriproxyfen is an insect growth regulator that is widely used in public health and pest control in agriculture. Our previous studies have shown that trace amounts of pyriproxyfen in the environment can cause serious toxic effects in the non-target insect silkworm, including failing to pupate, metamorphose and spin cocoons. However, it is unknown why pyriproxyfen not only has no lethal effects on fifth instar larvae but also tend to increase their body weight. The midgut is the main digestive organs of the silkworm, our results showed that the residual of pyriproxyfen in the silkworm at 24 h after 1 × 10^-4 mg/L pyriproxyfen treatment caused severe damage to the midgut microvilli, goblet cells, and nuclei of the silkworm, but body weight and digestibility of the larval were both increased. In addition, pyriproxyfen significantly (p < 0.05) increased the activities of digestive enzymes (α-amylase, trehalase, trypsin and lipase) in the midgut of silkworm. However, it caused down-regulation of ecdysone synthesis-related genes at the end of the fifth instar silkworm, decreased ecdysone titer, and prolonged larval instar. At the same time, pyriproxyfen also activated transcription of detoxification enzymes-related genes such as the cytochrome P450 enzyme genes Cyp9a22 and Cyp15C1, the carboxylesterase genes CarE-8 and CarE-11, and the glutathione S-transferase gene GSTo2. This study elucidated a novel toxicological effect of pyriproxyfen to insects, which not only expands the understanding of the effects of juvenile hormone pesticides on lepidopteran insects but also provides a reference for exploring the ecological security of non-target organisms.

Sexual dimorphism of diapause regulation in the hemipteran bug Pyrrhocoris apterus

Diapause is one of the major strategies for insects to prepare for and survive harsh seasons. In females, the absence of juvenile hormone (JH) is a hallmark of adult reproductive diapause, a developmental arrest, which is much less characterized in males. Here we show that juvenile hormone III skipped bisepoxide (JHSB₃) titers in hemolymph remarkably differ between reproductive males and females of the linden bug Pyrrhocoris apterus, whereas no JH was detected in diapausing adults of both sexes. Like in females, ectopic application of JH mimic effectively terminated male diapause through the canonical JH receptor components, Methoprene-tolerant and Taiman. In contrast to females, long photoperiod induced reproduction even in males with silenced JH reception or in males with removed corpus allatum (CA), the JH-producing gland. JHSB₃ was detected in the accessory glands (MAG) of reproductive males, unexpectedly, even in males without CA. If there is a source of JHSB₃ outside CA or a long-term storage of JHSB₃ in MAGs remains to be elucidated. These sex-related idiosyncrasies are further manifested in different dynamics of diapause termination in P. apterus by low temperature. We would like to propose that this sexual dimorphism of diapause regulation might be explained by the different reproductive costs for each sex.