Regulation of Juvenile Hormone on Summer Diapause of Geleruca daurica and Its Pathway Analysis

MicroRNA miR-285 modulates the metamorphosis in Galeruca daurica by targeting Br-C

BACKGROUND

Galeruca daurica has become a new pest on the Inner Mongolia grasslands since an abrupt outbreak in 2009 caused serious damage. As a pupa indicator during insect metamorphosis, the early response gene of the ecdysone signaling pathway, Broad-Complex (Br-C), plays a vital role in the growth and development of insects. MicroRNAs (miRNAs) are small non-coding RNAs which mediate various biological activities, but it is unknown whether and how Br-C is regulated by miRNAs.

RESULTS

Temporal expression profiles revealed that miR-285 and Br-C basically displayed an opposite trend during larval-adult development, and Br-C was sharply up-regulated on the last day of final-instar larvae while miR-285 was significantly down-regulated. Both dual-luciferase reporter assay and miRNA-mRNA interaction assay indicated that miR-285 interacts with the coding sequence of Br-C and represses its expression. Not only overexpression but also downexpression of miR-285 led to the failure of larval to pupal to adult metamorphosis. In addition, both overexpression of miR-285 and silence of Br-C inhibited the expression of Br-C and other ecdysone signaling pathway genes, including E74, E75, ECR, FTZ-F1, and HR3. On the contrary, suppressing miR-285 obtained opposite results. Further experiments showed that 20-hydroxyecdysone down-regulated miR-285 and up-regulated Br-C and above-mentioned genes, whereas juvenile hormone alalogue (JHA) resulted in opposite effects.

CONCLUSION

Our results reveal that miR-285 is involved in mediating the metamorphosis in G. daurica by targeting Br-C in the ecdysone signaling pathway. miR-285 and its target Br-C could be as a potential target for G. daurica management. © 2024 Society of Chemical Industry.

Differential gene expression and microRNA profile in corpora allata-corpora cardiaca of Aedes aegypti mosquitoes with weak juvenile hormone signalling

The corpora allata-corpora cardiaca (CA-CC) is an endocrine gland complex that regulates mosquito development and reproduction through the synthesis of juvenile hormone (JH). Epoxidase (Epox) is a key enzyme in the production of JH. We recently utilized CRISPR/Cas9 to establish an epoxidase-deficient (epox-/-) Aedes aegypti line. The CA from epox-/- mutants do not synthesize epoxidated JH III but methyl farneosate (MF), a weak agonist of the JH receptor, and therefore have reduced JH signalling. Illumina sequencing was used to examine the differences in gene expression between the CA-CC from wild type (WT) and epox-/- adult female mosquitoes. From 18,034 identified genes, 317 were significantly differentially expressed. These genes are involved in many biological processes, including the regulation of cell proliferation and apoptosis, energy metabolism, and nutritional uptake. In addition, the same CA-CC samples were also used to examine the microRNA (miRNA) profiles of epox-/- and WT mosquitoes. A total of 197 miRNAs were detected, 24 of which were differentially regulated in epox-/- mutants. miRNA binding sites for these particular miRNAs were identified using an in silico approach; they target a total of 101 differentially expressed genes. Our results suggest that a lack of epoxidase, besides affecting JH synthesis, results in the diminishing of JH signalling that have significant effects on Ae. aegypti CA-CC transcriptome profiles, as well as its miRNA repertoire.

Methoprene, a Juvenile Hormone Analog, Causes Winter Diapause Elimination in Univoltine Bee Species Osmia bicornis L

Osmia bicornis syn. O. rufa is a univoltine bee species in which adults fly in spring and the offspring overwinter as cocooned imagoes. The flight period of solitary bees is short, so methods of control for development and emergence time are needed to synchronize the activity of managed pollinators with blooming. In our study, we tested the effectiveness of a juvenile hormone analog for the prevention of winter diapause. Bees developed in settled nests outdoors or in the laboratory (22 °C) until the end of the pre-pupa stage, then cocoons were removed from the nest cells and treated with a JH analog-methoprene-during the pupa and young imago stages. Then, bees were activated at 25 °C until the adults left the cocoons. Topical application of methoprene to the cocoon at the pupa or imago stage induced the emergence of some adult bees in the pre-diapause period, while no adults emerged when the bees were not treated with methoprene. Most adults emerged (about 50%) when treated with methoprene on 3-week-old cocooned imagoes. Bees treated in the pupal stage had a lower emergence rate (20-30%), but adult bees emerged earlier. The emergence time of adults for the laboratory group was, on average, from 70 to 91 days, and that for outdoor groups was from 57 to 72 days.

MicroRNA miR-2765-3p regulates reproductive diapause by targeting FoxO in Galeruca daurica

The forkhead box O (FoxO), as a conserved transcription factor, plays an indispensable role in regulating insect diapause. However, how FoxO is regulated to control diapause in insects remains unknown. In this study, we discovered functional binding sites for miR-2765-3p in the 3' untranslated region of FoxO in Galeruca daurica. The luciferase reporter assay showed that miR-2765-3p targeted FoxO and suppressed its expression. The expression profiles of miR-2765-3p and FoxO displayed opposite patterns during the female developmental process. Overexpression of miR-2765-3p by the injection of the miR-2765-3p agomir into adult females reduced FoxO expression, leading to the suppression of lipid accumulation, promotion of ovarian development, and inhibition of reproductive diapause. This is similar to the phenotype that results from the depletion of FoxO by injecting dsFoxO into adult females. In addition, the repression of miR-2765-3p by injecting the miR-2765-3p antagomir increased the FoxO transcript level, leading to the stimulation of lipid accumulation, depression of ovarian development, and induction of reproductive diapause. A hormone injection assay showed that the juvenile hormone (JH) agonist (methoprene) upregulated miR-2765-3p and downregulated FoxO. Notably, injecting methoprene rescued ovarian development defects associated with miR-2765-3p inhibition. These findings indicate that the JH/miR-2765-3p/FoxO axis plays a vital role in the regulation of reproductive diapause in G. daurica.

In silico identification of potential phytochemical inhibitors targeting farnesyl diphosphate synthase of cotton bollworm (Helicoverpa armigera)

Helicoverpa armigera (Ha), a polyphagous pest, causes significant damage to several crop plants, including cotton. The control of this cosmopolitan pest is largely challenging due to the development of resistance to existing management practices. The Juvenile Hormone (JH) plays a pivotal role in the life cycle of insects by regulating their morphogenetic and gonadotropic development. Hence, enzymes involved in JH biosynthesis are an attractive target for the development of selective insecticides. Farnesyl diphosphate synthase (FPPS), a member protein of (E)-prenyl-transferases, is one of the most crucial enzymes in the biosynthetic pathway of JHs. It catalyzes the condensation of isopentenyl diphosphate (IPP) with dimethylallyl diphosphate (DMAPP), forming farnesyl diphosphate (FPP), a precursor of JH. The study was designed to identify an effective small inhibitory molecule that could inhibit the activity of Helicoverpa armigera - FPPS (HaFPPS) for an effective pest control intervention. Therefore, a 3D model of FPPS protein was generated using homology modeling. The FooDB database library of small molecules was selected for virtual screening, following which binding affinities were evaluated using docking studies. Three top-scored molecules were analyzed for various pharmacophore properties. Further, molecular dynamics (MD) simulation analysis showed that the identified molecules (mitraphylline-ZINC1607834, chlorogenic acid-ZINC2138728 and llagate-ZINC3872446) had a reasonably acceptable binding affinity for HaFPPS and resulted in the formation of a stable HaFPPS-inhibitor(s) complex. The identified phytochemical molecules may be used as potent inhibitors of HaFPPS thus, paving the way for further developing environment-friendly insect growth regulator(s). Communicated by Ramaswamy H. Sarma.

CO2 narcosis induces a metabolic shift mediated via juvenile hormone in Bombus impatiens gynes

Carbon dioxide (CO₂) has pleiotropic effects on insect physiology and behavior. Although diverse, many impacts are related to changes in metabolism and reallocation of macronutrients. Here we examined the metabolic shift induced by CO₂ and its regulation using Bombus impatiens. CO₂ applied to bumble bee gynes induces bypass of diapause and transition into reproduction. We analyzed ovary activation and macronutrient amounts in four tissues/body parts (fat body, thorax, ovaries, and crop) at three timepoints following CO₂ administration. To tease apart the effects of CO₂ on reproduction and metabolism, we monitored the metabolic changes in gynes following ovary removal and CO₂ narcosis. We also explored the role of juvenile hormone in mediating CO₂ impact by feeding queens with a JH antagonist (Precocene). Gynes ovary activation was increased following CO₂ treatment. Additionally, CO₂-treated gynes showed lower lipid amount in the fat body and higher glycogen and protein amount in the ovary ten days after the treatment. CO₂ treatment following ovary removal also resulted in decreased fat body lipids, suggesting that CO₂ operates by inducing a metabolic shift independent of reproduction. Lastly, gynes fed with precocence did not show a metabolic shift following CO₂, suggesting CO₂ impact is mediated via juvenile hormone. Overall, these data suggest that CO₂ induces transfer of macronutrients and utilization of stored reserved by accelerating metabolism. The proposed mechanism of CO₂ may explain many of the pleiotropic effects of CO₂ across species and can aid in understanding how this common anastatic influences insect physiology.

Transcriptome-wide identification of microRNAs in response to 20-hydroxyecdysone in Galeruca daurica

Both 20-hydroxyecdysone (20E) and miRNAs have multiple functions in the regulation of various physiological processes in insects. However, little is known about the interaction between 20E and miRNAs. In this study, six small RNA libraries were constructed from the adult Galeruca daurica treated with 20E and dimethyl sulfoxide (DMSO), respectively. Using small RNA sequencing, a total of 183 miRNAs, including 140 known and 43 novel miRNAs, were identified. Compared with the control (DMSO), 52 miRNAs (21 up-regulated and 31 down-regulated) were significantly differentially expressed after 20E treatment. The KEGG and GO analysis of the predicted genes targeted by 20E-responsive miRNAs indicate that 20E may influence the metabolic change during reproductive diapause in G. daurica via regulating miRNAs.

Enhanced Degradation of Juvenile Hormone Promotes Reproductive Diapause in the Predatory Ladybeetle Coccinella Septempunctata

Improved knowledge on the regulation of reproductive diapause in Coccinella septempunctata, an important predator of aphids, is crucial for improving shelf-life and mass production of the ladybeetles. In many insects, the absence of juvenile hormone (JH) is a central regulator of reproductive diapause. JH is principally degraded by JH esterase (JHE) and JH epoxide hydrolase (JHEH). Previous studies have shown that genes encoding these enzymes were upregulated in early diapause of C. septempunctata, but whether increased JH degradation contributes to the reduction of JH levels and facilitates reproductive diapause remains unknown. Here, we investigate the role of JH and JH degradation genes during reproductive diapause in C. septempunctata females. Applying methoprene, a JH analogue, to the diapause preparation females clearly elevated JH signaling and reversed diapause program, suggesting that a lower level of JH is critical for the induction of reproductive diapause in the ladybeetle. Full-length cDNA sequences of JHE and JHEH were cloned and characterized, and their deduced proteins contain all the conserved active domains and typical motifs as identified in other insects. The expressions of JHE and JHEH were both significantly increased in diapause preparation and remained at a high level for a period throughout diapause, and then decreased after the termination of diapause. Knocking down these JH degradation genes clearly increased the expression levels of JH-inducible genes Krüppel-homolog 1 (Kr-h1) and vitellogenin (Vg), indicating an elevated JH level. Simultaneously, silencing JH degradation genes distinctly reduced diapause-related features and promotes reproduction, indicated by accelerated ovary growth, yolk deposition, and suppressed lipid accumulation. These results indicate that the enhanced JH degradation plays a critical role in regulating reproductive diapause of C. septempunctata.

Transcriptional Regulation of Reproductive Diapause in the Convergent Lady Beetle, Hippodamia convergens

Simple Summary

Diapause is a dormant period typically controlled by daylength that ensures an insect’s survival through harsh environmental conditions. The convergent lady beetle, Hippodamia convergens, undergoes a reproductive diapause in winter, where female ovaries remain immature and no eggs are laid. This species is an important biological control agent, but during diapause, beetles are less likely to eat pest insects. Thus, knowledge of diapause mechanisms may facilitate manipulation thereof to improve biological control. Further, molecular studies of adult diapause and diapause in Coleoptera are relatively lacking. Here, we assembled and annotated a transcriptome for this species and quantified transcript expression changes during diapause. Female beetles were sampled at three times in diapause (early, mid, and late diapause), which allowed us to characterize the molecular processes occurring at distinct transitions throughout diapause. We found that transcripts involved in flight were consistently upregulated during diapause, which is consistent with dispersal flights at this stage, while transcripts involved in ovarian development were downregulated, which is consistent with the shutdown of reproduction in diapausing females. These findings identify key regulators of diapause in H. convergens and contribute to a growing body of literature on the molecular mechanisms of diapause across the insect phylogeny.

Abstract

Diapause is an alternate development program that synchronizes an insect’s life cycle with seasonally abundant resources and ensures survival in unfavorable conditions. The physiological basis of diapause has been well characterized, but the molecular mechanisms regulating it are still being elucidated. Here, we present a de novo transcriptome and quantify transcript expression during diapause in the convergent lady beetle Hippodamia convergens. H. convergens is used as an augmentative biocontrol agent, and adult females undergo reproductive diapause that is regulated by photoperiod. We sampled females at three stages (early, mid, and late diapause) and compared transcript expression to non-diapausing individuals. Based on principle component analysis, the transcriptomes of diapausing beetles were distinct from non-diapausing beetles, and the three diapausing points tended to cluster together. However, there were still classes of transcripts that differed in expression across distinct phases of diapause. In general, transcripts involved in muscle function and flight were upregulated during diapause, likely to support dispersal flights that occur during diapause, while transcripts involved in ovarian development were downregulated. This information could be used to improve biological control by manipulating diapause. Additionally, our data contribute to a growing understanding of the genetic regulation of diapause across diverse insects.

Functional Characterization of Allatostatin C (PISCF/AST) and Juvenile Hormone Acid O-Methyltransferase in Dendroctonus armandi

Allatostatin C (PISCF/AST) is a neuropeptide gene that affects juvenile hormone (JH) synthesis in the corpora allata. Juvenile hormone acid O-methyltransferase (JHAMT) is a key gene in the JH biosynthetic pathway. In this study, two genes encoding DaAST and DaJHAMT were cloned. Both DaAST and DaJHAMT were expressed in the larvae, pupae and adults of Chinese white pine beetle (Dendroctonus armandi), and highly expressed in the head and the gut. The expression of the two genes was induced by JH analog (JHA) methoprene and the functions of the two genes were then investigated by RNAi. Considering the role of hormones in metamorphosis, JHA significantly induced DaAST and DaJHAMT in the larval stage. DaAST knockdown in larvae, pupae and adults significantly increased the DaJHAMT mRNA levels. Moreover, knockdown of DaAST instead of DaJHAMT increased pupae mortality and the abnormal rate of emergence morphology and reduced emergence rates. However, knockdown of DaJHAMT instead of DaAST significantly reduced frontalin biosynthesis in adult males. The results showed that DaAST acts as an allatostatin and inhibits JH biosynthesis, and that JHAMT is a key regulatory enzyme for JH synthesis in the D. armandi.

MicroRNA let-7-5p targets the juvenile hormone primary response gene Krüppel homolog 1 and regulates reproductive diapause in Galeruca daurica

MicroRNAs (miRNAs) regulate various biological processes in insects. However, their roles in the regulation of insect diapause remain unknown. In this study, we address the biological function of a conserved miRNA, let-7-5p in the regulation of a juvenile hormone primary response gene, Krüppel homolog 1 (Kr-h1), which modulates reproductive diapause in Galeruca daurica. The dual luciferase reporter assay showed that let-7-5p depressed the expression of Kr-h1. The expression profiles of let-7-5p and Kr-h1 displayed opposite patterns in the adult developmental stage. Injection of let-7-5p agomir in pre-diapause adult females inhibited the expression of Kr-h1, which consequently led to delay ovarian development, increase lipid accumulation, expand fat body, and induce reproductive diapause just as depleting Kr-h1 did. Conversely, injection of let-7-5p antagomir resulted in opposite effects by reducing fat storage and stimulating reproduction. Moreover, JH receptor agonist methoprene reduced the expression of let-7-5p, and rescued the ovarian development defects associated with let-7-5p overexpression. These results indicate that let-7-5p plays an important role in the regulation of reproductive diapause and development of G. daurica adults through its target gene Kr-h1.

Endocrine Regulation of Lifespan in Insect Diapause

Diapause is a physiological adaptation to conditions that are unfavorable for growth or reproduction. During diapause, animals become long-lived, stress-resistant, developmentally static, and non-reproductive, in the case of diapausing adults. Diapause has been observed at all developmental stages in both vertebrates and invertebrates. In adults, diapause traits weaken into adaptations such as hibernation, estivation, dormancy, or torpor, which represent evolutionarily diverse versions of the traditional diapause traits. These traits are regulated through modifications of the endocrine program guiding development. In insects, this typically includes changes in molting hormones, as well as metabolic signals that limit growth while skewing the organism's energetic demands toward conservation. While much work has been done to characterize these modifications, the interactions between hormones and their downstream consequences are incompletely understood. The current state of diapause endocrinology is reviewed here to highlight the relevance of diapause beyond its use as a model to study seasonality and development. Specifically, insect diapause is an emerging model to study mechanisms that determine lifespan. The induction of diapause represents a dramatic change in the normal progression of age. Hormones such as juvenile hormone, 20-hydroxyecdysone, and prothoracicotropic hormone are well-known to modulate this plasticity. The induction of diapause-and by extension, the cessation of normal aging-is coordinated by interactions between these pathways. However, research directly connecting diapause endocrinology to the biology of aging is lacking. This review explores connections between diapause and aging through the perspective of endocrine signaling. The current state of research in both fields suggests appreciable overlap that will greatly contribute to our understanding of diapause and lifespan determination.

Juvenile hormone regulates the reproductive diapause through Methoprene-tolerant gene in Galeruca daurica

Juvenile hormone (JH) signalling plays an important role in regulation of reproductive diapause in insects. However, its underlying molecular mechanism has been unclear. Methoprene-tolerant (Met), as a universal JH receptor, is involved in JH action. To gain some insight into its function in the reproductive diapause of Galeruca daurica, a serious pest on the Inner Mongolia grasslands undergoing obligatory summer diapause at the adult stage, we cloned the complete open-reading frame (ORF) sequences of Met and other 7 JH signalling-related genes, including JH acid methyltransferase (JHAMT), JH esterase (JHE), JH epoxide hydrolase (JHEH), Krüppel homologue 1 (Kr-h1), vitellogenin (Vg), forkhead box O (FOXO) and fatty acid synthase 2 (FAS2), from this species. GdMet encoded a putative protein, which contained three domains typical of the bHLH-PAS family. Expression patterns of these eight genes were developmentally regulated during adult development. Topical application of JH analogue (JHA) methoprene into the 3-day-old and 5-day-old adults induced the expression of GdMet. Silencing GdMet by RNAi inhibited the expression of JHBP, JHE, Kr-h1 and Vg, whereas promoted the FAS2 expression, which enhanced lipid accumulation and fat body development, and finally induced the adults into diapause ahead. Combining with our previous results, we conclude that JH may regulate reproductive diapause through a conserved Met-dependent pathway in G. daurica.