20-Hydroxyecdysone (20E) Primary Response Gene E93 Modulates 20E Signaling to Promote Bombyx Larval-Pupal Metamorphosis

Effects of Novaluron Exposure on the Oviposition and Expression of Ovarian Development Related Genes in Silkworm, Bombyx mori (Lepidoptera: Bombycidae)

Bombyx mori (Lepidoptera: Bombycidae) is an important economic insect, which mainly feeds on mulberry leaves and is widely used in many research fields. The growth and development of silkworm larvae are easily affected by the use of chemical insecticides such as novaluron, a benzoylurea insecticide. However, the effect of novaluron exposure on the reproduction of silkworms has not yet been studied. In this study, the effect of trace novaluron on the oviposition of silkworms and histopathological changes were first evaluated, and then the gene expression level changes after novaluron exposure were also determined by employing qRT-PCR. It was found that the number of eggs and the hatching rate of eggs in silkworms decreased significantly after feeding on leaves with a trace amount of novaluron (p ≤ 0.01). Furthermore, novaluron exposure could affect the development of ovary tissue by reducing the number of oocytes and oogonia in the ovaries of silkworms fed with novaluron. In addition, the transcription levels of genes related to ovary development (Vg, Ovo, Otu, Sxl-S and Sxl-L) and hormone regulation (EcR and JHBP2) showed varying degrees of downregulation at 24 h, 48 h, and 72 h after novaluron treatment (p ≤ 0.05). Therefore, we speculated that novaluron can affect the energy metabolism, ovary development, and egg formation of silkworms, thus leading to reproductive disorders of silkworms after novaluron exposure.

E93 controls adult differentiation by repressing broad in Drosophila

In Drosophila melanogaster, successful development relies on the precise coordination of both spatial and temporal regulatory axes. The temporal axis governs stage-specific identity and developmental transitions through a number of genes, collectively forming the Metamorphic Gene Network. Among these, Ecdysone inducible protein 93F (E93) serves as the critical determinant for adult specification, but its mechanism of action remains unclear. Here, we found that, rather than acting mainly as an instructive signal, E93 promotes adult differentiation through the repression of the pupal specifier broad (br). In the absence of E93, sustained high levels of Br during the pupal stage strongly represses pupal-specific enhancers that are essential for the terminal differentiation of the wing. Notably, RNA-seq analysis confirmed that the majority of E93-dependent transcriptomic changes in pupal wings are primarily driven by br repression. In addition, we also show that Br represses the pupal-enhancers during the larval and prepupal stages preventing the premature implementation of the adult genetic program, and that it also dampens the activity of larval enhancers during the latter stages of larval development. This mechanism of action seems to be a derived feature acquired in Diptera, as in the coleopteran Tribolium castaneum, repression of br by E93 is not sufficient to allow adult differentiation. In summary, our study elucidates the crucial role of the intricate interplay between E93 and Br as the governing mechanism in the process of terminal differentiation in Drosophila. This finding holds significant implications for advancing our understanding of the evolution of insect metamorphosis.

Molecular basis of E93-dependent tissue morphogenesis and histolysis during insect metamorphosis

The evolution of insect metamorphosis has profoundly influenced their successful adaptation and diversification. Two key physiological processes during insect metamorphosis are notable: wing maturation and prothoracic gland (PG) histolysis. The ecdysone-induced protein 93 (E93) is a transcription factor indispensable for metamorphosis. While it has been established that both wing maturation and PG histolysis are dependent on E93, the molecular mechanisms through which E93 regulates these seemingly 'opposing' events remain poorly understood. In this study, time-course transcriptome profiles were generated for wing pads and PGs during metamorphosis in Blattella germanica, a hemimetabolous model insect. Comparative transcriptomic analyses demonstrated that E93 exerts predominant control over extensive gene transcription during wing morphogenesis and PG histolysis. During wing morphogenesis, E93 selectively enhances the expression of genes associated with cell proliferation, energy supply, signal transduction, actin cytoskeleton organization, and cell adhesion, etc. Additionally, E93 activates the transcription of the majority of genes within the wing gene network that are crucial for wing development in B. germanica. During PG histolysis, E93 preferentially promotes the expression of genes related to endocytosis, focal adhesion, the AMPK signaling pathway, adipocytokine signaling pathway, Toll and Imd signaling pathways, and autophagy, etc. The key genes involved in the aforementioned pathways were subsequently confirmed to contribute to the E93-dependent degeneration of the PG in B. germanica. In summary, our results reveal that E93 functions as a master transcriptional regulator orchestrating both tissue morphogenesis and histolysis during insect metamorphosis. These findings contribute to a deeper understanding of the genetic underpinnings of insect metamorphosis.

Transcription factor E93 regulates vitellogenesis via the vitelline membrane protein 26Ab gene in Chilo Suppressalis

BACKGROUND

Ecdysone-induced protein 93 F (E93, also known as Eip93F) plays a crucial role in the reproductive process of numerous insects. This study aims to delineate the function of E93 in Chilo suppressalis and elucidated the regulatory mechanism by which E93 influences the reproduction of C. suppressalis METHODS AND RESULTS: The results of the bioinformatics analysis indicate that C. suppressalis E93 shows the highest homology with E93 from Bombyx mori. We used qPCR to evaluate the expression profile of CsE93 from different developmental stages and tissues, revealed that CsE93 had the highest expression levels in the head, which peaked during the prepupal stage. Silencing CsE93 resulted in a significant reduction in yolk deposition and abnormal ovarian development. Moreover, the transcriptional levels of vitellogenin (Vg) and E74A, which are related to vitellogenesis and the 20E pathway, were significantly down-regulated in dsE93-treated female pupae. In addition, we identified Vitelline membrane protein 26Ab (VMP26Ab), a downstream gene associated with the integrity of the inner eggshell. The knockdown of VMP26Ab resulted in a significant reduction in the number of eggs and abnormal ovarian development, similar to RNAi E93. Finally, we identified an active promoter fragment (containing GAGA-containing motif) of CsVMP26Ab and demonstrated that CsE93 can bind to it.

RESULTS

Our results indicate that CsE93 plays an important role in C. suppressalis reproduction. CsE93 modulates the CsVMP26Ab expression by acting on its promoter involve in the reproduction of C. suppressalis finally.

Replacement of fish meal with full fat Hermetia illucens modulates hepatic FXR signaling in juvenile rainbow trout (Oncorhynchus mykiss): Exploring a potential role of ecdysteroids

The present study was conducted to investigate the effects of fish meal (FM) replacement with full fat Hermetia illucens (HI) on the molecular mechanisms regulating lipid and bile salt (BA) homeostasis in rainbow trout (Oncorhynchus mykiss) juveniles. We thus explore the presence of 20-hydroxyecdysone (20E) in an insect meal-based diet and evaluate its potential involvement in regulating the molecular mechanisms/basis of FXR:RXR axis signaling. Ecdysteroids are a category of steroid hormones which bind a nuclear-receptor complex composed of ecdysone receptor (EcR) and ultraspiracle protein (USP) and regulate insect molting and metamorphosis. In all vertebrates, including fish, EcR-USP homologs are the Farnesoid X receptors (FXR) and the Retinoid X receptors (RXR), which are known to regulate crucial physiological and metabolic aspects, including BA synthesis and cholesterol homeostasis. In silico prediction indicates that 20E binds the heterodimeric complex with a binding affinity constant Kd equals to 610 ± 60 nM and affects positively the dimerization process. Results also demonstrated the coordinated increased expression of FXR and RXR, as well as their downstream target genes (i.e. short heterodimer partner 1 and 2) in rainbow trout fed diets containing HI meal. This latter finding was paralleled by a significant down-regulation of CYP7a1 and CYP8b1 gene expression together with a decrease in hepatic total cholesterol, triglyceride, and BA levels. Overall, our study suggested that FXR is a potential target for 20E content in insect meal and provided preliminary data on the potential role of ecdysteroids in regulating the metabolic status of teleost fish through modulation of FXR signaling in the enterohepatic system.

Methoprene-Tolerant (Met) Acts as Methyl Farnesoate Receptor to Regulate Larva Metamorphosis in Mud Crab, Scylla paramamosain

The conserved role of juvenile hormone (JH) signals in preventing larvae from precocious metamorphosis has been confirmed in insects. Crustaceans have different metamorphosis types from insects; we previously proved that methyl farnesoate (MF) can prohibit larvae metamorphosis in mud crabs, but the molecular signal of this process still needs to be elucidated. In this study, methoprene-tolerant (Met) of Scylla paramamosain was obtained and characterized, which we named Sp-Met. Sp-Met contains a 3360 bp ORF that encodes 1119 amino acids; the predicted protein sequences of Sp-Met include one bHLH, two PAS domains, one PAC domain, and several long unusual Gln repeats at the C-terminal. AlphaFold2 was used to predict the 3D structure of Sp-Met and the JH binding domain of Met. Furthermore, the binding properties between Sp-Met and MF were analyzed using CD-DOCK2, revealing a putative high affinity between the receptor and ligand. In silico site-directed mutagenesis suggested that insect Mets may have evolved to exhibit a higher affinity for both MF or JH III compared to the Mets of crustaceans. In addition, we found that the expression of Sp-Met was significantly higher in female reproductive tissues than in males but lower in most of the other examined tissues. During larval development, the expression variation in Sp-Met and Sp-Kr-h1 was consistent with the immersion effect of MF. The most interesting finding is that knockdown of Sp-Met blocked the inhibitory effect of MF on metamorphosis in the fifth zoea stage and induced pre-metamorphosis phenotypes in the fourth zoea stage. The knockdown of Sp-Met significantly reduced the expression of Sp-Kr-h1 and two ecdysone signaling genes, Sp-EcR and Sp-E93. However, only the reduction in Sp-Kr-h1 could be rescued by MF treatment. In summary, this study provides the first evidence that MF inhibits crustacean larval metamorphosis through Met and that the MF-Met→Kr-h1 signal pathway is conserved in mud crabs. Additionally, the crosstalk between MF and ecdysteroid signaling may have evolved differently in mud crabs compared to insects.

CYP303A1 regulates molting and metamorphosis through 20E signaling in Nilaparvata lugens Stål (Hemiptera: Delphacidae)

Cytochrome P450s play a crucial role in the breakdown of external substances and perform important activities in the hormone system of insects. It has been understood that P450s were essential in the metabolism of ecdysteroids. CYP303A1 is a highly conserved CYP in most insects, but its specific physiological functions remain poorly understood in Nilaparvata lugens Stål. In this study, NlCYP303A1 was identified and highly expressed in the pre-molt stages, predominantly in the cuticle-producing tissues. Silencing of NlCYP303A1 caused a lethal phenotype with a molting defect. Moreover, the 20E titers, the expression levels of Halloween genes, and critical genes associated with the 20E signaling pathway in N. lugens nymphs were significantly decreased with the silencing NlCYP303A1. We further performed additional backfilling of 20E to rescue the RNAi effects on NlCYP303A1. The gene expression levels that were previously reduced caused by silencing NlCYP303A1 were significantly elevated. However, the molting defects of nymphs were not effectively improved. The results demonstrated NlCYP303A1 plays a crucial role in the molting and metamorphosis of N. lugens by regulating the 20E signaling pathway and cuticular formation, enhances the understanding of the functional role of CYP 2 clans, and identifies candidate gene for RNAi-based control of N. lugens.

E93 is indispensable for reproduction in ametabolous and hemimetabolous insects

Ecdysone-induced protein 93 (E93), known as the 'adult-specifier' transcription factor in insects, triggers metamorphosis in both hemimetabolous and holometabolous insects. Although E93 is conserved in ametabolous insects, its spatiotemporal expression and physiological function remain poorly understood. In this study, we first discover that, in the ametabolous firebrat Thermobia domestica, the previtellogenic ovary exhibits cyclically high E93 expression, and E93 mRNA is broadly distributed in previtellogenic ovarioles. E93 homozygous mutant females of T. domestica exhibit severe fecundity deficiency due to impaired previtellogenic development of the ovarian follicles, likely because E93 induces the expression of genes involved in ECM (extracellular matrix)-receptor interactions during previtellogenesis. Moreover, we reveal that in the hemimetabolous cockroach Blattella germanica, E93 similarly promotes previtellogenic ovarian development. In addition, E93 is also essential for vitellogenesis that is necessary to guarantee ovarian maturation and promotes the vitellogenesis-previtellogenesis switch in the fat body of adult female cockroaches. Our findings deepen the understanding of the roles of E93 in controlling reproduction in insects, and of E93 expression and functional evolution, which are proposed to have made crucial contributions to the origin of insect metamorphosis.

Development of the insect adult fat body relies on glycolysis, lipid synthesis, cell proliferation, and cell adhesion

The fat body of the holometabolous insect is remodeled by the degradation of the larval fat body and the development of the adult fat body during metamorphosis. However, the mechanism of adult fat body development is quite unclear. Using the agricultural pest Helicoverpa armigera, the cotton bollworm, as a model, we revealed that the development of adult fat body was regulated by glycolysis, triglyceride (triacylglycerol [TAG]) synthesis, cell proliferation, and cell adhesion. RNA sequencing detected a set of genes that were upregulated in the 8-d late pupal fat body at a late metamorphic stage compared with the 2-d pupal fat body at an earlier metamorphic stage. The pathways for glycolysis, TAG synthesis, cell proliferation, and cell adhesion were enriched by the differentially expressed genes, and the key genes linked with these pathways showed increased expression in the 8-d pupal fat body. Knockdown of phosphofructokinase (Pfk), acetyl-CoA carboxylase (Acc1), phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit (P110) and collagen alpha-1(IV) chain (Col4a1) by RNA interference resulted in abnormal eclosion and death at pupal stages, and repressed lipid droplets accumulation and adult fat body development. The expression of Acc1, P110, and Col4a1 was repressed by the insect steroid hormone 20-hydroxyecdysone (20E). The critical genes in the 20E pathway appeared to decrease at the late pupal stage. These data suggested that the development of the insect adult fat body is regulated by glycolysis, lipids synthesis, cell proliferation, and cell adhesion at the late pupal stage when the 20E signal decreases.

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.

Effect of silencing the E74B gene on the development and metamorphosis of Helicoverpa armigera

BACKGROUND

The growth and development transition of insects are mainly mediated by ecdysone. As one of the ecdysone-induced transcription factors, E74 is involved in many physiological processes of insect growth and development. However, E74 and its function in Helicoverpa armigera remains unclear.

RESULTS

In this study, E74B, a subtype of the E74, was identified for the first time in H. armigera. Bioinformatics analysis showed that H. armigera E74B shared the highest homology with E74B in Bombyx mori, which belongs to the E26 transformation-specific (ETS) superfamily. The expression profile showed that the transcription level of HaE74B increased in the late stages of fourth to sixth instars compared with the early stages; it was also high in the pupa and midgut. Moreover, we investigated the function of HaE74B through RNA interference and 20E rescue experiments. The results showed silencing of E74B affected the molting and growth of larvae, resulting in the death of more than 60% of larvae. In addition, it also seriously affected the metamorphosis of H. armigera, which reduced the pupae rate, the eclosion rate of the pupae, and fecundity. Application of 20E partially restored the defects in the molting, development and pupae rate of H. armigera.

CONCLUSION

Taken together, these results demonstrated that HaE74B plays a critical role in the growth, development, and metamorphosis of H. armigera, which serves as a molecular target and sets out a theoretical foundation for RNAi-mediated control of this key pest. © 2023 Society of Chemical Industry.

An efficient and safe strategy for germ cell-specific automatic excision of foreign DNA in F1 hybrid transgenic silkworms

The safety of transgenic technology is a major obstacle in the popularization and use of transgenic silkworms and their products. In sericulture, only the first filial generation (F1 ) hybrid eggs produced by cross-breeding Japanese and Chinese original strains are usually used for the large-scale breeding of silkworms, but this may result in uncontrolled transgene dispersal during the popularization and application of the F1 hybrid transgenic eggs. To address this issue, we developed a safe and efficient strategy using the GAL4/Upstream activating sequence (UAS) system, the FLP/flippase recognition target (FRT) system, and the gonad-specific expression gene promoters (RSHP1p and Nanosp) for the germ cell-specific automatic excision of foreign DNA in the F1 hybrid transgenic silkworms. We established 2 types of activator strains, R1p::GAL4-Gr and Nsp::GAL4-Gr, containing the testis-specific GAL4 gene expression cassettes driven by RSHP1p or Nanosp, respectively, and 1 type of effector strain, UAS::FLP-Rg, containing the UAS-linked FLP gene expression cassette. The FLP recombinase-mediated sperm-specific complete excision of FRT-flanked target DNA in the F1 double-transgenic silkworms resulting from the hybridization of R1p::GAL4-Gr and UAS::FLP-Rg was 100%, whereas the complete excision efficiency resulting from the hybridization of Nsp::GAL4-Gr and UAS::FLP-Rg ranged from 13.73% to 80.3%. Additionally, we identified a gene, sw11114, that is expressed in both testis and ovary of Bombyx mori, and can be used to establish novel gonad-specific expression systems in transgenic silkworms. This strategy has the potential to fundamentally solve the safety issue in the production of F1 transgenic silkworm eggs and provides an important reference for the safety of transgenic technology in other insect species.

E93 gene in the swimming crab, Portunus trituberculatus: Responsiveness to 20-hydroxyecdysone and methyl farnesoate and role on regulating ecdysteroid synthesis

Ecdysone-induced protein 93 (E93) is a metamorphic determinant involved in crosstalk between 20-hydroxyecdysone (20E) and juvenile hormone (JH) during the insect molting process. The present study identified the E93 gene from the swimming crab, P. trituberculatus, and found it was widely distributed in adult tissues. PtE93 mRNA levels in Y-organ and epidermis fluctuated during the molt cycle, suggesting its involvement in juvenile molting. In vitro and in vivo treatments with 20E led to an induction of PtE93 expression in Y-organ and epidermis, while we found the opposite effect for methyl farnesoate (MF) treatments, a crustacean equivalent of insect JH. We also observed that two genes for ecdysteroid biosynthesis, Spook (Spo) and Shadow (Sad), were suppressed by 20E and induced by MF, showing a negative correlation between PtE93 and ecdysteroid biosynthesis. PtE93 RNA interference (RNAi) induced Spo and Sad expression levels, elevated ecdysteroid content in culture medium, and relieved the 20E inhibitory effect on ecdysteroid synthesis, indicating an inhibitory role of PtE93 on ecdysteroid synthesis. Overall, our results suggest that E93 may be involved in the crosstalk between 20E and MF during crustacean molting, and its presence in Y-organ is closely related to ecdysteroid synthesis.

Knockout of nuclear receptor HR38 gene impairs pupal-adult development in silkworm Bombyx mori

Nuclear receptors are ligand-regulated transcription factors that play important role in regulating insect metamorphosis through the ecdysone signalling pathway. In this study, we investigated the nuclear receptor HR38 gene in Bombyx mori (BmHR38), belonging to the NR4A subfamily. BmHR38 mRNA was highly expressed in the head and epidermis at the pupal stage. The expression of the BmHR38 gene was influenced by different doses of 20E at different times. A BmHR38 deletion mutant silkworm was generated using the clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 system. Compared with the wild-type B. mori, the BmHR38 deletion mutant resulted in abnormal development during the pupal stage, leading to either failed eclosion or the formation of abnormal adult wings. After silencing of BmHR38 in the pupal stage, the phenotype of pupa or moth had no significant change, but it did result in reduced egg production. The mRNA levels of USP, E75 and E74 were significantly increased, while the transcript levels of FTZ-F1 were suppressed after RNA interference. Furthermore, interference with BmHR38 also inhibited the expressions of chitin metabolism genes, including Chs1, Chs2, Chi, Chi-h and CDA. Our results suggest that BmHR38 is essential for pupal development and pupa-adult metamorphosis in B. mori by regulating the expression of NRs and chitin metabolism genes.

5mC modification orchestrates choriogenesis and fertilization by preventing prolonged ftz-f1 expression

DNA methylation at the fifth position of cytosine (5-methylcytosine, 5mC) is a crucial epigenetic modification for regulating gene expression, but little is known about how it regulates gene expression in insects. Here, we pursue the detailed molecular mechanism by which DNMT1-mediated 5mC maintenance regulates female reproduction in the German cockroach, Blattella germanica. Our results show that Dnmt1 knockdown decreases the level of 5mC in the ovary, upregulating numerous genes during choriogenesis, especially the transcription factor ftz-f1. The hypomethylation at the ftz-f1 promoter region increases and prolongs ftz-f1 expression in ovarian follicle cells during choriogenesis, which consequently causes aberrantly high levels of 20-hydroxyecdysone and excessively upregulates the extracellular matrix remodeling gene Mmp1. These changes further impair choriogenesis and disrupt fertilization by causing anoikis of the follicle cells, a shortage of chorion proteins, and malformation of the sponge-like bodies. This study significantly advances our understanding of how DNA 5mC modification regulates female reproduction in insects.

Cold-stored mulberry leaves affect antioxidant system and silk proteins of silkworm (Bombyx mori) larva

BACKGROUND

Cold storage has been widely used to maintain the quality of vegetables, but whether eating cold-stored vegetables affects health remains unknown.

RESULTS

This study used silkworms as an animal model to evaluate the effects of nutrient changes in cold-stored mulberry leaves (CSML) on health. Compared with fresh mulberry leaves (FML), CSML contained lower vitamin C, soluble sugars and proteins, and higher H2 O2 , suggesting decreased antioxidant ability and nutrition. The CSML did not obviously affect larval survival rate, body weight or dry matter rate, cocoon shape, weight and size, or final rates of cluster and cocooning relative to the FML, suggesting CSML did not alter overall growth and development. However, the CSML increased the initial rates of cluster and cocooning and upregulated BmRpd3, suggesting CSML shortened larval lifespan and enhanced senescence. CSML upregulated BmNOX4, downregulated BmCAT, BmSOD and BmGSH-Px and increased H2 O2 in silkworms, suggesting CSML caused oxidative stress. CSML upregulated ecdysone biosynthesis and inactivation genes and elevated ecdysone concentration in silkworms, suggesting that CSML affected hormone homeostasis. CSML upregulated apoptosis-related genes, downregulated sericin and silk fibroin genes and decreased sericin content rate in silkworms, suggesting oxidative stress and protein deficiency.

CONCLUSION

Cold storage reduced nutrition and antioxidant capability of mulberry leaves. CSML did not influence growth and development of silkworm larva, but affected health by causing oxidative stress and reducing protein synthesis. The findings show that the ingredient changes in CSML had negative effects on health of silkworms. © 2023 Society of Chemical Industry.

Buprofezin affects the molting process by regulating nuclear receptors SfHR3 and SfHR4 in Sogatella furcifera

Nuclear receptors play a crucial role in various signaling and metabolic pathways, such as insect molting and development. Buprofezin (2-tert-butylimino-3-isopropyl-5-phenyl-perhydro-1, 3, 5-thiadiazin-4-one), a chitin synthesis inhibitor, causes molting deformities and slow death in insects by inhibiting chitin synthesis and interfering with their metabolism. This study investigated whether buprofezin affects insect ecdysteroid signaling pathway. The treatment of buprofezin significantly suppressed the transcription levels of SfHR3 and SfHR4, two nuclear receptor genes, in third-instar nymphs of Sogatella furcifera. Meanwhile, the transcription levels of SfHR3 and SfHR4 in first-day fifth-instar nymphs were induced at 12 h after 20E treatment. In addition, the silencing of SfHR3 and SfHR4 genes in first-day fifth-instar nymphs caused severe developmental delay and molting failure, resulting in a significant reduction of survival rates at 7.36% and 2.99% on the eighth day, respectively. Further analysis showed that the silencing SfHR3 and SfHR4 significantly inhibited the transcription levels of chitin synthesis and degradation-related genes. These results indicate that buprofezin can inhibits chitin synthesis and degradation by suppressing the signal transduction of 20E through SfHR3 and SfHR4, leading to molting failure and death. This study not only expands our understanding of the molecular mechanism of buprofezin in pest control but also lays a foundation for developing new control strategies of RNAi by targeting SfHR3 and SfHR4.

Research Progress on the Regulation of Autophagy and Apoptosis in Insects by Sterol Hormone 20-Hydroxyecdysone

20E (20-Hydroxyecdysone) is a central steroid hormone that orchestrates developmental changes and metamorphosis in arthropods. While its molecular mechanisms have been recognized for some time, detailed elucidation has primarily emerged in the past decade. PCD (Programmed cell death), including apoptosis, necrosis, efferocytosis, pyroptosis, ferroptosis, and autophagy, plays a crucial role in regulated cell elimination, which is vital for cells' development and tissue homeostasis. This review summarizes recent findings on 20E signaling regulated autophagy and apoptosis in insects, including Drosophila melanogaster, Bombyx mori, Helicoverpa armigera, and other species. Firstly, we comprehensively explore the biosynthesis of the sterol hormone 20E and its subsequent signal transduction in various species. Then, we focus on the involvement of 20E in regulating autophagy and apoptosis, elucidating its roles in both developmental contexts and bacterial infection scenarios. Furthermore, our discussion unfolds as a panoramic exposition, where we delve into the fundamental questions with our findings, anchoring them within the grander scheme of our study in insects. Deepening the understanding of 20E-autophagy/apoptosis axis not only underscores the intricate tapestry of endocrine networks, but also offers fresh perspectives on the adaptive mechanisms that have evolved in the face of environmental challenges.

Overexpression of BmJHBPd2 Repressed Silk Synthesis by Inhibiting the JH/Kr-h1 Signaling Pathway in Bombyx mori

The efficient production of silkworm silk is crucial to the silk industry. Silk protein synthesis is regulated by the juvenile hormone (JH) and 20-Hydroxyecdysone (20E). Therefore, the genetic regulation of silk production is a priority. JH binding protein (JHBP) transports JH from the hemolymph to target organs and cells and protects it. In a previous study, we identified 41 genes containing a JHBP domain in the Bombyx mori genome. Only one JHBP gene, BmJHBPd2, is highly expressed in the posterior silk gland (PSG), and its function remains unknown. In the present study, we investigated the expression levels of BmJHBPd2 and the major silk protein genes in the high-silk-producing practical strain 872 (S872) and the low-silk-producing local strain Dazao. We found that BmJHBPd2 was more highly expressed in S872 than in the Dazao strain, which is consistent with the expression pattern of fibroin genes. A subcellular localization assay indicated that BmJHBPd2 is located in the cytoplasm. In vitro hormone induction experiments showed that BmJHBPd2 was upregulated by juvenile hormone analogue (JHA) treatment. BmKr-h1 upregulation was significantly inhibited by the overexpression of BmJHBPd2 (BmJHBPd2OE) at the cell level when induced by JHA. However, overexpression of BmJHBPd2 in the PSG by transgenic methods led to the inhibition of silk fibroin gene expression, resulting in a reduction in silk yield. Further investigation showed that in the transgenic BmJHBPd2OE silkworm, the key transcription factor of the JH signaling pathway, Krüppel homolog 1 (Kr-h1), was inhibited, and 20E signaling pathway genes, such as broad complex (Brc), E74A, and ultraspiracle protein (USP), were upregulated. Our results indicate that BmJHBPd2 plays an important role in the JH signaling pathway and is important for silk protein synthesis. Furthermore, our findings help to elucidate the mechanisms by which JH regulates silk protein synthesis.

Toll-interacting protein participates in immunity and development of the lepidopteran insect Antheraea pernyi

Toll-interacting protein (Tollip) participates in multiple biological processes. However, the biological functions of Tollip proteins in insects remain to be further explored. Here, the genomic sequence of tollip gene from Antheraea pernyi (named Ap-Tollip) was identified with a length of 15,060 bp, including eight exons and seven introns. The predicted Ap-Tollip protein contained conserved C2 and CUE domains and was highly homologous to those tollips from invertebrates. Ap-Tollip was highly expressed in fat body compared with other determined tissues. As far as the developmental stages were concerned, the highest expression level was found at the 14th day in eggs or the 3rd day of the 1st instar. Ap-Tollip was also obviously regulated by lipopolysaccharide, polycytidylic acid or 20E in different tissues. In addition, the interaction between Ap-Tollip and ubiquitin was confirmed by western blotting and pull-down assay. RNAi of Ap-Tollip significantly affected the expression levels of apoptosis and autophagy-related genes. These results indicated that Ap-Tollip was involved in immunity and development of A. pernyi.

Sterol Regulation of Development and 20-Hydroxyecdysone Biosynthetic and Signaling Genes in Drosophila melanogaster

Ecdysteroids are crucial in regulating the growth and development of insects. In the fruit fly Drosophila melanogaster, both C27 and C28 ecdysteroids have been identified. While the biosynthetic pathway of the C27 ecdysteroid 20-hydroxyecdysone (20E) from cholesterol is relatively well understood, the biosynthetic pathway of C28 ecdysteroids from C28 or C29 dietary sterols remains unknown. In this study, we found that different dietary sterols (including the C27 sterols cholesterol and 7-dehydrocholesterol, the C28 sterols brassicasterol, campesterol, and ergosterol, and the C29 sterols β-sitosterol, α-spinasterol, and stigmasterol) differentially affected the expression of 20E biosynthetic genes to varying degrees, but similarly activated 20E primary response gene expression in D. melanogaster Kc cells. We also found that a single dietary sterol was sufficient to support D. melanogaster growth and development. Furthermore, the expression levels of some 20E biosynthetic genes were significantly altered, whereas the expression of 20E signaling primary response genes remained unaffected when flies were reared on lipid-depleted diets supplemented with single sterol types. Overall, our study provided preliminary clues to suggest that the same enzymatic system responsible for the classical C27 ecdysteroid 20E biosynthetic pathway also participated in the conversion of C28 and C29 dietary sterols into C28 ecdysteroids.

20-hydroxyecdysone reprograms amino acid metabolism to support the metamorphic development of Helicoverpa armigera

Amino acid metabolism is regulated according to nutrient conditions; however, the mechanism is not fully understood. Using the holometabolous insect cotton bollworm (Helicoverpa armigera) as a model, we report that hemolymph metabolites are greatly changed from the feeding larvae to the wandering larvae and to pupae. Arginine, alpha-ketoglutarate (α-KG), and glutamate (Glu) are identified as marker metabolites of feeding larvae, wandering larvae, and pupae, respectively. Arginine level is decreased by 20-hydroxyecdysone (20E) regulation via repression of argininosuccinate synthetase (Ass) expression and upregulation of arginase (Arg) expression during metamorphosis. α-KG is transformed from Glu by glutamate dehydrogenase (GDH) in larval midgut, which is repressed by 20E. The α-KG is then transformed to Glu by GDH-like in pupal fat body, which is upregulated by 20E. Thus, 20E reprogrammed amino acid metabolism during metamorphosis by regulating gene expression in a stage- and tissue-specific manner to support insect metamorphic development.

E93 promotes transcription of RHG genes to initiate apoptosis during Drosophila salivary gland metamorphosis

20-hydroxyecdysone (20E) induced transcription factor E93 is important for larval-adult transition, which functions in programmed cell death of larval obsolete tissues, and the formation of adult new tissues. However, the apoptosis-related genes directly regulated by E93 are still ambiguous. In this study, an E93 mutation fly strain was obtained by clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9-mediated long exon deletion to investigate whether and how E93 induces apoptosis during larval tissues metamorphosis. The transcriptional profile of E93 was consistent with 3 RHG (rpr, hid, and grim) genes and the effector caspase gene drice, and all their expressions peaked at the initiation of apoptosis during the degradation of salivary glands. The transcription expression of 3 RHG genes decreased and apoptosis was blocked in E93 mutation salivary gland during metamorphosis. In contrast, E93 overexpression promoted the transcription of 3 RHG genes, and induced advanced apoptosis in the salivary gland. Moreover, E93 not only enhance the promoter activities of the 3 RHG genes in Drosophila Kc cells in vitro, but also in the salivary gland in vivo. Our results demonstrated that 20E induced E93 promotes the transcription of RHG genes to trigger apoptosis during obsolete tissues degradation at metamorphosis in Drosophila.

Adenosine Monophosphate-Activated Protein Kinase (AMPK) Phosphorylation Is Required for 20-Hydroxyecdysone Regulates Ecdysis in Apolygus lucorum

The plant mirid bug Apolygus lucorum is an omnivorous pest that can cause considerable economic damage. The steroid hormone 20-hydroxyecdysone (20E) is mainly responsible for molting and metamorphosis. The adenosine monophosphate-activated protein kinase (AMPK) is an intracellular energy sensor regulated by 20E, and its activity is regulated allosterically through phosphorylation. It is unknown whether the 20E-regulated insect's molting and gene expression depends on the AMPK phosphorylation. Herein, we cloned the full-length cDNA of the AlAMPK gene in A. lucorum. AlAMPK mRNA was detected at all developmental stages, whereas the dominant expression was in the midgut and, to a lesser extent, in the epidermis and fat body. Treatment with 20E and AMPK activator 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AlCAR) or only AlCAR resulted in activation of AlAMPK phosphorylation levels in the fat body, probed with an antibody directed against AMPK phosphorylated at Thr172, enhancing AlAMPK expression, whereas no phosphorylation occurred with compound C. Compared to compound C, 20E and/or AlCAR increased the molting rate, the fifth instar nymphal weight and shortened the development time of A. lucorum in vitro by inducing the expression of EcR-A, EcR-B, USP, and E75-A. Similarly, the knockdown of AlAMPK by RNAi reduced the molting rate of nymphs, the weight of fifth-instar nymphs and blocked the developmental time and the expression of 20E-related genes. Moreover, as observed by TEM, the thickness of the epidermis of the mirid was significantly increased in 20E and/or AlCAR treatments, molting spaces began to form between the cuticle and epidermal cells, and the molting progress of the mirid was significantly improved. These composite data indicated that AlAMPK, as a phosphorylated form in the 20E pathway, plays an important role in hormonal signaling and, in short, regulating insect molting and metamorphosis by switching its phosphorylation status.

BmCaspase-8-like regulates autophagy by suppressing BmDREDD-mediated cleavage of BmATG6

Autophagy plays an important role in tissue remodeling during insect development. The interplay between autophagy-related (ATG) proteins and caspases regulates the autophagic activity of ATGs, thereby modulating the process of autophagy. Our previous study characterized BmCaspase-8-like (BmCasp8L) as a caspase suppressor that inhibits apoptosis and immune signaling by suppressing the activation of death-related ced-3/Nedd2-like caspase (DREDD), a caspase-8 homolog in silkworm. In this study, we explored the regulatory role of BmCasp8L in autophagy. We found that the expression of Bmcasp8l increased from the late spinning stage to the pupa stage in the posterior silk gland (PSG), correlating with the expression patterns of Bmatg8 and Bmatg6. RNA interference-mediated downregulation of BmCasp8L expression significantly decreased starvation-induced autophagic influx as determined by the levels of BmATG8-phosphatidylethanolamine and the percentage of cells displaying punctate enhanced green fluorescent protein-BmATG8. Conversely, the overexpression of BmCasp8L significantly increased autophagic influx. We also found that BmCasp8L underwent autophagic degradation induced by starvation and that it was colocalized with BmATG8. Lastly, we demonstrated that BmDREDD attenuated autophagy and BmCasp8L suppressed BmDREDD-mediated cleavage of BmATG6. Taken together, our results demonstrated that BmCasp8L is a novel proautophagic molecule which suppresses BmDREDD-mediated cleavage of BmATG6 and is a target for autophagy.

Low GSK3β activity is required for insect diapause through responding to ROS/AKT signaling and down-regulation of Smad1/EcR/HR3 cascade

Glycogen synthase kinase 3β (GSK3β) plays important roles in gene transcription, metabolism, apoptosis, development, and signal transduction. However, its role in the regulation of pupal diapause remains unclear. In this paper, we find that low GSK3β activity in brains of diapause-destined pupae of Helicoverpa armigera is caused by elevated AKT activity. In response to ROS, AKT phosphorylates GSK3β to decrease its activity. In developing pupal brains, GSK3β can activate the transcription factor Smad1, which binds to the promoter region of the ecdysone receptor (EcR) gene and increases its expression. In the presence of 20-hydroxyecdysone (20E), EcR can bind to USP and increase the expression of 20E-response genes, including HR3, for pupal-adult development. In contrast, high levels of ROS in brains of diapause-destined pupae up-regulate p-AKT, which in turn decreases GSK3β activity. Low GSK3β activity causes low expression of EcR/HR3 via down-regulation of Smad1 activity, leading to diapause initiation. These results suggest that low GSK3β activity plays a key role in pupal diapause via ROS/AKT/GSK3β/Smad/EcR/HR3 signaling.

Dimmed gene knockout shortens larval growth and reduces silk yield in the silkworm, Bombyx mori

The bHLH domain transcription factor, Bombyx mori-derived dimmed (Bmdimm), is directly regulated by the JH-BmMet/BmSRC-BmKr-h1 pathway and plays a key role in regulating the expression of FibH, which codes the main component of silk protein. However, the other roles of Bmdimm in silk protein synthesis remain unclear. Here, we established a Bmdimm knockout (KO) line containing a 7-bp deletion via CRISPR/Cas9 system, which led to the absence of the bHLH domain. The expression level of silk protein genes and silk yield decreased significantly in the Bmdimm KO line. Moreover, knocking out Bmdimm led to shortened larval stages and significant weight loss in larvae and adults. Bmdimm was found to be highly expressed in the silk gland, but it was also expressed in the fat body. The expression level of Bmkr-h1 in the fat body was significantly downregulated in the Bmdimm KO line. Exogenous JHA treatment upregulated Bmkr-h1 and rescued the phenotype of larval growth in the Bmdimm KO line. In conclusion, knocking out Bmdimm led to a shortened larval stage via the inhibition of Bmkr-h1 expression, then reduced silk yield. These findings help to elucidate the regulatory mechanism of fibroin synthesis and larval development in silkworms.

Autophagy genes AMBRA1 and ATG8 play key roles in midgut remodeling of the yellow fever mosquito, Aedes aegypti

The function of two autophagy genes, an activating molecule BECN1 regulated autophagy (AMBRA1) and autophagy-related gene 8 (ATG8) in the midgut remodeling of Aedes aegypti was investigated. Real-time quantitative polymerase chain reaction (RT-qPCR) analysis of RNA samples collected from the last instar larvae and pupae showed that these two genes are predominantly expressed during the last 12 h and first 24 h of the last larval and pupal stages, respectively. Stable ecdysteroid analog induced and juvenile hormone (JH) analog suppressed these genes. RNA interference (RNAi) studies showed that the ecdysone-induced transcription factor E93 is required for the expression of these genes. JH-induced transcription factor krüppel homolog 1 (Kr-h1) suppressed the expression of these genes. RNAi-mediated silencing of AMBRA1 and ATG8 blocked midgut remodeling. Histological studies of midguts from insects at 48 h after ecdysis to the final larval stage and 12 h after ecdysis to the pupal stage showed that ATG gene knockdown blocked midgut remodeling. AMBRA1 and ATG8 double-stranded (dsRNA)-treated insects retained larval midgut cells and died during the pupal stage. Together, these results demonstrate that ecdysteroid induction of ATG genes initiates autophagy programmed cell death during midgut remodeling. JH inhibits midgut remodeling during metamorphosis by interfering with the expression of ATG genes.

A critical role for ecdysone response genes in regulating egg production in adult female Rhodnius prolixus

Ecdysteroids control ovary growth and egg production through a complex gene hierarchy. In the female Rhodnius prolixus, a blood-gorging triatomine and the vector of Chagas disease, we have identified the ecdysone response genes in the ovary using transcriptomic data. We then quantified the expression of the ecdysone response gene transcripts (E75, E74, BR-C, HR3, HR4, and FTZ-F1) in several tissues, including the ovary, following a blood meal. These results confirm the presence of these transcripts in several tissues in R. prolixus and show that the ecdysone response genes in the ovary are mostly upregulated during the first three days post blood meal (PBM). Knockdown of E75, E74, or FTZ-F1 transcripts using RNA interference (RNAi) was used to understand the role of the ecdysone response genes in vitellogenesis and egg production. Knockdown significantly decreases the expression of the transcripts for the ecdysone receptor and Halloween genes in the fat body and the ovaries and reduces the titer of ecdysteroid in the hemolymph. Knockdown of each of these transcription factors typically alters the expression of the other transcription factors. Knockdown also significantly decreases the expression of vitellogenin transcripts, Vg1 and Vg2, in the fat body and ovaries and reduces the number of eggs produced and laid. Some of the laid eggs have an irregular shape and smaller volume, and their hatching rate is decreased. Knockdown also influences the expression of the chorion gene transcripts Rp30 and Rp45. The overall effect of knockdown is a decrease in number of eggs produced and a severe reduction in number of eggs laid and their hatching rate. Clearly, ecdysteroids and ecdysone response genes play a significant role in reproduction in R. prolixus.

Atg1 phosphorylation is activated by AMPK and indispensable for autophagy induction in insects

Phosphorylation is a key post-translational modification in regulating autophagy in yeast and mammalians, yet it is not fully illustrated in invertebrates such as insects. ULK1/Atg1 is a functionally conserved serine/threonine protein kinase involved in autophagosome initiation. As a result of alternative splicing, Atg1 in the silkworm, Bombyx mori, is present as three mRNA isoforms, with BmAtg1c showing the highest expression levels. Here, we found that BmAtg1c mRNA expression, BmAtg1c protein expression and phosphorylation, and autophagy simultaneously peaked in the fat body during larval-pupal metamorphosis. Importantly, two BmAtg1c phosphorylation sites were identified at Ser269 and Ser270, which were activated by BmAMPK, the major energy-sensing kinase, upon stimulation with 20-hydroxyecdysone and starvation; additionally, these Atg1 phosphorylation sites are evolutionarily conserved in insects. The two BmAMPK-activated phosphorylation sites in BmAtg1c were found to be required for BmAMPK-induced autophagy. Moreover, the two corresponding DmAtg1 phosphorylation sites in the fruit fly, Drosophila melanogaster, are functionally conserved for autophagy induction. In conclusion, AMPK-activated Atg1 phosphorylation is indispensable for autophagy induction and evolutionarily conserved in insects, shedding light on how various groups of organisms differentially regulate ULK1/Atg1 phosphorylation for autophagy induction.

Mblk-1/E93, an ecdysone related-transcription factor, targets synaptic plasticity-related genes in the honey bee mushroom bodies

Among hymenopteran insects, aculeate species such as bees, ants, and wasps have enlarged and morphologically elaborate mushroom bodies (MBs), a higher-order brain center in the insect, implying their relationship with the advanced behavioral traits of aculeate species. The molecular bases leading to the acquisition of complicated MB functions, however, remains unclear. We previously reported the constitutive and MB-preferential expression of an ecdysone-signaling related transcription factor, Mblk-1/E93, in the honey bee brain. Here, we searched for target genes of Mblk-1 in the worker honey bee MBs using chromatin immunoprecipitation sequence analyses and found that Mblk-1 targets several genes involved in synaptic plasticity, learning, and memory abilities. We also demonstrated that Mblk-1 expression is self-regulated via Mblk-1-binding sites, which are located upstream of Mblk-1. Furthermore, we showed that the number of the Mblk-1-binding motif located upstream of Mblk-1 homologs increased associated with evolution of hymenopteran insects. Our findings suggest that Mblk-1, which has been focused on as a developmental gene transiently induced by ecdysone, has acquired a novel expression pattern to play a role in synaptic plasticity in honey bee MBs, raising a possibility that molecular evolution of Mblk-1 may have partly contributed to the elaboration of MB function in insects.

CRISPR-Cas9 Genome Editing Uncovers the Mode of Action of Methoprene in the Yellow Fever Mosquito, Aedes aegypti

Methoprene, a juvenile hormone (JH) analog, is widely used for insect control, but its mode of action is not known. To study methoprene action in the yellow fever mosquito, Aedes aegypti, the E93 (ecdysone-induced transcription factor) was knocked out using the CRISPR-Cas9 system. The E93 mutant pupae retained larval tissues similar to methoprene-treated insects. These insects completed pupal ecdysis and died as pupa. In addition, the expression of transcription factors, broad complex and Krüppel homolog 1 (Kr-h1), increased and that of programmed cell death (PCD) and autophagy genes decreased in E93 mutants. These data suggest that methoprene functions through JH receptor, methoprene-tolerant, and induces the expression of Kr-h1, which suppresses the expression of E93, resulting in a block in PCD and autophagy of larval tissues. Failure in the elimination of larval tissues and the formation of adult structures results in their death. These results answered long-standing questions on the mode of action of methoprene.

RR-1 cuticular protein TcCPR69 is required for growth and metamorphosis in Tribolium castaneum

Cuticle is not only critical for protecting insects from noxious stimuli but is also involved in a variety of metabolic activities. Cuticular proteins (CPs) affect cuticle structure and mechanical properties during insect growth, reproduction, and environmental adaptation. Here, we describe the identification and characterization of a member of the RR-1 subfamily of CPs with an R&R consensus (CPR) in Tribolium castaneum (TcCPR69). Although it was previously reported to be highly expressed in the wings, we found that knocking down TcCPR69 by RNA interference (RNAi) did not cause obvious wing abnormalities but markedly disrupted the growth and metamorphosis of beetles with 100% cumulative mortality; additionally, the chitin content of the pharate adult was decreased and the new abdominal cuticle was significantly thinner before molting. TcCPR69 showed chitin-binding ability and the expression levels of key genes involved in chitin metabolism (trehalase [TcTRE], chitin synthase [TcCHSA and TcCHSB], and chitinase [TcCHT5 and TcCHT10]) were also decreased by TcCPR69 knockdown. TcCPR69 gene expression peaked shortly after molting and was increased 2.61 fold at 12 h after 20-hydroxyecdysone (20E) injection. This was reversed by RNAi of the ecdysone-related genes ecdysone receptor (TcECR) and fushi tarazu transcription factor 1 (TcFTZ-F1). These results indicate that TcCPR69 is positively regulated by 20E signaling to contribute to cuticle formation and maintain chitin accumulation during the growth and metamorphosis of beetles.

Knockdown of Ecdysone-Induced Protein 93F Causes Abnormal Pupae and Adults in the Eggplant Lady Beetle

Ecdysone-induced protein 93F (E93) plays triple roles during post-embryonic development in insects whose juvenile instars are more than four. However, it only acts as a specifier of adult structures in Drosophila flies whose larval instars are fixed at three. In this study, we determined the functions of E93 in the eggplant lady beetle (Henosepilachna vigintioctopunctata), which has four larval instars. We uncovered that E93 was abundantly expressed at the prepupal and pupal stages. A precocious inhibition of the juvenile hormone signal by RNA interference (RNAi) of HvKr-h1 or HvHairy, two vital downstream developmental effectors, at the penultimate instar larval stage increased the expression of E93, Conversely, ingestion of JH by the third-instar larvae stimulated the expression of HvKr-h1 but repressed the transcription of either HvE93X1 or HvE93X2. However, disturbance of the JH signal neither drove premature metamorphosis nor caused supernumerary instars. In contrast, depletion of E93 at the third- and fourth-instar larval and prepupal stages severely impaired pupation and caused a larval-pupal mixed phenotype: pupal spines and larval scoli were simultaneously presented on the cuticle. RNAi of E93 at the pupal stage affected adult eclosion. When the beetles had suffered from a dsE93 injection at the fourth-instar larval and pupal stages, a few resultant adults emerged, with separated elytra, abnormally folded hindwings, a small body size and short appendages. Taken together, our results suggest the larval instars are fixed in H. vigintioctopunctata; E93 serves as a repressor of larval characters and a specifier of adult structures during the larval–pupal–adult transition.

Functional characterization of a low-density lipoprotein receptor in the lepidopteran model, Bombyx mori

The growth and development of metabolous insects are mainly regulated by ecdysone and juvenile hormone. As a member of the low-density lipoprotein receptor (LDLR) family, megalin (mgl) is involved in the lipoprotein transport of cholesterol which is an essential precursor for the synthesis of ecdysone. Despite extensive studies in mammals, the function of mgl is still largely unknown in insects. In this study, we characterize the function of mgl in the silkworm Bombyx mori, the model species of Lepidoptera. We find that mgl is broadly present in the genomes of lepidopteran species and evolved with divergence between lepidopterans and Drosophila. The expression pattern suggests a ubiquitous role of mgl in the growth and development in the silkworm. We further perform clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9-based mutagenesis of Bmmgl and find that both the development and the silk production of the silkworm are seriously affected by the disruption of Bmmgl. Our results not only explore the function of mgl in Lepidoptera but also add to our understanding of how cholesterol metabolism is involved in the development of insects.

Cytokine receptor DOME controls wing disc development in Bombyx mori

In multicellular organisms, the JAK/STAT signaling pathway is involved in cell proliferation, differentiation, apoptosis, and immune regulation. Through activation of the Stat92E transcription factor, JAK/STAT signaling induced proper wing development in Drosophila. Domeless (DOME) was the first identified invertebrate JAK/STAT receptor. However, the function of DOME in Bombyx mori development remains unclear, especially in wing morphogenesis. In this study, we isolated the cytokine receptor DOME gene in B. mori and evaluated its function in DOME-knockout models. We found that overexpression of DOME at the cellular level upregulated the expression of JAK/STAT pathway-related genes, promoted proliferation, and inhibited apoptosis. The results of the interference with DOME had the opposite effects with those of overexpression at the cellular level. Using CRISPR/Cas9 technology, we constructed a DOME-knockout transgenic silkworm strain (KO-DOME) and found that the wings of the pupa and moth stages were vesicle-shaped and smaller than those of the wild-type silkworm. Some KO-DOME silkworms were unable to extend their wings from the pupal case after eclosion. We detected the expression of cyclin and apoptosis-related genes in the wing disc of the moth stage and found that some cyclin genes, such as CyclinA, CyclinB, and CyclinD, were downregulated, whereas apoptotic genes, such as Caspase1, Caspase3, and Caspase8, were upregulated. We propose that DOME regulates cell proliferation and apoptosis by affecting the JAK/STAT signaling pathway, ultimately influencing the development of wing discs. Our study provides empirical evidence for the biological function of the silkworm DOME gene, which is essential for the normal development of wings.

Conceptual framework for the insect metamorphosis from larvae to pupae by transcriptomic profiling, a case study of Helicoverpa armigera (Lepidoptera: Noctuidae)

BACKGROUND

Insect metamorphosis from larvae to pupae is one of the most important stages of insect life history. Relatively comprehensive information related to gene transcription profiles during lepidopteran metamorphosis is required to understand the molecular mechanism underlying this important stage. We conducted transcriptional profiling of the brain and fat body of the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) during its transition from last instar larva into pupa to explore the physiological processes associated with different phases of metamorphosis.

RESULTS

During metamorphosis, the differences in gene expression patterns and the number of differentially expressed genes in the fat body were found to be greater than those in the brain. Each stage had a specific gene expression pattern, which contributed to different physiological changes. A decrease in juvenile hormone levels at the feeding stage is associated with increased expression levels of two genes (juvenile hormone esterase, juvenile hormone epoxide hydrolase). The expression levels of neuropeptides were highly expressed at the feeding stage and the initiation of the wandering stage and less expressed at the prepupal stage and the initiation of the pupal stage. The transcription levels of many hormone (or neuropeptide) receptors were specifically increased at the initiation of the wandering stage in comparison with other stages. The expression levels of many autophagy-related genes in the fat body were found to be gradually upregulated during metamorphosis. The activation of apoptosis was probably related to enhanced expression of many key genes (Apaf1, IAP-binding motif 1 like, cathepsins, caspases). Active proliferation might be associated with enhanced expression levels in several factors (JNK pathway: jun-D; TGF-β pathway: decapentaplegic, glass bottom boat; insulin pathway: insulin-like peptides from the fat body; Wnt pathway: wntless, TCF/Pangolin).

CONCLUSIONS

This study revealed several vital physiological processes and molecular events of metamorphosis and provided valuable information for illustrating the process of insect metamorphosis from larvae to pupae.

Pupal Diapause Termination and Transcriptional Response of Antheraea pernyi (Lepidoptera: Saturniidae) Triggered by 20-Hydroxyecdysone

The pupal diapause of univoltine Antheraea pernyi hampers sericultural and biotechnological applications, which requires a high eclosion incidence after artificial diapause termination to ensure production of enough eggs. The effect of pupal diapause termination using 20-hydroxyecdysone (20E) on the eclosion incidence has not been well-documented in A. pernyi. Here, the dosage of injected 20E was optimized to efficiently terminate pupal diapause of A. pernyi, showing that inappropriate dosage of 20E can cause pupal lethality and a low eclosion incidence. The optimal ratio of 20E to 1-month-old pupae was determined as 6 μg/g. Morphological changes showed visible tissue dissociation at 3 days post-injection (dpi) and eye pigmentation at 5 dpi. Comprehensive transcriptome analysis identified 1,355/1,592, 494/203, 584/297, and 1,238/1,404 upregulated and downregulated genes at 1, 3, 6, and 9 dpi, respectively. The 117 genes enriched in the information processing pathways of “signal transduction” and “signaling molecules and interaction” were upregulated at 1 and 3 dpi, including the genes involved in FOXO signaling pathway. One chitinase, three trehalase, and five cathepsin genes related to energy metabolism and tissue dissociation showed high expression levels at the early stage, which were different from the upregulated expression of four other chitinase genes at the later stage. Simultaneously, the expression of several genes involved in molting hormone biosynthesis was also activated between 1 and 3 dpi. qRT-PCR further verified the expression patterns of two ecdysone receptor genes (EcRB1 and USP) and four downstream response genes (E93, Br-C, βFTZ-F1, and cathepsin L) at the pupal and pharate stages, respectively. Taken together, these genes serve as a resource for unraveling the mechanism underlying pupal-adult transition; these findings facilitate rearing of larvae more than once a year and biotechnological development through efficient termination of pupal diapause in A. pernyi in approximately half a month.

Silencing of transcription factor E93 inhibits adult morphogenesis and disrupts cuticle, wing and ovary development in Locusta migratoria

Ecdysone-induced protein 93F (E93) plays important roles during the metamorphosis process in insects. In this study, a cDNA of the LmE93 gene was identified from the transcriptome of Locusta migratoria, which consists of the 3378-nucleotide open-reading frame (ORF) and encodes 1125 amino acids with helix-turn-helix (HTH) motifs. Reverse transcription quantitative polymerase chain reaction analysis revealed that LmE93 was highest expressed in ovary. The LmE93 expression level was markedly low from the 3rd to 4th instar nymphs, and greatly increased in 1-day-old 5th instar nymphs with a peak on middle nymphal days, then declined in the late nymphal days. Moreover, injected dsLmE93 into 4th and 5th instar nymphs greatly reduced LmE93 transcripts, respectively, and prevented the process of metamorphosis, causing supernumerary nymphal stages. Hematoxylin-eosin staining of the integument showed that the apolysis occurred in advance in 4th instar nymphs, and old cuticle degradation was decreased in dsLmE93-injected locusts of 5th instar nymphs. Smaller and no fully developed wings with reduced columns between the anterior and posterior regions were found in N6 and N7 supernumerary nymphs. In addition, the development of the ovary in dsLmE93-injected locusts was severely blocked, the yolk was almost not formed and there was no development of ovarioles. The results indicated that LmE93 play key roles in the metamorphosis, cuticle, wing and ovarian development of locusts.

Transcription and Post-translational Regulation of Autophagy in Insects

Autophagy attracts great attention, and numerous progresses have been obtained in the last two decades. Autophagy is implicated in mammalian neurodegenerative diseases, tumorigenesis, as well as development in insects. The regulatory mechanism of autophagy is well documented in yeast and mammals, whereas it is not fully illustrated in insects. Drosophila melanogaster and Bombyx mori are the two well-studied insects for autophagy, and several insect-mammalian evolutionarily conserved or insect-specific mechanisms in regulating autophagy are reported. In this review, we summarize the most recent studies of autophagy regulated at both transcriptional and post-translational levels by insect hormone in cooperation with other signals, such as nutrient, which will provide a reference and deep thinking for studies on autophagy in insects.

Juvenile Hormone Studies in Drosophila melanogaster

In the field of insect endocrinology, juvenile hormone (JH) is one of the most wondrous entomological terms. As a unique sesquiterpenoid hormone produced and released by the endocrine gland, corpus allatum (CA), JH is a critical regulator in multiple developmental and physiological processes, such as metamorphosis, reproduction, and behavior. Benefited from the precise genetic interventions and simplicity, the fruit fly, Drosophila melanogaster, is an indispensable model in JH studies. This review is aimed to present the regulatory factors on JH biosynthesis and an overview of the regulatory roles of JH in Drosophila. The future directions of JH studies are also discussed, and a few hot spots are highlighted.

Sob gene is critical to wing development in Bombyx mori and Tribolium castaneum

The development of insect appendages requires the expression of multiple genes in a strict spatial and temporal order. The odd-skipped family genes are vital transcriptional factors involved in embryonic development. The development and morphogenesis of the insect wing requires multiple transcription factors to regulate the expression of wing patterning genes at the transcriptional level. However, the function of odd-related genes in insect wing morphogenesis and development during postembryonic stages is unclear. We focused on the roles of the sister of odd and bowl (sob) gene, a member of odd-skipped family genes, during the wing morphopoiesis in Bombyx mori using the clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9 system and in Tribolium castaneum by RNA interference. The results showed that the wings were significantly smaller and degenerated, and wing veins were indistinct in the sob gene loss-of-function group in both B. mori and T. castaneum. Quantitative real-time polymerase chain reaction revealed that the Tcsob gene regulated the expression of wing development genes, such as the cht 7 and the vg gene. The findings suggest the importance of sob gene in insect wing morphology formation during postembryonic stages.

Cuticular protein genes showing peaks at different stages are probably regulated by different ecdysone responsive transcription factors during larval-pupal transformation

We aimed to explain the reason and function of the successive expression of ecdysone-responsive transcription factors (ERTFs) and related cuticular protein (CP) genes during transformation from larva to pupa. The regulation of the expression of CP genes by ERTFs was examined by in vitro wing disc culture and reporter assay using a gene gun transduction system. Two CP genes that showed expression peaks at different stages-BmorCPG12 at W3L and BmorCPH2 at P0 stage-were selected and examined. Reporter constructs conveying putative BHR3, ßFTZ-F1, BHR39, and E74A binding sites of BmorCPG12 and BmorCPH2 showed promoter activity when introduced into wing discs. In the present study, we showed the functioning of the putative BHR3 and E74A binding sites, together with putative ßFTZ-F1 binding sites, on the activation of CP genes, and different ERTF binding sites functioned in one CP gene. From these, we conclude that BHR3, ßFTZ-F1, and E74A that are successively expressed bring about the successive expression of CP genes, resulting in insect metamorphosis. In addition to this, reporter constructs conveying putative BHR39 binding sites of BmorCPG12 and BmorCPH2 showed negative regulation.

Transcriptional and Post-Transcriptional Regulation of Autophagy

Autophagy is a widely conserved process in eukaryotes that is involved in a series of physiological and pathological events, including development, immunity, neurodegenerative disease, and tumorigenesis. It is regulated by nutrient deprivation, energy stress, and other unfavorable conditions through multiple pathways. In general, autophagy is synergistically governed at the RNA and protein levels. The upstream transcription factors trigger or inhibit the expression of autophagy- or lysosome-related genes to facilitate or reduce autophagy. Moreover, a significant number of non-coding RNAs (microRNA, circRNA, and lncRNA) are reported to participate in autophagy regulation. Finally, post-transcriptional modifications, such as RNA methylation, play a key role in controlling autophagy occurrence. In this review, we summarize the progress on autophagy research regarding transcriptional regulation, which will provide the foundations and directions for future studies on this self-eating process.

Drosophila E93 promotes adult development and suppresses larval responses to ecdysone during metamorphosis

Pulses of the steroid hormone ecdysone act through transcriptional cascades to direct the major developmental transitions during the Drosophila life cycle. These include the prepupal ecdysone pulse, which occurs 10 ​hours after pupariation and triggers the onset of adult morphogenesis and larval tissue destruction. E93 encodes a transcription factor that is specifically induced by the prepupal pulse of ecdysone, supporting a model proposed by earlier work that it specifies the onset of adult development. Although a number of studies have addressed these functions for E93, little is known about its roles in the salivary gland where the E93 locus was originally identified. Here we show that E93 is required for development through late pupal stages, with mutants displaying defects in adult differentiation and no detectable effect on the destruction of larval salivary glands. RNA-seq analysis demonstrates that E93 regulates genes involved in development and morphogenesis in the salivary glands, but has little effect on cell death gene expression. We also show that E93 is required to direct the proper timing of ecdysone-regulated gene expression in salivary glands, and that it suppresses earlier transcriptional programs that occur during larval and prepupal stages. These studies support the model that the stage-specific induction of E93 in late prepupae provides a critical signal that defines the end of larval development and the onset of adult differentiation.

The ecdysteroid receptor regulates salivary gland degeneration through apoptosis in Rhipicephalus haemaphysaloides

Background

It is well established that ecdysteroid hormones play an important role in arthropod development and reproduction, mediated by ecdysteroid receptors. Ticks are obligate hematophagous arthropods and vectors of pathogens. The salivary gland plays an essential role in tick growth and reproduction and in the transmission of pathogens to vertebrate hosts. During tick development, the salivary gland undergoes degeneration triggered by ecdysteroid hormones and activated by apoptosis. However, it is unknown how the ecdysteroid receptor and apoptosis regulate salivary gland degeneration. Here, we report the functional ecdysteroid receptor (a heterodimer of the ecdysone receptor [EcR] and ultraspiracle [USP]) isolated from the salivary gland of the tick Rhipicephalus haemaphysaloides and explore the molecular mechanism of ecdysteroid receptor regulation of salivary gland degeneration.

Methods

The full length of RhEcR and RhUSP open reading frames (ORFs) was obtained from the transcriptome. The RhEcR and RhUSP proteins were expressed in a bacterial heterologous system, Escherichia coli. Polyclonal antibodies were produced against synthetic peptides and were able to recognize recombinant and native proteins. Quantitative real-time PCR and western blot were used to detect the distribution of RhEcR, RhUSP, and RhCaspases in the R. haemaphysaloides organs. A proteomics approach was used to analyze the expression profiles of the ecdysteroid receptors, RhCaspases, and other proteins. To analyze the function of the ecdysteroid receptor, RNA interference (RNAi) was used to silence the genes in adult female ticks. Finally, the interaction of RhEcR and RhUSP was identified by heterologous co-expression assays in HEK293T cells.

Results

We identified the functional ecdysone receptor (RhEcR/RhUSP) of 20-hydroxyecdysone from the salivary gland of the tick R. haemaphysaloides. The RhEcR and RhUSP genes have three and two isoforms, respectively, and belong to a nuclear receptor family but with variable N-terminal A/B domains. The RhEcR gene silencing inhibited blood-feeding, blocked engorgement, and restrained salivary gland degeneration, showing the biological role of the RhEcR gene in ticks. In the ecdysteroid signaling pathway, RhEcR silencing inhibited salivary gland degeneration by suppressing caspase-dependent apoptosis. The heterologous expression in mammalian HEK293T cells showed that RhEcR1 interacts with RhUSP1 and induces caspase-dependent apoptosis.

Conclusions

These data show that RhEcR has an essential role in tick physiology and represents a putative target for the control of ticks and tick-borne diseases.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05052-2.

Expression of 20-hydroxyecdysone-related genes during gonadal development of Teleogryllus emma (Orthoptera: Gryllidae)

Insect gonads develop under endocrine signals. In this study, we assessed the characters of partial complementary DNAs encoding the Teleogryllus emma orthologs of 20-hydroxyecdysone (20E)-related genes (RXR, E75, HR3, Hsc70, and Hsp90) and analyzed their expression patterns in both nymph and adult crickets. 20E treatment suppressed expression of TeEcR, TeRXR, TeE75, TeHR3, TeHsc70, and TeHsp90. Temporal expression analysis demonstrated that TeERR and 20E-related genes were expressed in four stages of gonadal development from the fourth-instar nymph stage to the adult stage. The expression pattern of these genes differed in testicular and ovarian development. TeRXR, HR3, TeHsc70, and TeHsp90 were irregularly expressed in gonads of the same developmental stages, while mRNAs encoding TeERR, TeEcR, and TeE75 accumulated in higher levels in ovaries than in testes. RNA interference (RNAi) of TeEcR expression led to decrease of the expression levels of TeEcR, TeRXR, TeHR3, and TeHsc70, while it enhanced TeE75 and TeHsp90 expressions. These results demonstrate that the TeERR and 20E-related genes help regulate gonadal development, while TeEcR appears to inhibit TeE75 expression, TeE75 inhibits HR3 expression. Hsc70 indirectly regulated the expression of the primary and secondary response genes E74A, E75B, and HR3. Hsp90 regulated Usp expression with no direct regulatory relationship with EcR.

Transcriptional identification of differentially expressed genes during the prepupal-pupal transition in the oriental armyworm, Mythimna separata (Walker) (Lepidoptera: Noctuidae)

The oriental armyworm, Mythimna separata (Walker) is a serious pest of agriculture that does particular damage to Gramineae crops in Asia, Europe, and Oceania. Metamorphosis is a key developmental stage in insects, although the genes underlying the metamorphic transition in M. separata remain largely unknown. Here, we sequenced the transcriptomes of five stages; mature larvae (ML), wandering (W), and pupation (1, 5, and 10 days after pupation, designated P1, P5, and P10) to identify transition-associated genes. Four libraries were generated, with 22,884, 23,534, 26,643, and 33,238 differentially expressed genes (DEGs) for the ML-vs-W, W-vs-P1, P1-vs-P5, and P5-vs-P10, respectively. Gene ontology enrichment analysis of DEGs showed that genes regulating the biosynthesis of the membrane and integral components of the membrane, which includes the cuticular protein (CP), 20-hydroxyecdysone (20E), and juvenile hormone (JH) biosynthesis, were enriched. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that DEGs were enriched in the metabolic pathways. Of these DEGs, thirty CP, seventeen 20E, and seven JH genes were differentially expressed across the developmental stages. For transcriptome validation, ten CP, 20E, and JH-related genes were selected and verified by real-time PCR quantitative. Collectively, our results provided a basis for further studies of the molecular mechanism of metamorphosis in M. separata.

E93 confers steroid hormone responsiveness of digestive enzymes to promote blood meal digestion in the midgut of the mosquito Aedes aegypti

Anautogenous female mosquitoes obtain the nutrients needed for egg development from vertebrate blood, and consequently they transmit numerous pathogens of devastating human diseases. Digestion of blood proteins into amino acids that are used for energy production, egg maturation and replenishment of maternal reserves is an essential part of the female mosquito reproductive cycle. However, the regulatory mechanisms underlying this process remain largely unknown. Here, we report that the transcription factor E93 is a critical factor promoting blood meal digestion in adult females of the major arboviral vector Aedes aegypti in response to the steroid hormone 20-hydroxyecdysone (20E). E93 was upregulated in the female mosquito midgut after a blood meal, and RNA interference (RNAi)-mediated knockdown of E93 inhibited midgut blood digestion. E93 RNAi depletion repressed late trypsin (LT), serine protease I (SPI), SPVI and SPVII, and activated early trypsin (ET) expression in the female mosquito midgut after a blood meal. Injection of 20E activated E93, LT, SPI, SPVI and SPVII, and repressed ET expression, whereas RNAi knockdown of the ecdysone receptor (EcR) repressed E93, LT, SPI, SPVI and SPVII, and activated ET expression in the midgut. Furthermore, E93 depletion resulted in a complete loss of 20E responsiveness of LT, SPVI and SPVII. Our findings reveal important mechanisms regulating blood meal digestion in disease-transmitting mosquitoes.

Fat Body-Multifunctional Insect Tissue

Simple Summary

Efficient and proper functioning of processes within living organisms play key roles in times of climate change and strong human pressure. In insects, the most abundant group of organisms, many important changes occur within their tissues, including the fat body, which plays a key role in the development of insects. Fat body cells undergo numerous metabolic changes in basic energy compounds (i.e., lipids, carbohydrates, and proteins), enabling them to move and nourish themselves. In addition to metabolism, the fat body is involved in the development of insects by determining the time an individual becomes an adult, and creates humoral immunity via the synthesis of bactericidal proteins and polypeptides. As an important tissue that integrates all signals from the body, the processes taking place in the fat body have an impact on the functioning of the entire body.

Abstract

The biodiversity of useful organisms, e.g., insects, decreases due to many environmental factors and increasing anthropopressure. Multifunctional tissues, such as the fat body, are key elements in the proper functioning of invertebrate organisms and resistance factors. The fat body is the center of metabolism, integrating signals, controlling molting and metamorphosis, and synthesizing hormones that control the functioning of the whole body and the synthesis of immune system proteins. In fat body cells, lipids, carbohydrates and proteins are the substrates and products of many pathways that can be used for energy production, accumulate as reserves, and mobilize at the appropriate stage of life (diapause, metamorphosis, flight), determining the survival of an individual. The fat body is the main tissue responsible for innate and acquired humoral immunity. The tissue produces bactericidal proteins and polypeptides, i.e., lysozyme. The fat body is also important in the early stages of an insect’s life due to the production of vitellogenin, the yolk protein needed for the development of oocytes. Although a lot of information is available on its structure and biochemistry, the fat body is an interesting research topic on which much is still to be discovered.