MicroRNA miR-927 targets the juvenile hormone primary response gene Krüppel homolog1 to control Drosophila developmental growth

Juvenile hormone-induced microRNA miR-iab-8 regulates lipid homeostasis and metamorphosis in Drosophila melanogaster

Metamorphosis plays an important role in the evolutionary success of insects. Accumulating evidence indicated that microRNAs (miRNAs) are involved in the regulation of processes associated with insect metamorphosis. However, the miRNAs coordinated with juvenile hormone (JH)-regulated metamorphosis remain poorly reported. In the present study, using high-throughput miRNA sequencing combined with Drosophila genetic approaches, we demonstrated that miR-iab-8, which primarily targets homeotic genes to modulate haltere-wing transformation and sterility was up-regulated by JH and involved in JH-mediated metamorphosis. Overexpression of miR-iab-8 in the fat body resulted in delayed development and failure of larval-pupal transition. Furthermore, metabolomic analysis results revealed that overexpression of miR-iab-8 caused severe energy metabolism defects especially the lipid metabolism, resulting in significantly reduced triacylglycerol (TG) content and glycerophospholipids but enhanced accumulation of phosphatidylcholine (PC) and phosphatidylethanolamine (PE). In line with this, Nile red staining demonstrated that during the third larval development, the TG content in the miR-iab-8 overexpression larvae was continuously decreased, which is opposite to the control. Additionally, the transcription levels of genes committed to TG synthesis and breakdown were found to be significantly increased and the expression of genes responsible for glycerophospholipids metabolism were also altered. Overall, we proposed that JH induced miR-iab-8 expression to perturb the lipid metabolism homeostasis especially the TG storage in the fat body, which in turn affected larval growth and metamorphosis.

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.

Overexpression of miR-927-5p suppresses stalky expression and negatively reduces the spermatid production in Zeugodacus cucurbitae

BACKGROUND

The melon fly, Zeugodacus cucurbitae Coquillett, is one of the major pests attacking Cucurbitaceae crops. Identifying critical genes or proteins regulating fertility is essential for sustainable pest control and a research hotspot in insect physiology. MicroRNAs (miRNAs) are short RNAs that do not directly participate in protein translation, but instead function in post-transcriptional regulation of gene expression involved in male fertility.

RESULTS

We found that miR-927-5p is highly expressed in the testes and investigated its function in spermatogenesis in Z. cucurbitae. Fluorescence in situ hybridization (FISH) showed miR-927-5p in the transformation and maturation region of the testis, and overexpression of miR-927-5p reduced the number of sperms by 53%. In continuation, we predicted 12 target genes of miR-927-5p using bioinformatics combined with transcriptome sequencing data, and found that miR-927-5p targets the new gene Stalky in insects, which was validated by quantitative real-time PCR, RNA pull-down and dual luciferase reporter assays. FISH also confirmed the co-localization of miR-927-5p and the transcript Stalky_1 in the testis. Moreover, silencing of Stalky_1 by RNA interference reduced the number of sperms by 32% and reduced sperm viability by 39% in physiologically mature male adults. Meanwhile, the silencing of Stalky_1 also resulted in low hatchability.

CONCLUSION

Our work not only presents a new, so far unreported mechanism regulating spermatogenesis by miR-927-5p targeting a new unknown target, Stalky, which is providing new knowledge on the regulatory network of insect spermatogenesis, but also lays a foundation for the development of SIT against important tephritid fly pests. © 2024 Society of Chemical Industry.

Untangling the gordian knot: The intertwining interactions between developmental hormone signaling and epigenetic mechanisms in insects

Hormones control developmental and physiological processes, often by regulating the expression of multiple genes simultaneously or sequentially. Crosstalk between hormones and epigenetics is pivotal to dynamically coordinate this process. Hormonal signals can guide the addition and removal of epigenetic marks, steering gene expression. Conversely, DNA methylation, histone modifications and non-coding RNAs can modulate regional chromatin structure and accessibility and regulate the expression of numerous (hormone-related) genes. Here, we provide a review of the interplay between the classical insect hormones, ecdysteroids and juvenile hormones, and epigenetics. We summarize the mode-of-action and roles of these hormones in post-embryonic development, and provide a general overview of epigenetic mechanisms. We then highlight recent advances on the interactions between these hormonal pathways and epigenetics, and their involvement in development. Furthermore, we give an overview of several 'omics techniques employed in the field. Finally, we discuss which questions remain unanswered and possible avenues for future research.

Juvenile hormone inhibits adult cuticle formation in Drosophila melanogaster through Kr-h1/Dnmt2-mediated DNA methylation of Acp65A promoter

Differentiation of imaginal epidermal cells of Drosophila melanogaster to form adult cuticles occurs at approximately 40-93 h after puparium formation. Juvenile hormone (JH) given at pupariation results in formation of a second pupal cuticle in the abdomen instead of the adult cuticle. Although the adult cuticle gene Acp65A has been reported to be down-regulated following JH treatment, the regulatory mechanism remains unclear. Here, we found that the JH primary response gene Krüppel homologue 1 (Kr-h1) plays a vital role in the repression of adult cuticle formation through the mediation of JH action. Overexpression of Kr-h1 mimicked-while knocking down of Kr-h1 attenuated-the inhibitory action of JH on the formation of the adult abdominal cuticle. Further, we found that Kr-h1 inhibited the transcription of Acp65A by directly binding to the consensus Kr-h1 binding site (KBS) within the Acp65A promoter region. Moreover, the DNA methyltransferase Dnmt2 was shown to interact with Kr-h1, combined with the KBS to promote the DNA methylation of sequences around the KBS, in turn inhibiting the transcription of Acp65A. This study advances our understanding of the molecular basis of the "status quo" action of JH on the Drosophila adult metamorphosis.

MicroR-9c-5p and novel-mir50 co-target Akt to regulate Lasioderma serricorne reproduction

High fecundity is a common characteristic of insect pests which increases the difficulty of population control. Serine/threonine kinase Akt is an indispensable component of the insulin signaling pathway. Silencing of LsAkt severely hinders reproduction in Lasioderma serricorne, a stored product insect pest. However, the post-transcriptional pathway of LsAkt in L. serricorne remains unknown. This study identified 2 binding sites of miR-9c-5p and novel-mir50 in the coding sequences of LsAkt. The expression profiles of 2 microRNAs (miRNAs) and LsAkt displayed an opposite pattern during the adult stages. Luciferase reporter assay showed that novel-mir50 and miR-9c-5p could downregulate the expression of LsAkt. Overexpression of miR-9c-5p and novel-mir50 by injection of mimics inhibited the expression of LsAkt and reduced oviposition, decreased egg hatchability, and blocked ovarian development. It also decreased the expression of genes involved in ovarian development (LsVg and LsVgR) and the nutritional signaling pathway (LsTOR, LsS6K, and Ls4EBP), and reduced the phosphorylation of Akt. Conversely, injection of miR-9c-5p and novel-mir50 inhibitors induced the expressions of LsAkt, LsVg, LsVgR, LsTOR, LsS6K, and Ls4EBP, enhanced Akt phosphorylation level, and accelerated ovarian development. Injection of bovine insulin downregulated the expression of miR-9c-5p and novel-mir50 and upregulated the LsAkt expression. It also rescued the reproductive development defects associated with miR-9c-5p/novel-mir50 overexpression, forming a positive regulatory loop of insulin signaling. These results indicate that miR-9c-5p/novel-mir50 regulates the female reproduction of L. serricorne by targeting Akt in response to insulin signaling. The data also demonstrate the effects of the insulin/miRNA/Akt regulatory axis in insect reproduction.

MicroRNA Targets PAP1 to Mediate Melanization in Plutella xylostella (Linnaeus) Infected by Metarhizium anisopliae

MicroRNAs (miRNAs) play a pivotal role in important biological processes by regulating post-transcriptional gene expression and exhibit differential expression patterns during development, immune responses, and stress challenges. The diamondback moth causes significant economic damage to crops worldwide. Despite substantial advancements in understanding the molecular biology of this pest, our knowledge regarding the role of miRNAs in regulating key immunity-related genes remains limited. In this study, we leveraged whole transcriptome resequencing data from Plutella xylostella infected with Metarhizium anisopliae to identify specific miRNAs targeting the prophenoloxidase-activating protease1 (PAP1) gene and regulate phenoloxidase (PO) cascade during melanization. Seven miRNAs (pxy-miR-375-5p, pxy-miR-4448-3p, pxy-miR-279a-3p, pxy-miR-3286-3p, pxy-miR-965-5p, pxy-miR-8799-3p, and pxy-miR-14b-5p) were screened. Luciferase reporter assays confirmed that pxy-miR-279a-3p binds to the open reading frame (ORF) and pxy-miR-965-5p to the 3' untranslated region (3' UTR) of PAP1. Our experiments demonstrated that a pxy-miR-965-5p mimic significantly reduced PAP1 expression in P. xylostella larvae, suppressed PO activity, and increased larval mortality rate. Conversely, the injection of pxy-miR-965-5p inhibitor could increase PAP1 expression and PO activity while decreasing larval mortality rate. Furthermore, we identified four LncRNAs (MSTRG.32910.1, MSTRG.7100.1, MSTRG.6802.1, and MSTRG.22113.1) that potentially interact with pxy-miR-965-5p. Interference assays using antisense oligonucleotides (ASOs) revealed that silencing MSTRG.7100.1 and MSTRG.22113.1 increased the expression of pxy-miR-965-5p. These findings shed light on the potential role of pxy-miR-965-5p in the immune response of P. xylostella to M. anisopliae infection and provide a theoretical basis for biological control strategies targeting the immune system of this pest.

The microRNA pathway core genes are indispensable for development and reproduction in the brown planthopper, Nilaparvata lugens

MicroRNAs (miRNAs) are small single-stranded non-coding RNAs involved in a variety of cellular events by regulating gene expression at the post-transcriptional level. Several core genes in miRNA biogenesis have been reported to participate in a wide range of physiological events, in some insect species. However, the functional significance of miRNA pathway core genes in Nilaparvata lugens remains unknown. In the present study, we conducted a systematic characterisation of five core genes involved in miRNA biogenesis. We first performed spatiotemporal expression analysis and found that miRNA core genes exhibited similar expression patterns, with high expression levels in eggs and relatively high transcriptional levels in the ovaries and fat bodies of females. RNA interference experiments showed that injecting third-instar nymphs with dsRNAs targeting the miRNA core genes, NlAgo1, NlDicer1, and NlDrosha resulted in high mortality rates and various degrees of body melanism, moulting defects, and wing deformities. Further investigations revealed that the suppression of miRNA core genes severely impaired ovarian development and oocyte maturation, resulting in significantly reduced fecundity and disruption of intercellular spaces between follicle cells. Moreover, the expression profiles of miR-34-5p, miR-275-3p, miR-317-3p, miR-14, Let-7-1, and miR-2a-3p were significantly altered in response to the knockdown of miRNA core genes mixture, suggesting that they play essential roles in regulating miRNA-mediated gene expression. Therefore, our results provide a solid theoretical basis for the miRNA pathway in N. lugens and suggest that the NlAgo1, NlDicer1, and NlDrosha-dependent miRNA core genes are essential for the development and reproduction of this agricultural pest.

MicroRNA-989 targets 5-hydroxytryptamine receptor1 to regulate ovarian development and eggs production in Culex pipiens pallens

BACKGROUND

Female mosquitoes need a blood meal after mating for their eggs to develop, and this behavior leads to the spread of pathogens. Therefore, understanding the molecular regulation of reproduction in female mosquitoes is essential to control mosquito vector populations. In this study, we reported that microRNA-989 (miR-989), which targets 5-HTR1 (encoding secreted 5-hydroxytryptamine receptor1), is essential for mosquito reproduction.

METHODS

The spatiotemporal expression profile of miR-989 was detected using quantitative real-time reverse transcription PCR (RT-qPCR). miR-989 antagomirs and antagomir-negative control (NC) were designed and synthesized to knock down the expression of endogenous miR-989 in female mosquitoes. RNA sequencing was used to analyze the ovarian response to miR-989 deletion. The targets of miR-989 were predicted and confirmed using RNAhybrid and dual-luciferase assays.

RESULTS

miR-989 is exclusively expressed in female mosquito ovaries and responds to blood feeding. Injection of the miR-989 antagomir resulted in smaller ovaries and reduced egg production. 5-HTR1 was demonstrated as a target of miR-989. The deletion of miR-989 contributed to the upregulation of 5-HTR1 expression. Knockdown of 5-HTR1 rescued the adverse egg production caused by miR-989 silencing. Thus, miR-989 might play an essential role in female reproduction by targeting 5-HTR1.

CONCLUSIONS

We found that miR-989 targets 5-HTR1 and participates in the regulation of reproduction in female mosquitoes. These findings expand our understanding of reproduction-related miRNAs and promote new control strategies for mosquitoes.

Identification and Characterization of Development-Related microRNAs in the Red Flour Beetle, Tribolium castaneum

MicroRNAs (miRNAs) play important roles in insect growth and development, but they were poorly studied in insects. In this study, a total of 883 miRNAs were detected from the early embryo (EE), late larva (LL), early pupa (EP), late pupa (LP), and early adult (EA) of Tribolium castaneum by microarray assay. Further analysis identified 179 differentially expressed unique miRNAs (DEmiRNAs) during these developmental stages. Of the DEmiRNAs, 102 DEmiRNAs exhibited stage-specific expression patterns during development, including 53 specifically highly expressed miRNAs and 20 lowly expressed miRNAs in EE, 19 highly expressed miRNAs in LL, 5 weakly expressed miRNAs in EP, and 5 abundantly expressed miRNAs in EA. These miRNAs were predicted to target 747, 265, 472, 234, and 121 genes, respectively. GO enrichment analysis indicates that the targets were enriched by protein phosphorylation, calcium ion binding, sequence-specific DNA binding transcription factor activity, and cytoplasm. An RNA interference-mediated knockdown of the DEmiRNAs tca-miR-6-3p, tca-miR-9a-3p, tca-miR-9d-3p, tca-miR-11-3p, and tca-miR-13a-3p led to defects in metamorphosis and wing development of T. castaneum. This study has completed the identification and characterization of development-related miRNAs in T. castaneum, and will enable us to investigate their roles in the growth and development of insect.

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.

Systematic Characterization and Regulatory Role of lncRNAs in Asian Honey Bees Responding to Microsporidian Infestation

Long noncoding RNAs (lncRNAs) are pivotal regulators in gene expression and diverse biological processes, such as immune defense and host-pathogen interactions. However, little is known about the roles of lncRNAs in the response of the Asian honey bee (Apis cerana) to microsporidian infestation. Based on our previously obtained high-quality transcriptome datasets from the midgut tissues of Apis cerana cerana workers at 7 days post inoculation (dpi) and 10 dpi with Nosema ceranae (AcT7 and AcT10 groups) and the corresponding un-inoculated midgut tissues (AcCK7 and AcCK10 groups), the transcriptome-wide identification and structural characterization of lncRNAs were conducted, and the differential expression pattern of lncRNAs was then analyzed, followed by investigation of the regulatory roles of differentially expressed lncRNAs (DElncRNAs) in host response. Here, 2365, 2322, 2487, and 1986 lncRNAs were, respectively, identified in the AcCK7, AcT7, AcCK7, and AcT10 groups. After removing redundant ones, a total of 3496 A. c. cerana lncRNAs were identified, which shared similar structural characteristics with those discovered in other animals and plants, such as shorter exons and introns than mRNAs. Additionally, 79 and 73 DElncRNAs were screened from the workers' midguts at 7 dpi and 10 dpi, respectively, indicating the alteration of the overall expression pattern of lncRNAs in host midguts after N. ceranae infestation. These DElncRNAs could, respectively, regulate 87 and 73 upstream and downstream genes, involving a suite of functional terms and pathways, such as metabolic process and Hippo signaling pathway. Additionally, 235 and 209 genes co-expressed with DElncRNAs were found to enrich in 29 and 27 terms, as well as 112 and 123 pathways, such as ABC transporters and the cAMP signaling pathway. Further, it was detected that 79 (73) DElncRNAs in the host midguts at 7 (10) dpi could target 321 (313) DEmiRNAs and further target 3631 (3130) DEmRNAs. TCONS_00024312 and XR_001765805.1 were potential precursors for ame-miR-315 and ame-miR-927, while TCONS_00006120 was the putative precursor for both ame-miR-87-1 and ame-miR-87-2. These results together suggested that DElncRNAs are likely to play regulatory roles in the host response to N. ceranae infestation through the regulation of neighboring genes via a cis-acting effect, modulation of co-expressed mRNAs via trans-acting effect, and control of downstream target genes' expression via competing endogenous RNA networks. Our findings provide a basis for disclosing the mechanism underlying DElncRNA-mediated host N. ceranae response and a new perspective into the interaction between A. c. cerana and N. ceranae.

Noncoding RNA Regulation of Hormonal and Metabolic Systems in the Fruit Fly Drosophila

The importance of RNAs is commonly recognised thanks to protein-coding RNAs, whereas non-coding RNAs (ncRNAs) were conventionally regarded as 'junk'. In the last decade, ncRNAs' significance and roles are becoming noticeable in various biological activities, including those in hormonal and metabolic regulation. Among the ncRNAs: microRNA (miRNA) is a small RNA transcript with ~20 nucleotides in length; long non-coding RNA (lncRNA) is an RNA transcript with >200 nucleotides; and circular RNA (circRNA) is derived from back-splicing of pre-mRNA. These ncRNAs can regulate gene expression levels at epigenetic, transcriptional, and post-transcriptional levels through various mechanisms in insects. A better understanding of these crucial regulators is essential to both basic and applied entomology. In this review, we intend to summarise and discuss the current understanding and knowledge of miRNA, lncRNA, and circRNA in the best-studied insect model, the fruit fly Drosophila.

Cyromazine affects the ovarian germ cells of Drosophila via the ecdysone signaling pathway

Cyromazine, an insect growth regulator, has been extensively used against the insect pests of livestock and households. Previously, it was observed that the continuous selection of cyromazine from the larval to the adult stage decreased the number of germline stem cells (GSCs) and cystoblasts (CBs) in the adult ovary. In addition, in this study, we observed that the number of primordial germ cells (PGCs) was also decreased in the larval ovary after treatment with cyromazine. However, the mechanism by which it affects the germ cells is yet to be explored. Consequently, to deeply investigate the effects of cyromazine on the germ cells, we performed tissue-specific RNA sequencing. Bioinformatics analysis revealed that the ecdysone signaling pathway was significantly influenced under cyromazine stress. Based on that, we screened and selected 14 ecdysone signaling responsive genes and silenced their expression in the germ cells only. Results of that showed a considerable reduction in the number of germ cells. Furthermore, we mixed exogenous 20E with the cyromazine-containing diet to rescue the ecdysone signaling. Our results supported that the application of exogenous 20E significantly rescued the germ cells in the transgenic lines. Therefore, this implies that the cyromazine decreased the number of germ cells by affecting the ecdysone signaling pathway.

Characterization of MicroRNAs Associated with Reproduction in the Brown Planthopper, Nilaparvata lugens

Insects have a robust capacity to produce offspring for propagation, and the reproductive events of female insects have been achieved at the molecular and physiological levels via regulatory gene pathways. However, the roles of MicroRNAs (miRNAs) in the reproductive development of the brown planthopper (BPH), Nilaparvata lugens, remain largely unexplored. To understand the roles of miRNAs in reproductive development, miRNAs were identified by Solexa sequencing in short-winged (SW) female adults of BPH. Small RNA libraries derived from three developmental phases (1 day, 3 days, and 5 days after emergence) were constructed and sequenced. We identified 905 miRNAs, including 263 known and 642 novel miRNAs. Among them, a total of 43 miRNAs were differentially expressed in the three developmental phases, and 14,568 putative targets for 43 differentially expressed miRNAs (DEMs) were predicted by TargetScan and miRanda. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the predicted miRNA targets illustrated the putative roles for these DEMs in reproduction. The progress events were annotated, including oogenesis, lipid biosynthetic process, and related pathways such as apoptosis, ABC transporters, and amino acid metabolism. Four highly abundant DEMs (miR-9a-5p, miR-34-5p, miR-275-3p, and miR-317-3p) were further screened, and miR-34-5p was confirmed to be involved in the regulation of reproduction. Overexpression of miR-34-5p via injecting its mimics reduced fecundity and decreased Vg expression. Moreover, target genes prediction for miR-34-5p showed they might be involved in 20E signaling cascades, apoptosis, and gonadal development, including hormone receptor 4 (HR4), caspase-1 (Cp-1), and spermatogenesis-associated protein 20 (SPATA20). These findings provide a valuable resource for future studies on the role of miRNAs in BPH reproductive development.

Downregulation of the CsABCC2 gene is associated with Cry1C resistance in the striped stem borer Chilo suppressalis

Chilo suppressalis is a major target pest of transgenic rice expressing the Bacillus thuringiensis (Bt) Cry1C toxin in China. The evolution of resistance of this pest is a major threat to Bt rice. Since Bt functions by binding to receptors in the midgut (MG) of target insects, identification of Bt functional receptors in C. suppressalis is crucial for evaluating potential resistance mechanisms and developing effective management strategies. ATP-binding cassette (ABC) transporters have been vastly reported to interact with Cry1A toxins, as receptors and their mutations cause insect Bt resistance. However, the role of ABC transporters in Cry1C resistance to C. suppressalis remains unknown. Here, we measured CsABCC2 expression in C. suppressalis Cry1C-resistant (Cry1C-R) and Cry1C-susceptible strains (selected in the laboratory) via quantitative real-time PCR (qRT-PCR); the transcript level of CsABCC2 in the Cry1C-R strain was significantly lower than that in the Cry1C-susceptible strain. Furthermore, silencing CsABCC2 in C. suppressalis via RNA interference (RNAi) significantly decreased Cry1C susceptibility. Overall, CsABCC2 participates in Cry1C mode of action, and reduced expression of CsABCC2 is functionally associated with Cry1C resistance in C. suppressalis.

Kr-h1, a Cornerstone Gene in Insect Life History

Insect life cycle is coordinated by hormones and their downstream effectors. Krüppel homolog1 (Kr-h1) is one of the crucial effectors which mediates the actions of the two critical hormones of insects, the juvenile hormone (JH) and 20-hydroxyecdysone (20E). It is a transcription factor with a DNA-binding motif of eight C₂H₂ zinc fingers which is found to be conserved among insect orders. The expression of Kr-h1 is fluctuant during insect development with high abundance in juvenile instars and lower levels in the final instar and pupal stage, and reappearance in adults, which is governed by the coordination of JH, 20E, and miRNAs. The dynamic expression pattern of Kr-h1 is closely linked to its function in the entire life of insects. Over the past several years, accumulating studies have advanced our understanding of the role of Kr-h1 during insect development. It acts as a universal antimetamorphic factor in both hemimetabolous and holometabolous species by directly inhibiting the transcription of 20E signaling genes Broad-Complex (Br-C) and Ecdysone induced protein 93F (E93), and steroidogenic enzyme genes involved in ecdysone biosynthesis. Meanwhile, it promotes vitellogenesis and ovarian development in the majority of studied insects. In addition, Kr-h1 regulates insect behavioral plasticity and caste identity, neuronal morphogenesis, maturation of sexual behavior, as well as embryogenesis and metabolic homeostasis. Hence, Kr-h1 acts as a cornerstone regulator in insect life.

Dissection of the microRNA Network Regulating Hedgehog Signaling in Drosophila

The evolutionarily conserved Hedgehog (Hh) signaling plays a critical role in embryogenesis and adult tissue homeostasis. Aberrant Hh signaling often leads to various forms of developmental anomalies and cancer. Since altered microRNA (miRNA) expression is associated with developmental defects and tumorigenesis, it is not surprising that several miRNAs have been found to regulate Hh signaling. However, these miRNAs are mainly identified through small-scale in vivo screening or in vitro assays. As miRNAs preferentially reduce target gene expression via the 3' untranslated region, we analyzed the effect of reduced expression of core components of the Hh signaling cascade on downstream signaling activity, and generated a transgenic Drosophila toolbox of in vivo miRNA sensors for core components of Hh signaling, including hh, patched (ptc), smoothened (smo), costal 2 (cos2), fused (fu), Suppressor of fused (Su(fu)), and cubitus interruptus (ci). With these tools in hand, we performed a genome-wide in vivo miRNA overexpression screen in the developing Drosophila wing imaginal disc. Of the twelve miRNAs identified, seven were not previously reported in the in vivo Hh regulatory network. Moreover, these miRNAs may act as general regulators of Hh signaling, as their overexpression disrupts Hh signaling-mediated cyst stem cell maintenance during spermatogenesis. To identify direct targets of these newly discovered miRNAs, we used the miRNA sensor toolbox to show that miR-10 and miR-958 directly target fu and smo, respectively, while the other five miRNAs act through yet-to-be-identified targets other than the seven core components of Hh signaling described above. Importantly, through loss-of-function analysis, we found that endogenous miR-10 and miR-958 target fu and smo, respectively, whereas deletion of the other five miRNAs leads to altered expression of Hh signaling components, suggesting that these seven newly discovered miRNAs regulate Hh signaling in vivo. Given the powerful effects of these miRNAs on Hh signaling, we believe that identifying their bona fide targets of the other five miRNAs will help reveal important new players in the Hh regulatory network.

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.

MicroRNA miR-8 promotes cell growth of corpus allatum and juvenile hormone biosynthesis independent of insulin/IGF signaling in Drosophila melanogaster

The Drosophila melanogaster corpus allatum (CA) produces and releases three types of sesquiterpenoid hormones, including juvenile hormone III bisepoxide (JHB3), juvenile hormone III (JH III), and methyl farnesoate (MF). JH biosynthesis involves multiple discrete enzymatic reactions and is subjected to a comprehensive regulatory network including microRNAs (miRNAs). Using a high throughput sequencing approach, we have identified abundant miRNAs in the D. melanogaster ring gland, which consists of the CA, prothoracic gland, and corpus cardiaca. Genetic and qPCR screens were then performed in an attempt to uncover the full repertoire of CA miRNAs that are involved in regulating metamorphosis. miR-8 was identified as a potential candidate and further studied for its role in the CA. Overexpression of miR-8 in the CA increased cell size of the gland and expression of Jhamt (a gene coding for a key regulatory enzyme in JH biosynthesis), resulting in pupal lethality. By contrast, sponge-mediated reduction of miR-8 in the CA decreased cell size and Jhamt expression, but did not cause lethality. Further investigation revealed that miR-8 promotes cell growth independent of insulin/IGF signaling. Taken together, these experiments show that miR-8 is highly expressed in the CA and exerts its positive effects on cell growth and JH biosynthesis. The miRNAs data in the ring gland also provide a useful resource to study how miRNAs collaboratively regulate hormone synthesis in D. melanogaster.

Stage specific expression of milk fat globule membrane glycoproteins in mouse mammary gland: comparison of MFG-E8, butyrophilin, and CD36 with a major milk protein, beta-casein

The expression of mouse milk fat globule membrane (MFGM) glycoproteins, MFG-E8, butyrophilin, CD36 was analyzed by Northern blot analyses. MFG-E8 and butyrophilin mRNAs were specifically detected in the mammary gland of lactating mice, whereas CD36 mRNA was detected in the heart and lung as well as in the mammary gland of lactating mice. The mRNAs of the three MFGM glycoproteins accumulated at mid-lactation were about 2-10-times as much as those of the early and late gestation stages, whereas beta-casein mRNA accumulation was dramatically increased; the mRNA at mid-lactation was no less than 40-times as much as that before lactation. In mouse mammary epithelial cell lines, HC11 and COMMA-1D, only a slight or almost no enhancement for the expression of MFG-E8, butyrophilin and CD36 mRNAs was induced simply by the treatment with the lactogenic hormones such as prolactin, insulin and dexamethasone, whereas the beta-casein mRNA expression was remarkably enhanced only by that treatment. Furthermore, while the beta-casein protein was constantly detected in milk throughout the lactation stage, the content of MFG-E8 and butyrophilin proteins increased during the lactation with an increase in the milk fat content. These results suggest that the stage-specific expression of milk fat globule membrane glycoproteins in mammary epithelial cells is regulated in a similar but not necessarily identical mechanism to that of a major milk protein, beta-casein.