MicroRNA-dependent roles of Drosha and Pasha in the Drosophila larval ovary morphogenesis

Genetic circuitry controlling Drosophila female germline overgrowth

Germ cells mutant for bam or bgcn are locked in a germline stem cell (GSC)-like state, leading to tumor-like overgrowth in Drosophila ovaries. Our previous studies have demonstrated that germline overgrowth in bam mutants can be suppressed by defects in the miRNA pathway but enhanced by a null mutation in hippo. However, the genetic epistasis between the miRNA and Hippo pathways still remains unknown. Here, we determined that the miRNA pathway acts downstream of the Hippo pathway in regulating this process. Germ cells mutant for bam or bgcn and defective in both pathways divide very slowly, phenocopying those defective only in the miRNA pathway. In addition, we found that Yki, a key oncoprotein in the Hippo pathway, promotes the growth of both wild-type germ cells and bam mutant GSC-like cells. Like wild-type GSCs, bam mutant GSC-like cells predominantly stay in the G2 phase. Remarkably, many of those defective in the miRNA pathway are arrested before entering this phase. Furthermore, our studies identified bantam as a critical miRNA promoting germline overgrowth in bam or bgcn mutants. Taken together, these findings establish a genetic circuitry controlling Drosophila female germline overgrowth.

miR-317-3p and miR-283-5p Play a Crucial Role in Regulating the Resistance to Indoxacarb in Spodoptera frugiperda by Targeting GSTs4

Spodoptera frugiperda is primarily controlled through chemical insecticides. Our RNA-seq data highlight the overexpression of GSTs4 in indoxacarb-resistant S. frugiperda. However, the exact role of GSTs4 in indoxacarb resistance and its regulatory mechanisms remains elusive. Therefore, we investigated the functional role of GSTs4 in S. frugiperda and explored the underlying post-transcriptional regulatory mechanisms. GSTs4 was highly overexpressed (27.6-fold) in the indoxacarb-resistant strain, and GSTs4 silencing significantly increases the susceptibility of S. frugiperda to indoxacarb, increasing mortality by 27.3%. miR-317-3p and miR-283-5p can bind to the 3'UTR of GSTs4, and the targeting relationship was confirmed by dual-luciferase reporter assays. Injecting miR-317-3p and miR-283-5p agomirs reduces GSTs4 levels by 64.8 and 42.3%, respectively, resulting in an increased susceptibility of S. frugiperda to indoxacarb. Conversely, the administration of miR-317-3p and miR-283-5pantagomirs increases GSTs4 expression and reduces larval susceptibility to indoxacarb. These findings demonstrate that miR-317-3p and miR-283-5p contribute to indoxacarb resistance in S. frugiperda by regulating the overexpression of GSTs4.

Expression profiles of lncRNAs, miRNAs, and mRNAs and interaction analysis indicate their potential involvement during testicular fusion in Spodoptera litura

Testicular fusion of Spodoptera litura occures during metamorphosis, which benefits sperms development. Previous research identified involvement of ECM-integrin interaction pathways, MMPs in testicular fusion, but the regulatory mechanism remains unclear. RNA-seq was performed to analyze long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) in testes, aiming to uncover potential regulatory mechanisms of testicular fusion. 2150 lncRNAs, 2742 targeted mRNAs, and 347 miRNAs were identified in testes at three different developmental stages. Up-regulated DElncRNAs and DEmRNAs, as well as down-regulated DEmiRNAs, were observed during testicular fusion, while the opposite expression pattern was observed after fusion. Enrichment analysis of DEmRNAs revealed that cAMP signal pathway, ECM remodeling enzymes, ECM-integrin interaction pathways, and cell adhesion molecules were potentially associated with testicular fusion. The identified DElncRNA-DEmiRNA-DEmRNA regulatory network related to cAMP signal pathway, ECM remodeling enzymes suggests their roles during testicular fusion. Our research will provide new targets for studying the mechanism of testicular fusion.

Study on the Role of Mitophagy Receptor PHB2 in Doubly Uniparental Inheritance of Hyriopsis cumingii

In bivalves, the heterogeneity of mitochondrial DNA and its unique mode of transmission have been the focus of attention, which is called doubly uniparental inheritance (DUI). Prohibitin-2 (phb2) is a mitochondrial inner membrane protein that is a key mitophagy receptor for parental mitochondrial removal. Hyriopsis cumingii is a freshwater bivalve in China, the full-length cDNA of H. cumingii phb2 (named Hcphb2) is 2917 bp and encodes a total of 300 amino acids, a highly conserved sequence. Hcphb2 was highly expressed in the ovary. In the gonadal tissues of 5- to 8-month-old female mussels, the expression level of Hcphb2 continued to significantly increase. After Hcphb2 siRNA interference in 6-month-old female mussels, the expression of M-COII, a marker gene on M-type mitochondria, showed a considerable increase (p < 0.05). In contrast, the expression of autophagosome formation and maturation-related genes, atg4b, atg5, atg12, and atg16l, in the ATG family genes was significantly decreased (p < 0.01). Subcellular localization showed that Hcphb2 appeared in spermatogonia, spermatocyte, spermatid, and sperm, and its location changes synchronize with the behavior of M-type mitochondria location changes in DUI species. And it was found that miR-184 negatively regulated Hcphb2. The above results suggest that the mitochondrial autophagy receptor gene Hcphb2 may be associated with the degradation of M-type mitochondria in the freshwater mussel. This process requires multiple genes to participate, of which Hcphb2 and autophagy genes are only some of those that may play a role.

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.

RNA sequencing identifies an ovary-enriched microRNA, miR-311-3p, involved in ovarian development and fecundity by targeting Endophilin B1 in Bactrocera dorsalis

BACKGROUND

The oriental fruit fly, Bactrocera dorsalis, is a highly invasive pest in East Asia and the Pacific. With the development of pesticides resistance, environment-friendly pesticides are urgently needed. MicroRNAs (miRNAs) are critical regulators of numerous biological processes, including reproduction. Thus, it is significant to identify reproductive-related miRNAs in this notorious pest to facilitate its control, such as RNAi-based biopesticides targeting essential miRNAs.

RESULTS

A high-throughput sequencing was carried out to identify miRNAs involved in reproduction from the ovary and fat body at four developmental stages [1 day (d), 5, 9, and 13 days post-eclosion] in female B. dorsalis. Results showed that 98 and 74 miRNAs were differentially expressed in ovary and fat body, respectively, during sexual maturation. Gene ontology analysis showed that target genes involved in oogenesis and lipid particle accounted for 33% and 15% of the total targets, respectively. Among these differentially expressed miRNAs, we found by qPCR that miR-311-3p was enriched in the ovary and down-regulated during sexual maturation. Injection of agomir-miR-311-3p resulted in arrested ovarian development, reduced egg deposition and progeny viability. Endophilin B1 was confirmed to be the target of miR-311-3p, via dual-luciferase assay and expression profiling. Knockdown of Endophilin B1 resulted in reproductive defects similar to those caused by injection of miR-311-3p agomir. Thus, miR-311-3p might play a critical role in female reproduction by targeting Endophilin B1.

CONCLUSION

Our data not only provides knowledge on the abundance of reproductive-related miRNAs and target genes, but also promotes new control strategies for this pest. © 2022 Society of Chemical Industry.

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.

MicroRNAs reshape the immunity of insects in response to bacterial infection

The interaction between bacteria and insects can significantly impact a wide range of different areas because bacteria and insects are widely distributed around the globe. The bacterial-insect interactions have the potential to directly affect human health since insects are vectors for disease transmission, and their interactions can also have economic consequences. In addition, they have been linked to high mortality rates in economically important insects, resulting in substantial economic losses. MicroRNAs (miRNAs) are types of non-coding RNAs involved in regulating gene expression post-transcriptionally. The length of miRNAs ranges from 19 to 22 nucleotides. MiRNAs, in addition to their ability to exhibit dynamic expression patterns, have a diverse range of targets. This enables them to govern various physiological activities in insects, like innate immune responses. Increasing evidence suggests that miRNAs have a crucial biological role in bacterial infection by influencing immune responses and other mechanisms for resistance. This review focuses on some of the most recent and exciting discoveries made in recent years, including the correlation between the dysregulation of miRNA expression in the context of bacterial infection and the progression of the infection. Furthermore, it describes how they profoundly impact the immune responses of the host by targeting the Toll, IMD, and JNK signaling pathways. It also emphasizes the biological function of miRNAs in regulating immune responses in insects. Finally, it also discusses current knowledge gaps about the function of miRNAs in insect immunity, in addition to areas that require more research in the future.

Drosophila Relish-mediated miR-317 expression facilitates immune homeostasis restoration via inhibiting PGRP-LC

Innate immunity is the first and essential line for resisting pathogens, and the immune intensity and duration need to be strictly regulated to balance excessive or insufficient immune response. MicroRNAs (miRNAs) are crucial regulators of immune response in Drosophila, yet how immune-related miRNAs are regulated remains poorly understood. Herein, we elucidated that the involvement of miR-317 in NF-κB transcription factor Relish mediated Drosophila Imd pathway in response to Gram-negative (G-) bacteria stimulation. Remarkably, the dynamic expression profiling for immune response indicated that Relish simultaneously enhances the expression of the effector antimicrobial peptide Dpt as well as miR-317 post-infection. Upregulation of miR-317 could further down-regulate the expression of PGRP-LC, thereby forming a feedback in Drosophila Imd pathway to prevent over-activation and restore immune homeostasis. Taken together, our study not only uncovers a novel Relish/miR-317/PGRP-LC regulatory axis to attenuate Drosophila Imd immune response and facilitate immune homeostasis restoration, but also provides vital insights into the complex mechanisms of animal innate immune regulation.

The microRNA processor DROSHA is a candidate gene for a severe progressive neurological disorder

DROSHA encodes a ribonuclease that is a subunit of the Microprocessor complex and is involved in the first step of microRNA (miRNA) biogenesis. To date, DROSHA has not yet been associated with a Mendelian disease. Here, we describe two individuals with profound intellectual disability, epilepsy, white matter atrophy, microcephaly and dysmorphic features, who carry damaging de novo heterozygous variants in DROSHA. DROSHA is constrained for missense variants and moderately intolerant to loss-of-function (o/e = 0.24). The loss of the fruit fly ortholog drosha causes developmental arrest and death in third instar larvae, a severe reduction in brain size and loss of imaginal discs in the larva. Loss of drosha in eye clones causes small and rough eyes in adult flies. One of the identified DROSHA variants (p.Asp1219Gly) behaves as a strong loss-of-function allele in flies, while another variant (p.Arg1342Trp) is less damaging in our assays. In worms, a knock-in that mimics the p.Asp1219Gly variant at a worm equivalent residue causes loss of miRNA expression and heterochronicity, a phenotype characteristic of the loss of miRNA. Together, our data show that the DROSHA variants found in the individuals presented here are damaging based on functional studies in model organisms and likely underlie the severe phenotype involving the nervous system.

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.

Photoperiod-Dependent Expression of MicroRNA in Drosophila

Like many other insects in temperate regions, Drosophila melanogaster exploits the photoperiod shortening that occurs during the autumn as an important cue to trigger a seasonal response. Flies survive the winter by entering a state of reproductive arrest (diapause), which drives the relocation of resources from reproduction to survival. Here, we profiled the expression of microRNA (miRNA) in long and short photoperiods and identified seven differentially expressed miRNAs (dme-mir-2b, dme-mir-11, dme-mir-34, dme-mir-274, dme-mir-184, dme-mir-184*, and dme-mir-285). Misexpression of dme-mir-2b, dme-mir-184, and dme-mir-274 in pigment-dispersing, factor-expressing neurons largely disrupted the normal photoperiodic response, suggesting that these miRNAs play functional roles in photoperiodic timing. We also analyzed the targets of photoperiodic miRNA by both computational predication and by Argonaute-1-mediated immunoprecipitation of long- and short-day RNA samples. Together with global transcriptome profiling, our results expand existing data on other Drosophila species, identifying genes and pathways that are differentially regulated in different photoperiods and reproductive status. Our data suggest that post-transcriptional regulation by miRNA is an important facet of photoperiodic timing.

Advances in the Immune Regulatory Role of Non-Coding RNAs (miRNAs and lncRNAs) in Insect-Pathogen Interactions

Insects are by far the most abundant and diverse living organisms on earth and are frequently prone to microbial attacks. In other to counteract and overcome microbial invasions, insects have in an evolutionary way conserved and developed immune defense mechanisms such as Toll, immune deficiency (Imd), and JAK/STAT signaling pathways leading to the expression of antimicrobial peptides. These pathways have accessory immune effector mechanisms, such as phagocytosis, encapsulation, melanization, nodulation, RNA interference (RNAi), lysis, autophagy, and apoptosis. However, pathogens evolved strategies that circumvent host immune response following infections, which may have helped insects further sophisticate their immune response mechanisms. The involvement of ncRNAs in insect immunity is undeniable, and several excellent studies or reviews have investigated and described their roles in various insects. However, the functional analyses of ncRNAs in insects upon pathogen attacks are not exhaustive as novel ncRNAs are being increasingly discovered in those organisms. This article gives an overview of the main insect signaling pathways and effector mechanisms activated by pathogen invaders and summarizes the latest findings of the immune modulation role of both insect- and pathogen-encoded ncRNAs, especially miRNAs and lncRNAs during insect–pathogen crosstalk.

Abundant small RNAs in the reproductive tissues and eggs of the honey bee, Apis mellifera

Background

Polyandrous social insects such as the honey bee are prime candidates for parental manipulation of gene expression in offspring. Although there is good evidence for parent-of-origin effects in honey bees the epigenetic mechanisms that underlie these effects remain a mystery. Small RNA molecules such as miRNAs, piRNAs and siRNAs play important roles in transgenerational epigenetic inheritance and in the regulation of gene expression during development.

Results

Here we present the first characterisation of small RNAs present in honey bee reproductive tissues: ovaries, spermatheca, semen, fertilised and unfertilised eggs, and testes. We show that semen contains fewer piRNAs relative to eggs and ovaries, and that piRNAs and miRNAs which map antisense to genes involved in DNA regulation and developmental processes are differentially expressed between tissues. tRNA fragments are highly abundant in semen and have a similar profile to those seen in the semen of other animals. Intriguingly we also find abundant piRNAs that target the sex determination locus, suggesting that piRNAs may play a role in honey bee sex determination.

Conclusions

We conclude that small RNAs may play a fundamental role in honey bee gametogenesis and reproduction and provide a plausible mechanism for parent-of-origin effects on gene expression and reproductive physiology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08478-9.

Identification of wnt2 in the pearl mussel Hyriopsis cumingii and its role in innate immunity and gonadal development

Wnt2 is a significant factor in the Wnt signaling pathway, which is associated with a variety of physiological activities, including inflammatory response, cell apoptosis, reproductive system development, and cell differentiation. Hyriopsis cumingii is the main pearl breeding mussel in China. However, the role of wnt2 in this species remains unclear. In this study, wnt2 from H. cumingii was cloned and identified. The full-length cDNA of wnt2 is 1524 bp, containing a 963 bp open reading frame (ORF), encoding 320 amino acid residues. The tissue distribution of H. cumingii indicated that wnt2 was predominantly highly expressed in the ovary and gill. And the expression profile after Aeromonas hydrophila or LPS injection indicated that wnt2 was up-regulated in gill, suggesting its role in the innate immune response. The expression of wnt2 was high at 4-month-old of early gonadal development and throughout ovarian development. In situ hybridization (ISH) showed significant hybridization signals on the gills and mature eggs of female gonads. In addition, miR-1988b-5p was found to negatively regulate wnt2 to affect the expression of key genes (frizzled-5, ctnnb1, and tcf7l) in the Wnt signaling pathway. Thus, these findings suggest a key role for wnt2 in immune regulation and gonadal development in H. cumingii.

The microRNA miR-33 is a pleiotropic regulator of metabolic and developmental processes in Drosophila melanogaster

BACKGROUND

miR-33 family members are well characterized regulators of cellular lipid levels in mammals. Previous studies have shown that overexpression of miR-33 in Drosophila melanogaster leads to elevated triacylglycerol (TAG) levels in certain contexts. Although loss of miR-33 in flies causes subtle defects in larval and adult ovaries, the effects of miR-33 deficiency on lipid metabolism and other phenotypes impacted by metabolic state have not yet been characterized.

RESULTS

We found that loss of miR-33 predisposes flies to elevated TAG levels, and we identified genes involved in TAG synthesis as direct targets of miR-33, including atpcl, midway, and Akt1. miR-33 mutants survived longer upon starvation but showed greater sensitivity to an oxidative stressor. We also found evidence that miR-33 is a negative regulator of cuticle pigmentation and that miR-33 mutants show a reduction in interfollicular stalk cells during oogenesis.

CONCLUSION

Our data suggest that miR-33 is a conserved regulator of lipid homeostasis, and its targets are involved in both degradation and synthesis of fatty acids and TAG. The constellation of phenotypes involving tissues that are highly sensitive to metabolic state suggests that miR-33 serves to prevent extreme fluctuations in metabolically sensitive tissues.

Aedes aegypti miRNA-33 modulates permethrin induced toxicity by regulating VGSC transcripts

Aedes aegypti is a major vector of Zika, dengue, and other arboviruses. Permethrin adulticidal spraying, which targets the voltage-gated sodium channel (VGSC), is commonly done to reduce local mosquito populations and protect humans from exposure to arbovirus pathogens transmitted by this dangerous pest. Permethrin resistance, however, is a growing problem and understanding its underlying molecular basis may identify avenues to combat it. We identified a single G:C polymorphism in pre-miR-33 that was genetically associated with permethrin resistance; resulting isoforms had structural differences that may affect DICER-1/pre-miRNA processing rates. We then assessed the effects of overexpression of pre-miR-33 isoforms on permethrin toxicological phenotypes, VGSC transcript abundance and protein levels for two genetically related mosquito strains. One strain had its naturally high permethrin resistance levels maintained by periodic treatment, and the other was released from selection. VGSC protein levels were lower in the permethrin resistant strain than in the related permethrin-susceptible strain. Overexpression of the G-pre-miR-33 isoform reduced VGSC expression levels in both strains. To further elucidate changes in gene expression associated with permethrin resistance, exome-capture gDNA deep sequencing, genetic association mapping and subsequent gene set enrichment analysis revealed that transport genes, in particular, were selected in resistant versus susceptible mosquitoes. Collectively, these data indicate that miR-33 regulates VGSC expression as part of a nuanced system of neuronal regulation that contributes to a network of heritable features determining permethrin resistance.

Integrated mRNA and miRNA expression profile analysis of female and male gonads in Hyriopsis cumingii

Hyriopsis cumingii is an important species for freshwater pearl cultivation in China. In terms of pearl production, males have larger pearls and better glossiness than females, but there are few reports focusing on the sex of H. cumingii. In this study, six mRNA and six microRNA (miRNA) libraries were prepared from ovaries and testes. Additionally, 28,502 differentially expressed genes (DEGs) and 32 differentially expressed miRNAs (DEMs) were identified. Compared with testis, 14,360 mRNAs and 20 miRNAs were up-regulated in ovary, 14,142 mRNAs and 12 miRNAs were down-regulated. In DEGs, the known genes related to sex determinism and/or differentiation were also identified, such as DMRT1, SOX9, SF1 for males, FOXL2 for females, and other potentially significant candidate genes. Three sex-related pathways have also been identified, which are Wnt, Notch, and TGF-beta. In 32 DEMs, the three miRNAs (miR-9-5p, miR-92, miR-184) were paid more attention, they predicted 28 target genes, which may also be candidates for sex-related miRNAs and genes. Differential miRNAs target genes analysis reveals the pathway associated with oocyte meiosis and spermatogenesis. Overall, the findings of the study provide significant insights to enhance our understanding of sex differentiation and/or sex determination mechanisms for H. cumingii.

CREB1/Lin28/miR-638/VASP Interactive Network Drives the Development of Breast Cancer

Breast cancer is one of the most common malignant tumors worldwide. Metastasis remains the leading cause of death in breast cancer patients. Research on the mechanism of breast cancer metastasis has become a core issue in breast cancer research. Our previous series of studies have shown that VASP, as a key oncogene, plays an important role in the development of various tumors such as breast cancer. In this study, we find that miR-638 can target to inhibit VASP expression, and Lin28 acts as an RNA-binding protein to regulate the processing of miR-638, which inhibits its maturation and promotes the expression of VASP. In addition, we also find that CREB1 acts as a transcription factor that binds to the promoter of Lin28 gene and activates the Lin28/miR-638/VASP pathway. Furthermore, CREB1 can also directly bind to the promoter of VASP, and activate VASP expression, forming a CREB/Lin28/miR-638/VASP interactive network, which plays an important role in promoting cell proliferation and migration in breast cancer. Our study explained the mechanism of CREB1/Lin28/miR-638/VASP network promoting the development of breast cancer, which further elucidated the mechanism of VASP as a key oncogene, and also provided a theoretical basis for expanding new approaches to tumor biotherapy.

The miR-317 functions as a negative regulator of Toll immune response and influences Drosophila survival

The miR-317 has been revealed to involve in the reproductive response and the larval ovary morphogenesis of Drosophila. However, whether the miR-317 can also regulate Drosophila innate immune responses, which remains unclear to date. Here we have verified that miR-317 can directly target the 3'UTR of Dif-Rc to down-regulate the expression levels of AMP Drs to negatively control Drosophila Toll immune response in vivo and vitro. Specially, the Dif is an important transcription factor of Toll pathway with four transcripts (Dif-Ra, Dif-Rb, Dif-Rc and Dif-Rd). Our results show that miR-317 only targets to Dif-Rc, but not Dif-Ra/b/d, implying that miRNAs can regulate different isoforms of an alternative splicing gene to fine tune immune responses and maintain homeostasis in post-transcriptional level. Furthermore, we have demonstrated that the miR-317 sponge can restore the expression levels of Drs and Dif-Rc at mRNA and protein levels. Remarkably, during Gram-positive bacterial infection, the overexpressed miR-317 flies have poor survival outcome, whereas the knockout miR-317 flies have favorable survival compared to the control group, respectively, suggesting that the miR-317 might play a key role in Drosophila survival. Taken together, our current works not only reveal an innate immune function and a novel regulation pattern of miR-317, but also provide a new insight into the underlying molecular mechanisms of immunity disorder influencing on Drosophila survival.

Analysis of microRNA functions

MicroRNAs (miRNAs) are small non-coding RNAs that repress the translation and reduce the stability of target mRNAs in animal cells. Post-transcriptional regulation mediated by miRNAs is a highly conserved mechanism utilized by organisms throughout phylogeny to fine tune gene expression. We document the approaches used to study the function of a single miRNA and miRNA regulation of biological pathways in the sea urchin embryo. The protocols that are described include selection of miRNA inhibitors, test of miRNA direct targets, and the use of target protector morpholinos to evaluate the impact of miRNA inhibition on its targets. Using the described techniques and strategies, the sea urchin researcher will be able to validate a miRNA's direct targets and evaluate how inhibition of the miRNA affects developmental processes. These results will contribute to our understanding of the regulatory roles of miRNAs in development.

Knockdown of RNA interference pathway genes impacts the fitness of western corn rootworm

Western corn rootworm (Diabrotica virgifera virgifera) is a serious agricultural pest known for its high adaptability to various management strategies, giving rise to a continual need for new control options. Transgenic maize expressing insecticidal RNAs represents a novel mode of action for rootworm management that is dependent on the RNA interference (RNAi) pathways of the insect for efficacy. Preliminary evidence suggests that western corn rootworm could develop broad resistance to all insecticidal RNAs through changes in RNAi pathway genes; however, the likelihood of field-evolved resistance occurring through this mechanism remains unclear. In the current study, eight key genes involved in facilitating interference in the microRNA and small interfering RNA pathways were targeted for knockdown in order to evaluate impact on fitness of western corn rootworm. These genes include drosha, dicer-1, dicer-2, pasha, loquacious, r2d2, argonaute 1, and argonaute 2. Depletion of targeted transcripts in rootworm larvae led to changes in microRNA expression, decreased ability to pupate, reduced adult beetle emergence, and diminished reproductive capacity. The observed effects do not support evolution of resistance through changes in expression of these eight genes due to reduced insect fitness.

A comparative analysis of corpora allata-corpora cardiaca microRNA repertoires revealed significant changes during mosquito metamorphosis

The corpora allata (CA) are a pair of endocrine glands with neural connections to the brain and close association with another neuroendocrine organ, the corpora cardiaca (CC). The CA from adult female Aedes aegypti mosquitoes synthesize fluctuating levels of juvenile hormone (JH), which have been linked to the ovarian development and are influenced by nutritional signals. In this study, we investigated the potential involvement of microRNAs (miRNAs), a type of small non-coding RNAs, in the regulation of gene expression in CA-CC complexes during mosquito reproductive development, at stages with distinct JH biosynthesis patterns. We analyzed the miRNA repertoires expressed in the CA-CC of pupae, sugar-fed and blood-fed female Ae. aegypti. In total, 156 mature miRNAs were detected in the CA-CC, with 84 displaying significant differences in expression among the three CA-CC developmental stages. There were more miRNAs that were expressed in pupae, and decreased or were absent after adult emergence, when compared with changes between CA-CC of sugar and blood-fed females. Analysis of the genes identified as potential targets for the CA-CC miRNA repertoires classified them into the broad categories of metabolism, information storage and processing, and cellular processes and signaling; with genes involved in cellular processes and signaling representing the largest portion. Among them, the signal-transduction mechanisms and intracellular trafficking, secretion and vesicular transport contained almost 55% of the genes' targets. A substantial number of miRNAs were differentially abundant in the libraries of the three developmental stages, and those changes were much more notable when pupae and adult stages were compared. We detected putative binding sites for some of the most abundant miRNAs on genes encoding JH biosynthetic enzymes and CC neuropeptides. These studies should help us to gain a better understanding of the regulation of CA-CC activity mediated by miRNAs during major developmental stages in mosquitoes.

miRNA targeting and alternative splicing in the stress response - events hosted by membrane-less compartments

Stress can be temporary or chronic, and mild or acute. Depending on its extent and severity, cells either alter their metabolism, and adopt a new state, or die. Fluctuations in environmental conditions occur frequently, and such stress disturbs cellular homeostasis, but in general, stresses are reversible and last only a short time. There is increasing evidence that regulation of gene expression in response to temporal stress happens post-transcriptionally in specialized subcellular membrane-less compartments called ribonucleoprotein (RNP) granules. RNP granules assemble through a concentration-dependent liquid-liquid phase separation of RNA-binding proteins that contain low-complexity sequence domains (LCDs). Interestingly, many factors that regulate microRNA (miRNA) biogenesis and alternative splicing are RNA-binding proteins that contain LCDs and localize to stress-induced liquid-like compartments. Consequently, gene silencing through miRNAs and alternative splicing of pre-mRNAs are emerging as crucial post-transcriptional mechanisms that function on a genome-wide scale to regulate the cellular stress response. In this Review, we describe the interplay between these two post-transcriptional processes that occur in liquid-like compartments as an adaptive cellular response to stress.

Stereotypical architecture of the stem cell niche is spatiotemporally established by miR-125-dependent coordination of Notch and steroid signaling

Stem cell niches act as signaling platforms that regulate stem cell self-renewal and sustain stem cells throughout life; however, the specific developmental events controlling their assembly are not well understood. Here, we show that during Drosophila ovarian germline stem cell niche formation, the status of Notch signaling in the cell can be reprogrammed. This is controlled via steroid-induced miR-125, which targets a negative regulator of Notch signaling, Tom. Thus, miR-125 acts as a spatiotemporal coordinator between paracrine Notch and endocrine steroid signaling. Moreover, a dual security mechanism for Notch signaling activation exists to ensure the robustness of niche assembly. Particularly, stem cell niche cells can be specified either via lateral inhibition, in which a niche cell precursor acquires Notch signal-sending status randomly, or via peripheral induction, whereby Delta is produced by a specific cell. When one mechanism is perturbed due to mutations, developmental defects or environmental stress, the remaining mechanism ensures that the niche is formed, perhaps abnormally, but still functional. This guarantees that the germline stem cells will have their residence, thereby securing progressive oogenesis and, thus, organism reproduction.

Highlighted Article: In Drosophila, the robustness of stem cell niche assembly is safeguarded via a dual mechanism of Notch activation. Cellular Notch status can be reprogrammed by miR-125, which spatiotemporally coordinates paracrine and endocrine signaling.

Emerging roles for microRNA in the regulation of Drosophila circadian clock

Background

The circadian clock, which operates within an approximately 24-h period, is closely linked to the survival and fitness of almost all living organisms. The circadian clock is generated through a negative transcription-translation feedback loop. microRNAs (miRNAs) are small non-coding RNAs comprised of approximately 22 nucleotides that post-transcriptionally regulate target mRNA by either inducing mRNA degradation or inhibiting translation.

Results

In recent years, miRNAs have been found to play important roles in the regulation of the circadian clock, especially in Drosophila. In this review, we will use fruit flies as an example, and summarize the progress achieved in the study of miRNA-mediated clock regulation. Three main aspects of the circadian clock, namely, the free-running period, locomotion phase, and circadian amplitude, are discussed in detail in the context of how miRNAs are involved in these regulations. In addition, approaches regarding the discovery of circadian-related miRNAs and their targets are also discussed.

Conclusions

Research in the last decade suggests that miRNA-mediated post-transcriptional regulation is crucial to the generation and maintenance of a robust circadian clock in animals. In flies, miRNAs are known to modulate circadian rhythmicity and the free-running period, as well as circadian outputs. Further characterization of miRNAs, especially in the circadian input, will be a vital step toward a more comprehensive understanding of the functions underlying miRNA-control of the circadian clock.