The integrative analysis of microRNA and mRNA expression in Apis mellifera following maze-based visual pattern learning

Deformed wing virus genotypes A and B do not elicit immunologically different responses in naïve honey bee hosts

Iflavirus aladeformis (Picornavirales: Iflaviridae), commonly known as deformed wing virus(DWV), in association with Varroa destructor Anderson and Trueman (Mesostigmata: Varroidae), is a leading factor associated with honey bee (Apis mellifera L. [Hymenoptera: Apidae]) deaths. The virus and mite have a near global distribution, making it difficult to separate the effect of one from the other. The prevalence of two main DWV genotypes (DWV-A and DWV-B) has changed over time, leading to the possibility that the two strains elicit a different immune response by the host. Here, we use a honey bee population naïve to both the mite and the virus to investigate if honey bees show a different immunological response to DWV genotypes. We examined the expression of 19 immune genes by reverse transcription quantitative PCR (RT-qPCR) and analysed small RNA after experimental injection with DWV-A and DWV-B. We found no evidence that DWV-A and DWV-B elicit different immune responses in honey bees. RNA interference genes were up-regulated during DWV infection, and small interfering RNA (siRNA) responses were proportional to viral loads yet did not inhibit DWV accumulation. The siRNA response towards DWV was weaker than the response to another honey bee pathogen, Triatovirus nigereginacellulae (Picornavirales: Dicistroviridae; black queen cell virus), suggesting that DWV is comparatively better at evading host antiviral defences. There was no evidence for the production of virus-derived Piwi-interacting RNAs (piRNAs) in response to DWV. In contrast to previous studies, and in the absence of V. destructor, we found no evidence that DWV has an immunosuppressive effect. Overall, our results advance our understanding of the immunological effect that DWV in isolation elicits in honey bees.

The diverse roles of insulin signaling in insect behavior

In insects and other animals, nutrition-mediated behaviors are modulated by communication between the brain and peripheral systems, a process that relies heavily on the insulin/insulin-like growth factor signaling pathway (IIS). Previous studies have focused on the mechanistic and physiological functions of insulin-like peptides (ILPs) in critical developmental and adult milestones like pupation or vitellogenesis. Less work has detailed the mechanisms connecting ILPs to adult nutrient-mediated behaviors related to survival and reproductive success. Here we briefly review the range of behaviors linked to IIS in insects, from conserved regulation of feeding behavior to evolutionarily derived polyphenisms. Where possible, we incorporate information from Drosophila melanogaster and other model species to describe molecular and neural mechanisms that connect nutritional status to behavioral expression via IIS. We identify knowledge gaps which include the diverse functional roles of peripheral ILPs, how ILPs modulate neural function and behavior across the lifespan, and the lack of detailed mechanistic research in a broad range of taxa. Addressing these gaps would enable a better understanding of the evolution of this conserved and widely deployed tool kit pathway.

Differential Brain Expression Patterns of microRNAs Related to Olfactory Performance in Honey Bees (Apis mellifera)

MicroRNAs (miRNAs) play a vital role in the nerve regulation of honey bees (Apis mellifera). This study aims to investigate the differences in expression of miRNAs in a honey bee's brain for olfactory learning tasks and to explore their potential role in a honey bee's olfactory learning and memory. In this study, 12 day old honey bees with strong and weak olfactory performances were utilized to investigate the influence of miRNAs on olfactory learning behavior. The honey bee brains were dissected, and a small RNA-seq technique was used for high-throughput sequencing. The data analysis of the miRNA sequences revealed that 14 differentially expressed miRNAs (DEmiRNAs) between the two groups, strong (S) and weak (W), for olfactory performance in honey bees were identified, which included seven up-regulated and seven down-regulated. The qPCR verification results of the 14 miRNAs showed that four miRNAs (miR-184-3p, miR-276-3p, miR-87-3p, and miR-124-3p) were significantly associated with olfactory learning and memory. The target genes of these DEmiRNAs were subjected to the GO database annotation and KEGG pathway enrichment analyses. The functional annotation and pathway analysis showed that the neuroactive ligand-receptor interaction pathway, oxidative phosphorylation, biosynthesis of amino acids, pentose phosphate pathway, carbon metabolism, and terpenoid backbone biosynthesis may be a great important pathway related to olfactory learning and memory in honey bees. Our findings together further explained the relationship between olfactory performance and the brain function of honey bees at the molecular level and provides a basis for further study on miRNAs related to olfactory learning and memory in honey bees.

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.

The Expression of miRNAs Involved in Long-Term Memory Formation in the CNS of the Mollusk Helix lucorum

Mollusks are unique animals with a relatively simple central nervous system (CNS) containing giant neurons with identified functions. With such simple CNS, mollusks yet display sufficiently complex behavior, thus ideal for various studies of behavioral processes, including long-term memory (LTM) formation. For our research, we use the formation of the fear avoidance reflex in the terrestrial mollusk Helix lucorum as a learning model. We have shown previously that LTM formation in Helix requires epigenetic modifications of histones leading to both activation and inactivation of the specific genes. It is known that microRNAs (miRNAs) negatively regulate the expression of genes; however, the role of miRNAs in behavioral regulation has been poorly investigated. Currently, there is no miRNAs sequencing data being published on Helix lucorum, which makes it impossible to investigate the role of miRNAs in the memory formation of this mollusk. In this study, we have performed sequencing and comparative bioinformatics analysis of the miRNAs from the CNS of Helix lucorum. We have identified 95 different microRNAs, including microRNAs belonging to the MIR-9, MIR-10, MIR-22, MIR-124, MIR-137, and MIR-153 families, known to be involved in various CNS processes of vertebrates and other species, particularly, in the fear behavior and LTM. We have shown that in the CNS of Helix lucorum MIR-10 family (26 miRNAs) is the most representative one, including Hlu-Mir-10-S5-5p and Hlu-Mir-10-S9-5p as top hits. Moreover, we have shown the involvement of the MIR-10 family in LTM formation in Helix. The expression of 17 representatives of MIR-10 differentially changes during different periods of LTM consolidation in the CNS of Helix. In addition, using comparative analysis of microRNA expression upon learning in normal snails and snails with deficient learning abilities with dysfunction of the serotonergic system, we identified a number of microRNAs from several families, including MIR-10, which expression changes only in normal animals. The obtained data can be used for further fundamental and applied behavioral research.

Fluvalinate-Induced Changes in MicroRNA Expression Profile of Apis mellifera ligustica Brain Tissue

Fluvalinate is a widely used and relatively safe acaricide for honeybees, but it still has a negative impact on honeybee colonies. Such negative effects may be related to fluvalinate-induced brain nerve tissue damage, but the detailed molecular regulatory mechanism of this phenomenon is still poorly understood. In this study, we analyzed the miRNA expression profile changes in the brain tissue of Apis mellifera ligustica by miRNA sequencing after fluvalinate treatment. A total of 1,350 miRNAs were expressed in Apis mellifera ligustica brain tissue, of which only 180 were previously known miRNAs in honeybees. Among all known and novel miRNAs, 15 were differentially expressed between at least two of the four time periods before and after fluvalinate administration. Further analysis revealed five significantly enriched KEGG pathways of the differentially expressed miRNA (DEM) potential target genes, namely, "Hippo signaling pathway-fly," "Phototransduction-fly," "Apoptosis-fly," "Wnt signaling pathway," and "Dorso-ventral axis formation," which indicates that differentially expressed miRNA function may be related to cell apoptosis and memory impairment in the fluvalinate-treated Apis mellifera ligustica brain. Ame-miR-3477-5p, ame-miR-375-3p, and miR-281-x were identified as key miRNAs. Overall, our research provides new insights into the roles of miRNAs in brain tissue during the process of fluvalinate-induced Apis mellifera ligustica poisoning.

Integrated analysis of microRNA and mRNA expression profiles in Crassostrea gigas to reveal functional miRNA and miRNA-targets regulating shell pigmentation

MicroRNAs (miRNAs) regulate post-transcription gene expression by targeting genes and play crucial roles in diverse biological processes involving body color formation. However, miRNAs and miRNA-targets underlying shell color polymorphism remain largely unknown in mollusca. Using four shell colors full-sib families of the Pacific oyster Crassostrea gigas, we systematically identified miRNAs and miRNA-targets in the mantles, which organ could produce white, golden, black or partially pigmented shell. RNA sequencing and analysis identified a total of 53 known miRNA and 91 novel miRNAs, 47 of which were detected to differentially express among six pairwise groups. By integrating miRNA and mRNA expression profiles, a total of 870 genes were predicted as targets of differentially expressed miRNAs, mainly involving in biomineralization and pigmentation through functional enrichment. Furthermore, a total of four miRNAs and their target mRNAs were predicted to involve in synthesis of melanin, carotenoid or tetrapyrrole. Of them, lgi-miR-317 and its targets peroxidase and lncRNA TCONS_00951105 are implicated in acting as the competing endogenous RNA to regulate melanogenesis. Our studies revealed the systematic characterization of miRNAs profiles expressed in oyster mantle, which might facilitate understanding the intricate molecular regulation of shell color polymorphism and provide new insights into breeding research in oyster.

Comparative Identification of MicroRNAs in Apis cerana cerana Workers' Midguts in Responseto Nosema ceranae Invasion

Here, the expression profiles and differentially expressed miRNAs (DEmiRNAs) in the midguts of Apis cerana cerana workers at 7 d and 10 d post-inoculation (dpi) with N. ceranae were investigated via small RNA sequencing and bioinformatics. Five hundred and twenty nine (529) known miRNAs and 25 novel miRNAs were identified in this study, and the expression of 16 predicted miRNAs was confirmed by Stem-loop RT-PCR. A total of 14 DEmiRNAs were detected in the midgut at 7 dpi, including eight up-regulated and six down-regulated miRNAs, while 12 DEmiRNAs were observed in the midgut at 10 dpi, including nine up-regulated and three down-regulated ones. Additionally, five DEmiRNAs were shared, while nine and seven DEmiRNAs were specifically expressed in midguts at 7 dpi and 10 dpi. Gene ontology analysis suggested some DEmiRNAs and corresponding target mRNAs were involved in various functions including immune system processes and response to stimulus. KEGG pathway analysis shed light on the potential functions of some DEmiRNAs in regulating target mRNAs engaged in material and energy metabolisms, cellular immunity and the humoral immune system. Further investigation demonstrated a complex regulation network between DEmiRNAs and their target mRNAs, with miR-598-y, miR-252-y, miR-92-x and miR-3654-y at the center. Our results can facilitate future exploration of the regulatory roles of miRNAs in host responses to N. ceranae, and provide potential candidates for further investigation of the molecular mechanisms underlying eastern honeybee-microsporidian interactions.

A comparison of honeybee (Apis mellifera) queen, worker and drone larvae by RNA-Seq

Honeybees (Apis mellifera) have haplodiploid sex determination: males develop from unfertilized eggs and females develop from fertilized ones. The differences in larval food also determine the development of females. Here we compared the total somatic gene expression profiles of 2-day and 4-day-old drone, queen and worker larvae by RNA-Seq. The results from a co-expression network analysis on all expressed genes showed that 2-day-old drone and worker larvae were closer in gene expression profiles than 2-day-old queen larvae. This indicated that for young larvae (2-day-old) environmental factors such as larval diet have a greater effect on gene expression profiles than ploidy or sex determination. Drones had the most distinct gene expression profiles at the 4-day larval stage, suggesting that haploidy, or sex dramatically affects the gene expression of honeybee larvae. Drone larvae showed fewer differences in gene expression profiles at the 2-day and 4-day time points than the worker and queen larval comparisons (598 against 1190 and 1181), suggesting a different pattern of gene expression regulation during the larval development of haploid males compared to diploid females. This study indicates that early in development the queen caste has the most distinct gene expression profile, perhaps reflecting the very rapid growth and morphological specialization of this caste compared to workers and drones. Later in development the haploid male drones have the most distinct gene expression profile, perhaps reflecting the influence of ploidy or sex determination on gene expression.

Cognitive specialization for learning faces is associated with shifts in the brain transcriptome of a social wasp

The specialized ability to learn and recall individuals based on distinct facial features is known in only a few, large-brained social taxa. Social paper wasps in the genus Polistes are the only insects known to possess this form of cognitive specialization. We analyzed genome-wide brain gene expression during facial and pattern training for two species of paper wasps (P. fuscatus, which has face recognition, and P. metricus, which does not) using RNA sequencing. We identified 237 transcripts associated with face specialization in P. fuscatus, including some transcripts involved in neuronal signaling (serotonin receptor and tachykinin). Polistes metricus that learned faces (without specialized learning) and P. fuscatus in social interactions with familiar partners (from a previous study) showed distinct sets of brain differentially expressed transcripts. These data suggest face specialization in P. fuscatus is related to shifts in the brain transcriptome associated with genes distinct from those related to general visual learning and social interactions.

Large-scale transcriptome changes in the process of long-term visual memory formation in the bumblebee, Bombus terrestris

Many genes have been implicated in mechanisms of long-term memory formation, but there is still much to be learnt about how the genome dynamically responds, transcriptionally, during memory formation. In this study, we used high-throughput sequencing to examine how transcriptome profiles change during visual memory formation in the bumblebee (Bombus terrestris). Expression of fifty-five genes changed immediately after bees were trained to associate reward with a single coloured chip, and the upregulated genes were predominantly genes known to be involved in signal transduction. Changes in the expression of eighty-one genes were observed four hours after learning a new colour, and the majority of these were upregulated and related to transcription and translation, which suggests that the building of new proteins may be the predominant activity four hours after training. Several of the genes identified in this study (e.g. Rab10, Shank1 and Arhgap44) are interesting candidates for further investigation of the molecular mechanisms of long-term memory formation. Our data demonstrate the dynamic gene expression changes after associative colour learning and identify genes involved in each transcriptional wave, which will be useful for future studies of gene regulation in learning and long-term memory formation.

Solexa sequencing and custom microRNA chip reveal repertoire of microRNAs in mammary gland of bovine suffering from natural infectious mastitis

Identification of microRNAs (miRNAs), target genes and regulatory networks associated with innate immune and inflammatory responses and tissue damage is essential to elucidate the molecular and genetic mechanisms for resistance to mastitis. In this study, a combination of Solexa sequencing and custom miRNA chip approaches was used to profile the expression of miRNAs in bovine mammary gland at the late stage of natural infection with Staphylococcus aureus, a widespread mastitis pathogen. We found 383 loci corresponding to 277 known and 49 putative novel miRNAs, two potential mitrons and 266 differentially expressed miRNAs in the healthy and mastitic cows' mammary glands. Several interaction networks and regulators involved in mastitis susceptibility, such as ALCAM, COL1A1, APOP4, ITIH4, CRP and fibrinogen alpha (FGA), were highlighted. Significant down-regulation and location of bta-miR-26a, which targets FGA in the mastitic mammary glands, were validated using quantitative real-time PCR, in situ hybridization and dual-luciferase reporter assays. We propose that the observed miRNA variations in mammary glands of mastitic cows are related to the maintenance of immune and defense responses, cell proliferation and apoptosis, and tissue injury and healing during the late stage of infection. Furthermore, the effect of bta-miR-26a in mastitis, mediated at least in part by enhancing FGA expression, involves host defense, inflammation and tissue damage.

Genome-wide DNA methylation changes associated with olfactory learning and memory in Apis mellifera

The honeybee is a model organism for studying learning and memory formation and its underlying molecular mechanisms. While DNA methylation is well studied in caste differentiation, its role in learning and memory is not clear in honeybees. Here, we analyzed genome-wide DNA methylation changes during olfactory learning and memory process in A. mellifera using whole genome bisulfite sequencing (WGBS) method. A total of 853 significantly differentially methylated regions (DMRs) and 963 differentially methylated genes (DMGs) were identified. We discovered that 440 DMRs of 648 genes were hypermethylated and 274 DMRs of 336 genes were hypomethylated in trained group compared to untrained group. Of these DMGs, many are critical genes involved in learning and memory, such as Creb, GABA_BR and Ip3k, indicating extensive involvement of DNA methylation in honeybee olfactory learning and memory process. Furthermore, key enzymes for histone methylation, RNA editing and miRNA processing also showed methylation changes during this process, implying that DNA methylation can affect learning and memory of honeybees by regulating other epigenetic modification processes.

The microRNA ame-miR-279a regulates sucrose responsiveness of forager honey bees (Apis mellifera)

Increasing evidence demonstrates that microRNAs (miRNA) play an important role in the regulation of animal behaviours. Honey bees (Apis mellifera) are eusocial insects, with honey bee workers displaying age-dependent behavioural maturation. Many different miRNAs have been implicated in the change of behaviours in honey bees and ame-miR-279a was previously shown to be more highly expressed in nurse bee heads than in those of foragers. However, it was not clear whether this difference in expression was associated with age or task performance. Here we show that ame-miR-279a shows significantly higher expression in the brains of nurse bees relative to forager bees regardless of their ages, and that ame-miR-279a is primarily localized in the Kenyon cells of the mushroom body in both foragers and nurses. Overexpression of ame-miR-279a attenuates the sucrose responsiveness of foragers, while its absence enhances their sucrose responsiveness. Lastly, we determined that ame-miR-279a directly target the mRNA of Mblk-1. These findings suggest that ame-miR-279a plays important roles in regulating honey bee division of labour.

miR-12 and miR-124 contribute to defined early phases of long-lasting and transient memory

MicroRNAs (miRNAs) are important epigenetic regulators of mRNA translation implicated in long-lasting synaptic plasticity and long-term memory (LTM). Since recent findings demonstrated a role of epigenetic regulation of gene expression in early memory phases we investigated whether epigenetic regulation by miRNAs also contributes to early memory phases. We used the olfactory associative learning paradigm in honeybees and addressed the contribution of miRNAs depending on the conditioning strength. We selected miR-12, miR-124, and miR-125 that have been implicated in processes of neuronal plasticity and analysed their contribution to non-associative and associative learning using miRNA inhibitors. Blocking miR-12, miR-124, or miR125 neither affects gustatory sensitivity nor habituation nor sensitization. Blocking the function of miR-12 and miR-124 during and shortly after 3-trial conditioning impairs different early memory phases. Although different, the function of miR-12 and miR-124 is also required for early phases of transient memory that is induced by 1-trial conditioning. Blocking miR-125 has no effect on early memory independent of the conditioning strength. These findings demonstrate that distinct miRNAs contribute to early phases of both, transient memories as well as long-lasting memories.

High throughput sequencing of small RNAs reveals dynamic microRNAs expression of lipid metabolism during Camellia oleifera and C. meiocarpa seed natural drying

BACKGROUND

Camellia species are ancient oilseed plants with a history of cultivation over two thousand years. Prior to oil extraction, natural seed drying is often practiced, a process affecting fatty acid quality and quantity. MicroRNAs (miRNA) of lipid metabolism associated with camellia seed natural drying are unexplored. To obtain insight into the function of miRNAs in lipid metabolism during natural drying, Illumina sequencing of C. oleifera and C. meiocarpa small-RNA was conducted.

RESULTS

A total of 274 candidate miRNAs were identified and 3733 target unigenes were annotated by performing a BLASTX. Through integrated GO and KEGG function annotation, 23 miRNA regulating 131 target genes were identified as lipid metabolism, regulating fatty acid biosynthesis, accumulation and catabolism. We observed one, two, and four miRNAs of lipid metabolism which were specially expressed in C. Meiocarpa, C. oleifera, and the two species collectively, respectively. At 30% moisture contents, C. meiocarpa and C. oleifer produced nine and eight significant differentially expressed miRNAs, respectively, with high fatty acid synthesis and accumulation activities. Across the two species, 12 significant differentially expressed miRNAs were identified at the 50% moisture content.

CONCLUSIONS

Sequencing of small-RNA revealed the presence of 23 miRNAs regulating lipid metabolism in camellia seed during natural drying and permitted comparative miRNA profiles between C. Meiocarpa and C. oleifera. Furthermore, this study successfully identified the best drying environment at which the quantity and quality of lipid in camellia seed are at its maximum.

Age-dependent transcriptional and epigenomic responses to light exposure in the honey bee brain

Light is a powerful environmental stimulus of special importance in social honey bees that undergo a behavioral transition from in-hive to outdoor foraging duties. Our previous work has shown that light exposure induces structural neuronal plasticity in the mushroom bodies (MBs), a brain center implicated in processing inputs from sensory modalities. Here, we extended these analyses to the molecular level to unravel light-induced transcriptomic and epigenomic changes in the honey bee brain. We have compared gene expression in brain compartments of 1- and 7-day-old light-exposed honey bees with age-matched dark-kept individuals. We have found a number of differentially expressed genes (DEGs), both novel and conserved, including several genes with reported roles in neuronal plasticity. Most of the DEGs show age-related changes in the amplitude of light-induced expression and are likely to be both developmentally and environmentally regulated. Some of the DEGs are either known to be methylated or are implicated in epigenetic processes suggesting that responses to light exposure are at least partly regulated at the epigenome level. Consistent with this idea light alters the DNA methylation pattern of bgm, one of the DEGs affected by light exposure, and the expression of microRNA miR-932. This confirms the usefulness of our approach to identify candidate genes for neuronal plasticity and provides evidence for the role of epigenetic processes in driving the molecular responses to visual stimulation.

Profiling the proteomics in honeybee worker brains submitted to the proboscis extension reflex

The proboscis extension reflex (PER) is an unconditioned stimulus (US) widely used to access the ability of honeybees to correlate it with a conditioned stimulus (CS) during learning and memory acquisition. However, little is known about the biochemical/genetic changes in worker honeybee brains induced by the PER alone. The present investigation profiled the proteomic complement associated with the PER to further the understanding of the major molecular transformations in the honeybee brain during the execution of a US. In the present study, a quantitative shotgun proteomic approach was employed to assign the proteomic complement of the honeybee brain. The results were analyzed under the view of protein networking for different processes involved in PER behavior. In the brains of PER-stimulated individuals, the metabolism of cyclic/heterocyclic/aromatic compounds was activated in parallel with the metabolism of nitrogenated compounds, followed by the up-regulation of carbohydrate metabolism, the proteins involved with the anatomic and cytoskeleton; the down-regulation of the anatomic development and cell differentiation in other neurons also occurred.

SIGNIFICANCE

The assay of proboscis extension reflex is frequently used to access honeybees' ability to correlate an unconditioned stimulus with a conditioned stimulus (such as an odor) to establish learning and memory acquisition. The reflex behavior of proboscis extension was associated with various conditioned stimuli, and the biochemical/genetic evaluation of the changes occurring in honeybee brains under these conditions reflect the synergistic effects of both insect manipulations (training to answer to an unconditioned stimulus and training to respond to a conditioned stimulus). Little or no information is available regarding the biochemical changes stimulated by an unconditioned stimulus alone, such as the proboscis extension reflex. The present investigation characterizes the proteomic changes occurring in the brains of honeybee workers submitted to proboscis extension reflex. A series of metabolic and cellular processes were identified to be related to the reflex of an unconditioned stimulus. This strategy may be reproduced to further understand the processes of learning and memory acquisition in honeybees.

Dnmts and Tet target memory-associated genes after appetitive olfactory training in honey bees

DNA methylation and demethylation are epigenetic mechanisms involved in memory formation. In honey bees DNA methyltransferase (Dnmt) function is necessary for long-term memory to be stimulus specific (i.e. to reduce generalization). So far, however, it remains elusive which genes are targeted and what the time-course of DNA methylation is during memory formation. Here, we analyse how DNA methylation affects memory retention, gene expression, and differential methylation in stimulus-specific olfactory long-term memory formation. Out of 30 memory-associated genes investigated here, 9 were upregulated following Dnmt inhibition in trained bees. These included Dnmt3 suggesting a negative feedback loop for DNA methylation. Within these genes also the DNA methylation pattern changed during the first 24 hours after training. Interestingly, this was accompanied by sequential activation of the DNA methylation machinery (i.e. Dnmts and Tet). In sum, memory formation involves a temporally complex epigenetic regulation of memory-associated genes that facilitates stimulus specific long-term memory in the honey bee.

Function and evolution of microRNAs in eusocial Hymenoptera

The emergence of eusociality (“true sociality”) in several insect lineages represents one of the most successful evolutionary adaptations in the animal kingdom in terms of species richness and global biomass. In contrast to solitary insects, eusocial insects evolved a set of unique behavioral and physiological traits such as reproductive division of labor and cooperative brood care, which likely played a major role in their ecological success. The molecular mechanisms that support the social regulation of behavior in eusocial insects, and their evolution, are mostly unknown. The recent whole-genome sequencing of several eusocial insect species set the stage for deciphering the molecular and genetic bases of eusociality, and the possible evolutionary modifications that led to it. Studies of mRNA expression patterns in the brains of diverse eusocial insect species have indicated that specific social behavioral states of individual workers and queens are often associated with particular tissue-specific transcriptional profiles. Here, we discuss recent findings that highlight the role of non-coding microRNAs (miRNAs) in modulating traits associated with reproductive and behavioral divisions of labor in eusocial insects. We provide bioinformatic and phylogenetic data, which suggest that some Hymenoptera-specific miRNA may have contributed to the evolution of traits important for the evolution of eusociality in this group.

Identification and comparative analysis of differentially expressed miRNAs in leaves of two wheat (Triticum aestivum L.) genotypes during dehydration stress

BACKGROUND

MicroRNAs (miRNAs) play critical roles in the processes of plant growth and development, but little is known of their functions during dehydration stress in wheat. Moreover, the mechanisms by which miRNAs confer different levels of dehydration stress tolerance in different wheat genotypes are unclear.

RESULTS

We examined miRNA expressions in two different wheat genotypes, Hanxuan10, which is drought-tolerant, and Zhengyin1, which is drought-susceptible. Using a deep-sequencing method, we identified 367 differentially expressed miRNAs (including 46 conserved miRNAs and 321 novel miRNAs) and compared their expression levels in the two genotypes. Among them, 233 miRNAs were upregulated and 10 were downregulated in both wheat genotypes after dehydration stress. Interestingly, 13 miRNAs exhibited opposite patterns of expression in the two wheat genotypes, downregulation in the drought-tolerant cultivar and upregulation in the drought-susceptible cultivar. We also identified 111 miRNAs that were expressed predominantly in only one or the other genotype after dehydration stress. We verified the expression patterns of a number of representative miRNAs using qPCR analysis and northern blot, which produced results consistent with those of the deep-sequencing method. Moreover, monitoring the expression levels of 10 target genes by qPCR analysis revealed negative correlations with the levels of their corresponding miRNAs.

CONCLUSIONS

These results indicate that differentially expressed patterns of miRNAs between these two genotypes may play important roles in dehydration stress tolerance in wheat and may be a key factor in determining the levels of stress tolerance in different wheat genotypes.

Neuroligin-associated microRNA-932 targets actin and regulates memory in the honeybee

Increasing evidence suggests small non-coding RNAs (ncRNAs) such as microRNAs (miRNAs) control levels of mRNA expression during experience-related remodelling of the brain. Here we use an associative olfactory learning paradigm in the honeybee Apis mellifera to examine gene expression changes in the brain during memory formation. Brain transcriptome analysis reveals a general downregulation of protein-coding genes, including asparagine synthetase and actin, and upregulation of ncRNAs. miRNA-mRNA network predictions together with PCR validation suggest miRNAs including miR-210 and miR-932 target the downregulated protein-coding genes. Feeding cholesterol-conjugated antisense RNA to bees results in the inhibition of miR-210 and of miR-932. Loss of miR-932 impairs long-term memory formation, but not memory acquisition. Functional analyses show that miR-932 interacts with Act5C, providing evidence for direct regulation of actin expression by an miRNA. An activity-dependent increase in miR-932 expression may therefore control actin-related plasticity mechanisms and affect memory formation in the brain.