Honey bee PTEN--description, developmental knockdown, and tissue-specific expression of splice-variants correlated with alternative social phenotypes

Transcriptome analysis of Apis mellifera antennae reveals molecular divergence underlying the division of labour in worker bees

The olfactory system plays a fundamental role in mediating insect behaviour. Worker bees exhibit an age-dependent division of labour, performing discrete sets of behaviours throughout their lifespan. The behavioural states of bees rely on their sense of the environment and chemical communication via their olfactory system, the antennae. However, the olfactory adaptation mechanism of worker bees during their behavioural development remains unclear. In this study, we conducted a comprehensive and quantitative analysis of antennal gene expression in the Apis mellifera of newly emerged workers, nurses, foragers and defenders using RNA-seq. We found that the antenna tissues of honey bees continued developing after transformation from newly emerged workers to adults. Additionally, we identified differentially expressed genes associated with bee development and division of labour. We validated that major royal jelly protein genes are highly and specifically expressed in nurse honey bee workers. Furthermore, we identified and validated significant alternative splicing events correlated with the development and division of labour. These findings provide a comprehensive transcriptome profile and a new perspective on the molecular mechanisms that may underlie the worker honey bee division of labour.

Examining parent-of-origin effects on transcription and RNA methylation in mediating aggressive behavior in honey bees (Apis mellifera)

Conflict between genes inherited from the mother (matrigenes) and the father (patrigenes) is predicted to arise during social interactions among offspring if these genes are not evenly distributed among offspring genotypes. This intragenomic conflict drives parent-specific transcription patterns in offspring resulting from parent-specific epigenetic modifications. Previous tests of the kinship theory of intragenomic conflict in honey bees (Apis mellifera) provided evidence in support of theoretical predictions for variation in worker reproduction, which is associated with extreme variation in morphology and behavior. However, more subtle behaviors - such as aggression - have not been extensively studied. Additionally, the canonical epigenetic mark (DNA methylation) associated with parent-specific transcription in plant and mammalian model species does not appear to play the same role as in honey bees, and thus the molecular mechanisms underlying intragenomic conflict in this species is an open area of investigation. Here, we examined the role of intragenomic conflict in shaping aggression in honey bee workers through a reciprocal cross design and Oxford Nanopore direct RNA sequencing. We attempted to probe the underlying regulatory basis of this conflict through analyses of parent-specific RNA m6A and alternative splicing patterns. We report evidence that intragenomic conflict occurs in the context of honey bee aggression, with increased paternal and maternal allele-biased transcription in aggressive compared to non-aggressive bees, and higher paternal allele-biased transcription overall. However, we found no evidence to suggest that RNA m6A or alternative splicing mediate intragenomic conflict in this species.

Honey bee functional genomics using symbiont-mediated RNAi

Honey bees are indispensable pollinators and model organisms for studying social behavior, development and cognition. However, their eusociality makes it difficult to use standard forward genetic approaches to study gene function. Most functional genomics studies in bees currently utilize double-stranded RNA (dsRNA) injection or feeding to induce RNAi-mediated knockdown of a gene of interest. However, dsRNA injection is laborious and harmful, and dsRNA feeding is difficult to scale cheaply. Further, both methods require repeated dsRNA administration to ensure a continued RNAi response. To fill this gap, we engineered the bee gut bacterium Snodgrassella alvi to induce a sustained host RNA interference response that reduces expression of a targeted gene. To employ this functional genomics using engineered symbionts (FUGUES) procedure, a dsRNA expression plasmid is cloned in Escherichia coli using Golden Gate assembly and then transferred to S. alvi. Adult worker bees are then colonized with engineered S. alvi. Finally, gene knockdown is verified through qRT-PCR, and bee phenotypes of interest can be further assessed. Expression of targeted genes is reduced by as much as 50-75% throughout the entire bee body by 5 d after colonization. This protocol can be accomplished in 4 weeks by bee researchers with microbiology and molecular cloning skills. FUGUES currently offers a streamlined and scalable approach for studying the biology of honey bees. Engineering other microbial symbionts to influence their hosts in ways that are similar to those described in this protocol may prove useful for studying additional insect and animal species in the future.

Extent and complexity of RNA processing in honey bee queen and worker caste development

The distinct honeybee (Apis mellifera) worker and queen castes have become a model for the study of genomic mechanisms of phenotypic plasticity. Here we performed a nanopore-based direct RNA sequencing with exceptionally long reads to compare the mRNA transcripts between queen and workers at three points during their larval development. We found thousands of significantly differentially expressed transcript isoforms (DEIs) between queen and worker larvae. These DEIs were formatted by a flexible splicing system. We showed that poly(A) tails participated in this caste differentiation by negatively regulating the expression of DEIs. Hundreds of isoforms uniquely expressed in either queens or workers during their larval development, and isoforms were expressed at different points in queen and worker larval development demonstrating a dynamic relationship between isoform expression and developmental mechanisms. These findings show the full complexity of RNA processing and transcript expression in honey bee phenotypic plasticity.

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Honeybee caste differentiation has a complexity of RNA processing

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Isoforms differentially express between queens and workers during larval development

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Isoforms are formatted by a flexible alternative splicing system

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Poly(A) tails are negatively correlated with isoform expression

Glucosamine-6-phosphate N-acetyltransferase gene silencing by parental RNA interference in rice leaf folder, Cnaphalocrocis medinalis (Lepidoptera: Pyralidae)

Parental RNAi (pRNAi) is a response of RNA interference in which treated insect pests progenies showed a gene silencing phenotypes. pRNAi of CmGNA gene has been studied in Cnaphalocrocis medinalis via injection. Our results showed significant reduction in ovulation per female that was 26% and 35.26% in G1 and G2 generations, respectively. Significant reduction of hatched eggs per female were observed 23.53% and 45.26% as compared to control in G1–G2 generations, respectively. We also observed the significant variation in the sex ratio between female (40% and 53%) in G1–G2 generations, and in male (65%) in G1 generation as compared to control. Our results also demonstrated the significant larval mortality (63% and 55%) and pupal mortality (55% and 41%), and significant reduction of mRNA expression level in G1 and G2 generations. Our findings have confirmed that effectiveness of pRNAi induced silencing on the CmGNA target gene in G1–G2 generations of C. medinalis. These results suggested the potential role of pRNAi in insect pest resistance management strategies.

Tyramine and its receptor TYR1 linked behavior QTL to reproductive physiology in honey bee workers (Apis mellifera)

Honey bees (Apis mellifera) provide an excellent model for studying how complex social behavior evolves and is regulated. Social behavioral traits such as the division of labor have been mapped to specific genomic regions in quantitative trait locus (QTL) studies. However, relating genomic mapping to gene function and regulatory mechanism remains a big challenge for geneticists. In honey bee workers, division of labor is known to be regulated by reproductive physiology, but the genetic basis of this regulation remains unknown. In this case, QTL studies have identified tyramine receptor 1 (TYR1) as a candidate gene in region pln2, which is associated with multiple worker social traits and reproductive anatomy. Tyramine (TA), a neurotransmitter, regulates physiology and behavior in diverse insect species including honey bees. Here, we examine directly the effects of TYR1 and TA on worker reproductive physiology, including ovariole number, ovary function and the production of vitellogenin (VG, an egg yolk precursor). First, we used a pharmacology approach to demonstrate that TA affects ovariole number during worker larval development and increases ovary maturation during the adult stage. Second, we used a gene knockdown approach to show that TYR1 regulates vg transcription in adult workers. Finally, we estimated correlations in gene expression and propose that TYR1 may regulate vg transcription by coordinating hormonal and nutritional signals. Taken together, our results suggest TYR1 and TA play important roles in regulating worker reproductive physiology, which in turn regulates social behavior. Our study exemplifies a successful forward-genetic strategy going from QTL mapping to gene function.

Ferritin RNA interference inhibits the formation of iron granules in the trophocytes of worker honey bees (Apis mellifera)

Iron granules containing superparamagnetic magnetite act as magnetoreceptor for magnetoreception in honey bees. Biomineralization of iron granules occurs in the iron deposition vesicles of trophocytes and requires the participation of actin, myosin, ferritin2, and ATP synthase. The mechanism of magnetoreception in honey bees can be explored by suppressing the formation of iron granules. Toward this goal, we injected double-stranded RNA of ferritin2 and ferritin1 into newly emerged worker honey bees to knock down these genes via RNA interference. We confirmed that mRNA and protein production of the ferritins was inhibited, leading to immature iron granules. Downregulating ferritin2 and ferritin1, moreover, leads to different deposition morphology of 7.5-nm diameter iron particles, indicating that the two genes play different roles in the formation of iron granules in worker honey bees.

Horizons in the evolution of aging

Between the 1930s and 50s, evolutionary biologists developed a successful theory of why organisms age, firmly rooted in population genetic principles. By the 1980s the evolution of aging had a secure experimental basis. Since the force of selection declines with age, aging evolves due to mutation accumulation or a benefit to fitness early in life. Here we review major insights and challenges that have emerged over the last 35 years: selection does not always necessarily decline with age; higher extrinsic (i.e., environmentally caused) mortality does not always accelerate aging; conserved pathways control aging rate; senescence patterns are more diverse than previously thought; aging is not universal; trade-offs involving lifespan can be 'broken'; aging might be 'druggable'; and human life expectancy continues to rise but compressing late-life morbidity remains a pressing challenge.

Differential expression of a fructose receptor gene in honey bee workers according to age and behavioral role

Honey bee (Apis mellifera) workers contribute to the maintenance of colonies in various ways. The primary functions of workers are divided into two types depending on age: young workers (nurses) primarily engage in such behaviors as cleaning and food handling within the hive, whereas older workers (foragers) acquire floral nutrients beyond the colony. Concomitant with this age-dependent change in activity, physiological changes occur in the tissues and organs of workers. Nurses supply younger larvae with honey containing high levels of glucose and supply older larvae with honey containing high levels of fructose. Given that nurses must determine both the concentration and type of sugar used in honey, gustatory receptors (Gr) expressed in the chemosensory organs likely play a role in distinguishing between sugars. Glucose is recognized by Gr1 in honey bees (AmGr1); however, it remains unclear which Gr are responsible for fructose recognition. This study aimed to identify fructose receptors in honey bees and reported that AmGr3, when transiently expressed in Xenopus oocytes, responded only to fructose, and to no other sugars. We analyzed expression levels of AmGr3 to identify which tissues and organs of workers are involved in fructose recognition and determined that expression of AmGr3 was particularly high in the antennae and legs of nurses. Our results suggest that nurses use their antennae and legs to recognize fructose, and that AmGr3 functions as an accurate nutrient sensor used to maintain food quality in honey bee hives.

Negligible uptake and transfer of diet-derived pollen microRNAs in adult honey bees

The putative transfer and gene regulatory activities of diet-derived miRNAs in ingesting animals are still debated. Importantly, no study to date has fully examined the role of dietary uptake of miRNA in the honey bee, a critical pollinator in both agricultural and natural ecosystems. After controlled pollen feeding experiments in adult honey bees, we observed that midguts demonstrated robust increases in plant miRNAs after pollen ingestion. However, we found no evidence of biologically relevant delivery of these molecules to proximal or distal tissues of recipient honey bees. Our results, therefore, support the premise that pollen miRNAs ingested as part of a typical diet are not robustly transferred across barrier epithelia of adult honey bees under normal conditions. Key future questions include whether other small RNA species in honey bee diets behave similarly and whether more specialized and specific delivery mechanisms exist for more efficient transport, particularly in the context of stressed barrier epithelia.

DNA base modifications in honey bee and fruit fly genomes suggest an active demethylation machinery with species- and tissue-specific turnover rates

Well-known epigenetic DNA modifications in mammals include the addition of a methyl group and a hydroxyl group to cytosine, resulting in 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) respectively. In contrast, the abundance and the functional implications of these modifications in invertebrate model organisms such as the honey bee (Apis mellifera) and the fruit fly (Drosophila melanogaster) are not well understood. Here we show that both adult honey bees and fruit flies contain 5mC and also 5hmC. Using a highly sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) technique, we quantified 5mC and 5hmC in different tissues of adult honey bee worker castes and in adult fruit flies. A comparison of our data with reports from human and mouse shed light on notable differences in 5mC and 5hmC levels between tissues and species.

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Reporting cytosine modifications in uncharacterized tissues, phenotypes and species.

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Quantification of 5mC and 5hmC suggests species-specific roles and turnover.​

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Low levels of 5hmC relative to 5mC and cytosine in honey bees compared to mammals.

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Honey bee abdominal tissues are richer in5hmC than the brain.

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We found a higher 5hmC to 5mC ratio in fruit flies as compared to the honey bee.

Developing an in vivo toxicity assay for RNAi risk assessment in honey bees, Apis mellifera L

Maize plants expressing dsRNA for the management of Diabrotica virgifera virgifera are likely to be commercially available by the end of this decade. Honey bees, Apis mellifera, can potentially be exposed to pollen from transformed maize expressing dsRNA. Consequently, evaluation of the biological impacts of RNAi in honey bees is a fundamental component for ecological risk assessment. The insecticidal activity of a known lethal dsRNA target for D. v. virgifera, the vATPase subunit A, was evaluated in larval and adult honey bees. Activity of both D. v. virgifera (Dvv)- and A. mellifera (Am)-specific dsRNA was tested by dietary exposure to dsRNA. Larval development, survival, adult eclosion, adult life span and relative gene expression were evaluated. The results of these tests indicated that Dvv vATPase-A dsRNA has limited effects on larval and adult honey bee survival. Importantly, no effects were observed upon exposure of Am vATPase-A dsRNA suggesting that the lack of response involves factors other than sequence specificity. The results from this study provide guidance for future RNAi risk analyses and for the development of a risk assessment framework that incorporates similar hazard assessments.

RNAi and Antiviral Defense in the Honey Bee

Honey bees play an important agricultural and ecological role as pollinators of numerous agricultural crops and other plant species. Therefore, investigating the factors associated with high annual losses of honey bee colonies in the US is an important and active area of research. Pathogen incidence and abundance correlate with Colony Collapse Disorder- (CCD-) affected colonies in the US and colony losses in the US and in some European countries. Honey bees are readily infected by single-stranded positive sense RNA viruses. Largely dependent on the host immune response, virus infections can either remain asymptomatic or result in deformities, paralysis, or death of adults or larvae. RNA interference (RNAi) is an important antiviral defense mechanism in insects, including honey bees. Herein, we review the role of RNAi in honey bee antiviral defense and highlight some parallels between insect and mammalian immune systems. A more thorough understanding of the role of pathogens on honey bee health and the immune mechanisms bees utilize to combat infectious agents may lead to the development of strategies that enhance honey bee health and result in the discovery of additional mechanisms of immunity in metazoans.

Changes in the Gene Expression Profiles of the Hypopharyngeal Gland of Worker Honeybees in Association with Worker Behavior and Hormonal Factors

The hypopharyngeal glands (HPGs) of worker honeybees undergo physiological changes along with the age-dependent role change from nursing to foraging: nurse bee HPGs secrete mainly major royal jelly proteins, whereas forager HPGs secrete mainly α-glucosidase III, which converts the sucrose in the nectar into glucose and fructose. We previously identified two other genes, Apis mellifera buffy (Ambuffy) and Apis mellifera matrix metalloproteinase 1 (AmMMP1), with enriched expression in nurse bee and forager HPGs, respectively. In the present study, to clarify the molecular mechanisms that coordinate HPG physiology with worker behavior, we first analyzed whether Ambuffy, AmMMP1, mrjp2 (a gene encoding one of major royal jelly protein isoforms), and Hbg3 (a gene encoding α-glucosidase III) expression, is associated with worker behavior in 'single-cohort colonies' where workers of almost the same age perform different tasks. Expression of these genes correlated with the worker’s role, while controlling for age, indicating their regulation associated with the worker’s behavior. Associated gene expression suggested the possible involvement of some hormonal factors in its regulation. We therefore examined the relationship between ecdysone- and juvenile hormone (JH)-signaling, and the expression profiles of these ‘indicator’ genes (nurse bee HPG-selective genes: mrjp2 and Ambuffy, and forager HPG-selective genes: Hbg3 and AmMMP1). Expression of both ecdysone-regulated genes (ecdysone receptor, mushroom body large type Kenyon cell specific protein-1, and E74) and JH-regulated genes (Methoprene tolerant and Krüppel homolog 1) was higher in the forager HPGs than in the nurse bee HPGs, suggesting the possible roles of ecdysone- and JH-regulated genes in worker HPGs. Furthermore, 20-hydroxyecdysone-treatment repressed both nurse bee- and forager-selective gene expression, whereas methoprene-treatment enhanced the expression of forager-selective genes and repressed nurse bee-selective genes in the HPGs. Our findings suggest that both ecdysone- and JH-signaling cooperatively regulate the physiological state of the HPGs in association with the worker’s behavior.

Epigenetic variation in the Egfr gene generates quantitative variation in a complex trait in ants

Complex quantitative traits, like size and behaviour, are a pervasive feature of natural populations. Quantitative trait variation is the product of both genetic and environmental factors, yet little is known about the mechanisms through which their interaction generates this variation. Epigenetic processes, such as DNA methylation, can mediate gene-by-environment interactions during development to generate discrete phenotypic variation. We therefore investigated the developmental role of DNA methylation in generating continuous size variation of workers in an ant colony, a key trait associated with division of labour. Here we show that, in the carpenter ant Camponotus floridanus, global (genome-wide) DNA methylation indirectly regulates quantitative methylation of the conserved cell-signalling gene Epidermal growth factor receptor to generate continuous size variation of workers. DNA methylation can therefore generate quantitative variation in a complex trait by quantitatively regulating the transcription of a gene. This mechanism, alongside genetic variation, may determine the phenotypic possibilities of loci for generating quantitative trait variation in natural populations.

Differential involvement of glutamate-gated chloride channel splice variants in the olfactory memory processes of the honeybee Apis mellifera

Glutamate-gated chloride channels (GluCl) belong to the cys-loop ligand-gated ion channel superfamily and their expression had been described in several invertebrate nervous systems. In the honeybee, a unique gene amel_glucl encodes two alternatively spliced subunits, Amel_GluCl A and Amel_GluCl B. The expression and differential localization of those variants in the honeybee brain had been previously reported. Here we characterized the involvement of each variant in olfactory learning and memory processes, using specific small-interfering RNA (siRNA) targeting each variant. Firstly, the efficacy of the two siRNAs to decrease their targets' expression was tested, both at mRNA and protein levels. The two proteins showed a decrease of their respective expression 24h after injection. Secondly, each siRNA was injected into the brain to test whether or not it affected olfactory memory by using a classical paradigm of conditioning the proboscis extension reflex (PER). Amel_GluCl A was found to be involved only in retrieval of 1-nonanol, whereas Amel_GluCl B was involved in the PER response to 2-hexanol used as a conditioned stimulus or as new odorant. Here for the first time, a differential behavioral involvement of two highly similar GluCl subunits has been characterized in an invertebrate species.

Nutritional models of foetal programming and nutrigenomic and epigenomic dysregulations of fatty acid metabolism in the liver and heart

Barker's concept of 'foetal programming' proposes that intrauterine growth restriction (IUGR) predicts complex metabolic diseases through relationships that may be further modified by the postnatal environment. Dietary restriction and deficit in methyl donors, folate, vitamin B12, and choline are used as experimental conditions of foetal programming as they lead to IUGR and decreased birth weight. Overfeeding and deficit in methyl donors increase central fat mass and lead to a dramatic increase of plasma free fatty acids (FFA) in offspring. Conversely, supplementing the mothers under protein restriction with folic acid reverses metabolic and epigenomic phenotypes of offspring. High-fat diet or methyl donor deficiency (MDD) during pregnancy and lactation produce liver steatosis and myocardium hypertrophy that result from increased import of FFA and impaired fatty acid β-oxidation, respectively. The underlying molecular mechanisms show dysregulations related with similar decreased expression and activity of sirtuin 1 (SIRT1) and hyperacetylation of peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α). High-fat diet and overfeeding impair AMPK-dependent phosphorylation of PGC-1α, while MDD decreases PGC-1α methylation through decreased expression of PRMT1 and cellular level of S-adenosyl methionine. The visceral manifestations of metabolic syndrome are under the influence of endoplasmic reticulum (ER) stress in overnourished animal models. These mechanisms should also deserve attention in the foetal programming effects of MDD since vitamin B12 influences ER stress through impaired SIRT1 deacetylation of HSF1. Taken together, similarities and synergies of high-fat diet and MDD suggest, therefore, considering their consecutive or contemporary influence in the mechanisms of complex metabolic diseases.

Insulin-like peptides (AmILP1 and AmILP2) differentially affect female caste development in the honey bee (Apis mellifera L.)

The food a honey bee female larva receives determines whether she develops into a large long-lived fertile queen or a short-lived sterile worker. Through well-established nutrient-sensing and growth-promoting functions in metazoans, the insulin/insulin-like growth factor 1 signaling (IIS) pathway has become a focal topic in investigations on how differences in food environment can be translated into internal signals responsible for queen-worker determination. However, low expression levels of two insulin receptors (AmInRs) in honey bee larvae and the failure of one AmInR to influence caste differentiation are in potential conflict with such a classical growth-promoting role of IIS in queen-worker development. In view of such an apparent contradiction, and the fact that binding partners and affinities of these two AmInRs have not been worked out, we performed a functional study on insulin-like peptide genes (AmILP1 and AmILP2) in honey bee larvae by using a double-stranded RNA (dsRNA)-mediated gene knockdown approach. We found that juvenile hormone (JH) levels were diminished by AmILP1 dsRNA treatment, while the AmILP2 knockdown caused a reduction in ovary size. Blood sugar titers were not significantly affected by the treatments. From these results we conclude that AmILP2 transcript levels may influence specific organ development, such as the ovary and body mass, while more general traits of caste differentiation, such as mandibles, may require additional regulators. In addition, JH production may be regulated by AmILP1 expressed locally in the brain, similar to the function of certain ILPs in Drosophila.

Non-Target Effects of Green Fluorescent Protein (GFP)-Derived Double-Stranded RNA (dsRNA-GFP) Used in Honey Bee RNA Interference (RNAi) Assays

RNA interference has been frequently applied to modulate gene function in organisms where the production and maintenance of mutants is challenging, as in our model of study, the honey bee, Apis mellifera. A green fluorescent protein (GFP)-derived double-stranded RNA (dsRNA-GFP) is currently commonly used as control in honey bee RNAi experiments, since its gene does not exist in the A. mellifera genome. Although dsRNA-GFP is not expected to trigger RNAi responses in treated bees, undesirable effects on gene expression, pigmentation or developmental timing are often observed. Here, we performed three independent experiments using microarrays to examine the effect of dsRNA-GFP treatment (introduced by feeding) on global gene expression patterns in developing worker bees. Our data revealed that the expression of nearly 1,400 genes was altered in response to dsRNA-GFP, representing around 10% of known honey bee genes. Expression changes appear to be the result of both direct off-target effects and indirect downstream secondary effects; indeed, there were several instances of sequence similarity between putative siRNAs generated from the dsRNA-GFP construct and genes whose expression levels were altered. In general, the affected genes are involved in important developmental and metabolic processes associated with RNA processing and transport, hormone metabolism, immunity, response to external stimulus and to stress. These results suggest that multiple dsRNA controls should be employed in RNAi studies in honey bees. Furthermore, any RNAi studies involving these genes affected by dsRNA-GFP in our studies should use a different dsRNA control.

Expression and localization of glutamate-gated chloride channel variants in honeybee brain (Apis mellifera)

Due to its specificity to invertebrate species, glutamate-gated chloride channels (GluCls) are the target sites of antiparasitic agents and insecticides, e.g. ivermectin and fipronil, respectively. In nematodes and insects, the GluCls diversity is broadened by alternative splicing. GluCl subunits have been characterized according to their sensitivity to drugs, and to their anatomical localization. In the honeybee, the GluCl gene can encode different alpha subunits due to alternative splicing of exon 3. We examined mRNA expression in brain parts and we confirmed the existence of two GluCl variants with RT-PCR, Amel_GluCl A and Amel_GluCl B. Surprisingly, a mixed isoform not yet described in insect was obtained, we called it Amel_GluCl C. We determined precise immunolocalization of peptide sequence corresponding to Amel_GluCl A and Amel_GluCl B in the honeybee brain. Amel_GluCl A is mainly located in neuropils, whereas Amel_GluCl B is mostly expressed in cell bodies. Both proteins can also be co-localized. According to their anatomical localization, different GluCl variants might be involved in olfactory and visual modalities and in learning and memory.

PtdIns(4,5)P2-mediated cell signaling: emerging principles and PTEN as a paradigm for regulatory mechanism

PtdIns(4,5)P2 (phosphatidylinositol 4,5-bisphosphate) is a relatively common anionic lipid that regulates cellular functions by multiple mechanisms. Hydrolysis of PtdIns(4,5)P2 by phospholipase C yields inositol trisphosphate and diacylglycerol. Phosphorylation by phosphoinositide 3-kinase yields PtdIns(3,4,5)P3, which is a potent signal for survival and proliferation. Also, PtdIns(4,5)P2 can bind directly to integral and peripheral membrane proteins. As an example of regulation by PtdIns(4,5)P2, we discuss phosphatase and tensin homologue deleted on chromosome 10 (PTEN) in detail. PTEN is an important tumor suppressor and hydrolyzes PtdIns(3,4,5)P3. PtdIns(4,5)P2 enhances PTEN association with the plasma membrane and activates its phosphatase activity. This is a critical regulatory mechanism, but a detailed description of this process from a structural point of view is lacking. The disordered lipid bilayer environment hinders structural determinations of membrane-bound PTEN. A new method to analyze membrane-bound protein measures neutron reflectivity for proteins bound to tethered phospholipid membranes. These methods allow determination of the orientation and shape of membrane-bound proteins. In combination with molecular dynamics simulations, these studies will provide crucial structural information that can serve as a foundation for our understanding of PTEN regulation in normal and pathological processes.

Gustatory perception and fat body energy metabolism are jointly affected by vitellogenin and juvenile hormone in honey bees

Honey bees (Apis mellifera) provide a system for studying social and food-related behavior. A caste of workers performs age-related tasks: young bees (nurses) usually feed the brood and other adult bees inside the nest, while older bees (foragers) forage outside for pollen, a protein/lipid source, or nectar, a carbohydrate source. The workers' transition from nursing to foraging and their foraging preferences correlate with differences in gustatory perception, metabolic gene expression, and endocrine physiology including the endocrine factors vitellogenin (Vg) and juvenile hormone (JH). However, the understanding of connections among social behavior, energy metabolism, and endocrine factors is incomplete. We used RNA interference (RNAi) to perturb the gene network of Vg and JH to learn more about these connections through effects on gustation, gene transcripts, and physiology. The RNAi perturbation was achieved by single and double knockdown of the genes ultraspiracle (usp) and vg, which encode a putative JH receptor and Vg, respectively. The double knockdown enhanced gustatory perception and elevated hemolymph glucose, trehalose, and JH. We also observed transcriptional responses in insulin like peptide 1 (ilp1), the adipokinetic hormone receptor (AKHR), and cGMP-dependent protein kinase (PKG, or "foraging gene" Amfor). Our study demonstrates that the Vg-JH regulatory module controls changes in carbohydrate metabolism, but not lipid metabolism, when worker bees shift from nursing to foraging. The module is also placed upstream of ilp1, AKHR, and PKG for the first time. As insulin, adipokinetic hormone (AKH), and PKG pathways influence metabolism and gustation in many animals, we propose that honey bees have conserved pathways in carbohydrate metabolism and conserved connections between energy metabolism and gustatory perception. Thus, perhaps the bee can make general contributions to the understanding of food-related behavior and metabolic disorders.

Membrane association of the PTEN tumor suppressor: molecular details of the protein-membrane complex from SPR binding studies and neutron reflection

The structure and function of the PTEN phosphatase is investigated by studying its membrane affinity and localization on in-plane fluid, thermally disordered synthetic membrane models. The membrane association of the protein depends strongly on membrane composition, where phosphatidylserine (PS) and phosphatidylinositol diphosphate (PI(4,5)P₂) act pronouncedly synergistic in pulling the enzyme to the membrane surface. The equilibrium dissociation constants for the binding of wild type (wt) PTEN to PS and PI(4,5)P₂ were determined to be K_d∼12 µM and 0.4 µM, respectively, and K_d∼50 nM if both lipids are present. Membrane affinities depend critically on membrane fluidity, which suggests multiple binding sites on the protein for PI(4,5)P₂. The PTEN mutations C124S and H93R show binding affinities that deviate strongly from those measured for the wt protein. Both mutants bind PS more strongly than wt PTEN. While C124S PTEN has at least the same affinity to PI(4,5)P₂ and an increased apparent affinity to PI(3,4,5)P₃, due to its lack of catalytic activity, H93R PTEN shows a decreased affinity to PI(4,5)P₂ and no synergy in its binding with PS and PI(4,5)P₂. Neutron reflection measurements show that the PTEN phosphatase “scoots" along the membrane surface (penetration <5 Å) but binds the membrane tightly with its two major domains, the C2 and phosphatase domains, as suggested by the crystal structure. The regulatory C-terminal tail is most likely displaced from the membrane and organized on the far side of the protein, ∼60 Å away from the bilayer surface, in a rather compact structure. The combination of binding studies and neutron reflection allows us to distinguish between PTEN mutant proteins and ultimately may identify the structural features required for membrane binding and activation of PTEN.

A conceptual model for the origin of worker behaviour and adaptation of eusociality

In a model based on the wasp family Vespidae, the origin of worker behaviour, which constitutes the eusociality threshold, is not based on relatedness, therefore the origin of eusociality does not depend on inclusive fitness, and workers at the eusociality threshold are not altruistic. Instead, incipient workers and queens behave selfishly and are subject to direct natural selection. Beyond the eusociality threshold, relatedness enables 'soft inheritance' as the framework for initial adaptations of eusociality. At the threshold of irreversibility, queen and worker castes become fixed in advanced eusociality. Transitions from solitary to facultative, facultative to primitive, and primitive to advanced eusociality occur via exaptation, phenotypic accommodation and genetic assimilation. Multilevel selection characterizes the solitary to highly eusocial transition, but components of multilevel selection vary across levels of eusociality. Roles of behavioural flexibility and developmental plasticity in the evolutionary process equal or exceed those of genotype.

Development of an RNA interference tool, characterization of its target, and an ecological test of caste differentiation in the eusocial wasp polistes

Recent advancements in genomics provide new tools for evolutionary ecological research. The paper wasp genus Polistes is a model for social insect evolution and behavioral ecology. We developed RNA interference (RNAi)-mediated gene silencing to explore proposed connections between expression of hexameric storage proteins and worker vs. gyne (potential future foundress) castes in naturally-founded colonies of P. metricus. We extended four fragments of putative hexamerin-encoding P. metricus transcripts acquired from a previous study and fully sequenced a gene that encodes Hexamerin 2, one of two proposed hexameric storage proteins of P. metricus. MALDI-TOF/TOF, LC-MSMS, deglycosylation, and detection of phosphorylation assays showed that the two putative hexamerins diverge in peptide sequence and biochemistry. We targeted the hexamerin 2 gene in 5(th) (last)-instar larvae by feeding RNAi-inducing double-stranded hexamerin 2 RNA directly to larvae in naturally-founded colonies in the field. Larval development and adult traits were not significantly altered in hexamerin 2 knockdowns, but there were suggestive trends toward increased developmental time and less developed ovaries, which are gyne characteristics. By demonstrating how data acquisition from 454/Roche pyrosequencing can be combined with biochemical and proteomics assays and how RNAi can be deployed successfully in field experiments on Polistes, our results pave the way for functional genomic research that can contribute significantly to learning the interactions of environment, development, and the roles they play in paper wasp evolution and behavioral ecology.