Shuttling between species for pathways of lifespan regulation: A central role for the vitellogenin gene family?

New insight into molecular mechanisms underlying division of labor in honeybees

Honeybees are highly organized eusocial insects displaying a distinct division of labor. Juvenile hormone (JH) has long been hypothesized to be the major driver of behavioral transitions. However, more and more experiments in recent years have suggested that the role of this hormone is not as fundamental as hypothesized. Vitellogenin, a common egg yolk precursor protein, seems to be the major regulator of division of labor in honeybees, in connection with nutrition and the neurohormone and transmitter octopamine. Here, we review the role of vitellogenin in controlling honeybee division of labor and its modulation by JH, nutrition, and the catecholamine octopamine.

Single-cell transcriptomic analysis of honeybee brains identifies vitellogenin as caste differentiation-related factor

The honeybee (Apis mellifera) is a well-known eusocial insect. In honeybee colonies, thousands of sterile workers, including nurse and forager bees, perform various tasks within or outside the hive, respectively. The queen is the only fertile female and is responsible for reproduction. The queen and workers share similar genomes but occupy different caste statuses. We established single-cell transcriptomic atlases of brains from queens and worker subcastes and identified five major cell groups: Kenyon, optic lobe, olfactory projection, glial, and hemocyte cells. By dividing Kenyon and glial cells into multiple subtypes based on credible markers, we observed that vitellogenin (vg) was highly expressed in specific glial-cell subtypes in brains of queens. Knockdown of vg at the early larval stage significantly suppressed the development into adult queens. We demonstrate vg expression as a "molecular signature" for the queen caste and suggest involvement of vg in regulating caste differentiation.

•

scRNA-seq revealed distinct gene expression in the brains of queens and workers

•

Vitellogenin (vg) may represent a "molecular signature" of the queen caste

•

Knockdown of vg at early larval stage suppressed development into adult queens

•

Vg may be involved in regulating caste differentiation

Double-stranded RNA Oral Delivery Methods to Induce RNA Interference in Phloem and Plant-sap-feeding Hemipteran Insects

Phloem and plant sap feeding insects invade the integrity of crops and fruits to retrieve nutrients, in the process damaging food crops. Hemipteran insects account for a number of economically substantial pests of plants that cause damage to crops by feeding on phloem sap. The brown marmorated stink bug (BMSB), Halyomorpha halys (Heteroptera: Pentatomidae) and the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae) are hemipteran insect pests introduced in North America, where they are an invasive agricultural pest of high-value specialty, row, and staple crops and citrus fruits, as well as a nuisance pest when they aggregate indoors. Insecticide resistance in many species has led to the development of alternate methods of pest management strategies. Double-stranded RNA (dsRNA)-mediated RNA interference (RNAi) is a gene silencing mechanism for functional genomic studies that has potential applications as a tool for the management of insect pests. Exogenously synthesized dsRNA or small interfering RNA (siRNA) can trigger highly efficient gene silencing through the degradation of endogenous RNA, which is homologous to that presented. Effective and environmental use of RNAi as molecular biopesticides for biocontrol of hemipteran insects requires the in vivo delivery of dsRNAs through feeding. Here we demonstrate methods for delivery of dsRNA to insects: loading of dsRNA into green beans by immersion, and absorbing of gene-specific dsRNA with oral delivery through ingestion. We have also outlined non-transgenic plant delivery approaches using foliar sprays, root drench, trunk injections as well as clay granules, all of which may be essential for sustained release of dsRNA. Efficient delivery by orally ingested dsRNA was confirmed as an effective dosage to induce a significant decrease in expression of targeted genes, such as juvenile hormone acid O-methyltransferase (JHAMT) and vitellogenin (Vg). These innovative methods represent strategies for delivery of dsRNA to use in crop protection and overcome environmental challenges for pest management.

Mitigating effects of pollen during paraquat exposure on gene expression and pathogen prevalence in Apis mellifera L

Honey bee (Apis mellifera L.) populations have been experiencing notable mortality in Europe and North America. No single cause has been identified for these dramatic losses, but rather multiple interacting factors are likely responsible (such as pesticides, malnutrition, habitat loss, and pathogens). Paraquat is one of the most widely used non-selective herbicides, especially in developing countries. This herbicide is considered slightly toxic to honey bees, despite being reported as a highly effective inducer of oxidative stress in a wide range of living systems. Here, we test the effects of paraquat on the expression of detoxification and antioxidant-related genes, as well as on the dynamics of pathogen titers. Moreover, we tested the effects of pollen as mitigating factor to paraquat exposure. Our results show significant changes in the expression of several antioxidant-related and detoxification-related genes in the presence of paraquat, as well as an increase of pathogens titers. Finally, we demonstrate a mitigating effect of pollen through the up-regulation of specific genes and improvement of survival of bees exposed to paraquat. The presence of pollen in the diet was also correlated with a reduced prevalence of Nosema and viral pathogens. We discuss the importance of honey bees' nutrition, especially the availability of pollen, on colony losses chronically reported in the USA and Europe.

Endocrine uncoupling of the trade-off between reproduction and somatic maintenance in eusocial insects

In most animals reproduction trades off with somatic maintenance and survival. Physiologically this trade-off is mediated by hormones with opposite effects on reproduction and maintenance. In many insects, this regulation is achieved by an endocrine network that integrates insulin-like/IGF-1 signaling (IIS), juvenile hormone (JH), and the yolk precursor vitellogenin (Vg) (or, more generally, yolk proteins [YPs]). Downregulation of this network promotes maintenance and survival at the expense of reproduction. Remarkably, however, queens of highly eusocial social insects exhibit both enormous reproductive output and longevity, thus escaping the trade-off. Here we argue - based on recent evidence - that the proximate reason for why eusocial insects can decouple this trade-off is that they have evolved a different 'wiring' of the IIS-JH-Vg/YP circuit.

Long-chain acyl-CoA synthetase 2 knockdown leads to decreased fatty acid oxidation in fat body and reduced reproductive capacity in the insect Rhodnius prolixus

Long-chain acyl-CoA esters are important intermediates in lipid metabolism and are synthesized from fatty acids by long-chain acyl-CoA synthetases (ACSL). The hematophagous insect Rhodnius prolixus, a vector of Chagas' disease, produces glycerolipids in the midgut after a blood meal, which are stored as triacylglycerol in the fat body and eggs. We identified twenty acyl-CoA synthetase genes in R. prolixus, two encoding ACSL isoforms (RhoprAcsl1 and RhoprAcsl2). RhoprAcsl1 transcripts increased in posterior midgut on the second day after feeding, and RhoprAcsl2 was highly transcribed on the tenth day. Both enzymes were expressed in Escherichia coli. Recombinant RhoprACSL1 and RhoprACSL2 had broad pH optima (7.5-9.5 and 6.5-9.5, respectively), were inhibited by triacsin C, and were rosiglitazone-insensitive. Both showed similar apparent Km for palmitic and oleic acid (2-6 μM), but different Km for arachidonic acid (0.5 and 6 μM for RhoprACSL1-Flag and RhoprACSL2-Flag, respectively). The knockdown of RhoprAcsl1 did not result in noticeable phenotypes. However, RhoprACSL2 deficient insects exhibited a 2.5-fold increase in triacylglycerol content in the fat body, and 90% decrease in fatty acid β-oxidation. RhoprAcsl2 knockdown also resulted in 20% increase in lifespan, delayed digestion, 30% reduced oviposition, and 50% reduction in egg hatching. Laid eggs and hatched nymphs showed remarkable alterations in morphology. In summary, R. prolixus ACSL isoforms have distinct roles on lipid metabolism. Although RhoprACSL1 functions remain unclear, we propose that RhoprACSL2 is the main contributor for the formation of the intracellular acyl-CoA pool channeled for β-oxidation in the fat body, and is also required for normal reproduction.

Vitellogenin-RNAi and ovariectomy each increase lifespan, increase protein storage, and decrease feeding, but are not additive in grasshoppers

Reduced reproduction has been shown to increase lifespan in many animals, yet the mechanisms behind this trade-off are unclear. We addressed this question by combining two distinct, direct means of life-extension via reduced reproduction, to test whether they were additive. In the lubber grasshopper, Romalea microptera, ovariectomized (OVX) individuals had a ~20% increase in lifespan and a doubling of storage relative to controls (Sham operated). Similarly, young female grasshoppers treated with RNAi against vitellogenin (the precursor to egg yolk protein) had increased fat body mass and halted ovarian growth. In this study, we compared VgRNAi to two control groups that do not reduce reproduction, namely buffer injection (Buffer) and injection with RNAi against a hexameric storage protein (Hex90RNAi). Each injection treatment was tested with and without ovariectomy. Hence, we tested feeding, storage, and lifespans in six groups: OVX and Buffer, OVX and Hex90RNAi, OVX and VgRNAi, Sham and Buffer, Sham and Hex90RNAi, and Sham and VgRNAi. Ovariectomized grasshoppers and VgRNAi grasshoppers each had similar reductions in feeding (~40%), increases in protein storage in the hemolymph (150-300%), and extensions in lifespan (13-21%). Ovariectomized grasshoppers had higher vitellogenin protein levels than did VgRNAi grasshoppers. Last but not least, when ovariectomy and VgRNAi were applied together, there was no greater effect on feeding, protein storage, or longevity. Hence, feeding regulation, and protein storage in insects, may be conserved components of life-extension via reduced reproduction.

Functional characterization of GH-like homolog in amphioxus reveals an ancient origin of GH/GH receptor system

Amphioxus belongs to the subphylum cephalochordata, an extant representative of the most basal chordates. Despite many studies on the endocrine system of amphioxus, no evidence showed the presence of pituitary hormones. In this study, we clearly demonstrated the existence of a functional GH-like hormone in amphioxus, which is able to bind purified GH receptors, stimulate IGF-I expression, promote growth rate of fish, and rescue embryonic defects caused by a shortage of GH. We also showed the presence of a GH/prolactin-like-binding protein containing the entire hormone binding domain of GH/prolactin receptors in amphioxus, which is widely expressed among tissues, and interacts with the GH-like hormone. It is clear from these results that the GH/GH receptor-like system is present in amphioxus and, hence, in all classes of chordates. Notably, the GH-like hormone appears to be the only member of the vertebrate pituitary hormones family in amphioxus, suggesting that the hormone is the ancestral peptide that originated first in the molecular evolution of the pituitary hormones family in chordates. These data collectively suggest that a vertebrate-like neuroendocrine axis setting has already emerged in amphioxus, which lays a foundation for subsequent formation of hypothalamic-pituitary system in vertebrates.

Vitellogenin RNAi halts ovarian growth and diverts reproductive proteins and lipids in young grasshoppers

Reduced reproduction extends lifespan of females in many animals. To test the effects of reproduction on storage of macronutrients, we block reproductive output in the lubber grasshopper by injecting RNAi against the precursor to egg-yolk protein, vitellogenin, in early adulthood. Controls were injected with either buffer or RNAi against the major storage protein in the hemolymph, hexamerin-90. Vitellogenin RNAi greatly reduced both levels of mRNA for vitellogenin and ovarian growth, in comparison to both controls. Fat body mass was increased upon vitellogenin RNAi, but concentrations of the three hexameric storage proteins from the hemolymph were not. Surprisingly, hemolymph vitellogenin levels were increased upon vitellogenin RNAi. Total reproductive protein (hemolymph vitellogenin plus ovarian vitellin) was unchanged by vitellogenin RNAi, as reproductive protein was diverted to the hemolymph. Similarly, the increased lipid storage upon vitellogenin RNAi was largely attributable to the reduction in lipid in the ovary, due to decreased ovarian growth. A BLAST search revealed that the 515 bp sequence of vitellogenin used for RNAi had three 11 bp regions identical to the vitellogenin receptor of the cockroach Leucophaea maderae. This suggests that our treatment, in addition to reducing levels of vitellogenin transcript, may have also blocked transport of vitellogenin from the hemolymph to the ovary. This would be consistent with halted ovarian growth simultaneous with high levels of vitellogenin in the hemolymph. Nonetheless, the accumulation of vitellogenin, instead of hexameric storage proteins, is inconsistent with a simple model of the trade-off between reproduction and storage. This was observed in young females; future studies will address whether investment of proteins may shift to the soma as individuals age. Overall, our results suggest that blockage of reproduction in young grasshoppers redirects lipids to storage and reproductive proteins to the hemolymph.

Vitellogenin family gene expression does not increase Drosophila lifespan or fecundity

One of the most striking patterns in comparative biology is the negative correlation between lifespan and fecundity observed in comparisons among species. This pattern is consistent with the idea that organisms need to allocate a fixed energy budget among competing demands of growth, development, reproduction and somatic maintenance. However, exceptions to this pattern have been observed in many social insects, including ants, bees, and termites.  In honey bees ( Apismellifera), Vitellogenin ( Vg), a yolk protein precursor, has been implicated in mediating the long lifespan and high fecundity of queen bees. To determine if Vg-like proteins can regulate lifespan in insects generally, we examined the effects of expression of ApisVg and Drosophila CG31150 (a Vg-like gene recently identified as cv-d) on Drosophilamelanogaster lifespan and fecundity using the RU486-inducible GeneSwitch system. For all genotypes tested, overexpression of Vg and CG31150 decreased Drosophila lifespan and did not affect total or age-specific fecundity. We also detected an apparent effect of the GeneSwitch system itself, wherein RU486 exposure (or the GAL4 expression it induces) led to a significant increase in longevity and decrease in fecundity in our fly strains. This result is consistent with the pattern reported in a recent meta-analysis of Drosophila aging studies, where transgenic constructs of the UAS/GAL4 expression system that should have no effect (e.g. an uninduced GeneSwitch) significantly extended lifespan in some genetic backgrounds. Our results suggest that Vg-family genes are not major regulators of Drosophila life history traits, and highlight the importance of using appropriate controls in aging studies.

Alternative Perspectives on Aging in Caenorhabditis elegans: Reactive Oxygen Species or Hyperfunction?

SIGNIFICANCE

The biological mechanisms at the heart of the aging process are a long-standing mystery. An influential theory has it that aging is the result of an accumulation of molecular damage, caused in particular by reactive oxygen species produced by mitochondria. This theory also predicts that processes that protect against oxidative damage (involving detoxification, repair, and turnover) protect against aging and increase lifespan.

RECENT ADVANCES

However, recent tests of the oxidative damage theory, many using the short-lived nematode worm Caenorhabditis elegans, have often failed to support the theory. This motivates consideration of alternative models. One new theory, conceived by M.V. Blagosklonny, proposes that aging is caused by hyperfunction, that is, overactivity during adulthood of processes (particularly biosynthetic) that contribute to development and reproduction. Such hyperfunction can lead to hypertrophy-associated pathologies, which cause the age increase in death.

CRITICAL ISSUES

Here we assess whether the hyperfunction theory is at all consistent with what is known about C. elegans aging, and conclude that it is. In particular, during adulthood, C. elegans shows a number of changes that may reflect pathology and/or hyperfunction. Such changes seem to contribute to death, at least in some cases (e.g., yolk accumulation).

FUTURE DIRECTIONS

Our assessment suggests that the hyperfunction theory is a plausible alternative to the molecular damage theory to explain aging in C. elegans.

Vitellogenins increase stress resistance of Caenorhabditis elegans after Photorhabdus luminescens infection depending on the steroid-signaling pathway

Resistance against environmental stress is a crucial factor in determining the lifespan of organisms. A central role herein has been recently attributed to the transport and storage of lipids with the vitellogenin family emerging as a potential key factor. Here we show that the knockdown of one out of five functional vitellogenin genes, encoding apolipoprotein B homologues, results in a reduced survival of the nematode Caenorhabditis elegans at 37 °C subsequent to infection with the bacterial pathogen Photorhabdus luminescens. An active steroid-signaling pathway, including supply of cholesterol by vitellogenins, steroid ligand formation by the cytochrome P450 dependent DAF-9, and activation of the nuclear hormone receptor DAF-12, in the presence of pathogenic bacteria was associated with reduced nuclear translocation of the forkhead transcription factor DAF-16 and increased antioxidative capacity. Taken together, the study provides functional evidence for a crucial role of vitellogenins and the steroid-signaling pathway in determination of resistance against bacteria.

Phytoestrogens genistein and daidzein affect immunity in the nematode Caenorhabditis elegans via alterations of vitellogenin expression

SCOPE

Phytoestrogens, such as the soy isoflavones genistein and daidzein, are suggested to beneficially affect lipid metabolism in humans and thereby contribute to healthy ageing. New evidences show that phytoestrogens might slow ageing processes also by affecting immune processes.

METHODS AND RESULTS

We tested in the nematode Caenorhabditis elegans the effects of 17β-estradiol, genistein, and daidzein on resistance versus the nematode pathogen Photorhabdus luminescens with focus on vitellogenins, which are invertebrate estrogen-responsive genes that encode homologues to ApoB100 with impact on immune functions. Here, we show that the estrogen 17β-estradiol increases the resistance of C. elegans versus P. luminescens by enhancing vitellogenin-expression at the mRNA and protein level. Knockdown of single out of five functional vits by RNA-interference blunted the life-extending effects under heat-stress of 17β-estradiol, demonstrating a lack of redundancy for the vitellogenins. RNAi for nhr-14, a suggested nuclear hormone receptor for estrogens, displayed no influence on 17β-estradiol effects. The soy isoflavone genistein reduced vitellogenin-expression and also resistance versus P. luminescens whereas daidzein increased resistance versus the pathogen in a vitellogenin-dependent manner.

CONCLUSION

Our studies show that induction of estrogen-responsive vitellogenin(s) by the phytoestrogen daidzein potently increases resistance of C. elegans versus pathogenic bacteria and heat whereas genistein acts in an antiestrogenic manner.

Comparative proteome analysis of Milnesium tardigradum in early embryonic state versus adults in active and anhydrobiotic state

Tardigrades have fascinated researchers for more than 300 years because of their extraordinary capability to undergo cryptobiosis and survive extreme environmental conditions. However, the survival mechanisms of tardigrades are still poorly understood mainly due to the absence of detailed knowledge about the proteome and genome of these organisms. Our study was intended to provide a basis for the functional characterization of expressed proteins in different states of tardigrades. High-throughput, high-accuracy proteomics in combination with a newly developed tardigrade specific protein database resulted in the identification of more than 3000 proteins in three different states: early embryonic state and adult animals in active and anhydrobiotic state. This comprehensive proteome resource includes protein families such as chaperones, antioxidants, ribosomal proteins, cytoskeletal proteins, transporters, protein channels, nutrient reservoirs, and developmental proteins. A comparative analysis of protein families in the different states was performed by calculating the exponentially modified protein abundance index which classifies proteins in major and minor components. This is the first step to analyzing the proteins involved in early embryonic development, and furthermore proteins which might play an important role in the transition into the anhydrobiotic state.

Genetic variation in the Yolk protein expression network of Drosophila melanogaster: sex-biased negative correlations with longevity

One of the persistent problems in biology is understanding how genetic variation contributes to phenotypic variation. Associations at many levels have been reported, and yet causal inference has remained elusive. We propose to rely on the knowledge of causal relationships established by molecular biology approaches. The existing molecular knowledge forms a firm backbone upon which hypotheses connecting genetic variation, transcriptional variation and phenotypic variation can be built. The sex determination pathway is a well-established molecular network, with the Yolk protein 1-3 (Yp) genes as the most downstream target. Our analyses reveal that genetic variation in expression for genes known to be upstream in the pathway explains variation in downstream targets. Relationships differ between the two sexes, and each Yp has a distinct transcriptional pattern. Yp expression is significantly negatively correlated with longevity, an important life history trait, for both males and females.

The mystery of C. elegans aging: an emerging role for fat. Distant parallels between C. elegans aging and metabolic syndrome?

New C. elegans studies imply that lipases and lipid desaturases can mediate signaling effects on aging. But why might fat homeostasis be critical to aging? Could problems with fat handling compromise health in nematodes as they do in mammals? The study of signaling pathways that control longevity could provide the key to one of the great unsolved mysteries of biology: the mechanism of aging. But as our view of the regulatory pathways that control aging grows ever clearer, the nature of aging itself has, if anything, grown more obscure. In particular, focused investigations of the oxidative damage theory have raised questions about an old assumption: that a fundamental cause of aging is accumulation of molecular damage. Could fat dyshomeostasis instead be critical?

In vitro studies on the sexual maturation of the bovine lungworm Dictyocaulus viviparus during the development of preadult larvae to adult worms

The bovine lungworm Dictyocaulus viviparus is one of the most important parasites in grazing cattle. However, not much is known about morphology and molecular aspects of sexual maturation occurring during development of preadult larvae (L5) to adults. Since studies in the pulmonary compartments are infeasible, an in vitro cultivation method was established. The study was conducted with L5 during in vitro cultivation, assessing longitudinal growth and sexual maturation. Best results were achieved with RPMI-1640 medium with L-glutamine, 50% fetal bovine serum, amphotericin B (0.25 mg/ml), penicillin (10,000 U/ml), and streptomycin (10 mg/ml) at 39°C and 5% atmospheric CO₂. During cultivation, individuals grew from an average length of 4.64 to 9.88 mm independent of their density per setup. Regarding sexual maturation, female individuals started to lay eggs, whereas the testes of male individuals were filled with spermatozoa. Consequently, adult female and adult male worms developed. However, no copulation was observable and eggs did not embryonate. Development was further investigated by quantitative real-time PCR transcriptional analysis of major sperm protein (msp) and vitellogenin (vit) representing male and female sexual development, respectively. Male msp transcription peaked after 5 days of cultivation [corresponding to 20 days post infection (dpi)] and decreased gradually afterwards. Female vit transcription showed the highest rate after 15 days of cultivation (30 dpi), however it never reached the transcription rate in female adults isolated from the host. All in all, the present study gives not only insights into morphological differentiation but provides data lightening molecular aspects of sexual maturation in D. viviparus.

The developmental genetics and physiology of honeybee societies

Eusocial animal societies, as diverse as those found in the ants, bees, wasps, shrimp and naked mole-rats, are structured around one or few reproductive females. The remaining females are helpers called 'workers' that are mostly sterile. A paradigm in studies of eusociality is that worker sterility is a key to societal functions because advanced sociality cannot be achieved when there is conflict over reproduction. Yet, traits such as sensory responsiveness, foraging and hoarding behaviour that change between female reproductive life stages also vary between workers. This variation is central to worker division of labour, a complex social trait believed to be instrumental for the ecological success of animal societies. Thus, we took a step back from established views on worker sterility and societal functions, and hypothesized that division of labour can be better understood if adaptive variation in worker behaviour is seen as emerging from pre-existing mechanisms associated with female reproduction. In exploring this reproductive ground plan hypothesis (RGPH) in honeybee workers, we established that variation in foraging division of labour correlates with ovary size and is affected by expression changes in vitellogenin, an egg yolk protein precursor. Here, we explain and reconcile the RGPH with data on honeybee sensory sensitivity, genomic mapping, transcript and endocrine profiling, and link our discussion with Ihle et al. (2010, this issue, pp. xx-xx). The findings bring together mechanistic and evolutionary explanations of honeybee worker behaviour. This essay suggests that a broader view on worker reproductive traits can increase the understanding of animal social behaviour.

The curious case of aging plasticity in honey bees

As in all advanced insect societies, colony-organization in honey bees emerges through a structured division of labor between essentially sterile helpers called workers. Worker bees are sisters that conduct all social tasks except for egg-laying, for example nursing brood and foraging for food. Curiously, aging progresses slowly in workers that engage in nursing and even slower when bees postpone nursing during unfavorable periods. We, therefore, seek to understand how senescence can emerge as a function of social task performance. The alternative utilization of a common yolk precursor protein (vitellogenin) in nursing and somatic maintenance can link behavior and aging plasticity in worker bees. Beneficial effects of vitellogenin may also be mediated by inhibitory action on juvenile hormone and insulin-like signaling.

Brood pheromone suppresses physiology of extreme longevity in honeybees (Apis mellifera)

Honeybee (Apis mellifera) society is characterized by a helper caste of essentially sterile female bees called workers. Workers show striking changes in lifespan that correlate with changes in colony demography. When rearing sibling sisters (brood), workers survive for 3-6 weeks. When brood rearing declines, worker lifespan is 20 weeks or longer. Insects can survive unfavorable periods on endogenous stores of protein and lipid. The glyco-lipoprotein vitellogenin extends worker bee lifespan by functioning in free radical defense, immunity and behavioral control. Workers use vitellogenin in brood food synthesis, and the metabolic cost of brood rearing (nurse load) may consume vitellogenin stores and reduce worker longevity. Yet, in addition to consuming resources, brood secretes a primer pheromone that affects worker physiology and behavior. Odors and odor perception can influence invertebrate longevity but it is unknown whether brood pheromone modulates vitellogenin stores and survival. We address this question with a 2-factorial experiment where 12 colonies are exposed to combinations of absence vs presence of brood and brood pheromone. Over an age-course of 24 days, we monitor the amount of vitellogenin stored in workers' fat body (adipose tissue). Thereafter, we track colony survival for 200 days. We demonstrate that brood rearing reduces worker vitellogenin stores and colony long-term survival. Yet also, we establish that the effects can result solely from exposure to brood pheromone. These findings indicate that molecular systems of extreme lifespan regulation are integrated with the sensory system of honeybees to respond to variation in a primer pheromone secreted from larvae.

Bioinformatic analysis of abundant, gender-enriched transcripts of adult Ascaris suum (Nematoda) using a semi-automated workflow platform

Expressed sequence tag (EST) data representing transcripts with a high level of differential hybridization in suppressive-subtractive hybridization (SSH)-based microarray analysis between adult female and male Ascaris suum were subjected to detailed bioinformatic analysis. A total of 361 ESTs clustered into 209 sequences, of which 52 and 157 represented transcripts that were enriched in female and male A. suum, respectively. Thirty (57.7%) of the 'female' subset of 52 sequences had orthologues/homologues in other parasitic nematodes and/or Caenorhabditis elegans, 13 (25%) exclusively in other parasitic nematodes and nine (17.3%) had no match in any other organism for which sequence data are currently available; the C. elegans orthologues encoded molecules involved in reproduction as well as embryonic and gamete development, such as vitellogenins and chitin-binding proteins. Of the 'male' subset of 157 sequences, 73 (46.5%) had orthologues/homologues in other parasitic nematodes and/or C. elegans, 57 (37.5%) in other parasitic nematodes only, and 22 (14.5%) had no significant similarity match in any other organism; the C. elegans orthologues encoded predominantly major sperm proteins (MSPs), kinases and phosphatases, actins, myosins and an Ancylostoma secreted protein-like molecule. The findings of the present study should support further genomic investigations of A. suum.

The evolution of plasma cholesterol: direct utility or a "spandrel" of hepatic lipid metabolism?

Fats provide a concentrated source of energy for multicellular organisms. The efficient transport of fats through aqueous biological environments raises issues concerning effective delivery to target tissues. Furthermore, the utilization of fatty acids presents a high risk of cytotoxicity. Improving the efficiency of fat transport while simultaneously minimizing the cytotoxic risk confers distinct selective advantages. In humans, most of the plasma cholesterol is associated with low-density lipoprotein (LDL), a metabolic by-product of very-low-density lipoprotein (VLDL), which originates in the liver. However, the functions of VLDL are not clear. This paper reviews the evidence that LDL arose as a by-product during the natural selection of VLDL. The latter, in turn, evolved as a means of improving the efficiency of diet-derived fatty acid storage and utilization, as well as neutralizing the potential cytotoxicity of fatty acids while conserving their advantages as a concentrated energy source. The evolutionary biology of lipid transport processes has provided a fascinating insight into how and why these VLDL functions emerged during animal evolution. As causes of historical origin must be separated from current utilities, our spandrel-LDL theory proposes that LDL is a spandrel of VLDL selection, which appeared non-adaptively and may later have become crucial for vertebrate fitness.

Ageing in a eusocial insect: molecular and physiological characteristics of life span plasticity in the honey bee

Commonly held views assume that ageing, or senescence, represents an inevitable, passive, and random decline in function that is strongly linked to chronological age. In recent years, genetic intervention of life span regulating pathways, for example, in Drosophila as well as case studies in non-classical animal models, have provided compelling evidence to challenge these views.Rather than comprehensively revisiting studies on the established genetic model systems of ageing, we here focus on an alternative model organism with a wild type (unselected genotype) characterized by a unique diversity in longevity - the honey bee.Honey bee (Apis mellifera) life span varies from a few weeks to more than 2 years. This plasticity is largely controlled by environmental factors. Thereby, although individuals are closely related genetically, distinct life histories can emerge as a function of social environmental change.Another remarkable feature of the honey bee is the occurrence of reverted behavioural ontogeny in the worker (female helper) caste. This behavioural peculiarity is associated with alterations in somatic maintenance functions that are indicative of reverted senescence. Thus, although intraspecific variation in organismal life span is not uncommon, the honey bee holds great promise for gaining insights into regulatory pathways that can shape the time-course of ageing by delaying, halting or even reversing processes of senescence. These aspects provide the setting of our review.We will highlight comparative findings from Drosophila melanogaster and Caenorhabditis elegans in particular, and focus on knowledge spanning from molecular- to behavioural-senescence to elucidate how the honey bee can contribute to novel insights into regulatory mechanisms that underlie plasticity and robustness or irreversibility in ageing.

The gene vitellogenin has multiple coordinating effects on social organization

Temporal division of labor and foraging specialization are key characteristics of honeybee social organization. Worker honeybees (Apis mellifera) initiate foraging for food around their third week of life and often specialize in collecting pollen or nectar before they die. Variation in these fundamental social traits correlates with variation in worker reproductive physiology. However, the genetic and hormonal mechanisms that mediate the control of social organization are not understood and remain a central question in social insect biology. Here we demonstrate that a yolk precursor gene, vitellogenin, affects a complex suite of social traits. Vitellogenin is a major reproductive protein in insects in general and a proposed endocrine factor in honeybees. We show by use of RNA interference (RNAi) that vitellogenin gene activity paces onset of foraging behavior, primes bees for specialized foraging tasks, and influences worker longevity. These findings support the view that the worker specializations that characterize hymenopteran sociality evolved through co-option of reproductive regulatory pathways. Further, they demonstrate for the first time how coordinated control of multiple social life-history traits can originate via the pleiotropic effects of a single gene that affects multiple physiological processes.

Animals that live in groups often specialize in different tasks, creating a division of labor. One extreme example can be seen in honeybees, in which most tasks are performed by thousands of worker females that are essentially sterile helpers. Workers start out as nurse bees that care for larvae in the nest. Later they embark on foraging trips, specializing in either pollen or nectar collection, and continue to forage until they die. The age when workers initiate foraging and the tendency to collect pollen or nectar have been linked to a rudimentary reproductive physiology in which the protein vitellogenin appears to play a central role. Vitellogenin is normally used to produce egg yolk, but it may affect behavior and lifespan in workers. We tested this hypothesis by knocking down the vitellogenin gene of worker bees. Workers with suppressed vitellogenin levels foraged earlier, preferred nectar, and lived shorter lives. Thus, vitellogenin has multiple effects on honeybee social organization. By using gene knockdown to understand insect social behavior, our study supports the view that social life in bees evolved by co-opting genes involved in reproduction.

vitellogenin gene activity paces onset of foraging behavior in worker bees, demonstrating how coordinated control of multiple social life-history traits can originate via the pleiotropic effects of a single gene.

Genome-wide analysis reveals differences in brain gene expression patterns associated with caste and reproductive status in honey bees (Apis mellifera)

A key characteristic of eusocial species is reproductive division of labour. Honey bee colonies typically have a single reproductive queen and thousands of sterile workers. Adult queens differ dramatically from workers in anatomy, physiology, behaviour and lifespan. Young female workers can activate their ovaries and initiate egg laying; these 'reproductive' workers differ from sterile workers in anatomy, physiology, and behaviour. These differences, however, are on a much smaller scale than those observed between the queen and worker castes. Here, we use microarrays to monitor expression patterns of several thousand genes in the brains of same-aged virgin queens, sterile workers, and reproductive workers. We found large differences in expression between queens and both worker groups (~2000 genes), and much smaller differences between sterile and reproductive workers (221 genes). The expression patterns of these 221 genes in reproductive workers are more queen-like, and may represent a core group of genes associated with reproductive physiology. Furthermore, queens and reproductive workers preferentially up-regulate genes associated with the nurse bee behavioural state, which supports the hypothesis of an evolutionary link between worker division of labour and molecular pathways related to reproduction. Finally, several functional groups of genes associated with longevity in other species are significantly up-regulated in queens. Identifying the genes that underlie the differences between queens, sterile workers, and reproductive workers will allow us to begin to characterize the molecular mechanisms underlying the evolution of social behaviour and large-scale remodelling of gene networks associated with polyphenisms.

Gender-enriched transcripts in Haemonchus contortus--predicted functions and genetic interactions based on comparative analyses with Caenorhabditis elegans

In the present study, a bioinformatic-microarray approach was employed for the analysis of selected expressed sequence tags (ESTs) from Haemonchus contortus, a key parasitic nematode of small ruminants. Following a bioinformatic analysis of EST data using a semiautomated pipeline, 1885 representative ESTs (rESTs) were selected, to which oligonucleotides (three per EST) were designed and spotted on to a microarray. This microarray was hybridized with cyanine-dye labelled cRNA probes synthesized from RNA from female or male adults of H. contortus. Differential hybridisation was displayed for 301 of the 1885 rESTs ( approximately 16%). Of these, 165 (55%) had significantly greater signal intensities for female cRNA and 136 (45%) for male cRNA. Of these, 113 with increased signals in female or male H. contortus had homologues in Caenorhabditis elegans, predicted to function in metabolism, information storage and processing, cellular processes and signalling, and embryonic and/or larval development. Of the rESTs with no known homologues in C. elegans, 24 ( approximately 40%) had homologues in other nematodes, four had homologues in various other organisms and 30 (52%) had no homology to any sequence in current gene databases. A genetic interaction network was predicted for the C. elegans orthologues of the gender-enriched H. contortus genes, and a focused analysis of a subset revealed a tight network of molecules involved in amino acid, carbohydrate or lipid transport and metabolism, energy production and conversion, translation, ribosomal structure and biogenesis and, importantly, those associated with meiosis and/or mitosis in the germline during oogenesis or spermatogenesis. This study provides a foundation for the molecular, biochemical and functional exploration of selected molecules with differential transcription profiles in H. contortus, for further microarray analyses of transcription in different developmental stages of H. contortus, and for an extended functional analysis once the full genome sequence of this nematode is known.

Molecular Chaperones and the Epigenetics of Longevity and Cancer Resistance

The inherent immortality of embryonic stem cells demonstrates that replicative senescence as possibly the aging of species are epigenetic phenomena. The cellular level of expression of the housekeeping molecular chaperones correlates with longevity and cancer resistance of species. The chaperones are cancer antagonists by acting as genetic buffers, stabilizing the normal phenotype. Probably the progressive age-related silencing of the housekeeping genes contributes to the phenotype of aging, with the associated increase in cancer incidence. The present review concerns epigenetic chemical, immunological, and hormonal mechanisms, activating chaperone- and immune-response genes, which have proved effective in increasing longevity and cancer resistance. The relation of steroid hormone levels to species longevity, the anticarcinogenic activity of pregnancy hormones, and the influence of hormones on the longevity of social insects, illustrates the importance of hormonal mechanisms for the activation of longevity genes.

Contributions of genomics to life-history theory

Life-history theory seeks to understand the factors that produce variation in life histories that are found both among and within species. At the organismal level there is a well developed mathematical framework, and an important focus of the current research is determining the biological underpinnings of this framework, with particular attention to the causal mechanisms that underlie trade-offs. Genomic approaches are proving useful in addressing this issue.

Lipoprotein particle profiles mark familial and sporadic human longevity

BACKGROUND

Genetic and biochemical studies have indicated an important role for lipid metabolism in human longevity. Ashkenazi Jewish centenarians and their offspring have large low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles as compared with control individuals. This profile also coincided with a lower prevalence of disease. Here, we investigate whether this observation can be confirmed for familial longevity in an outbred European population and whether it can be extended to sporadic longevity in the general population.

METHODS AND FINDINGS

NMR-measured lipoprotein profiles were analyzed in 165 families from the Leiden Longevity Study, consisting of 340 long-lived siblings (females >91 y, males >89 y), 511 of their offspring, and 243 partners of the offspring. Offspring had larger (21.3 versus 21.1 nm; p = 0.020) and fewer (1,470 versus 1,561 nmol/l; p = 0.011) LDL particles than their same-aged partners. This effect was even more prominent in the long-lived siblings (p < 10(-3)) and could be pinpointed to a reduction specifically in the concentration of small LDL particles. No differences were observed for HDL particle phenotypes. The mean LDL particle sizes in 259 90-y-old singletons from a population-based study were similar to those in the long-lived siblings and thus significantly larger than in partners of the offspring, suggesting that the relevance of this phenotype extends beyond familial longevity. A low concentration of small LDL particles was associated with better overall health among both long-lived siblings (p = 0.003) and 90-y-old singletons (p = 0.007).

CONCLUSIONS

Our study indicates that LDL particle profiles mark both familial and sporadic human longevity already in middle age.

C. elegans DAF-12, Nuclear Hormone Receptors and human longevity and disease at old age

In Caenorhabditis elegans, DAF-12 appears to be a decisive checkpoint for many life history traits including longevity. The daf-12 gene encodes a Nuclear Hormone Receptor (NHR) and is member of a superfamily that is abundantly represented throughout the animal kingdom, including humans. It is, however, unclear which of the human receptor representatives are most similar to DAF-12, and what their role is in determining human longevity and disease at old age. Using a sequence similarity search, we identified human NHRs similar to C. elegans DAF-12 and found that, based on sequence similarity, Liver X Receptor A and B are most similar to C. elegans DAF-12, followed by the Pregnane X Receptor, Vitamin D Receptor, Constitutive Andosteron Receptor and the Farnesoid X Receptor. Their biological functions include, amongst others, detoxification and immunomodulation. Both are processes that are involved in protecting the body from harmful environmental influences. Furthermore, the DAF-12 signalling systems seem to be functionally conserved and all six human NHRs have cholesterol derived compounds as their ligands. We conclude that the DAF-12 signalling system seems to be evolutionary conserved and that NHRs in man are critical for body homeostasis and survival. Genomic variations in these NHRs or their target genes are prime candidates for the regulation of human lifespan and disease at old age.