Cricket body size is altered by systemic RNAi against insulin signaling components and epidermal growth factor receptor

A long-standing problem of developmental biology is how body size is determined. In Drosophila melanogaster, the insulin/insulin-like growth factor (I/IGF) and target of rapamycin (TOR) signaling pathways play important roles in this process. However, the detailed mechanisms by which insect body growth is regulated are not known. Therefore, we have attempted to utilize systemic nymphal RNA interference (nyRNAi) to knockdown expression of insulin signaling components including Insulin receptor (InR), Insulin receptor substrate (chico), Phosphatase and tensin homologue (Pten), Target of rapamycin (Tor), RPS6-p70-protein kinase (S6k), Forkhead box O (FoxO) and Epidermal growth factor receptor (Egfr) and observed the effects on body size in the Gryllus bimaculatus cricket. We found that crickets treated with double-stranded RNA (dsRNA) against Gryllus InR, chico, Tor, S6k and Egfr displayed smaller body sizes, while Gryllus FoxO nyRNAi-ed crickets exhibited larger than normal body sizes. Furthermore, RNAi against Gryllus chico and Tor displayed slow growth and RNAi against Gryllus chico displayed longer lifespan than control crickets. Since no significant difference in ability of food uptake was observed between the Gryllus chico(nyRNAi) nymphs and controls, we conclude that the adult cricket body size can be altered by knockdown of expressions of Gryllus InR, chico, Tor, S6k, FoxO and Egfr by systemic RNAi. Our results suggest that the cricket is a promising model to study mechanisms underlying controls of body size and life span with RNAi methods.     

The demography of slow aging in male and female Drosophila mutant for the insulin-receptor substrate homologue chico

Hypomorphic mutants affecting the Drosophila insulin/IGF signal pathway are reported to increase longevity in females but not in males. To understand this sex-difference, we conducted a large-scale demographic study with three new isogenic strains of alleles at chico, the insulin-receptor substrate homologue. We verify that female dwarf homozygotes (ch1/ch1) and normal-sized heterozygotes (ch1/+) are long-lived, as originally reported. We find for the first time that male heterozygotes are long-lived relative to wildtype, by about 50%. The life span of male ch1/ch1 is similar to that of wildtype but these dwarf males age at a slow demographic rate. The levels of demographic frailty and of age-independent mortality are elevated in ch1/ch1 males, counteracting the effect of slow aging upon life expectancy. Mortality deceleration occurs amongst the oldest-old wildtype adults, as seen in many organisms. Remarkably, in similarly sized cohorts of male and female ch1/ch1 and of male ch1/+ mortality deceleration is absent. Mortality deceleration is a phenotype of chico.     

Insulin signaling is necessary for vitellogenesis in Drosophila melanogaster independent of the roles of juvenile hormone and ecdysteroids: female sterility of the chico1 insulin signaling mutation is autonomous to the ovary

It has been suggested that insulin signaling mutations of Drosophila melanogaster are sterile and long-lived because of juvenile hormone (JH) and ecdysteroid deficiency. However, female sterility of an insulin/IGF-like signaling mutant (chico(1)) of D. melanogaster is not mediated by downstream systemic signaling in terms of major alterations in JH or ecdysteroid levels. chico(1) is a null mutation in the insulin substrate protein (CHICO) gene of D. melanogaster. Homozygous chico(1) females are sterile and their oocytes do not mature beyond the last previtellogenic stage. Homozygous chico(1) females exhibit approximately wild-type rates of JH biosynthesis, ovarian release of ecdysteroids and haemolymph ecdysteroid levels, suggesting that these two major hormone systems play no role in producing the sterility. Previtellogenic wild-type ovaries transplanted into homozygous chico(1) females underwent vitellogenesis, showing that systemic factors present in mutant females are sufficient to support normal vitellogenesis. chico(1) ovaries transplanted into wild-type females did not undergo vitellogenesis indicating that CHICO is necessary in the ovary for vitellogenic maturation. The ovary transplant experiments corroborate the endocrine results and demonstrate that insulin/insulin-like signaling (IIS) is necessary for vitellogenesis even when sufficient levels of JH, ecdysteroids or other factors are present.     

Disruption of insulin pathways alters trehalose level and abolishes sexual dimorphism in locomotor activity in Drosophila

Insulin signaling pathways are implicated in several physiological processes in invertebrates, including the control of growth and life span; the latter of these has also been correlated with juvenile hormone (JH) deficiency. In turn, JH levels have been correlated with sex-specific differences in locomotor activity. Here, the involvement of the insulin signaling pathway in sex-specific differences in locomotor activity was investigated in Drosophila. Ablation of insulin-producing neurons in the adult pars-intercerebralis was found to increase trehalosemia and to abolish sexual dimorphism relevant to locomotion. Conversely, hyper-insulinemia induced by insulin injection or by over-expression of an insulin-like peptide decreases trehalosemia but does not affect locomotive behavior. Moreover, we also show that in the head of adult flies, the insulin receptor (InR) is expressed only in the fat body surrounding the brain. While both male and female InR mutants are hyper-trehalosemic, they exhibit similar patterns of locomotor activity. Our results indicate that first, insulin controls trehalosemia in adults, and second, like JH, it controls sex-specific differences in the locomotor activity of adult Drosophila in a manner independent of its effect on trehalose metabolism.     

Nectarine promotes longevity in Drosophila melanogaster

Fruits containing high antioxidant capacities and other bioactivities are ideal for promoting longevity and health span. However, few fruits are known to improve the survival and health span in animals, let alone the underlying mechanisms. Here we investigate the effects of nectarine, a globally consumed fruit, on life span and health span in Drosophila melanogaster. Wild-type flies were fed standard, dietary restriction (DR), or high-fat diet supplemented with 0-4% nectarine extract. We measured life span, food intake, locomotor activity, fecundity, gene expression changes, and oxidative damage indicated by the level of 4-hydroxynonenal-protein adduct in these flies. We also measured life span, locomotor activity, and oxidative damage in sod1 mutant flies on the standard diet supplemented with 0-4% nectarine. Supplementation with 4% nectarine extended life span, increased fecundity, and decreased expression of some metabolic genes, including a key gluconeogenesis gene, PEPCK, and oxidative stress-response genes, including peroxiredoxins, in female wild-type flies fed the standard, DR, or high-fat diet. Nectarine reduced oxidative damage in wild-type females fed the high-fat diet. Moreover, nectarine improved the survival of and reduced oxidative damage in female sod1 mutant flies. Together, these findings suggest that nectarine promotes longevity and health span partly by modulating glucose metabolism and reducing oxidative damage.     

Dietary complementation across life stages in the polyphagous lady beetle Coleomegilla maculata

We investigated the life history consequences of changes in diet between larval and adult life stages in the polyphagous lady beetle Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae). Beetles were reared on three larval diets: greenbug, Schizaphis graminum Rondani (Homoptera: Aphididae), eggs of the flour moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), and bee pollen. The reproductive performance of females was then evaluated on an adult diet of either greenbug or moth eggs. Moth eggs appeared to be the most suitable diet for larvae, yielding the largest adults, and pollen the least suitable, resulting in the smallest adults and greatly extended developmental time. Pollen‐reared beetles tended to have lower fecundity and fertility than those reared on animal protein, regardless of adult diet. Female fitness was generally increased by a change in diet upon emergence to the alternative source of animal protein, suggesting that dietary complementation occurred across life stages. Among females reared on greenbug, a change of diet to moth eggs reduced the period required for production of 12 clutches and increased egg fertility compared to continued feeding on greenbug. Among females reared on moth eggs, a change of diet to greenbug increased fecundity compared to continued feeding on moth eggs. Among females fed an adult diet of greenbug, those fed moth eggs as larvae had faster production of 12 clutches and higher fecundity. We discuss these novel results in the context of coccinellid life history and ecology and their potential implications for other insects that are predatory as both larvae and adults.     

Are fecundity and longevity of female Aphelinus abdominalis affected by development in GNA‐dosed Macrosiphum euphorbiae?

Abstract. Snowdrop lectin ( Galanthus nivalis agglutinin, GNA) confers partial resistance to several aphid species when incorporated into an artificial diet and/or expressed in transgenic potato. First-tier laboratory-scale experiments were conducted to assess the potential effect of GNA on the longevity and fecundity of female parasitoid Aphelinus abdominalis (Dalman) that had developed in Macrosiphum euphorbiae (Thomas) fed artificial diet containing 0.1% GNA (w/v). In a previous study it was shown that GNA ingested by A. abdominalis larvae is not acutely toxic. It was also shown that GNA has a host-size mediated effect on parasitoid sex ratio and larval development, but no apparent direct effect.         In this study, we report that A. abdominalis larvae that developed in GNA-dosed aphids that were smaller than control aphids of the same age, produced smaller adults with a reduced longevity and fecundity. Aphelinus abdominalis larvae that developed in GNA-dosed aphids older than the control but of the same size, produced adults of similar size that lived as long as the control but had a reduced fecundity.         Our results suggest that GNA fed to aphids in artificial diet has both a host-mediated effect (via aphid-size) and a direct effect on adult parasitoid fecundity. It is not known how GNA affects parasitoid larval development and subsequently adult fecundity, but it is hypothesized that GNA acted as an antifeedant to parasitoid larvae, thus disturbing nutrient assimilation and conversion necessary for egg maturation.     

The effects of selection for larval behavior on adult life-history features in Drosophila melanogaster

Selection for late-life fecundity and longevity in adult Drosophila melanogaster is well known to modify numerous characteristics of life history and physiology. We report experiments here in which selection applied to behavior affects features in an identical fashion. Selection for feeding rate of larval D. melanogaster modifies caloric intake, as measured by the uptake and incorporation of labeled glucose. Selection for slow larval feeding produced lines of D. melanogaster in which larvae synthesized significantly less lipid prior to pupation and eclosed to have low early-life fecundity and a long life as adults. They also had greater lifetime fecundity, but lower viability of egg to hatched adult. Alternatively, fast-feeding larvae incorporated more lipid before pupation and eclosed with high early-fecundity that declined rapidly throughout their short adult life. Slow-feeding populations also had a significantly enhanced expression of the stress-resistance genes CuZn-SOD, CATALASE, and HSP70. Selection on larval feeding behavior reproduced the antagonistic evolutionary trade-off found under selection for adult life span and mimicked the physiological response in life span as seen in many species when dietary restriction is imposed on adults. Thus, nutrient acquisition during development appears to share a common evolutionary and genetic basis with the allocation processes that determine adult life-history traits and the related phenotypic dietary restriction phenomena.     

Phenotypic plasticity and variation in morphological and life-history traits of antlion adults across a climatic gradient

We report here on two complementary experiments examining the effect of climate on morphological and life-history traits of antlion adults. We first examined whether body size and wing loading of emerging adults are plastic by raising larvae, collected from five antlion populations along Israel's sharp climatic gradient, in two environmental chambers simulating temperature and humidity of desert and Mediterranean climates. The variance in adult morphology was mostly related to body size, with adults of Mediterranean populations being larger than those of desert populations. Wing-to-thorax ratio was negatively correlated with temperature, compensating for the decrease in wing-beat frequency in colder environments. Differences between climatic treatments were significant for body size but not for the wing-to-thorax ratio, suggesting that body size is more plastic than the ratio between different body components. We next investigated how the exposure of antlion pupae to different climatic conditions influences the emerging adults. Adult body mass increased with final larval body mass at a faster rate when exposed to Mediterranean rather than desert conditions. Duration of the pupa stage was positively correlated with final larval mass, but only under Mediterranean conditions. Adult survival increased with initial mass (after eclosion), but was lower under desert conditions. Similarly, adults lost mass at a faster rate when exposed to desert conditions. Notably, the exposure of the pupae to varying climatic conditions had no effect on adult morphology. Climate is a major factor affecting insect life span and body size. Since body size is strongly linked to fecundity and survival, climate thus has a twofold effect on fitness: directly, and indirectly through body size.     

Drosophila short neuropeptide F signalling regulates growth by ERK-mediated insulin signalling

Insulin and insulin growth factor have central roles in growth, metabolism and ageing of animals, including Drosophila melanogaster. In Drosophila, insulin-like peptides (Dilps) are produced by specialized neurons in the brain. Here we show that Drosophila short neuropeptide F (sNPF), an orthologue of mammalian neuropeptide Y (NPY), and sNPF receptor sNPFR1 regulate expression of Dilps. Body size was increased by overexpression of sNPF or sNPFR1. The fat body of sNPF mutant Drosophila had downregulated Akt, nuclear localized FOXO, upregulated translational inhibitor 4E-BP and reduced cell size. Circulating levels of glucose were elevated and lifespan was also extended in sNPF mutants. We show that these effects are mediated through activation of extracellular signal-related kinases (ERK) in insulin-producing cells of larvae and adults. Insulin expression was also increased in an ERK-dependent manner in cultured Drosophila central nervous system (CNS) cells and in rat pancreatic cells treated with sNPF or NPY peptide, respectively. Drosophila sNPF and the evolutionarily conserved mammalian NPY seem to regulate ERK-mediated insulin expression and thus to systemically modulate growth, metabolism and lifespan.     

Worker honey bee ovary development: seasonal variation and the influence of larval and adult nutrition

We examined the effect of larval and adult nutrition on worker honey bee (Apis mellifera L.) ovary development. Workers were fed high or low-pollen diets as larvae, and high or low-protein diets as adults. Workers fed low-protein diets at both life stages had the lowest levels of ovary development, followed by those fed high-protein diets as larvae and low- quality diets as adults, and then those fed diets poor in protein as larvae but high as adults. Workers fed high-protein diets at both life stages had the highest levels of ovary development. The increases in ovary development due to improved dietary protein in the larval and adult life stages were additive. Adult diet also had an effect on body mass. The results demonstrate that both carry-over of larval reserves and nutrients acquired in the adult life stage are important to ovary development in worker honey bees. Carry-over from larval development, however, appears to be less important to adult fecundity than is adult nutrition. Seasonal trends in worker ovary development and mass were examined throughout the brood rearing season. Worker ovary development was lowest in spring, highest in mid-summer, and intermediate in fall.     

植物乳杆菌、苹果醋酸杆菌和酿酒酵母三种微生物对黑腹果蝇行为和发育的影响

[目的]肠道微生物在宿主的多种生命活动中发挥重要作用.本研究旨在通过研究植物乳杆菌Lactobacillus plantarum,苹果醋酸杆菌Acetobacter malorum和酿酒酵母Saccharomyces cerevisiae 3种微生物对黑腹果蝇Drosophila melanogaster觅食、产卵和发...     

Alcohol dehydrogenase and ethanol tolerance at the cellular level in Drosophila melanogaster

Exposure of early third instar larvae of Drosophila melanogaster to a nonlethal dose of ethanol was detrimental to larvae lacking alcohol dehydrogenase (ADH) but beneficial to wild-type larvae in terms of surviving a later ethanol tolerance test, indicating that one of the important functions of the ADH system is to supply derivatives of ethanol to larvae that in turn promote ethanol tolerance. High intracellular concentrations of ethanol in ADH-deficient (Adhn2) larvae fed ethanol were accompanied by a decrease in the cell membrane infoldings of fat body cells, suggesting that the capacities to absorb and release molecules were reduced. Marked effects of ethanol on the endoplasmic reticulum and mitochondria of ADH-deficient larvae were also evident. The absence of similar changes in wild-type larvae that were fed moderate levels of ethanol showed that the ADH system kept the intracellular level of ethanol at a concentration low enough to avoid cell damage. A cytometric analysis of electron micrographs showed that there were ethanol-induced reductions in glycogen, lipid, and protein stores in the fat body cells of ADH-deficient larvae fed 1.25% ethanol (v/v) compared with null larvae fed an ethanol-free diet. This finding implied that the capacities to synthesize or store these compounds may be limited by high intracellular concentrations of ethanol. The cytometric analysis also revealed that the consumption of diets containing 2.5% and 4.5% ethanol by Canton-S wild-type larvae for 3 days after 4 days of feeding on an ethanol-free diet resulted in decreases in glycogen and protein deposits in fat body cells, but increased the amount of lipid deposits compared to larvae fed an ethanol-free diet. This observation, coupled with the greater weight of wild-type adults that were fed a growth-limiting concentration of ethanol compared with control adults, suggested that a metabolic defense mechanism in larvae is to convert toxic ethanol to nontoxic storage products. Dietary ethanol alone and in combination with isopropanol stimulated an increase in the size of the NAD-pool in larvae, a condition that may favor the activity of ADH. A low dietary level of isopropanol (1%) completely blocked glycogen deposition in wild-type larvae, whereas ethanol did not. Thus ethanol and isopropanol exert some different toxic effects on larval fat bodies.     

苦瓜素Ⅰ对亚洲玉米螟的生物活性及对其幼虫体内代谢酶活性的影响

【目的】为研究苦瓜素Ⅰ对亚洲玉米螟 Ostrinina furnacalis (Güenée)的生物活性和体内相关酶活性的影响。【方法】采用饲料混药法测定了苦瓜素Ⅰ对亚洲玉米螟生长发育和繁殖的影响,并以生命表的方法评价了苦瓜素Ⅰ对亚洲玉米螟实验种群增长的控制作用;采用酶标仪测定了苦瓜素Ⅰ对亚洲玉米螟幼虫海藻糖酶和磷酸酯酶活性的影响。【结果】用含0.25, 0.5, 1.0, 2.0和4.0 mg/g浓度苦瓜素Ⅰ的人工饲料饲喂亚洲玉米螟3龄幼虫3 d,幼虫的存活率明显降低, LC₅₀为3.2 mg/g;对幼虫体重增长的抑制作用显著,在4.0 mg/g浓度下,第1, 2和3 天体重增长的抑制率分别为76.87%, 78.24%和79.94%,且发育历期明显延长;苦瓜素Ⅰ各浓度处理组中亚洲玉米螟蛹的历期和成虫寿命与对照相比差异不显著,但苦瓜素Ⅰ明显降低了亚洲玉米螟雌成虫的产卵量,4.0 mg/g浓度下,产卵抑制率高达73.55%。苦瓜素Ⅰ对亚洲玉米螟幼虫海藻糖酶、酸性磷酸酯酶和碱性磷酸酯酶活性均有明显的抑制作用,处理24, 48和72 h后,对亚洲玉米螟幼虫海藻糖酶活性的IC₅₀分别为3.8, 2.9和4.9 mg/g;对酸性磷酸酯酶活性的IC₅₀分别为3.1, 2.6和1.5 mg/g,对碱性磷酸酯酶活性的IC₅₀分别为3.3 ,1.9和3.6 mg/g。【结论】苦瓜素Ⅰ能显著抑制亚洲玉米螟幼虫的生长发育及成虫的生殖力,使其实验种群的增长受到明显控制。苦瓜素Ⅰ抑制亚洲玉米螟幼虫体内海藻糖酶和磷酸酯酶活性是其作用机制之一。     

Insulin/IGF-I-signaling pathway: an evolutionarily conserved mechanism of longevity from yeast to humans

Although the underlying mechanisms of longevity are not fully understood, it is known that mutation in genes that share similarities with those in humans involved in the insulin/insulin-like growth factor I (IGF-I) signal response pathway can significantly extend life span in diverse species, including yeast, worms, fruit flies, and rodents. Intriguingly, the long-lived mutants, ranging from yeast to mice, share some important phenotypic characteristics, including reduced insulin signaling, enhanced sensitivity to insulin, and reduced IGF-I plasma levels. Such genetic homologies and phenotypic similarities between insulin/IGF-I pathway mutants raise the possibility that the fundamental mechanism of aging may be evolutionarily conserved from yeast to mammals. Very recent findings also provide novel and intriguing evidence for the involvement of insulin and IGF-I in the control of aging and longevity in humans. In this study, we focus on how the insulin/IGF-I pathway controls yeast, nematode, fruit fly, and rodent life spans and how it is related to the aging process in humans to outline the prospect of a unifying mechanism in the genetics of longevity.     

The functions of insulin signaling: size isn't everything,even in Drosophila

Mammalian insulin and insulin-like growth factors (IGFs) signal through several receptors with different ligand specificities to regulate metabolism and growth. This regulation is defective in diabetes and in a wide variety of human tumors. Recent analysis in Drosophila melanogaster has revealed that insulin-like molecules (known as DILPs in flies) also control growth and metabolism, but probably do so by signaling through a single insulin receptor (InR). The intracellular signaling molecules regulated by this receptor are highly evolutionarily conserved. Work in flies has helped to dissect the network of InR-regulated intracellular signaling pathways and identify some of the critical players in these pathways and in interacting signaling cascades. Surprisingly, these studies have shown that DILPs control tissue and body growth primarily by regulating cell growth and cell size. Changes in cell growth produced by these molecules may subsequently modulate the rate of cell proliferation in a cell type-specific fashion. At least part of this growth effect is mediated by two small groups of neurons in the Drosophila brain, which secrete DILPs into the circulatory system at levels that are modulated by nutrition. This signaling center is also involved in DILP-dependent control of the fly's rate of development, fertility, and life span. These surprisingly diverse functions of InR signaling, which appear to be conserved in all higher animals, reflect a central role for this pathway in coordinating development, physiology, and properly proportioned growth of the organism in response to its nutritional state. Studies in flies are providing important new insights into the biology of this system, and the identification of novel components in the InR-regulated signaling cascade is already beginning to inform the development of new therapeutic strategies for insulin-linked diseases in the clinic.     

Effects of dietary protein:carbohydrate balance on life-history traits in six laboratory strains of Drosophila melanogaster

Drosophila melanogaster Meigen (Diptera: Drosophilidae) is a key model insect for studying life span and aging. Many laboratory strains of D. melanogaster are currently used by laboratories worldwide, but they are known to vary considerably in their physiology, behavior, and life histories. Although the importance of dietary protein:carbohydrate (P:C) balance as a predominant determinant of life span and other life-history traits has been highlighted in recent research, it remains unexplored whether the impacts of P:C balance on these fitness-related traits vary in a strain-specific manner in D. melanogaster. In this study, we compared the life-history consequences (life span, egg production rate, pre-adult survival, development time, and body mass at eclosion) of six laboratory strains of D. melanogaster (w1118, yw, Oregon-R, white Canton-S, Canton-S-SNU, and Canton-S-Inha) allocated to one of four synthetic diets differing in P:C ratio (1:16, 1:4, 1:1, or 4:1). The effects of dietary P:C balance on various adult and larval life-history traits were qualitatively similar across all strains studied in this study. Regardless of fly strain, adults exhibited a shortened life span and improved egg production on a diet with the highest P:C ratio of 4:1. In all strains, larvae raised on a diet comprising the lowest P:C ratio of 1:16 suffered high mortality, delayed development time, and reduced body mass. Despite the general similarity in the direction of the effect of P:C balance across strains, fly strains differed in the magnitude of their life-history responses to dietary P:C balance, as indicated by a significant interaction between fly strain and dietary P:C ratio for all measured traits except body mass at eclosion. Possible mechanisms explaining such strain-specific responses are discussed.     

Partial ablation of adult Drosophilainsulin-producing neurons modulates glucose homeostasis and extends life span without insulin resistance

In Drosophila melanogaster (D. melanogaster), neurosecretory insulin-like peptide-producing cells (IPCs), analogous to mammalian pancreatic b cells are involved in glucose homeostasis. Extending those findings, we have developed in the adult fly an oral glucose tolerance test and demonstrated that IPCs indeed are responsible for executing an acute glucose clearance response. To further develop D. melanogaster as a relevant system for studying age-associated metabolic disorders, we set out to determine the impact of adult-specific partial ablation of IPCs (IPC knockdown) on insulin-like peptide (ILP) action, metabolic outcomes and longevity. Interestingly, while IPC knockdown flies are hyperglycemic and glucose intolerant, these flies remain insulin sensitive as measured by peripheral glucose disposal upon insulin injection and serine phosphorylation of a key insulin-signaling molecule, Akt. Significant increases in stored glycogen and triglyceride levels as well as an elevated level of circulating lipid measured in adult IPC knockdown flies suggest profound modulation in energy metabolism. Additional physiological outcomes measured in those flies include increased resistance to starvation and impaired female fecundity. Finally, increased life span and decreased mortality rates measured in IPC knockdown flies demonstrate that it is possible to modulate ILP action in adult flies to achieve life span extension without insulin resistance. Taken together, we have established and validated an invertebrate genetic system to further investigate insulin action, metabolic homeostasis and regulation of aging regulated by adult IPCs.