Comparative Transcriptomics of Fat Bodies between Symbiotic and Quasi-Aposymbiotic Adult Females of Blattella germanica with Emphasis on the Metabolic Integration with Its Endosymbiont Blattabacterium and Its Immune System

We explored the metabolic integration of Blattella germanica and its obligate endosymbiont Blattabacterium cuenoti by the transcriptomic analysis of the fat body of quasi-aposymbiotic cockroaches, where the endosymbionts were almost entirely removed with rifampicin. Fat bodies from quasi-aposymbiotic insects displayed large differences in gene expression compared to controls. In quasi-aposymbionts, the metabolism of phenylalanine and tyrosine involved in cuticle sclerotization and pigmentation increased drastically to compensate for the deficiency in the biosynthesis of these amino acids by the endosymbionts. On the other hand, the uricolytic pathway and the biosynthesis of uric acid were severely decreased, probably because the reduced population of endosymbionts was unable to metabolize urea to ammonia. Metabolite transporters that could be involved in the endosymbiosis process were identified. Immune system and antimicrobial peptide (AMP) gene expression was also reduced in quasi-aposymbionts, genes encoding peptidoglycan-recognition proteins, which may provide clues for the maintenance of the symbiotic relationship, as well as three AMP genes whose involvement in the symbiotic relationship will require additional analysis. Finally, a search for AMP-like factors that could be involved in controlling the endosymbiont identified two orphan genes encoding proteins smaller than 200 amino acids underexpressed in quasi-aposymbionts, suggesting a role in the host-endosymbiont relationship.

From the fat body to the hemolymph: Profiling tick immune and storage proteins through transcriptomics and proteomics

Ticks are blood-feeding arachnids that are known to transmit various pathogenic microorganisms to their hosts. During blood feeding, ticks activate their metabolism and immune system to efficiently utilise nutrients from the host's blood and complete the feeding process. In contrast to insects, in which the fat body is known to be a central organ that controls essential metabolic processes and immune defense mechanisms, the function of the fat body in tick physiology is still relatively unexplored. To fill this gap, we sought to uncover the repertoire of genes expressed in the fat body associated with trachea (FB/Tr) by analyzing the transcriptome of individual, partially fed (previtellogenic) Ixodes ricinus females. The resulting catalog of individual mRNA sequences reveals a broad repertoire of transcripts encoding proteins involved in nutrient storage and distribution, as well as components of the tick immune system. To gain a detailed insight into the secretory products of FB/Tr specifically involved in inter-tissue transport and humoral immunity, the transcriptomic data were complemented with the proteome of soluble proteins in the hemolymph of partially fed female ticks. Among these proteins, the hemolipoglyco-carrier proteins were predominant. When comparing immune peptides and proteins from the fat body with those produced by hemocytes, we found that the fat body serves as a unique producer of certain immune components. Finally, time-resolved transcriptional regulation of selected immune transcripts from the FB/Tr was examined in response to experimental challenges with model microbes and analyzed by RT-qPCR. Overall, our data show that the fat body of ticks, similar to insects, is an important metabolic tissue that also plays a remarkable role in immune defense against invading microbes. These findings improve our understanding of tick biology and its impact on the transmission of tick-borne pathogens.

Inducible Cytochrome P450s in the Fat Body and Malpighian Tubules of the Polyphagous Pests of Spodoptera litura Confer Xenobiotic Tolerance

Cytochrome P450 plays vital roles in detoxifying xenobiotics. In this study, SlCYP340A and SlCYP340L expression in the Spodoptera litura fat body and SlCYP332A1, SlCYP6AB12, SlCYP6AB58, SlCYP6AB59, and SlCYP6AN4 expression in the Malpighian tubules were significantly upregulated after cyantraniliprole exposure, and SlCYP6AB58 and SlCYP6AB59 expression levels were simultaneously increased in the Malpighian tubules after gossypol treatment. Drosophila ectopically expressing candidate P450 genes showed that SlCYP332A1, SlCYP6AB12, SlCYP6AB59, SlCYP6AN4, and SlCYP340A conferred cyantraniliprole tolerance. The overexpression of SlCYP6AB58 and SlCYP6AB59 in Drosophila increased the number of eggs laid under the gossypol treatment. Moreover, the knockdown of SlCYP332A1, SlCYP6AB12, SlCYP6AB59, SlCYP6AN4, and SlCYP340A increased S. litura mortality under the cyantraniliprole treatment. Homology modeling and molecular docking results suggested that candidate P450 has the potential to bind with cyantraniliprole. These results indicate that the CYP3 and CYP4 genes participate in cyantraniliprole detoxification and that SlCYP6AB59 may be simultaneously involved in the gossypol tolerance of S. litura.

The fat body cortical actin network regulates Drosophila inter-organ nutrient trafficking, signaling, and adipose cell size

Defective nutrient storage and adipocyte enlargement (hypertrophy) are emerging features of metabolic syndrome and type 2 diabetes. Within adipose tissues, how the cytoskeletal network contributes to adipose cell size, nutrient uptake, fat storage, and signaling remain poorly understood. Utilizing the Drosophila larval fat body (FB) as a model adipose tissue, we show that a specific actin isoform-Act5C-forms the cortical actin network necessary to expand adipocyte cell size for biomass storage in development. Additionally, we uncover a non-canonical role for the cortical actin cytoskeleton in inter-organ lipid trafficking. We find Act5C localizes to the FB cell surface and cell-cell boundaries, where it intimately contacts peripheral LDs (pLDs), forming a cortical actin network for cell architectural support. FB-specific loss of Act5C perturbs FB triglyceride (TG) storage and LD morphology, resulting in developmentally delayed larvae that fail to develop into flies. Utilizing temporal RNAi-depletion approaches, we reveal that Act5C is indispensable post-embryogenesis during larval feeding as FB cells expand and store fat. Act5C-deficient FBs fail to grow, leading to lipodystrophic larvae unable to accrue sufficient biomass for complete metamorphosis. In line with this, Act5C-deficient larvae display blunted insulin signaling and reduced feeding. Mechanistically, we also show this diminished signaling correlates with decreased lipophorin (Lpp) lipoprotein-mediated lipid trafficking, and find Act5C is required for Lpp secretion from the FB for lipid transport. Collectively, we propose that the Act5C-dependent cortical actin network of Drosophila adipose tissue is required for adipose tissue size-expansion and organismal energy homeostasis in development, and plays an essential role in inter-organ nutrient transport and signaling.

Seasonal changes in ultrastructure and gene expression in the fat body of worker honey bees

The anatomical, physiological, and behavioral characteristics of honey bees are affected by the season as well as division of labor. In this study, we examined the structure, ultrastructure, and gene expression of fat body cells in both long-lived winter and short-lived summer worker bees (the youngest stage of hive bees and forager bees). In contrast to hive bees, foragers and winter bees have a higher metabolism due to intensive muscle activity during their flight (foragers) or endothermic heat production (winter bees). These workers differ from hive bees in the biology of their mitochondria, peroxisomes, and lysosomes as well as in the expression of the genes involved in lipid, carbohydrate, amino acid metabolism, insulin, and TGF- β signaling. Additionally, the expression of genes related to phospholipid metabolism was higher in the hive bees. However, we found no differences between workers in the expression of genes controlling cell organelles, such as the Golgi apparatus, endoplasmic reticulum, ribosomes, nucleus, and vacuoles, as well as genes for DNA replication, cell cycle control, and autophagy. Furthermore, lysosomes, autophagic processes and lipofuscin particles were more frequently observed in winter bees using electron microscopy.

The role of SR protein kinases in regulating lipid storage in the Drosophila fat body

The survival of animals during periods of limited nutrients is dependent on the organism's ability to store lipids during times of nutrient abundance. However, the increased availability of food in modern western society has led to an excess storage of lipids resulting in metabolic diseases. To better understand the genes involved in regulating lipid storage, genome-wide RNAi screens were performed in cultured Drosophila cells and one group of genes identified includes mRNA splicing factor genes. Our lab has previously shown that a group of splicing factors important for intron/exon border recognition known as SR proteins are involved in controlling lipid storage in Drosophila; however, how these SR proteins are regulated to control lipid storage is not fully understood. Here, we focus on two SR protein kinases (SRPKs) in Drosophila: SRPK and SRPK79D. Decreasing the expression of these genes specifically in the adult fat body using RNAi resulted in lower levels of triglycerides and this is due to a decrease in the amount of fat stored per cell, despite having more fat cells, when compared to control flies. Decreasing SRPK and SRPK79D levels in the fat body leads to altered splicing of the β-oxidation gene, carnitine palmitoyltransferase 1 (CPT1), resulting in increased production of a more active enzyme, which would increase lipid breakdown and be consistent with the lean phenotype observed in these flies. In addition, flies with decreased SRPK and SRPK79D levels in their fat bodies eat less, which may also contribute to the decreased triglyceride phenotype. Together, these findings provide evidence to support that lipid storage is controlled by the phosphorylation of factors involved in mRNA splicing.

The ESCRT-III Protein Chmp1 Regulates Lipid Storage in the Drosophila Fat Body

Defects in how excess nutrients are stored as triglycerides can result in several diseases including obesity, heart disease, and diabetes. Understanding the genes responsible for normal lipid homeostasis will help understand the pathogenesis of these diseases. RNAi screens performed in Drosophila cells identified genes involved in vesicle formation and protein sorting as important for the formation of lipid droplets; however, all of the vesicular trafficking proteins that regulate lipid storage are unknown. Here, we characterize the function of the Drosophila Charged multivesicular protein 1 (Chmp1) gene in regulating fat storage. Chmp1 is a member of the ESCRT-III complex that targets membrane localized signaling receptors to intralumenal vesicles in the multivesicular body of the endosome and then ultimately to the lysosome for degradation. When Chmp1 levels are decreased specifically in the fly fat body, triglyceride accumulates while fat-body-specific Chmp1 overexpression decreases triglycerides. Chmp1 controls triglyceride storage by regulating the number and size of fat body cells produced and not by altering food consumption or lipid metabolic enzyme gene expression. Together, these data uncover a novel function for Chmp1 in controlling lipid storage in Drosophila and supports the role of the endomembrane system in regulating metabolic homeostasis.

Vitellogenin-2 Accumulation in the Fat Body and Hemolymph of Babesia-Infected Haemaphysalis longicornis Ticks

The protozoan parasite Babesia spp. invades into tick oocytes and remains in the offspring. The transovarial transmission phenomenon of Babesia in ticks has been demonstrated experimentally, but the molecular mechanisms remain unclear. Babesia invasion into oocytes occurs along with the progression of oogenesis. In the present study, to find the key tick factor(s) for Babesia transmission, we focused on molecules involved in yolk protein precursor (vitellogenin, Vg) synthesis and Vg uptake, which are crucial events in tick oogenesis. With a Haemaphysalis longicornis tick–Babesia ovata experimental model, the expression profiles of Akt, target of rapamycin, S6K, GATA, and Vg, Vg synthesis-related genes, and Vg receptor (VgR) and autophagy-related gene 6 (ATG6), Vg uptake-related genes, were analyzed using real-time PCR using tissues collected during the preovipositional period in Babesia-infected ticks. The expression levels of H. longicornis Vg-2 (HlVg-2) and HlVg-3 decreased in the fat body of Babesia-infected ticks 1 day after engorgement. In the ovary, HlVg-2 mRNA expression was significantly higher in Babesia-infected ticks than in uninfected ticks 1 and 2 days after engorgement and decreased 3 days after engorgement. HlVgR expression was significantly lower in Babesia-infected ticks than in uninfected ticks 2 and 4 days after engorgement. HlATG6 had a lower gene expression in Babesia-infected ticks compared to uninfected ticks 2 days after engorgement. Additionally, western blot analysis using protein extracts from each collected tissue revealed that H. longicornis Vg-2 (HlVg-2) accumulate in the fat body and hemolymph of Babesia-infected ticks. These results suggest that Vg uptake from the hemolymph to the ovary was suppressed in the presence of B. ovata. Moreover, HlVg-2 knockdown ticks had a lower detection rate of B. ovata DNA in the ovary and a significant reduction of B. ovata DNA in the hemolymph compared with control ticks. Taken together, our results suggest that accumulated HlVg-2 is associated with Babesia infection or transmission in the tick body. These findings, besides previous reports on VgR, provide important information to elucidate the transovarial transmission mechanisms of pathogens in tick vectors.

Bilateral asymmetry in bullfrog testes and fat bodies: correlations with steroidogenic activity, mast cells number and structural proteins

In seasonal breeders, such as amphibians, testicular functions depend on complex processes that change according to seasonality, including Leydig cell (LC) differentiation and lipid-dependent steroidogenesis, extracellular proteins remodeling and actin-dependent cellular dynamics. Speculating that fat bodies (FB) could support some of these processes in L. catesbeianus, we evaluated bilaterally the FB weights, correlating them to testicular parameters such as weight, testosterone (T) immunoexpression, mast cells (MC) number, vascularization and structural proteins. In an attempt to better understand the testicular asymmetry in amphibians, correlations between these different testicular parameters were also established. Right testes (RT), left testes (LT) and associated FB of bullfrogs were weighed, and testes were processed for light and transmission electron microscopy. Collagen content (COL) and MC number were quantified. T and actin immunoexpressions and vascular areas were measured. Statistical analyses and Pearson's correlation were performed. The LT and its associated FB were heavier than the right ones, and showed intense T and actin immunoexpressions, numerous lipid-rich LC, and greater MC number, COL and vascularization than the RT. Positive correlations were detected between: a) FB and testis weights, b) T immunoexpression and testis and FB weights, c) T and actin immunoexpressions and COL. Otherwise, MC number was inversely correlated to T immunoexpression and COL. In right and left sides, the proportional correlation between T immunoexpression and FB weight suggests that FB-stored lipid amount depends on the steroidogenic demand of its associated testis. Thus, the asymmetry in the testes and FB may be associated, at least in part, to the LC steroidogenic activity, which tends to be more intense in LT than in RT. The results also point to a role of COL and mast cells in the LC differentiation and steroidogenesis. Actin was also greater in LT and correlated with T immunoexpression, indicating that the amount of this structural protein depends on androgenic control. Therefore, the testicular asymmetry in bullfrogs seems to be associated to different morphofunctional processes occurring, bilaterally, at different intensities. In this case, there is a tendency of LT, in association with its FB, to be more active than RT. The findings highlight the FB-testis interplay for the comprehension of reproduction in amphibians.

Analyzing cachectic phenotypes in the muscle and fat body of Drosophila larvae

Drosophila has become a popular model for examining the metabolic wasting syndrome, cachexia, characterized by degradation of muscles and fat. Here we present a protocol for quick and consistent scoring of muscle detachment, fat body lipid droplet size, and extracellular matrix (ECM) quantifications in Drosophila larvae. We detail the procedures for dissecting, staining, and imaging third instar Drosophila larval muscle fillets and fat body, and how to utilize FIJI macros for robust quantification of cachectic phenotypes in these dissected tissues.

For complete details on the use and execution of this protocol, please refer to Lodge et al. (2021).

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Detailed description of larval muscle preparation for muscle detachment analysis

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Detailed description of fat body dissection

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Quantification of fat body lipid droplet size and ECM disruption using FIJI macros

Regulation of insulin-like peptide expression in adult Blattella germanica females

The insulin-IGF-signalling (IIS) pathway regulates key processes in metazoans. The pathway is activated through the binding of the ligands, which in insects are usually referred to as insulin-like peptides (ILPs), to a class of receptor tyrosine kinases, the insect insulin receptor. To study the pathway regulation, it is therefore essential to understand how ILPs are produced and released. In this study we analysed the factors that regulate the expression of the seven ILPs (BgILPs) expressed in adult females of the German cockroach, Blattella germanica. The results showed that the starvation-induced expression reduction of brain BgILP3, 5 and 6 and fat body BgILP7 is not due to reduced juvenile hormone (JH) or decreased TOR pathway activity. In addition, depletion of FoxO in starved females did not correct the low levels of these BgILPs, but even reduced further BgILP5 expression, indicating the need to maintain certain basal levels of BgILP5 even during starvation. Furthermore, JH promoted increased BgILP5 and decreased BgILP3 expression in the brain, an effect that required Methoprene-tolerant (Met), the JH receptor, but not Krüppel homolog 1 (Kr-h1), the main JH transducer. On the other hand, JH inhibited the expression of BgILP7 in the fat body, although in this case, the action required both Met and Kr-h1. In addition, JH reduction treatments produced a decrease in the expression of the insulin receptor in the fat body, which suggests an increase in IIS. The results show a peculiar regulation of ILP expression in adult B. germanica females, which is clearly different than that seen in other species. This is understandable given that gene duplications in recent clades have resulted in different sets of ILP genes, involving substantial changes in gene regulatory networks.

Exercise and/or Cold Exposure Alters the Gene Expression Profile in the Fat Body and Changes the Heart Function in Drosophila

The major reason of human morbidity and mortality is obesity and related diseases. Brown adipose tissue (BAT) is associated with low total adipose tissue content and a lower risk of type 2 diabetes mellitus. Studies have shown that exercise and cold expose may induce browning. In this study, we verified (1) whether exercise and/or cold exposure can improve the expression level of ucp4c, serca, ampkα, camkII, sirt1, octβ3r, and hamlet; (2) if these interventions can save cardiac dysfunction induced by a high-fat diet (HFD) in Drosophila. w1118 (wild-type) virgin female flies collected within 8 h after eclosion were divided into eight groups: the normal feed control group (NFD-C), the normal feed exercise group (NFD-E), the normal feed cold exposure group (NFD-CA), the normal feed exercise/cold exposure group (NFD-EC), the HFD control group (HFD-C), the HFD exercise group (HFD-E), the HFD cold exposure group (HFD-CA), and the HFD exercise/cold exposure group (HFD-EC). After exercise and/or cold exposure for 7 days, the mRNA expression levels of ucp4c, serca, ampkα, camk II, sirt1, octβ3r, and hamlet were tested by qRT-PCR, and m-mode was used to assess cardiac function. In addition, we assessed the triacylglycerol (TAG) levels, motor ability, fat mass (by Oil Red O [ORO] staining), and morphological features. The results of TAG, ORO staining, and morphological features all indicate that after interventions, body size of Drosophila was smaller compared with the control group, irrespective of the feeding patterns. The mRNA expression levels of ucp4c, serca, octβ3r, hamlet, ampkα, camkII, and sirt1 were changed to varying degrees under different intervention states (exercise and/or cold exposure). Cold exposure and exercise/cold exposure partly improved cardiac function and the normal fruit flies' cardiac function and exercise ability. However, after exercise intervention, exercise ability and heart function were improved in both HFD and normal-fat diet (NFD) fruit flies. In conclusion, different intervention states (exercise and/or cold exposure) can change the mRNA expression levels of ucp4c, serca, octβ3r, hamlet, ampkα, camkII, and sirt1. Exercise is the most effective way to restore HFD-induced cardiac dysfunction.

Unraveling the innate immune responses of Bombyx mori hemolymph, fat body, and midgut to Bombyx mori nucleopolyhedrovirus oral infection by metabolomic analysis

Bombyx mori nucleopolyhedrovirus (BmNPV) infection causes a series of physiological and pathological changes in Bombyx mori (B. mori). Here, a metabolomic study of the innate immunity organs including hemolymph, fat body, and midgut of the silkworm strain Dazao following BmNPV challenge was conducted to reveal the metabolic variations in B. mori. Compared to the control, 4964 and 4942 features with 4077 and 4327 high-quality features were generated under positive and negative modes, respectively, from BmNPV-infected larvae. The principal component analysis and supervised learning method using partial least squares discrimination analysis demonstrated good analytical stability and experimental reproducibility of the metabolic profiles. Based on database annotations, a total of 296, 108, and 215 differential expressed metabolites (DEMs) were identified from BmNPV-infected group of hemolymph, fat body, and midgut, respectively, which were all mainly grouped into carboxylic acids and derivatives, fatty acyls, and glycerophospholipids. Kyoto Encyclopedia of Genes and Genomes Database enrichment analysis of the DEMs showed that amino acid metabolism was increased at 24 h after BmNPV infection. BmNPV induction was adopted to significantly alter a series of immune-related pathways including phospholipase D signaling pathway, FoxO signaling pathway, metabolism of xenobiotics by cytochrome P450, melanogenesis, membrane transport, carbohydrate metabolism, and lipid metabolism. The different levels of expression of several DEMs including l-glutamate, naphthalene, 3-succinoylpyridine 1-acyl-sn-glycerol 3-phosphate, and l-tyrosine which were involved in those pathways exhibited the immune responses of B. mori to BmNPV infection. Our findings are valuable for a better understanding of the antiviral mechanism of B. mori underlying the interaction between the silkworm and BmNPV.

Increased insulin signaling in the Anopheles stephensi fat body regulates metabolism and enhances the host response to both bacterial challenge and Plasmodium falciparum infection

In vertebrates and invertebrates, the insulin/insulin-like growth factor 1 (IGF1) signaling (IIS) cascade is highly conserved and plays a vital role in many different physiological processes. Among the many tissues that respond to IIS in mosquitoes, the fat body has a central role in metabolism, lifespan, reproduction, and innate immunity. We previously demonstrated that fat body specific expression of active Akt, a key IIS signaling molecule, in adult Anopheles stephensi and Aedes aegypti activated the IIS cascade and extended lifespan. Additionally, we found that transgenic females produced more vitellogenin (Vg) protein than non-transgenic mosquitoes, although this did not translate into increased fecundity. These results prompted us to further examine how IIS impacts immunity, metabolism, growth and development of these transgenic mosquitoes. We observed significant changes in glycogen, trehalose, triglycerides, glucose, and protein in young (3-5 d) transgenic mosquitoes relative to non-transgenic sibling controls, while only triglycerides were significantly changed in older (18 d) transgenic mosquitoes. More importantly, we demonstrated that enhanced fat body IIS decreased both the prevalence and intensity of Plasmodium falciparum infection in transgenic An. stephensi. Additionally, challenging transgenic An. stephensi with Gram-positive and Gram-negative bacteria altered the expression of several antimicrobial peptides (AMPs) and two anti-Plasmodium genes, nitric oxide synthase (NOS) and thioester complement-like protein (TEP1), relative to non-transgenic controls. Increased IIS in the fat body of adult female An. stephensi had little to no impact on body size, growth or development of progeny from transgenic mosquitoes relative to non-transgenic controls. This study both confirms and expands our understanding of the critical roles insulin signaling plays in regulating the diverse functions of the mosquito fat body.

The steroid-induced microRNA let-7 regulates developmental growth by targeting cdc7 in the Drosophila fat body

In insects, 20-hydroxyecdysone (20E) limits systemic growth by triggering developmental transitions. Previous studies have shown that 20E-induced let-7 exhibits crosstalk with the cell cycle. Here, we examined the underlying molecular mechanisms and physiological functions of 20E-induced let-7 in the fat body, an organ for energy storage and nutrient mobilization which plays a critical role in the larval growth. First, the overexpression of let-7 decreased the body size and led to the reduction of both nucleolus and cell sizes in the larval fat body. In contrast, the overexpression of let-7-Sponge increased the nucleolus and cell sizes. Moreover, we found that cdc7, encoding a conserved protein kinase that controls the endocycle, is a target of let-7. Notably, the mutation of cdc7 in the fat body resulted in growth defects. Overall, our findings revealed a novel role of let-7 in the control of endoreduplication-related growth during larval-prepupal transition in Drosophila.

Influence of Serratia marcescens and Rhodococcus rhodnii on the Humoral Immunity of Rhodnius prolixus

Chagas disease is a human infectious disease caused by Trypanosoma cruzi and can be transmitted by triatomine vectors, such as Rhodnius prolixus. One limiting factor for T. cruzi development is the composition of the bacterial gut microbiota in the triatomine. Herein, we analyzed the humoral immune responses of R. prolixus nymphs treated with antibiotics and subsequently recolonized with either Serratia marcescens or Rhodococcus rhodnii. The treatment with antibiotics reduced the bacterial load in the digestive tract, and the recolonization with each bacterium was successfully detected seven days after treatment. The antibiotic-treated insects, recolonized with S. marcescens, presented reduced antibacterial activity against Staphylococcus aureus and phenoloxidase activity in hemolymph, and lower nitric oxide synthase (NOS) and higher defensin C gene (DefC) gene expression in the fat body. These insects also presented a higher expression of DefC, lower prolixicin (Prol), and lower NOS levels in the anterior midgut. However, the antibiotic-treated insects recolonized with R. rhodnii had increased antibacterial activity against Escherichia coli and lower activity against S. aureus, higher phenoloxidase activity in hemolymph, and lower NOS expression in the fat body. In the anterior midgut, these insects presented higher NOS, defensin A (DefA) and DefC expression, and lower Prol expression. The R. prolixus immune modulation by these two bacteria was observed not only in the midgut, but also systemically in the fat body, and may be crucial for the development and transmission of the parasites Trypanosoma cruzi and Trypanosoma rangeli.

Adipokine and fat body in flies: Connecting organs

Under conditions of nutritional and environmental stress, organismal homeostasis is preserved through inter-communication between multiple organs. To do so, higher organisms have developed a system of interorgan communication through which one tissue can affect the metabolism, activity or fate of remote organs, tissues or cells. In this review, we discuss the latest findings emphasizing Drosophila melanogaster as a powerful model organism to study these interactions and may constitute one of the best documented examples depicting the long-distance communication between organs. In flies, the adipose tissue appears to be one of the main organizing centers for the regulation of insect development and behavior: it senses nutritional and hormonal signals and in turn, orchestrates the release of appropriate adipokines. We discuss the nature and the role of recently uncovered adipokines, their regulations by external cues, their secretory routes and their modes of action to adjust developmental growth and timing accordingly. These findings have the potential for identification of candidate factors and signaling pathways that mediate conserved interorgan crosstalk.

Identification of G protein-coupled receptors required for vitellogenesis and egg development in an insect with panoistic ovary

G protein-coupled receptors (GPCRs), a superfamily of integral transmembrane proteins regulate a variety of physiological processes in insects. Juvenile hormone (JH) is known to stimulate Vitellogenin (Vg) synthesis in the fat body, secretion into the hemolymph and uptake by developing oocytes. However, the role of GPCRs in JH-dependent insect vitellogenesis and oocyte maturation remains elusive. In the present study, we performed transcriptomic analysis and RNA interference (RNAi) screening in vitellogenic females of the migratory locust Locusta migratoria. Of 22 GPCRs identified in ovarian transcriptome, LGR4, OR-A1, OR-A2, Mthl1, Mthl5 and Smo were most abundant in the ovary. By comparison, mAChR-C expressed at higher levels in the fat body, whereas Oct/TyrR, OARβ, AdoR and ADGRA3 were at higher expression levels in the brain. Our RNAi screening demonstrated that knockdown of six GPCRs resulted in defective phenotypes of Vg accumulation in developing oocytes, accompanied by blocked ovarian development and impaired oocyte maturation. While LGR4 and Oct/TyrR appeared to control Vg synthesis in the fat body, OR-A1, OR-A2, mAChR-C and CirlL regulated Vg transportation and uptake. The findings provide fundamental evidence for deciphering the regulatory mechanisms of GPCRs in JH-stimulated insect reproduction.

A Short-Type Peptidoglycan Recognition Protein 1 (PGRP1) Is Involved in the Immune Response in Asian Corn Borer, Ostrinia furnacalis (Guenée)

The insect immune response is initiated by the recognition of invading microorganisms. Peptidoglycan recognition proteins (PGRPs) function primarily as pattern recognition receptors by specifically binding to peptidoglycans expressed on microbial surfaces. We cloned a full-length cDNA for a PGRP from the Asian corn borer Ostrinia furnacalis (Guenée) and designated it as PGRP1. PGRP1 mRNA was mainly detected in the fat bodies and hemocytes. Its transcript levels increased significantly upon bacterial and fungal challenges. Purified recombinant PGRP1 exhibited binding activity to the gram-positive Micrococcus luteus, gram-negative Escherichia coli, entomopathogenic fungi Beauveria bassiana, and yeast Pichia pastoris. The binding further induced their agglutination. Additionally, PGRP1 preferred to bind to Lys-type peptidoglycans rather than DAP-type peptidoglycans. The addition of recombinant PGRP1 to O. furnacalis plasma resulted in a significant increase in phenoloxidase activity. The injection of recombinant PGRP1 into larvae led to a significantly increased expression of several antimicrobial peptide genes. Taken together, our results suggest that O. furnacalis PGRP1 potentially recognizes the invading microbes and is involved in the immune response in O. furnacalis.

Characterization of calcium signaling proteins from the fat body of the Colorado Potato Beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae): Implications for diapause and lipid metabolism

Calcium (Ca²⁺) regulates many cellular and physiological processes from development to reproduction. Ca²⁺ is also an important factor in the metabolism of lipids, the primary energy source used during insect starvation and diapause. Ca²⁺ signaling proteins bind to Ca²⁺ and maintain intracellular Ca²⁺ levels. However, knowledge about Ca²⁺ signaling proteins is mostly restricted to the model Drosophila melanogaster and the response of Ca²⁺ signaling genes to starvation or diapause is not known. In this study, we identified three Ca²⁺ signaling proteins; the primary Ca²⁺ binding protein Calmodulin (LdCaM), phosphatase Calcineurin B (LdCaNB), and the senescence marker protein Regucalcin (LdRgN), from the fat body of the Colorado Potato Beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae). This insect is a major pest of potato worldwide and overwinters under hibernation diapause as adults while utilizing lipids as the primary energy source. Putative EF-hand domains involved in Ca²⁺ binding were present in LdCaM, LdCaNB, but absent in LdRgN. LdCaM and LdCaNB were expressed in multiple tissues, while LdRgN was primarily expressed in the fat body. LdCaM was constitutively-expressed throughout larval development and at the adult stage. LdCaNB was primarily expressed in feeding larvae, and LdRgN in both feeding larvae and adults at comparable levels; however, both genes were down-regulated by molting. A response to starvation was observed only for LdRgN. Transcript abundance analysis in the entire body in relation to diapause revealed differential regulation with a general suppression during diapause, and higher mRNA levels in favor of females at post-diapause for LdCaM, and in favor of males at non-diapause for LdCaNB. Fat body-specific transcript abundance was not different between non-diapause and post-diapause for LdCaNB, but both LdCaM and LdRgN were down-regulated in males and both sexes, respectively by post-diapause. Silencing LdCaNB or LdRgN in larvae led to decreased fat content, indicating their involvement in lipid accumulation, while RNAi of LdCaM led to lethality.

A look into Colorado potato beetle lipid metabolism through the lens of lipid storage droplet proteins

The Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) inflicts serious damage to potato plants by feeding ravenously on their leaves. Adult L.decemlineata have a photoperiod-induced dormancy response, also known as diapause, which allows them to survive severe winter conditions by digging into soil. Most insects that undergo diapause accumulate abundant lipid reserves prior to diapause and utilize most of them during the diapause. This process is likely to be governed by the interplay of lipid storage droplet proteins (LSDs), also known as perilipins, with the help of other proteins. Here, genes encoding L. decemlineata LSD1 and LSD2 were identified. Both were expressed primarily in the fat body with LdLSD1 and LdLSD2 being primarily expressed in adult and larval stages, respectively. LdLSD1 was up-regulated in starving larvae, while LdLSD2 was primarily expressed in feeding larvae. The expression pattern of LdLSD1 in adults during feeding, diapause and post-diapause contrasted to the total body fat levels, while the expression pattern of LdLSD2 was positively correlated with total body fat levels. RNA interference (RNAi) of LdLSD2 in larvae suggested a core role for LSD2 in the protection/assembly of storage lipids as this treatment reduced overall lipid droplet volume. These data shed light on the functions of these proteins in L. decemlineata and their roles in both diapause and during starvation.

dHNF4 regulates lipid homeostasis and oogenesis in Drosophila melanogaster

The fly genome contains a single ortholog of the evolutionarily conserved transcription factor hepatocyte nuclear factor 4 (HNF4), a broadly and constitutively expressed member of the nuclear receptor superfamily. Like its mammalian orthologs, Drosophila HNF4 (dHNF4) acts as a critical regulator of fatty acid and glucose homeostasis. Because of its role in energy storage and catabolism, the insect fat body controls non-autonomous organs including the ovaries, where lipid metabolism is essential for oogenesis. The present paper used dHNF4 overexpression (OE) in the fat bodies and ovaries to investigate its potential roles in lipid homeostasis and oogenesis. When the developing fat body overexpressed dHNF4, animals exhibited reduced size and failed to pupariate, but no changes in body composition were observed. Conditional OE of dHNF4 in the adult fat body produced a reduction in triacylglycerol content and reduced oogenesis. Ovary-specific dHNF4 OE increased oogenesis and egg-laying, but reduced the number of adult offspring. The phenotypic effects on oogenesis that arise upon dHNF4 OE in the fat body or ovary may be due to its function in controlling lipid utilization.

The piRNA response to BmNPV infection in the silkworm fat body and midgut

Bombyx mori nucleopolyhedrovirus (BmNPV) is a DNA virus that causes huge losses to the silkworm industry but the piRNA responses during BmNPV infection in the silkworm remain uninvestigated. Here, silkworm piRNA profiles of uninfected and BmNPV-infected fat body and midgut were determined by high-through sequencing in the early stages of BmNPV infection. A total of 2675 and 3396 genome-derived piRNAs were identified from fat body and midgut, respectively. These genome-derived piRNAs mainly originated from unannotated instead of transposon regions in the silkworm genome. In total, 572 piRNAs were associated with 280 putative target genes in fat body and 805 piRNAs with 380 target genes in midgut. Compared to uninfected tissues, 322 and 129 piRNAs were significantly upregulated in BmNPV-infected fat body and midgut, respectively. In addition, 276 and 117 piRNAs were significantly downregulated. Moreover, differentially expressed (DE) piRNAs during BmNPV infection differed significantly between fat body and midgut. Putative DE piRNA-targeted genes were associated with "response to stimulus" and "environmental information processing" in fat body after infection with BmNPV, which may indicate an active piRNA response to BmNPV infection in fat body. This study may lay the foundation for future research of the potential roles of the piRNA pathway and specific piRNAs in BmNPV pathogenesis.

Blood meal drives de novo lipogenesis in the fat body of Rhodnius prolixus

In insects, lipids are stored in the fat body mainly as triacylglycerol. Lipids can be directly provided by digestion and incorporated from the hemolymph, or synthesized de novo from other substrates such as carbohydrates and amino acids. The first step in de novo lipid synthesis is catalyzed by acetyl-CoA carboxylase (ACC), which carboxylates acetyl-CoA to form malonyl-CoA. Rhodnius prolixus is a hematophagous insect vector of Chagas disease and feeds exclusively on large and infrequent blood meals. Adult females slowly digest the blood and concomitantly accumulate lipids in the fat body. In this study, we investigated the regulation of R. prolixus ACC (RhoprACC) expression and de novo lipogenesis activity in adult females at different nutritional and metabolic conditions. A phylogenetic analysis showed that insects, similar to other arthropods and unlike vertebrate animals, have only one ACC gene. In females on the fourth day after a blood meal, RhoprACC transcript levels were similar in the anterior and posterior midgut, fat body and ovary and higher in the flight muscles. In the fat body, gene expression was higher in fasted females and decreased after a blood meal. In the posterior midgut it increased after feeding, and no variation was observed in the flight muscle. RhoprACC protein content analysis of the fat body revealed a profile similar to the gene expression, with higher protein contents before feeding and in the first two days after a blood meal. Radiolabeled acetate was used to follow de novo lipid synthesis in the fat body and it was incorporated mainly into triacylglycerol, diacylglycerol and phospholipids. This lipogenic activity was inhibited by soraphen A, an ACC inhibitor, and it varied according to the insect metabolic status. De novo lipogenesis was very low in starved females and increased during the initial days after a blood meal. The flight muscles had a very low capacity to synthesize lipids when compared to the fat body. Radiolabeled leucine was also used as a substrate for de novo lipogenesis and the same lipid classes were formed. In conclusion, our results indicate that the blood meal induces the utilization of diet-derived amino acids by de novo lipogenesis in the fat body, and that the control of this activity does not occur at the RhoprACC gene or protein expression level.

Functional Diversification, Redundancy, and Epistasis among Paralogs of the Drosophila melanogaster Obp50a-d Gene Cluster

Large multigene families, such as the insect odorant-binding proteins (OBPs), are thought to arise through functional diversification after repeated gene duplications. Whereas many OBPs function in chemoreception, members of this family are also expressed in tissues outside chemosensory organs. Paralogs of the Obp50 gene cluster are expressed in metabolic and male reproductive tissues, but their functions and interrelationships remain unknown. Here, we report the genetic dissection of four members of the Obp50 cluster, which are in close physical proximity without intervening genes. We used CRISPR technology to excise the entire cluster while introducing a PhiC31 reintegration site to reinsert constructs in which different combinations of the constituent Obp genes were either intact or rendered inactive. We performed whole transcriptome sequencing and assessed sexually dimorphic changes in transcript abundances (transcriptional niches) associated with each gene-edited genotype. Using this approach, we were able to estimate redundancy, additivity, diversification, and epistasis among Obp50 paralogs. We analyzed the effects of gene editing of this cluster on organismal phenotypes and found a significant skewing of sex ratios attributable to Obp50a, and sex-specific effects on starvation stress resistance attributable to Obp50d. Thus, there is functional diversification within the Obp50 cluster with Obp50a contributing to development and Obp50d to stress resistance. The deletion-reinsertion approach we applied to the Obp50 cluster provides a general paradigm for the genetic dissection of paralogs of multigene families.

Larval nutrition influences adult fat stores and starvation resistance in Drosophila

Insulin plays a major role in connecting nutrient availability to energy homeostasis by regulating metabolic pathways. Defects in insulin signalling is the primary cause for diabetes, obesity and various metabolic disorders. Nutritional status during growth and developmental stages play a crucial role in determining adult size, fecundity and ageing. However, the association between developmental nutrition and adult metabolic disorders has not been fully explored. Here, we address the effects of nutrient status during the larval growth phase on adult metabolism in Drosophila. We report that restricted food supply in larvae led to higher fat reserves and starvation resistance in mature adult flies, which we attribute to low insulin signalling. A lesser amount of stored fat was mobilised during early adult stages and during acute starvation, which accounts for the metabolic effects. Furthermore, larval diet influenced the expression of fat mobilisation genes brummer and lipid storage droplet-2 in adult flies, which led to the metabolic phenotypes reported here. Thus, the restricted nutrient environment in developing larvae led to adaptive changes that entrain the adult flies for scarce food availability.

The validation of the role of several genes related to Bombyx mori nucleopolyhedrovirus infection in vivo

Bombyx mori nucleopolyhedrovirus (BmNPV) is one of primary silkworm pathogens and causes a serious damage of cocoon losses every year. Recent years, many works have been done to clarify the silkworm anti-BmNPV mechanism, and a significant progress has been made in screening and studying of genes and proteins related to BmNPV infection, but several of them lacked the proofs in vivo. In this study, to further validate the function of seven newly reported genes in vivo, including BmAtlatin-n, Bmferritin-heavy chain (BmFerHCH), Bmthymosin (BmTHY), Bmseroin1, Bmseroin2, Bmnuclear hormone receptors 96 (BmNHR96), and BmE3 ubiquitin-protein ligase SINA-like 10 (BmSINAL10), the response of them in the midgut, fat body, and hemolymph of differentially resistant strains (resistant strain YeA and susceptible strain YeB) at 48 h following BmNPV infection were analyzed. The results showed that the relative stable or upregulated expression level of BmAtlatin-n, BmTHY, Bmseroin1, and Bmseroin2 in YeA resistant strain following BmNPV infection further indicated their antiviral role in vivo, compared with susceptible YeB strain. Moreover, the significant downregulation of BmFerHCH, BmNHR96, and BmSINAL10 in both strains following BmNPV infection revealed their role in benefiting virus infection, as well as the upregulation of BmFerHCH in YeB midgut and BmSINAL10 in YeB hemolymph. These data could be used to complementary the proofs of the function of these genes in response to BmNPV infection.

The conserved transmembrane protein TMEM-39 coordinates with COPII to promote collagen secretion and regulate ER stress response

Dysregulation of collagen production and secretion contributes to aging and tissue fibrosis of major organs. How procollagen proteins in the endoplasmic reticulum (ER) route as specialized cargos for secretion remains to be fully elucidated. Here, we report that TMEM39, an ER-localized transmembrane protein, regulates production and secretory cargo trafficking of procollagen. We identify the C. elegans ortholog TMEM-39 from an unbiased RNAi screen and show that deficiency of tmem-39 leads to striking defects in cuticle collagen production and constitutively high ER stress response. RNAi knockdown of the tmem-39 ortholog in Drosophila causes similar defects in collagen secretion from fat body cells. The cytosolic domain of human TMEM39A binds to Sec23A, a vesicle coat protein that drives collagen secretion and vesicular trafficking. TMEM-39 regulation of collagen secretion is independent of ER stress response and autophagy. We propose that the roles of TMEM-39 in collagen secretion and ER homeostasis are likely evolutionarily conserved.

As the most abundant protein in animals, collagen plays diverse roles and its dysregulation impacts aging and many fibrotic disorders. It is important to understand how premature collagen proteins in the ER are processed and secreted, as many other aspects of collagen regulation have been elucidated in mechanistic detail. In this paper, we have characterized a novel conserved family of TMEM39 proteins, including human TMEM39A and C. elegans tmem-39 that regulates ER stress response and collagen secretion. Human TMEM39A directly interacts with SEC23A, a core component of the COPII vesicle coating complex responsible for vesicular cargo secretion to the Golgi apparatus. The function of TMEM-39 proteins in collagen secretion appears highly conserved and independent to the ER stress response and the autophagy pathway. Our results provide insights into functions and mechanisms of TMEM39 proteins in collagen secretion and suggest it as a plausible target for tissue fibrotic diseases.

Two calcium-binding chaperones from the fat body of the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) involved in diapause

Molecular chaperones are crucial for the correct folding of newly synthesized polypeptides, in particular, under stress conditions. Various studies have revealed the involvement of molecular chaperones, such as heat shock proteins, in diapause maintenance and starvation; however, the role of other chaperones in diapause and starvation relatively is unknown. In the current study, we identified two lectin-type chaperones with calcium affinity, a calreticulin (LdCrT) and a calnexin (LdCnX), that were present in the fat body of the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) during diapause. Both proteins possessed an N-globular domain, a P-arm domain, and a highly charged C-terminal domain, while an additional transmembrane domain was present in LdCnX. Phylogenetic analysis revealed distinction at the order level. Both genes were expressed in multiple tissues in larval and adult stages, and constitutively throughout development, though a starvation response was detected only for LdCrT. In females, diapause-related expression analysis in the whole body revealed an upregulation of both genes by post-diapause, but a downregulation by diapause only for LdCrT. By contrast, males revealed no alteration in their diapause-related expression pattern in the entire body for both genes. Fat body-specific expression analysis of both genes in relation to diapause revealed the same expression pattern with no alteration in females and downregulation in males by post-diapause. This study suggests that calcium-binding chaperones play similar and possibly gender-specific roles during diapause.

A deep insight into the transcriptome of midgut and fat body reveals the toxic mechanism of fluoride exposure in silkworm

Fluoride generally exists in the natural environment, and has been reported to induce serious environmental hazard to animals, plants, and even humans via ecological cycle. Silkworm, Bombyx mori, which showed significant growth and reproductivity reduction when exposed to fluoride, has become a model to evaluate the toxicity of fluoride. However, the detailed mechanism underlying fluoride toxicity and corresponding transport proteins remain unclear. In this study, we performed RNA-seq of the larval midgut and fat body with fluoride exposure and normal treatment. Differential analysis showed that there were 4405 differentially expressed genes in fat body and 4430 DEGs in midgut with fluoride stress. By Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses, we identified several key pathways involved in the fluoride exposure and poisoning. We focused on the oxidative phosphorylation and MAPK signal pathway. QRT-PCR confirmed that oxidative phosphorylation process was remarkably inhibited by fluoride exposure and resulted in the blocking of ATP synthesis. The MAPK signal pathway was stimulated via phosphorylation signal transduction. Moreover, by protein structure analysis combined with the DEGs, we screen 36 potential membrane proteins which might take part in transporting fluoride. Taken together, the results of our study expanded the underlying mechanisms of fluoride poisoning on silkworm larval growth and development, and implied potential fluoride transport proteins in silkworm.

Juvenile hormone upregulates sugarbabe for vitellogenesis and egg development in the migratory locust Locusta migratoria

Sugarbabe is a C₂ H₂ zinc-finger transcription factor that is sensitive to sugar and essential for lipid biosynthesis in larvae of Drosophila melanogaster. However, the role of Sugarbabe in adult insect development remains unexplored. Vitellogenesis is a nutrient-dependent process that is promoted by juvenile hormone (JH) in many insect species. Here, we cloned an ortholog gene of D. melanogaster Sugarbabe (DmSug) in the migratory locust Locusta migratoria. The locust Sugarbabe (LmSug) has five C₂ H₂ zinc-finger motifs similar to DmSug. LmSug was expressed at a low level in adult female locusts raised under poor nutrient conditions. JH treatment increased the expression level of LmSug. Knockdown of the JH receptor gene Met caused a reduction of LmSug expression. Depletion of the LmSug transcript level caused a significant reduction in vitellogenin expression in the fat body, resulting in impaired oocyte development and ovary growth. The results suggest that LmSug is expressed in response to JH, and plays an essential role in female insect reproduction.

Identification of Gonadulin and Insulin-Like Growth Factor From Migratory Locusts and Their Importance in Reproduction in Locusta migratoria

Many insect species have several genes coding for insulin-related peptides (IRPs), but so far only a single IRP gene has been identified in migratory locusts. Here, we report and characterize two other genes coding for peptides that are related to insulin, namely gonadulin and arthropod insulin-like growth factor (aIGF); peptides postulated to be orthologs of Drosophila melanogaster insulin-like peptides 8 and 6 respectively. In Locusta migratoria the aIGF transcript is expressed in multiple tissues as was previously reported for IRP in both L. migratoria and Schistocerca gregaria, but there are significant differences in expression patterns between the two species. The gonadulin transcript, however, seems specific to the ovary, whereas its putative receptor transcript is expressed most abundantly in the ovary, fat body and the central nervous system. Since the central nervous system-fat body-ovary axis is essential for successful reproduction, we studied the influence of gonadulin on vitellogenesis and oocyte growth. A reduction in the gonadulin transcript (via RNA interference) led to a significant reduction in vitellogenin mRNA levels in the fat body and a strong oocyte growth inhibition, thus suggesting an important role for gonadulin in reproduction in this species.

Bmintegrin β1: A broadly expressed molecule modulates the innate immune response of Bombyx mori

Integrins are transmembrane glycoproteins that are broadly distributed in living organisms. As a heterodimer, they contain an α and a β subunit, which are reported to be associated with various physiological and pathological processes. In the present study, a 2502 bp full-length cDNA sequence of Bmintegrin β1 was obtained from the silkworm, Bombyx mori. Bmintegrin β1 belongs to the β subunit of the integrin family and contains several typical structures of integrins. Gene expression profile analysis demonstrated that Bmintegrin β1 was ubiquitously expressed in all tested tissues and organs, with the maximum expression levels in fat body and hemocytes. The immunofluorescence results showed that Bmintegrin β1 was located in the cell membrane and widely distributed in fat bodies and different types of hemocytes. Bmintegrin β1 expression was remarkably increased after challenging with different kinds of bacteria and pathogen-associated molecular patterns (PAMPs). Further investigation revealed that Bmintegrin β1 could participate in the agglutination of pathogenic bacteria possibly through direct binding with the relative bacteria and PAMPs. Altogether, this study provides a novel insight into the immune functional features of Bmintegrin β1.

Galleria mellonella larvae fat body disruption (Lepidoptera: Pyralidae) caused by the venom of Habrobracon brevicornis (Hymenoptera: Braconidae)

The ability of Habrobracon brevicornis venom to elevate the nutritional suitability of a host by affecting the host larvae fat body condition was studied. To understand whether H. brevicornis crude venom impacts the host biochemical profile, the concentrations of total lipids and main sugars in the host larvae lymph were analyzed. All measurements were carried out during the first 3 days after envenomation. A significant increase in the lipid level was fixed only on the second day after envenomation. A significant increase in the total trehalose count was detected during all 3 days, while a significant increase in glucose concentration was noted only on the first day. Well-observed disruptions were fixed in thin and semithin sections of the G. mellonella larval fat body starting from the second day after envenomation. Significant increases in both phospholipase A₂ and C enzyme activity as well as acid proteases were detected in the wax moth fat body after envenomation during all experimental times. At the same time, imbalances in the antioxidant system, including changes in the activities of superoxide dismutase, peroxidases, catalase, and glutathione-S-transferase, were detected. The reliable increase in the expression of the gene encoding Hsp70 was fixed both for 24 and 48 h after envenomation, while a reliable increase in the expression of the gene encoding inhibitor of apoptosis protein was detected only 24 h after wax moth larvae envenomation. Considering the absence of DNA fragmentation, the imbalance in the "ROS/antioxidants" system, and the increased activity of phospholipases and acid proteases in the fat body cells from envenomated wax moth larvae, we can hypothesize that the fat body disruption occurs in a necrotic manner. The results of the work expand the knowledge about the biochemical aspects of interaction between ectoparasitoids and their hosts.

Silencing of ATG6 and ATG8 promotes increased levels of triacylglycerol (TAG) in the fat body during prolonged starvation periods in the Chagas disease vector Rhodnius prolixus

Rhodnius prolixus is an obligatorily hematophagous insect known as an important vector of Chagas disease. Autophagy is a conserved cellular mechanism that acts in response to nutrient starvation, where components of the cytoplasm are sequestered by a double membrane organelle, named autophagosome, which is targeted to fuse with the lysosome for degradation. Lipophagy is the process of lipid degradation by selective autophagy, where autophagosomes sequester lipid droplets and degrade triacylglycerol (TAG) generating free fatty acids for β-oxidation. Here, two essential genes of the autophagic pathway, Atg6/Beclin1 (RpAtg6) and Atg8/LC3 (RpAtg8), were silenced and the storage of lipids during starvation in Rhodnius prolixus was monitored. We found that RNAi knockdown of both RpAtg6 and RpAtg8 resulted in higher levels of TAG in the fat body and the flight muscle, 24 days after the blood meal, as well as a larger average diameter of the lipid droplets in the fat body, as seen by Nile Red staining under the confocal fluorescence microscope. Silenced starved insects had lower survival rates when compared to control insects. Accordingly, when examined during the starvation period for monitored activity, silenced insects had lower spontaneous locomotor activity and lower forced flight rates. Furthermore, we found that some genes involved in lipid metabolism had their expression levels altered in silenced insects, such as the Brummer lipase (down regulated) and the adipokinetic hormone receptor (up regulated), suggesting that, as previously observed in mammalian models, the autophagy and neutral lipolysis machineries are interconnected at the transcriptional level. Altogether, our data indicate that autophagy in the fat body is important to allow insects to mobilize energy from lipid stores.

MicroRNA miR-927 targets the juvenile hormone primary response gene Krüppel homolog1 to control Drosophila developmental growth

Krüppel homolog1 (Kr-h1) is a juvenile hormone (JH) response transcriptional factor that transduces JH signalling to repress insect metamorphosis in both hemimetabolous and holometabolous insects. While few studies about microRNAs (miRNAs) downregulating Kr-h1 expression to mediate insect metamorphosis have been demonstrated in hemimetabolous insects, the miRNAs that target the Kr-h1 of holometabolous insects have not been reported. Here, we identified two miR-927 binding sites within the 3'UTR region of Kr-h1 in Drosophila melanogaster, and miR-927 was found to downregulate the expression of Kr-h1. The expression profiles of miR-927 and Kr-h1 displayed relatively opposite pattern during most of the larval development stages. Overexpression of miR-927 in the fat body significantly decreased the expression of Kr-h1 and resulted in reduced oviposition, increased mortality, delayed pupation, and reduced pupal size. Notably, the co-overexpression of Kr-h1 rescued the developmental and growth defects associated with miR-927 overexpression, indicating that Kr-h1 is a biologically relevant target of miR-927. Moreover, the expression of miR-927 was found to be repressed by JH and its receptor Met/gce, forming a positive regulatory loop of JH signalling. Overall, our studies support a conserved role for the JH/miRNA/Kr-h1 regulatory axis in growth control during insect development.

Insulin receptor deficiency reduces lipid synthesis and reproductive function in the insect Rhodnius prolixus

Rhodnius prolixus, a vector of Chagas disease, is a hematophagous insect that feeds exclusively on blood. Each blood meal is digested within the first fourteen days after feeding, providing substrates for lipid synthesis for storage and egg production. These events are precisely regulated and emerging evidence points to a key function of insulin-like peptides (ILPs) in this control. Here we investigated the role of insulin receptor in the regulation of nutrient metabolism in fed adult females. The expression of insulin receptor (RhoprIR) gene was determined in adult organs, and it was highest in ovaries and previtellogenic follicles. We generated insects with RNAi-mediated knockdown of RhoprIR to address the physiological role of this receptor. RhoprIR deficiency improved longevity and reduced triacylglycerol storage in the fat body, whereas blood digestion remained unchanged for seven days after blood meal. The lower lipid content was attributable to decreased de novo lipogenesis as well as reduced incorporation of hemolymph-derived fatty acids into newly synthesized lipids within this organ. Consistent with that, fat bodies from RhoprIR-deficient insects exhibited decreased gene expression levels of lipophorin receptor (RhoprLpR), glycerol-3-phosphate acyltransferase 1 and 4 (RhoprGpat1 and RhoprGpat4), and carnitine palmitoyltransferase 1 (RhoprCpt1). Although hemolymph lipid profile was not affected by RhoprIR disruption, the concentration of circulating vitellogenin was increased. In line with these changes, RhoprIR-deficient females exhibited smaller ovaries and a marked reduction in oviposition. Taken together, these findings support a key role of insulin receptor in nutrient homeostasis, lipid synthesis and egg production following a blood meal.

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.

Innate immune system function following systemic RNA-interference of the Fragile X Mental Retardation 1 gene in the cricket Acheta domesticus

Fragile X syndrome (FXS), caused by a mutation in the Fragile X Mental Retardation 1 (FMR1) gene, is a common form of inherited mental retardation. Mutation of the gene leads to a loss of the gene product Fragile X Mental Retardation Protein (FMRP). While a loss of FMRP has been primarily associated with neural and cognitive deficits, it has also been reported to lead to immune system dysfunction in both humans and flies. We used the Acheta domesticus transcriptome to identify a highly conserved cricket ortholog of FMR1 (adfmr1). We cloned a partial cDNA of adfmr1, used systemic RNA interference (RNAi) to knockdown adfmr1 expression, and examined the impact of this knockdown (KD) on the cellular and humoral responses of the insect innate immune system. Following RNAi, both male and female crickets exhibited an increase in the number of circulating hemocytes, a decrease in total hemolymph phenoloxidase (PO) activity, and an increase in fat body lysozyme expression. Despite similar changes in these immune parameters in both sexes, male and female crickets responded differently to an immune challenge. Most KD males failed to survive an intra-abdominal injection of bacterial lipopolysaccharide, while KD females were just as likely as control females to survive this challenge. Our results support that decreased fmr1 expression can alter the cellular and humoral defenses of the insect innate immune system, and may lead to a decrease in male, but not female, immunocompetence.

What happens after a blood meal? A transcriptome analysis of the main tissues involved in egg production in Rhodnius prolixus, an insect vector of Chagas disease

The blood-sucking hemipteran Rhodnius prolixus is a vector of Chagas disease, one of the most neglected tropical diseases affecting several million people, mostly in Latin America. The blood meal is an event with a high epidemiological impact since adult mated females feed several times, with each meal resulting in a bout of egg laying, and thereby the production of hundreds of offspring. By means of RNA-Sequencing (RNA-Seq) we have examined how a blood meal influences mRNA expression in the central nervous system (CNS), fat body and ovaries in order to promote egg production, focusing on tissue-specific responses under controlled nutritional conditions. We illustrate the cross talk between reproduction and a) lipids, proteins and trehalose metabolism, b) neuropeptide and neurohormonal signaling, and c) the immune system. Overall, our molecular evaluation confirms and supports previous studies and provides an invaluable molecular resource for future investigations on different tissues involved in successful reproductive events. These analyses serve as a starting point for new investigations, increasing the chances of developing novel strategies for vector population control by translational research, with less impact on the environment and more specificity for a particular organism.

Role of a versatile peptide motif controlling Hox nuclear export and autophagy in the Drosophila fat body

Hox proteins are major regulators of embryonic development, acting in the nucleus to regulate the expression of their numerous downstream target genes. By analyzing deletion forms of the Drosophila Hox protein Ultrabithorax (Ubx), we identified the presence of an unconventional nuclear export signal (NES) that overlaps with a highly conserved motif originally described as mediating the interaction with the PBC proteins, a generic and crucial class of Hox transcriptional cofactors that act in development and cancer. We show that this unconventional NES is involved in the interaction with the major exportin protein CRM1 (also known as Embargoed in flies) in vivo and in vitro We find that this interaction is tightly regulated in the Drosophila fat body to control the autophagy-repressive activity of Ubx during larval development. The role of the PBC interaction motif as part of an unconventional NES was also uncovered in other Drosophila and human Hox proteins, highlighting the evolutionary conservation of this novel function. Together, our results reveal the extreme molecular versatility of a unique short peptide motif for controlling the context-dependent activity of Hox proteins both at transcriptional and non-transcriptional levels.

Cellular metabolic reprogramming controls sugar appetite in Drosophila

Cellular metabolic reprogramming is an important mechanism by which cells rewire their metabolism to promote proliferation and cell growth. This process has been mostly studied in the context of tumorigenesis, but less is known about its relevance for nonpathological processes and how it affects whole-animal physiology. Here, we show that metabolic reprogramming in Drosophila female germline cells affects nutrient preferences of animals. Egg production depends on the upregulation of the activity of the pentose phosphate pathway in the germline, which also specifically increases the animal's appetite for sugar, the key nutrient fuelling this metabolic pathway. We provide functional evidence that the germline alters sugar appetite by regulating the expression of the fat-body-secreted satiety factor Fit. Our findings demonstrate that the cellular metabolic program of a small set of cells is able to increase the animal's preference for specific nutrients through inter-organ communication to promote specific metabolic and cellular outcomes.

Molecular characterization of Antheraea mylitta arylphorin gene and its encoded protein

Antheraea mylitta arylphorin protein was extracted from the silk gland of fifth instar larvae and purified by ammonium sulphate precipitation, ion-exchange, and gel filtration chromatography. The N-terminal sequencing of ten amino acids (NH₂-SVVHPPHHEV-COOH) showed similarity with Antheraea pernyi arylphorin. Based on N-terminal and C-terminal A. pernyi arylphorin sequences, primers were designed, and A. mylitta arylphorin cDNA was cloned by RT-PCR from silk gland mRNA. Sequencing of complete cDNA including 25 nucleotides at 5' UTR (obtained by 5' RACE) showed that it consisted of an ORF of 2115 nucleotides which could encode a protein of 704 amino acids (predominantly aromatic residues) having molecular weight 83 kDa. Homology modelling was done using A. pernyi arylphorin as a template. Cloned arylphorin cDNA was expressed in E. coli and recombinant His-tagged protein was purified by Ni-NTA affinity chromatography. Analysis of tissue-specific expression of arylphorin by real-time PCR showed maximum expression in the fat body followed by silk gland and integument. 5' flanking region (759 bp) of arylphorin gene was amplified by inverse PCR and the full length gene (5359 nucleotides) containing five exons and four introns was cloned from the A. mylitta genomic DNA and sequenced. Polyclonal antibody was raised against purified arylphorin and more native arylphorin protein (500 kDa) was purified from the fat body by antibody affinity chromatography. Study of mitogenic effect of native and chymotrypsin hydrolysate of arylphorin on different insect cell lines showed that arylphorin could be used as serum substitute for in vitro cultivation of insect cells.

Down-regulation of a cytokine secreted from peripheral fat bodies improves visual attention while reducing sleep in Drosophila

Sleep is vital for survival. Yet under environmentally challenging conditions, such as starvation, animals suppress their need for sleep. Interestingly, starvation-induced sleep loss does not evoke a subsequent sleep rebound. Little is known about how starvation-induced sleep deprivation differs from other types of sleep loss, or why some sleep functions become dispensable during starvation. Here, we demonstrate that down-regulation of the secreted cytokine unpaired 2 (upd2) in Drosophila flies may mimic a starved-like state. We used a genetic knockdown strategy to investigate the consequences of upd2 on visual attention and sleep in otherwise well-fed flies, thereby sidestepping the negative side effects of undernourishment. We find that knockdown of upd2 in the fat body (FB) is sufficient to suppress sleep and promote feeding-related behaviors while also improving selective visual attention. Furthermore, we show that this peripheral signal is integrated in the fly brain via insulin-expressing cells. Together, these findings identify a role for peripheral tissue-to-brain interactions in the simultaneous regulation of sleep quality and attention, to potentially promote adaptive behaviors necessary for survival in hungry animals.

Alpha- and beta-adrenergic octopamine receptors in muscle and heart are required for Drosophila exercise adaptations

Endurance exercise has broadly protective effects across organisms, increasing metabolic fitness and reducing incidence of several age-related diseases. Drosophila has emerged as a useful model for studying changes induced by chronic endurance exercise, as exercising flies experience improvements to various aspects of fitness at the cellular, organ and organismal level. The activity of octopaminergic neurons is sufficient to induce the conserved cellular and physiological changes seen following endurance training. All 4 octopamine receptors are required in at least one target tissue, but only one, Octβ1R, is required for all of them. Here, we perform tissue- and adult-specific knockdown of alpha- and beta-adrenergic octopamine receptors in several target tissues. We find that reduced expression of Octβ1R in adult muscles abolishes exercise-induced improvements in endurance, climbing speed, flight, cardiac performance and fat-body catabolism in male Drosophila. Importantly, Octβ1R and OAMB expression in the heart is also required cell-nonautonomously for adaptations in other tissues, such as skeletal muscles in legs and adult fat body. These findings indicate that activation of distinct octopamine receptors in skeletal and cardiac muscle are required for Drosophila exercise adaptations, and suggest that cell non-autonomous factors downstream of octopaminergic activation play a key role.

Biosynthesis and immunity of epoxyeicosatrienoic acids in a lepidopteran insect, Spodoptera exigua

Eicosanoids mediate both cellular and humoral immune responses in insects. Epoxyeicosatrienoic acids (EETs) are a group of eicosanoids containing epoxide formed by epoxygenase (EPX) activity of cytochrome P450 (CYP). Although EETs have been considered to mediate immune responses in some insects, their synthetic machinery was little understood in insects. This study monitored EETs in a lepidopteran insect, Spodoptera exigua, immunized with bacteria and found all four EETs (5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET) from larval fat body at 247-1,736 pg/g levels. Then to predict EPXs, 140 CYPs were collected from S. exigua transcriptomes and compared with human EPXs. Four CYPs (SeEPX1-SeEPX4) sharing homologies with human EPXs were chosen and assessed in subsequent expression and functional analyses. All four EPXs were expressed in all development stages. In larval stage, all four EPXs were expressed in immune-associated tissues such as fat body and hemocytes. Furthermore, their expression levels were highly enhanced by bacterial challenge in different tissues. RNA interference (RNAi) using gene-specific double stranded RNA injection suppressed their expression levels by more than 55%. RNAi treatments interfered with hemocyte-spreading behavior and nodule formation upon bacterial challenge except RNAi treatment against SeEPX2. All four EETs stimulated cellular immune response measured by nodule formation in S. exigua. The suppressed immune responses by the RNAi treatments against three SeEPXs were rescued by the addition of 8,9-EET. However, other three EETs gave their specific rescue effect depending on SeEPX types under RNAi. In humoral immune response, all four RNAi treatments suppressed expression of antimicrobial peptide genes. This study reports the presence of all four EETs in larval fat body of S. exigua and suggests that four SeEPXs are associated with immune responses mediated by EETs.

Lipidomics reveals how the endoparasitoid wasp Pteromalus puparum manipulates host energy stores for its young

Endoparasitoid wasps inject venom along with their eggs to adjust the physiological and nutritional environment inside their hosts to benefit the development of their offspring. In particular, wasp venoms are known to modify host lipid metabolism, lipid storage in the fat body, and release of lipids into the hemolymph, but how venoms accomplish these functions remains unclear. Here, we use an UPLC-MS-based lipidomics approach to analyze the identities and concentrations of lipids in both fat body and hemolymph of host cabbage butterfly (Pieris rapae) infected by the pupal endoparasitoid Pteromalus puparum. During infection, host fat body levels of highly unsaturated, soluble triacylglycerides (TAGs) increased while less unsaturated, less soluble forms decreased. Furthermore, in infected host hemolymph, overall levels of TAG and phospholipids (the major component of cell membranes) increased, suggesting that fat body cells are destroyed and their contents are dispersed. Altogether, these data suggest that wasp venom induces host fat body TAGs to be transformed into lower melting point (more liquid) forms and released into the host hemolymph following infection, allowing simple absorption and nutritional acquisition by wasp larvae. Finally, cholesteryl esters (CEs, a dietary lipid derived from cholesterol) increased in host hemolymph following infection with no concomitant decrease in host cholesterol, implying that the wasp may provide this necessary food resource to its offspring via its venom. This study provides novel insight into how parasitoid infection alters lipid metabolism in insect hosts, and begins to uncover the wasp venom proteins responsible for host physiological changes and offspring development.

Transcriptomic analysis of epigenetic modification genes in the termite Reticulitermes speratus

Eusocial insects display a caste system in which different castes are morphologically and physiologically specialized for different tasks. Recent studies have revealed that epigenetic modifications, including DNA methylation and histone modification, mediate caste determination and differentiation, longevity, and polyethism in eusocial insects. Although there has been a growing interest in the relationship between epigenetic mechanisms and phenotypic plasticity in termites, there is little information about differential expression levels among castes and expression sites for these genes in termites. Here we show royal-tissue-specific expression of epigenetic modification genes in the termite Reticulitermes speratus. Using RNA-seq, we identified 74 genes, including three DNA methyltransferases, seven sirtuins, 48 Trithorax group proteins, and 16 Polycomb group proteins. Among these genes, 15 showed king-specific expression, and 52 showed age-dependent differential expression in kings and queens. Quantitative real-time PCR revealed that DNA methyltransferase 3 is expressed specifically in the king's testis and fat body, whereas some histone modification genes are remarkably expressed in the king's testis and queen's ovary. These findings imply that epigenetic modification plays important roles in the gamete production process in termite kings and queens.

Transcriptome analysis reveals gene expression changes of the fat body of silkworm (Bombyx mori L.) in response to selenium treatment

A comparative transcriptome analysis was conducted to investigate the gene expression changes in the fat body of silkworm after treatment with different concentrations (50 μM and 200 μM) of selenium (Se). 912 differential expression genes (DEGs) (371 up-regulated and 541 down-regulated) and 1420 DEGs (1078 up-regulated and 342 down-regulated) were identified in silkworm fat body treated with 50 μM and 200 μM of Se, respectively. In case of 50 μM group, DEGs were mainly enriched in the peroxisome pathway and fatty acid metabolism pathway, and later were associated with antioxidant defense and nutrition regulation. After 200 μM Se-treatment, DEGs were mainly located in the glycerolipid metabolism and arachidonic acid metabolism pathways, which further encoded detoxification related genes. Furthermore, 32 candidate DEGs from these pathways had been selected to confirm the RNA-seq data. Among these DEGs, 14 genes were up-regulated in the 50 μM Se-treated group (only three genes in the 200 μM Se-treated group) which were involved in lipid metabolism and antioxidant defense, and 13 up-regulated genes (only two genes were up-regulated in the 50 μM Se-treated group) were involved in detoxification of the 200 μM Se-treated group. These changes showed that lower concentration of Se could regulate the nutrition and promote antioxidation pathways; whereas, high levels of Se promoted the detoxification of silkworm. These findings can be helpful to understand the possible mechanisms of Se action and detoxification in silkworm and other insects.

Gene-Diet Interactions: Dietary Rescue of Metabolic Effects in spen-Depleted Drosophila melanogaster

Obesity and its comorbidities are a growing health epidemic. Interactions between genetic background, the environment, and behavior (i.e., diet) greatly influence organismal energy balance. Previously, we described obesogenic mutations in the gene Split ends (Spen) in Drosophila melanogaster, and roles for Spen in fat storage and metabolic state. Lipid catabolism is impaired in Spen-deficient fat storage cells, accompanied by a compensatory increase in glycolytic flux and protein catabolism. Here, we investigate gene-diet interactions to determine if diets supplemented with specific macronutrients can rescue metabolic dysfunction in Spen-depleted animals. We show that a high-yeast diet partially rescues adiposity and developmental defects. High sugar partially improves developmental timing as well as longevity of mated females. Gene-diet interactions were heavily influenced by developmental-stage-specific organismal needs: extra yeast provides benefits early in development (larval stages) but becomes detrimental in adulthood. High sugar confers benefits to Spen-depleted animals at both larval and adult stages, with the caveat of increased adiposity. A high-fat diet is detrimental according to all tested criteria, regardless of genotype. Whereas Spen depletion influenced phenotypic responses to supplemented diets, diet was the dominant factor in directing the whole-organism steady-state metabolome. Obesity is a complex disease of genetic, environmental, and behavioral inputs. Our results show that diet customization can ameliorate metabolic dysfunction underpinned by a genetic factor.