New players in the regulation of ecdysone biosynthesis

Differential regulation of reproduction and molting by juvenile hormone in aphids

Insects rely on juvenile hormones to regulate various physiological processes, including reproduction and molting; currently eight forms of this hormone are known. In most insects, only JH Ⅲ is synthesized. Meanwhile, aphids produce JH Ⅲ and JH Ⅲ skipped bisepoxide (JHSB3). However, it remains unclear whether these compounds play distinct roles in functional regulation. In this study, we demonstrated that the tested concentrations of JH Ⅲ effectively increased the number of aphid offspring, whereas high concentrations of JHSB3 affected the molting process. Drip experiments showed that 10 mg/L JH Ⅲ increased the number of offspring from 39.38 ± 8.03 to 56.50 ± 13.17, whereas 10 mg/L JHSB3 resulted in a 60.00 %± 5.77 % failure rate in molting before adulthood. Transcriptomic analysis also revealed that in the JH Ⅲ treatment group, 9 genes and 7 pathways associated with reproduction were expressed, but not genes or pathways associated with molting. In addition, 16 genes and 9 pathways associated with molting as well as 5 genes and 4 pathways associated with reproduction were identified in the JHSB3 treatment group. JH Ⅲ promotes reproduction in aphids by enhancing Vg expression, whereas JHSB3 affects molting by inhibiting the synthesis of molting hormone-related enzymes. The results indicate that JH Ⅲ and JHSB3 exhibit diverse functions in Aphis craccivora. The findings have significant implications for further studies on the physiological functions of different JHs.

Effects of tebuconazole on insecticidal activity and symbionts in brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

Harnessing symbionts as targets for pest management is an emerging and promising strategy that can contribute to sustainable agriculture and environmental protection. Brown planthopper (BPH), a major rice pest, significantly threatens crop yields and quality. In this study, we discovered that BPHs exhibited a significant increase in mortality after consuming the fungicide tebuconazole, indicating its direct toxic effect. Tebuconazole negatively impacts the body weight, digestive enzyme activity, and reproductive capacity in BPHs, and it also leads to a significant downregulation of the expression levels of the ecdysteroid biosynthetic genes. The number of symbionts and the expression level of Noda in the BPH treated with tebuconazole was significantly reduced. Sequencing results showed that tebuconazole had a significant effect on the richness of symbiotic fungi and bacteria in BPH. As a fungicide, tebuconazole can offer new approaches and insights for managing resistance and integrated pest control.

Disordered Electron Transfer: New Forms of Defective Steroidogenesis and Mitochondriopathy

Most disorders of steroidogenesis, such as forms of congenital adrenal hyperplasia (CAH) are caused by mutations in genes encoding the steroidogenic enzymes and are often recognized clinically by cortisol deficiency, hyper- or hypo-androgenism, and/or altered mineralocorticoid function. Most steroidogenic enzymes are forms of cytochrome P450. Most P450s, including several steroidogenic enzymes, are microsomal, requiring electron donation by P450 oxidoreductase (POR); however, several steroidogenic enzymes are mitochondrial P450s, requiring electron donation via ferredoxin reductase (FDXR) and ferredoxin (FDX). POR deficiency is a rare but well-described form of CAH characterized by impaired activity of 21-hydroxylase (P450c21, CYP21A2) and 17-hydroxylase/17,20-lyase (P450c17, CYP17A1); more severely affected individuals also have the Antley-Bixler skeletal malformation syndrome and disordered genital development in both sexes, and hence is easily recognized. The 17,20-lyase activity of P450c17 requires both POR and cytochrome b5 (b5), which promote electron transfer. Mutations of POR, b5, or P450c17 can cause selective 17,20-lyase deficiency. In addition to providing electrons to mitochondrial P450s, FDX, and FDXR are required for the synthesis of iron-sulfur clusters, which are used by many enzymes. Recent work has identified FDXR mutations in patients with visual impairment, optic atrophy, neuropathic hearing loss, and developmental delay, resembling the global neurologic disorders seen with mitochondrial diseases. Many of these patients have had life-threatening events or deadly infections, often without an apparent triggering event. Adrenal insufficiency has been predicted in such individuals but has only been documented recently. Neurologists, neonatologists, and geneticists should seek endocrine assistance in evaluating and treating patients with mutations in FDXR.

Spätzle Regulates Developmental and Immune Trade-Offs Induced by Bacillus thuringiensis Priming in Rhynchophorus ferrugineus

The red palm weevil (RPW) is an invasive pest that causes devastating damage to a variety of palm plants, which exhibit specific immune priming to Bacillus thuringiensis (Bt). However, immune priming in RPW may incur a high fitness cost, and its molecular signaling pathways have not yet been reported. Here, we investigated the effect of Bt priming on RPW development and subsequently analyzed the hormonal and immune-related molecular pathways influencing the fitness cost induced by Bt priming. Bt priming delayed the body weight gain of fifth-instar larvae and prolonged their developmental duration. Bt priming significantly reduced the 20-hydroxyecdysone (20E) content in RPW hemolymph, and the expression levels of the 20E biosynthesis-related genes SHADOW and SHADE were significantly downregulated. Furthermore, we analyzed Toll pathway genes influencing Bt priming and found that only Spätzle (SPZ) transcription was significantly activated under Bt priming. After silencing SPZ expression, the negative effects of Bt priming on development, SHADOW expression, and 20E synthesis were eliminated, thereby suggesting that SPZ is a key molecular signal mediating developmental and immune trade-offs induced by Bt priming. Our results elucidate the molecular cascade pathway of immune priming and provide new targets for improving the efficiency of RPW biological controls.

PTTH-Torso Signaling System Controls Developmental Timing, Body Size, and Reproduction through Regulating Ecdysone Homeostasis in the Brown Planthopper, Nilaparvata lugens

In holometabolous insects, such as Drosophila and Bombyx, prothoracicotropic hormone (PTTH) is well established to be critical in controlling developmental transitions and metamorphosis by stimulating the biosynthesis of ecdysone in the prothoracic glands (PGs). However, the physiological role of PTTH and the receptor Torso in hemimetabolous insects remains largely unexplored. In this study, homozygous PTTH- and Torso-null mutants of the brown planthopper (BPH), Nilaparvata lugens, were successfully generated by employing clustered regularly interspaced short palindromic repeats/CRISPR-associated 9 (CRISPR-Cas9). Further characterization showed that both NlPTTH-/- and NlTorso-/- mutants exhibited prolonged nymphal duration and increased final adult size. Enzyme-linked immunosorbent assay (ELISA) revealed that NlPTTH-/- and NlTorso-/- mutants exhibited a significant reduction in 20-hydroxyecdysone (20E) in fifth-instar nymphs at 48 h post-ecdysis compared to Wt controls. Furthermore, our results indicated that both NlPTTH-/- and NlTorso-/- mutants had shortened lifespan, reduced female fecundity, and reduced egg hatching rates in adults. These findings suggest a conserved role for the PTTH-Torso signaling system in the regulation of developmental transitions by stimulating ecdysone biosynthesis in hemimetabolous insects.

Fecundity is optimized by levels of nutrient signal-dependent expression of Dve and EcR in Drosophila male accessory gland

Steroid hormones play various physiological roles including metabolism and reproduction. Steroid hormones in insects are ecdysteroids, and the major form in Drosophila melanogaster is ecdysone. In Drosophila males, the accessory gland is responsive to nutrient-dependent regulation of fertility/fecundity. The accessory gland is composed of two types of binucleated epithelial cells: a main cell and a secondary cell (SC). The transcription factors Defective proventriculus (Dve), Abdominal-B, and Ecdysone receptors (EcRs) are strongly expressed in adult SCs. We show that this EcR expression is regulated by parallel pathways of nutrient signaling and the Dve activity. Induction of Dve expression is also dependent on nutrient signaling, and it becomes nutrient signal-independent during a restricted period of development. Forced dve expression during the restricted period significantly increased the number of SCs. Here, we provide evidence that the level of nutrient signal-dependent Dve expression during the restricted period determines the number of SCs, and that ecdysone signaling is also crucial to optimize male fecundity through nutrient signal-dependent survival and maturation of SCs.

The Sterol Transporter Npc2c Controls Intestinal Stem Cell Mitosis and Host-Microbiome Interactions in Drosophila

Cholesterol is necessary for all cells to function. The intracellular cholesterol transporters Npc1 and Npc2 control sterol trafficking and their malfunction leads to Neimann-Pick Type C disease, a rare disorder affecting the nervous system and the intestine. Unlike humans that encode single Npc1 and Npc2 transporters, flies encompass two Npc1 (Npc1a-1b) and eight Npc2 (Npc2a-2h) members, and most of the Npc2 family genes remain unexplored. Here, we focus on the intestinal function of Npc2c in the adult. We find that Npc2c is necessary for intestinal stem cell (ISC) mitosis, maintenance of the ISC lineage, survival upon pathogenic infection, as well as tumor growth. Impaired mitosis of Npc2c-silenced midguts is accompanied by reduced expression of Cyclin genes, and genes encoding ISC regulators, such as Delta, unpaired1 and Socs36E. ISC-specific Npc2c silencing induces Attacin-A expression, a phenotype reminiscent of Gram-negative bacteria overabundance. Metagenomic analysis of Npc2c-depleted midguts indicates intestinal dysbiosis, whereby decreased commensal complexity is accompanied by increased gamma-proteobacteria. ISC-specific Npc2c silencing also results in increased cholesterol aggregation. Interestingly, administration of the non-steroidal ecdysone receptor agonist, RH5849, rescues mitosis of Npc2c-silenced midguts and increases expression of the ecdysone response gene Broad, underscoring the role of Npc2c and sterols in ecdysone signaling. Assessment of additional Npc2 family members indicates potential redundant roles with Npc2c in ISC control and response to ecdysone signaling. Our results highlight a previously unidentified essential role of Npc2c in ISC mitosis, as well as an important role in ecdysone signaling and microbiome composition in the Drosophila midgut.

Immunoglobulin A as a Key Immunological Molecular Signature of Post-COVID-19 Conditions

COVID-19 has infected humans worldwide, causing millions of deaths or prolonged symptoms in survivors. The transient or persistent symptoms after SARS-CoV-2 infection have been defined as post-COVID-19 conditions (PCC). We conducted a study of 151 Brazilian PCC patients to analyze symptoms and immunoglobulin profiles, taking into account sex, vaccination, hospitalization, and age. Fatigue and myalgia were the most common symptoms, and lack of vaccination, hospitalization, and neuropsychiatric and metabolic comorbidities were relevant to the development of PCC. Analysis of serological immunoglobulins showed that IgA was higher in PCC patients, especially in the adult and elderly groups. Also, non-hospitalized and hospitalized PCC patients produced high and similar levels of IgA. Our results indicated that the detection of IgA antibodies against SARS-CoV-2 during the course of the disease could be associated with the development of PCC and may be an immunological signature to predict prolonged symptoms in COVID-19 patients.

The sulfoximine insecticide sulfoxaflor exposure reduces the survival status and disrupts the intestinal metabolism of the honeybee Apis mellifera

Honeybees (Apis mellifera) are indispensable pollinators in agricultural production, biodiversity conservation, and nutrients provision. The abundance and diversity of honeybees have been rapidly diminishing, possibly related to the extensive use of insecticides in ecosystems. Sulfoxaflor is a novel sulfoximine insecticide that, like neonicotinoids, acts as a competitive modulator of nicotinic acetylcholine receptors (nAChR) in insects. However, few studies have addressed the negative effects of sulfoxaflor on honeybees at environmentally relevant concentrations. In the present study, adult workers were fed a 50% (w/v) of sugar solution containing different concentrations (0, 0.05, 0.5 and 2.0 mg/L) of sulfoxaflor for two weeks consecutively. The survival rates, food intake, and body weight of the honeybees significantly decreased after continuous exposure at higher doses (0.5 and 2.0 mg/L) of sulfoxaflor when compared with the control. The change in the metabolites in the honeybee gut was determined using high-throughput non-targeted metabolomics on day 14 after sulfoxaflor treatment. The results revealed that 24 and 105 metabolites changed after exposure to 0.5 and 2.0 mg/L sulfoxaflor, respectively, compared with that of the control groups. A total of 12 changed compounds including pregenolone and glutathione were detected as potential biomarkers, which were eventually found to be enriched in pathways of the steroid hormone biosynthesis (p = 0.0001) and glutathione metabolism (p = 0.021). These findings provide a new perspective on the physiological influence of sulfoxaflor stress in honeybees.

Knockdown of the Halloween Genes spook, shadow and shade Influences Oocyte Development, Egg Shape, Oviposition and Hatching in the Desert Locust

Ecdysteroids are widely investigated for their role during the molting cascade in insects; however, they are also involved in the development of the female reproductive system. Ecdysteroids are synthesized from cholesterol, which is further converted via a series of enzymatic steps into the main molting hormone, 20-hydoxyecdysone. Most of these biosynthetic conversion steps involve the activity of cytochrome P450 (CYP) hydroxylases, which are encoded by the Halloween genes. Three of these genes, spook (spo), phantom (phm) and shade (shd), were previously characterized in the desert locust, Schistocerca gregaria. Based on recent sequencing data, we have now identified the sequences of disembodied (dib) and shadow (sad), for which we also analyzed spatiotemporal expression profiles using qRT-PCR. Furthermore, we investigated the possible role(s) of five different Halloween genes in the oogenesis process by means of RNA interference mediated knockdown experiments. Our results showed that depleting the expression of SchgrSpo, SchgrSad and SchgrShd had a significant impact on oocyte development, oviposition and hatching of the eggs. Moreover, the shape of the growing oocytes, as well as the deposited eggs, was very drastically altered by the experimental treatments. Consequently, it can be proposed that these three enzymes play an important role in oogenesis.

Endocrine control of glycogen and triacylglycerol breakdown in the fly model

Over the last decade, the combination of genetics, transcriptomic and proteomic approaches yielded substantial insights into the mechanisms behind the synthesis and breakdown of energy stores in the model organisms. The fruit fly Drosophila melanogaster has been particularly useful to unravel genetic regulations of energy metabolism. Despite the considerable evolutionary distance between humans and flies, the energy storage organs, main metabolic pathways, and even their genetic regulations remained relatively conserved. Glycogen and fat are universal energy reserves used in all animal phyla and several of their endocrine regulators, such as the insulin pathway, are highly evolutionarily conserved. Nevertheless, some of the factors inducing catabolism of energy stores have diverged significantly during evolution. Moreover, even within a single insect species, D. melanogaster, there are substantial developmental and context-dependent variances in the regulation of energy stores. These differences include, among others, the endocrine pathways that govern the catabolic events or the predominant fuel which is utilized for the given process. For example, many catabolic regulators that control energy reserves in adulthood seem to be largely dispensable for energy mobilization during development. In this review, we focus on a selection of the most important catabolic regulators from the group of peptide hormones (Adipokinetic hormone, Corazonin), catecholamines (octopamine), steroid hormones (20-hydroxyecdysone), and other factors (extracellular adenosine, regulators of lipase Brummer). We discuss their roles in the mobilization of energy reserves for processes such as development through non-feeding stages, flight or starvation survival. Finally, we conclude with future perspectives on the energy balance research in the fly model.

Toxicity of Ribavirin to Spodoptera litura by Inhibiting the Juvenile Hormone

Ribavirin is an antiviral drug showing high and delayed toxicity to the destructive agricultural pest Spodoptera litura. Larvae fed with artificial diets containing ribavirin could not molt successfully and showed abnormal phenotypes, including cuticle melanization and heavy wrinkle of the newly formed procuticle. RNA-Seq analysis suggested that ribavirin has great negative influence on cuticle. Quantitative real-time-polymerase chain reaction results indicated that ribavirin treatment decreased the expression of key genes in juvenile hormone (JH) biosynthesis (CYP15C1 and JH acid methyltransferase) and most cuticle protein genes, whereas the genes in melanin biosynthesis and bursicon genes were upregulated by ribavirin treatment. These results coincided with the decreased titer of JH I, JH II, and JH III determined by enzyme-linked immunosorbent assay, the much thinner procuticle layer exhibited by histopathological examination, and the cuticle melanization after ribavirin treatment. These results provided a valuable theoretical basis for the creation of green insecticides targeting JH and the development of new insecticide derivatives from 1,2,4-triazole.

Neurotransmitters Affect Larval Development by Regulating the Activity of Prothoracicotropic Hormone-Releasing Neurons in Drosophila melanogaster

Ecdysone, an essential insect steroid hormone, promotes larval metamorphosis by coordinating growth and maturation. In Drosophila melanogaster, prothoracicotropic hormone (PTTH)-releasing neurons are considered to be the primary promoting factor in ecdysone biosynthesis. Recently, studies have reported that the regulatory mechanisms of PTTH release in Drosophila larvae are controlled by different neuropeptides, including allatostatin A and corazonin. However, it remains unclear whether neurotransmitters provide input to PTTH neurons and control the metamorphosis in Drosophila larvae. Here, we report that the neurotransmitters acetylcholine (ACh) affect larval development by modulating the activity of PTTH neurons. By downregulating the expression of different subunits of nicotinic ACh receptors in PTTH neurons, pupal volume was significantly increased, whereas pupariation timing was relatively unchanged. We also identified that PTTH neurons were excited by ACh application ex vivo in a dose-dependent manner via ionotropic nicotinic ACh receptors. Moreover, in our Ca2+ imaging experiments, relatively low doses of OA caused increased Ca2+ levels in PTTH neurons, whereas higher doses led to decreased Ca2+ levels. We also demonstrated that a low dose of OA was conveyed through OA β-type receptors. Additionally, our electrophysiological experiments revealed that PTTH neurons produced spontaneous activity in vivo, which provides the possibility of the bidirectional regulation, coming from neurons upstream of PTTH cells in Drosophila larvae. In summary, our findings indicate that several different neurotransmitters are involved in the regulation of larval metamorphosis by altering the activity of PTTH neurons in Drosophila.

Understanding molt control switches: Transcriptomic and expression analysis of the genes involved in ecdysteroidogenesis and cholesterol uptake pathways in the Y-organ of the blue crab, Callinectes sapidus

The crustacean molting process is regulated by an interplay of hormones produced by the eyestalk ganglia and Y-organs (YO). Molt-inhibiting hormone and crustacean hyperglycemic hormone released by the sinus gland of the eyestalk ganglia (EG) inhibit the synthesis and secretion of ecdysteroid by the YO, hence regulating hemolymph levels during the molt cycle. The purpose of this study is to investigate the ecdysteroidogenesis pathway, specifically genes linked to changes in ecdysteroid levels occurring at early premolt (ePM). To this end, a reference transcriptome based on YO, EG, and hepatopancreas was de novo assembled. Two genes (cholesterol 7-desaturase Neverland and cytochrome p450 307a1-like Spook) involved in ecdysteroidogenesis were identified from the YO transcriptome using sequence comparisons and transcript abundance. Two other candidates, Hormone receptor 4 and probable cytochrome p450 49a1 potentially involved in ecdysteroidogenesis were also identified. Since cholesterol is the ecdysteroid precursor, a putative cholesterol carrier (Apolipoprotein D-like) was also examined to understand if cholesterol uptake coincided with the increase in the ecdysteroid levels at the ePM stage. The expression level changes of the five candidate genes in the YO were compared between intermolt (IM) and induced ePM (iePM) stages using transcriptomic analysis. Expression analysis using qPCR were carried out at IM, iePM, and normal ePM. The increase in Spook and Neverland expression in the YO at the ePM was accompanied by a concomitant rise in ecdysteroid levels. The data obtained from iePM stage were congruent with those obtained from the normal ePM stage of intact control animals. The present findings support the role of Halloween genes in the ecdysteroidogenesis and molt cycle in the blue crab, Callinectes sapidus.

Gene annotation of nuclear receptor superfamily genes in the kissing bug Rhodnius prolixus and the effects of 20-hydroxyecdysone on lipid metabolism

The hormone 20-hydroxyecdysone is fundamental for regulating moulting and metamorphosis in immature insects, and it plays a role in physiological regulation in adult insects. This hormone acts by binding and activating a receptor, the ecdysone receptor, which is part of the nuclear receptor gene superfamily. Here, we analyse the genome of the kissing bug Rhodnius prolixus to annotate the nuclear receptor superfamily genes. The R. prolixus genome displays a possible duplication of the HNF4 gene. All the analysed insect organs express most nuclear receptor genes as shown by RT-PCR. The quantitative PCR analysis showed that the RpEcR and RpUSP genes are highly expressed in the testis, while the RpHNF4-1 and RpHNF4-2 genes are more active in the fat body and ovaries and in the anterior midgut, respectively. Feeding does not induce detectable changes in the expression of these genes in the fat body. However, the expression of the RpHNF4-2 gene is always higher than that of RpHNF4-1. Treating adult females with 20-hydroxyecdysone increased the amount of triacylglycerol stored in the fat bodies by increasing their lipogenic capacity. These results indicate that 20-hydroxyecdysone acts on the lipid metabolism of adult insects, although the underlying mechanism is not clear.

Reciprocal Relationship Between Calcium Signaling and Circadian Clocks: Implications for Calcium Homeostasis, Clock Function, and Therapeutics

In animals, circadian clocks impose a daily rhythmicity to many behaviors and physiological processes. At the molecular level, circadian rhythms are driven by intracellular transcriptional/translational feedback loops (TTFL). Interestingly, emerging evidence indicates that they can also be modulated by multiple signaling pathways. Among these, Ca²⁺ signaling plays a key role in regulating the molecular rhythms of clock genes and of the resulting circadian behavior. In addition, the application of in vivo imaging approaches has revealed that Ca²⁺ is fundamental to the synchronization of the neuronal networks that make up circadian pacemakers. Conversely, the activity of circadian clocks may influence Ca²⁺ signaling. For instance, several genes that encode Ca²⁺ channels and Ca²⁺-binding proteins display a rhythmic expression, and a disruption of this cycling affects circadian function, underscoring their reciprocal relationship. Here, we review recent advances in our understanding of how Ca²⁺ signaling both modulates and is modulated by circadian clocks, focusing on the regulatory mechanisms described in Drosophila and mice. In particular, we examine findings related to the oscillations in intracellular Ca²⁺ levels in circadian pacemakers and how they are regulated by canonical clock genes, neuropeptides, and light stimuli. In addition, we discuss how Ca²⁺ rhythms and their associated signaling pathways modulate clock gene expression at the transcriptional and post-translational levels. We also review evidence based on transcriptomic analyzes that suggests that mammalian Ca²⁺ channels and transporters (e.g., ryanodine receptor, ip3r, serca, L- and T-type Ca²⁺ channels) as well as Ca²⁺-binding proteins (e.g., camk, cask, and calcineurin) show rhythmic expression in the central brain clock and in peripheral tissues such as the heart and skeletal muscles. Finally, we discuss how the discovery that Ca²⁺ signaling is regulated by the circadian clock could influence the efficacy of pharmacotherapy and the outcomes of clinical interventions.

Control of the insect metamorphic transition by ecdysteroid production and secretion

Ecdysteroids are a class of steroid hormones that controls molting and metamorphic transitions in Ecdysozoan species including insects, in which ecdysteroid biosynthesis and its regulation have been extensively studied. Insect ecdysteroids are produced from dietary sterols by a series of reduction-oxidation reactions in the prothoracic gland and in Drosophila they are released into the hemolymph via vesicle-mediated secretion at the time of metamorphosis. To initiate precisely controlled ecdysteroid pulses, the prothoracic gland functions as a central node integrating both intrinsic and extrinsic signals to control ecdysteroid biosynthesis and secretion. In this review, we outline recent progress in the characterization of ecdysone biosynthesis and steroid trafficking pathways and the discoveries of novel factors regulating prothoracic gland function.

Expression, Purification, Refolding, and Characterization of a Neverland Protein From Caenorhabditis elegans

Steroid hormones that serve as vital compounds are necessary for the development and metabolism of a variety of organisms. The neverland (NVD) family genes encode the conserved Rieske-type oxygenases, which are accountable for the dehydrogenation during the synthesis and regulation of steroid hormones. However, the His-tagged NVD protein from Caenorhabditis elegans expresses as inclusion bodies in Escherichia coli BL21 (DE3). This bottleneck can be solved through refolding by urea or the introduction of a maltose-binding protein (MBP) tag at the N-terminus. Through further research on purification after the introduction of a MBP tag at the N-terminus, the CD measurement and fluorescence-based thermal shift assay indicated that MBP was favorable for the NVD proteins' solubility and stability, which may be beneficial for the large-scale manufacture of NVD protein for further research. The structural model contained the Rieske [2Fe-2S] domain and non-heme iron-binding motif, which were similar to 3-ketosteroid 9 α-hydroxylase.

A journey into the world of insect lipid metabolism

Lipid metabolism is fundamental to life. In insects, it is critical, during reproduction, flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. Fat body contains various different cell types; however, adipocytes and oenocytes are the primary cells related to lipid metabolism. Lipid metabolism starts with the hydrolysis of dietary lipids, absorption of lipid monomers, followed by lipid transport from midgut to the fat body, lipogenesis or lipolysis in the fat body, and lipid transport from fat body to other sites demanding energy. Lipid metabolism is under the control of hormones, transcription factors, secondary messengers and posttranscriptional modifications. Primarily, lipogenesis is under the control of insulin-like peptides that activate lipogenic transcription factors, such as sterol regulatory element-binding proteins, whereas lipolysis is coordinated by the adipokinetic hormone that activates lipolytic transcription factors, such as forkhead box class O and cAMP-response element-binding protein. Calcium is the primary-secondary messenger affecting lipid metabolism and has different outcomes depending on the site of lipogenesis or lipolysis. Phosphorylation is central to lipid metabolism and multiple phosphorylases are involved in lipid accumulation or hydrolysis. Although most of the knowledge of insect lipid metabolism comes from the studies on the model Drosophila; other insects, in particular those with obligatory or facultative diapause, also have great potential to study lipid metabolism. The use of these models would significantly improve our knowledge of insect lipid metabolism.

Sex-specific expression profiles of ecdysteroid biosynthesis and ecdysone response genes in extreme sexual dimorphism of the mealybug Planococcus kraunhiae (Kuwana)

Insect molting hormone (ecdysteroids) and juvenile hormone regulate molting and metamorphic events in a variety of insect species. Mealybugs undergo sexually dimorphic metamorphosis: males develop into winged adults through non-feeding, pupa-like stages called prepupa and pupa, while females emerge as neotenic wingless adults. We previously demonstrated, in the Japanese mealybug Planococcus kraunhiae (Kuwana), that the juvenile hormone titer is higher in males than in females at the end of the juvenile stage, which suggests that juvenile hormone may regulate male-specific adult morphogenesis. Here, we examined the involvement of ecdysteroids in sexually dimorphic metamorphosis. To estimate ecdysteroid titers, quantitative RT-PCR analyses of four Halloween genes encoding for cytochrome P450 monooxygenases in ecdysteroid biosynthesis, i.e., spook, disembodied, shadow and shade, were performed. Overall, their expression levels peaked before each nymphal molt. Transcript levels of spook, disembodied and shadow, genes that catalyze the steps in ecdysteroid biosynthesis in the prothoracic gland, were higher in males from the middle of the second nymphal instar to adult emergence. In contrast, the expression of shade, which was reported to be involved in the conversion of ecdysone into 20-hydroxyecdysone in peripheral tissues, was similar between males and females. These results suggest that ecdysteroid biosynthesis in the prothoracic gland is more active in males than in females, although the final conversion into 20-hydroxyecdysone occurs at similar levels in both sexes. Moreover, expression profiles of ecdysone response genes, ecdysone receptor and ecdysone-induced protein 75B, were also analyzed. Based on these expression profiles, we propose that the changes in ecdysteroid titer differ between males and females, and that high ecdysteroid titer is essential for directing male adult development.

Ecdysone controlled cell and tissue deletion

The removal of superfluous and unwanted cells is a critical part of animal development. In insects the steroid hormone ecdysone, the focus of this review, is an essential regulator of developmental transitions, including molting and metamorphosis. Like other steroid hormones, ecdysone works via nuclear hormone receptors to direct spatial and temporal regulation of gene transcription including genes required for cell death. During insect metamorphosis, pulses of ecdysone orchestrate the deletion of obsolete larval tissues, including the larval salivary glands and the midgut. In this review we discuss the molecular machinery and mechanisms of ecdysone-dependent cell and tissue removal, with a focus on studies in Drosophila and Lepidopteran insects.

Roles of the insulin signaling pathway in insect development and organ growth

Organismal development is a complex process as it requires coordination of many aspects to grow into fit individuals, such as the control of body size and organ growth. Therefore, the mechanisms of precise control of growth are essential for ensuring the growth of organisms at a correct body size and proper organ proportions during development. The control of the growth rate and the duration of growth (or the cessation of growth) are required in size control. The insulin signaling pathway and the elements involved are essential in the control of growth. On the other hand, the ecdysteroid molting hormone determines the duration of growth. The secretion of these hormones is controlled by environmental factors such as nutrition. Moreover, the target of rapamycin (TOR) pathway is considered as a nutrient sensing pathway. Important cross-talks have been shown to exist among these pathways. In this review, we outline the control of body and organ growth by the insulin/TOR signaling pathway, and also the interaction between nutrition via insulin/TOR signaling and ecdysteroids at the coordination of organismal development and organ growth in insects, mainly focusing on the well-studied fruit fly Drosophila melanogaster.

Comparative Transcriptomic Analysis Reveals Molecular Profiles of Central Nervous System in Maternal Diapause Induction of Locusta migratoria

Egg diapause in Locusta migratoria L. (Orthoptera: Acridoidea) is believed to be influenced by maternal photoperiod. However, the molecular mechanism regulating the phenomenon of maternal diapause induction is unclear. Here we performed transcriptomic analyses from the central nervous system (CNS) of migratory locusts under long and short photoperiods to identify differentially expressed genes (DEGs) related to diapause induction. There were total of 165750 unigenes from 569491 transcripts, and 610 DEGs were obtained in S_CNS (CNS of short photoperiod treated locusts) vs. L_CNS (CNS of long photoperiod treated locusts). Of these, 360 were up-regulated, 250 were down-regulated, and 84 DEGs were found to be related to FOXO signaling pathways, including citrate cycle/TCA cycle, glycolysis/ gluconeogenesis, oxidative phosphorylation, and PI3K-Akt. The qRT-PCR validation of mRNA expression of 12 randomly selected DEGs showed consistency with transcriptome analysis. Furthermore, the takeout gene thought to be involved in circadian rhythm was cloned and used for RNAi to observe its function in maternal diapause induction. We found that the mRNA level of Lm-takeout was significantly lower in dstakeout treatments as compared to the control under both long and short photoperiods. Similarly, the offspring diapause rate was significantly higher in dstakeout treatment as compared to the control only in short photoperiod. This shows that the Lm-takeout gene might be involved in the inhibition of maternal diapause induction of L. migratoria under short photoperiods. The present study provides extensive data of the CNS transcriptome and particular insights into the molecular mechanisms of maternal effects on egg diapause of L. migratoria. As well for the future, the researchers can explore other factors and genes that may promote diapause in insect species.

Involvement of Ecdysone Signaling in the Expression of the doublesex Gene during Embryonic Development in the Silkworm, Bombyx mori

Steroid hormones, represented by estrogen and testosterone, act as sex hormones that play an essential role in the sexual differentiation of vertebrates. However, it remains unclear whether ecdysteroids, typical steroid hormones in insects, function as sex hormones. In this study, we investigated whether ecdysteroids or ecdysone signals are involved in the sexual differentiation of the silkworm (Bombyx mori) embryo. Quantitative analysis using LC-MS/MS demonstrated that there was no significant difference in the 20-hydroxyecdysone (20E) titer between sexes during embryonic development. Consistent with this result, expression levels of 2 genes encoding ecdysteroid-phosphate phosphatase (EPPase) and ecdysone 20-hydroxylase (E20OHase), which are essential for the biosynthesis of ecdysone and 20E in eggs, did not show a significant difference between male and female embryos. Expression levels of ecdysone receptor (EcR) and E75, which is one of a small set of genes induced directly by 20E, were also similar between the 2 sexes. However, knockdown of EPPase and one isoform of EcR (EcR-A) resulted in decreased expression of Bombyx doublesex (Bmdsx), a master regulatory gene for sexual differentiation of the silkworm in both male and female embryos. In vitro analysis with cultured testes revealed that expression levels of Bmdsx were increased in a dose-dependent manner of the ecdysone analog, ponasterone A. These results suggest that ecdysone signaling may play a role in indirectly regulating the expression of some genes involved in sexual differentiation through inducing expression of Bmdsx in the silkworm.

Activated Ras/JNK driven Dilp8 in imaginal discs adversely affects organismal homeostasis during early pupal stage in Drosophila, a new checkpoint for development

BACKGROUND

Dilp8-mediated inhibition of ecdysone synthesis and pupation in holometabolous insects maintains developmental homeostasis through stringent control of timing and strength of molting signals. We examined reasons for normal pupation but early pupal death observed in certain cases.

RESULTS

Overexpression of activated Ras in developing eye/wing discs inhibited Ptth expression in brain via upregulated JNK signaling mediated Dilp8 secretion from imaginal discs, which inhibited ecdysone synthesis in prothoracic gland after pupariation, leading to death of ~25- to 30-hour-old pupae. Inhibition of elevated Ras signaling completely rescued early pupal death while post-pupation administration of ecdysone to organisms with elevated Ras signaling in eye discs partially rescued their early pupal death. Unlike the earlier known Dilp8 action in delaying pupation, hyperactivated Ras mediated elevation of pJNK signaling in imaginal discs caused Dilp8 secretion after pupariation. Ectopic expression of certain other transgene causing pupal lethality similarly enhanced pJNK and early pupal Dilp8 levels. Suboptimal ecdysone levels after 8 hours of pupation prevented the early pupal metamorphic changes and caused organismal death.

CONCLUSIONS

Our results reveal early pupal stage as a novel Dilp8 mediated post-pupariation checkpoint and provide further evidence for interorgan signaling during development, wherein a peripheral tissue influences the CNS driven endocrine function.

Nuclear receptors, cholesterol homeostasis and the immune system

Cholesterol is essential for maintaining membrane fluidity in eukaryotes. Additionally, the synthetic cascade of cholesterol results in precursor molecules important for cellular function such as lipid raft formation and protein prenylation. As such, cholesterol homeostasis is tightly regulated. Interestingly, it is now known that some cholesterol precursors and many metabolites serve as active signaling molecules, binding to different classes of receptors including the nuclear receptors. Furthermore, many cholesterol metabolites or their nuclear receptors have been implicated in the regulation of the immune system in normal physiology and disease. Therefore, in this focused review, cholesterol homeostasis and nuclear receptors involved in this regulation will be discussed, with particular emphasis on how these cascades influence the immune system.

Ecdysteroidogenesis in Heliothis virescens (Lepidoptera: Noctuidae): Recombinant Prothoracicotropic Hormone and Brain Extract Show Comparable Effects

Prothoracicotropic hormone (PTTH) is a neuropeptide that triggers a cascade of events within the prothoracic gland (PG) cells, leading to the activation of all the crucial enzymes involved in ecdysone biosynthesis, the main insect steroid hormone. Studies concerning ecdysteroidogenesis predicted PTTH action using brain extract (BE), consisting in a complex mixture in which some components positively or negatively interfere with PTTH-stimulated ecdysteroidogenesis. Consequently, the integration of these opposing factors in steroidogenic tissues leads to a complex secretory pattern. A recombinant form of prothoracicotropic hormone (rPTTH) from the tobacco budworm Heliothis virescens (F.) (Lepidoptera: Noctuidae) was expressed and purified to perform in vitro tests in a standard and repeatable manner. A characterization of rPTTH primary and secondary structures was performed. The ability of rPTTH and H. virescens BE to stimulate ecdysteroidogenesis was investigated on the third day of fifth larval stage. rPTTH activity was compared with the BE mixture by enzyme immunoassay and western blot, revealing that they equally stimulate the production of significant amount of ecdysone, through a transduction cascade that includes the TOR pathway, by the phosphorylation of 4E binding protein (4E-BP) and S6 kinase (S6K), the main targets of TOR protein. The results of these experiments suggest the importance of obtaining a functional pure hormone to perform further studies, not depending on the crude brain extract, composed by different elements and susceptible to different uncontrollable variables.

Makorin 1 Regulates Developmental Timing in Drosophila

The central mechanisms coordinating growth and sexual maturation are well conserved across invertebrates and vertebrates. Although mutations in the gene encoding makorin RING finger protein 3 (mkrn3 ) are associated with central precocious puberty in humans, a causal relationship has not been elucidated. Here, we examined the role of mkrn1, a Drosophila ortholog of mammalian makorin genes, in the regulation of developmental timing. Loss of MKRN1 in mkrn1 exS prolonged the 3rd instar stage and delayed the onset of pupariation, resulting in bigger size pupae. MKRN1 was expressed in the prothoracic gland, where the steroid hormone ecdysone is produced. Furthermore, mkrn1 exS larvae exhibited reduced mRNA levels of phantom, which encodes ecdysone-synthesizing enzyme and E74, which is a downstream target of ecdysone. Collectively, these results indicate that MKRN1 fine-tunes developmental timing and sexual maturation by affecting ecdysone synthesis in Drosophila. Moreover, our study supports the notion that malfunction of makorin gene family member, mkrn3 dysregulates the timing of puberty in mammals.

Body size regulation by maturation steroid hormones: a Drosophila perspective

The mechanism that determines the specific body size of an animal is a fundamental biological question that remains largely unanswered. This aspect is now beginning to be understood in insect models, particularly in Drosophila melanogaster, with studies highlighting the importance of nutrient-responsive growth signaling pathways involving insulin/insulin-like growth factor signaling (IIS) and target of rapamycin (TOR) (IIS/TOR). These pathways operate in animals, from insects to mammals, adjusting the growth rate in response to the nutritional condition of the organism. Organismal growth is closely coupled with the process of developmental maturation mediated by maturation steroid hormones, which is influenced greatly by environmental and nutritional conditions. Recent Drosophila studies have been revealing the mechanisms responsible for this phenomenon. In this review, I summarize some important findings about the steroid hormone regulation of Drosophila body growth, calling attention to the influence of developmental nutritional conditions on animal size determination.

Control of pheromone production by ovaries in Drosophila

Drosophila pheromones are long chain hydrocarbons (CHCs) produced by specialized epidermal cells, the oenocytes. Here we were explored the role of ovaries in CHC regulation. We studied tudor, a grandchildless-like mutation, resulting in progeny without ovaries and three alleles of ovoD, resulting in ovarian defects depending on the strength of the allele. We show here that these mutant flies with no or abnormal ovaries have a decrease in C29 length CHC ratio, balanced by an increase in C23 and C25 length ratio; this effect is dependent on the strength of the mutation. An increase in the amount of CHCs also occurred but was not related to the strength of ovoD alleles. As ovaries are the main site of ecdysone production in females, we knocked down the receptor to ecdysone EcR in the oenocytes and obtained increased amounts of CHCs and inhibition of long chain CHC synthesis, showing that the lack of an ecdysone signal arriving into the oenocytes is responsible for these defects. We then investigated the role of follicular cells and oocyte on CHC regulation: we RNAi-knocked down the LPR receptors in the oocyte to hinder vitellogenesis without significantly modifying CHC profile. We then expressed apoptosis genes within the follicle cells or within the ovocytes and obtained less long chain and more short chain CHC levels in the former case and an enhanced CHC production in the latter case. Together, these results support the notion of an interaction between oocyte and follicular cells, which send an ecdysone signal to the oenocytes to regulate CHC synthesis.

Transcriptome analysis of abscisic acid induced 20E regulation in suspension Ajuga lobata cells

Ajuga lobata D. Don is a medicinal plant rich in 20-hydroxyecdysone (20E), alkaloids, and other active substances. In this study, the cell suspension was incubated for 7 days, followed by the analysis on the effects of abscisic acid (ABA) on the regulation of 20E synthesis. Then A. lobata suspension cells treated with 0.15 mg/l ABA were used as material, with the Illumina technology applied for transcriptome sequencing. Digital analysis on the gene expression profile was carried out on ABA treated and control samples, respectively. Finally, transcriptomics was applied to assess the molecular response of A. lobata induced by ABA through applying transcriptomics by evaluating differentially expressed genes. The results suggested that ABA promoted 20E accumulation, while longer processing time caused cell browning. A total of 154 genes were significantly regulated after ABA treatment, with 99 up-regulated and 55 down-regulated, respectively. In addition to 20E-related pathways, the genes belonged to the ko00900 (terpenoid backbone biosynthesis) pathway (six differentially expressed genes [DEGs]), ko00100 (steroid biosynthesis) pathway (four DEGs), and ko00140 (steroid hormone biosynthesis) pathway (six DEGs). Providing a better understanding of the 20E biosynthetic pathway and its regulation, in particular in plants, this study is necessary.

Refining a steroidogenic model: an analysis of RNA-seq datasets from insect prothoracic glands

BACKGROUND

The prothoracic gland (PG), the principal steroidogenic organ of insects, has been proposed as a model for steroid hormone biosynthesis and regulation.

RESULTS

To validate the robustness of the model, we present an analysis of accumulated transcriptomic data from PGs of two model species, Drosophila melanogaster and Bombyx mori. We identify that the common core components of the model in both species are encoded by nine genes. Five of these are Halloween genes whose expression differs substantially between the PGs of these species.

CONCLUSIONS

We conclude that the PGs can be a model for steroid hormone synthesis and regulation within the context of mitochondrial cholesterol transport and steroid biosynthesis but beyond these core mechanisms, gene expression in insect PGs is too diverse to fit in a context-specific model and should be analysed within a species-specific framework.

Expression profile changes of cytochrome P450 genes between thiamethoxam susceptible and resistant strains of Aphis gossypii Glover

Cytochrome P450 monooxygenases represent a key detoxification mechanism in neonicotinoids resistance in Aphis gossypii Glover. Synergism analysis has indicates that P450s are involved in thiamethoxam resistance. In this study, expression changes in the transcripts of P450 genes were determined in thiamethoxam-susceptible and thiamethoxam-resistant strains. Nine P450 genes in CYP3 clade were significantly overexpressed in the resistant strain (especially CYP6CY14, which was increased 17.67-fold) compared with the susceptible strain. Transcripts of ecdysone synthesis-related P450 genes, including CYP302A1, CYP306A1, CYP307A1 and CYP315A1, were up-regulated in the resistant strain, which may accelerate molting hormone production. The ecdysone response genes (ecdysone receptor (EcR), ultra-spiracle (USP) and Broad-complex protein (Br-C)) were overexpressed in the resistant strain. RNA interference (RNAi) targeting CYP6CY14 significantly increased the sensitivity of the resistant aphid to thiamethoxam. The results of the present study indicate the possible involvement of these P450 genes in thiamethoxam resistance. Our findings may facilitate further work to validate the roles of these P450s in thiamethoxam resistance based on heterologous expression, and show that screening the expression changes in P450 genes can reveal the impact of thiamethoxam on ecdysone synthesis-related P450 genes. These results are useful for understanding the mechanism of thiamethoxam resistance and will contribute to the management of insecticide-resistant cotton aphids in China.

Cholesterol internalization and metabolism in insect prothoracic gland, a steroidogenic organ, via lipoproteins

Dietary sterols including cholesterol and phytosterols are essential substrates for insect steroid hormone (ecdysteroid) synthesis in the prothoracic glands (PGs). In the silkworm Bombyx mori, one of the model species of insects, the steroidogenesis has been well demonstrated that cholesterol biotransformation into ecdysone in the PG cells. Because insects lack the ability to synthesize cellular sterol de novo, lipoprotein, lipophorin (Lp), has been thought to be the major cholesterol supply source; however, details of cholesterol behavior from Lp to the PG cells has not been analyzed till date. In this report, we developed Lp incorporation method using labeled cholesterols such as 22-NBD-cholesterol and cholesterol-25,26,26,26,27,27,27-d7 (cholesterol-d7), and analyzed the internalization and metabolism of cholesterol in PGs in vitro using the silkworm Bombyx mori. The internalization of cholesterol was visualized using 22-NBD-cholesterol. PGs showed an enriched cellular 22-NBD-cholesterol signal, which dissociated from the Lp localizing at the close area of cell membrane. The distribution pattern observed in the PGs was different from other tissues such as the brain, fat body, and Malpighian tubules, suggesting that the internalization of cholesterol in the PGs was distinct from other tissues. The metabolism of cholesterol was traced using LC-MS/MS methods to detect cholesterol-d7, 7-dehydrocholesterol-d7 (an expected intermediate metabolite), and the final product ecdysone-d6. 7-Dehydrocholesterol-d7 and ecdysone-d6 were detected in the PG culture incubated with labeled Lp, showing that the cholesterol of Lp was utilized for ecdysone synthesis in the PGs. Our results reveal the distinct behavior of cholesterol in the PGs, with the first direct evidence of biochemical fate of lipoprotein cholesterol in insect steroidogenic organ. This will aid in the understanding of the involvement of lipoprotein cholesterol in steroid hormone synthesis in insects.

Ecdysteroidogenesis and development in Heliothis virescens (Lepidoptera: Noctuidae): Focus on PTTH-stimulated pathways

Post-embryonic development and molting in insects are regulated by endocrine changes, including prothoracicotropic hormone (PTTH)-stimulated ecdysone secretion by the prothoracic glands (PGs). In Lepidoptera, two pathways are potentially involved in PTTH-stimulated ecdysteroidogenesis, mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase/protein kinase B/target of rapamycin (PI3K/Akt/TOR). We investigated the potential roles of both these pathways in Heliothis virescens ecdysteroidogenesis. We identified putative proteins belonging to MAPK and PI3K/Akt/TOR signaling cascades, using transcriptomic analyses of PGs from last (fifth) instar larvae. Using western blots, we measured the phosphorylation of 4E-BP and S6K proteins, the main targets of TOR, following the in vitro exposure of PGs to brain extract containing PTTH (hereafter referred to as PTTH) and/or the inhibitors of MAPK (U0126), PI3K (LY294002) or TOR (rapamycin). Next, we measured ecdysone production, under the same experimental conditions, by enzyme immunoassay (EIA). We found that in Heliothis virescens last instar larvae, both pathways modulated PTTH-stimulated ecdysteroidogenesis. Finally, we analyzed the post-embryonic development of third and fourth instar larvae fed on diet supplemented with rapamycin, in order to better understand the role of the TOR pathway in larval growth. When rapamycin was added to the diet of larvae, the onset of molting was delayed, the growth rate was reduced and abnormally small larvae/pupae with high mortality rates resulted. In larvae fed on diet supplemented with rapamycin, the growth of PGs was suppressed, and ecdysone production and secretion were inhibited. Overall, the in vivo and in vitro results demonstrated that, similarly to Bombyx mori, MAPK and PI3K/Akt/TOR pathways are involved in PTTH signaling-stimulated ecdysteroidogenesis, and indicated the important role of TOR protein in H. virescens systemic growth.

Phylogeny and evolution of the cholesterol transporter NPC1 in insects

Sterols are essential nutrients for eukaryotes. Insects are obligate sterol auxotrophs and must acquire this key nutrient from their diets. The digestive tract is the organ for absorbing nutrients as well as sterols from food. In mice, the Niemann-Pick type C1 Like 1 (NPC1L1) gene is highly expressed in the intestine and is critical for cholesterol absorption. In contrast, the molecular mechanisms for the absorption of dietary sterols in insects have not been well studied. We annotated NPC1 genes in 39 insects from 10 orders using available genomic and transcriptomic information and inferred phylogenetic relationships. Insect NPC1 genes were grouped into two sister-clades, NPC1a and NPC1b, suggesting a likely duplication in the ancestor of insects. The former exhibited weaker gut-biased expression or a complete lack of tissue-biased expression, depending on the species, while the latter was highly enriched in the gut of three lepidopteran species. This result is similar to previous findings in Drosophila melanogaster. In insects, NPC1a accumulated non-synonymous substitutions at a lower rate than NPC1b. This pattern was consistent across orders, indicating that NPC1a evolved under stronger molecular constraint than NPC1b.

Stingless Bee Larvae Require Fungal Steroid to Pupate

The larval stage of the stingless bee Scaptotrigona depilis must consume a specific brood cell fungus in order to continue development. Here we show that this fungus is a member of the genus Zygosaccharomyces and provides essential steroid precursors to the developing bee. Insect pupation requires ecdysteroid hormones, and as insects cannot synthesize sterols de novo, they must obtain steroids in their diet. Larval in vitro culturing assays demonstrated that consuming ergosterol recapitulates the developmental effects on S. depilis as ingestion of Zygosaccharomyces sp. cells. Thus, we determined the molecular underpinning of this intimate mutualistic symbiosis. Phylogenetic analyses showed that similar cases of bee-Zygosaccharomyces symbiosis may exist. This unprecedented case of bee-fungus symbiosis driven by steroid requirement brings new perspectives regarding pollinator-microbiota interaction and preservation.

Evolutionarily Conserved Roles for Blood-Brain Barrier Xenobiotic Transporters in Endogenous Steroid Partitioning and Behavior

Central nervous system (CNS) chemical protection depends upon discrete control of small-molecule access by the blood-brain barrier (BBB). Curiously, some drugs cause CNS side-effects despite negligible transit past the BBB. To investigate this phenomenon, we asked whether the highly BBB-enriched drug efflux transporter MDR1 has dual functions in controlling drug and endogenous molecule CNS homeostasis. If this is true, then brain-impermeable drugs could induce behavioral changes by affecting brain levels of endogenous molecules. Using computational, genetic, and pharmacologic approaches across diverse organisms, we demonstrate that BBB-localized efflux transporters are critical for regulating brain levels of endogenous steroids and steroid-regulated behaviors (sleep in Drosophila and anxiety in mice). Furthermore, we show that MDR1-interacting drugs are associated with anxiety-related behaviors in humans. We propose a general mechanism for common behavioral side effects of prescription drugs: pharmacologically challenging BBB efflux transporters disrupts brain levels of endogenous substrates and implicates the BBB in behavioral regulation.

A Drosophila Genome-Wide Screen Identifies Regulators of Steroid Hormone Production and Developmental Timing

Steroid hormones control important developmental processes and are linked to many diseases. To systematically identify genes and pathways required for steroid production, we performed a Drosophila genome-wide in vivo RNAi screen and identified 1,906 genes with potential roles in steroidogenesis and developmental timing. Here, we use our screen as a resource to identify mechanisms regulating intracellular levels of cholesterol, a substrate for steroidogenesis. We identify a conserved fatty acid elongase that underlies a mechanism that adjusts cholesterol trafficking and steroidogenesis with nutrition and developmental programs. In addition, we demonstrate the existence of an autophagosomal cholesterol mobilization mechanism and show that activation of this system rescues Niemann-Pick type C1 deficiency that causes a disorder characterized by cholesterol accumulation. These cholesterol-trafficking mechanisms are regulated by TOR and feedback signaling that couples steroidogenesis with growth and ensures proper maturation timing. These results reveal genes regulating steroidogenesis during development that likely modulate disease mechanisms.

Adipocyte Metabolic Pathways Regulated by Diet Control the Female Germline Stem Cell Lineage in Drosophila melanogaster

Nutrients affect adult stem cells through complex mechanisms involving multiple organs. Adipocytes are highly sensitive to diet and have key metabolic roles, and obesity increases the risk for many cancers. How diet-regulated adipocyte metabolic pathways influence normal stem cell lineages, however, remains unclear. Drosophila melanogaster has highly conserved adipocyte metabolism and a well-characterized female germline stem cell (GSC) lineage response to diet. Here, we conducted an isobaric tags for relative and absolute quantification (iTRAQ) proteomic analysis to identify diet-regulated adipocyte metabolic pathways that control the female GSC lineage. On a rich (relative to poor) diet, adipocyte Hexokinase-C and metabolic enzymes involved in pyruvate/acetyl-CoA production are upregulated, promoting a shift of glucose metabolism toward macromolecule biosynthesis. Adipocyte-specific knockdown shows that these enzymes support early GSC progeny survival. Further, enzymes catalyzing fatty acid oxidation and phosphatidylethanolamine synthesis in adipocytes promote GSC maintenance, whereas lipid and iron transport from adipocytes controls vitellogenesis and GSC number, respectively. These results show a functional relationship between specific metabolic pathways in adipocytes and distinct processes in the GSC lineage, suggesting the adipocyte metabolism-stem cell link as an important area of investigation in other stem cell systems.

Origin of an ancient hormone/receptor couple revealed by resurrection of an ancestral estrogen

The origin of ancient ligand/receptor couples is often analyzed via reconstruction of ancient receptors and, when ligands are products of metabolic pathways, they are not supposed to evolve. However, because metabolic pathways are inherited by descent with modification, their structure can be compared using cladistic analysis. Using this approach, we studied the evolution of steroid hormones. We show that side-chain cleavage is common to most vertebrate steroids, whereas aromatization was co-opted for estrogen synthesis from a more ancient pathway. The ancestral products of aromatic activity were aromatized steroids with a side chain, which we named "paraestrols." We synthesized paraestrol A and show that it effectively binds and activates the ancestral steroid receptor. Our study opens the way to comparative studies of biologically active small molecules.

Steroid Hormones and the Physiological Regulation of Tissue-Resident Stem Cells: Lessons from the Drosophila Ovary

PURPOSE OF REVIEW

Stem cells respond to local paracrine signals; more recently, however, systemic hormones have also emerged as key regulators of stem cells. This review explores the role of steroid hormones in stem cells, using the Drosophila germline stem cell as a centerpiece for discussion.

RECENT FINDINGS

Stem cells sense and respond directly and indirectly to steroid hormones, which regulate diverse sets of target genes via interactions with nuclear hormone receptors. Hormone-regulated networks likely integrate the actions of multiple systemic signals to adjust the activity of stem cell lineages in response to changes in physiological status.

SUMMARY

Hormones are inextricably linked to animal physiology, and can control stem cells and their local niches. Elucidating the molecular mechanisms of hormone signaling in stem cells is essential for our understanding of the fundamental underpinnings of stem cell biology, and for informing new therapeutic interventions against cancers or for regenerative medicine.

Transcriptome Analysis of Drosophila melanogaster Third Instar Larval Ring Glands Points to Novel Functions and Uncovers a Cytochrome p450 Required for Development

In Drosophila melanogaster larvae, the ring gland (RG) is a control center that orchestrates major developmental transitions. It is a composite organ, consisting of the prothoracic gland, the corpus allatum, and the corpora cardiaca, each of which synthesizes and secretes a different hormone. Until now, the RG’s broader developmental roles beyond endocrine secretion have not been explored. RNA sequencing and analysis of a new transcriptome resource from D. melanogaster wandering third instar larval RGs has provided a fascinating insight into the diversity of developmental signaling in this organ. We have found strong enrichment of expression of two gene pathways not previously associated with the RG: immune response and fatty acid metabolism. We have also uncovered strong expression for many uncharacterized genes. Additionally, RNA interference against RG-enriched cytochrome p450s Cyp6u1 and Cyp6g2 produced a lethal ecdysone deficiency and a juvenile hormone deficiency, respectively, flagging a critical role for these genes in hormone synthesis. This transcriptome provides a valuable new resource for investigation of roles played by the RG in governing insect development.

A Genetic Mosaic Screen Reveals Ecdysone-Responsive Genes Regulating Drosophila Oogenesis

Multiple aspects of Drosophila oogenesis, including germline stem cell activity, germ cell differentiation, and follicle survival, are regulated by the steroid hormone ecdysone. While the transcriptional targets of ecdysone signaling during development have been studied extensively, targets in the ovary remain largely unknown. Early studies of salivary gland polytene chromosomes led to a model in which ecdysone stimulates a hierarchical transcriptional cascade, wherein a core group of ecdysone-sensitive transcription factors induce tissue-specific responses by activating secondary branches of transcriptional targets. More recently, genome-wide approaches have identified hundreds of putative ecdysone-responsive targets. Determining whether these putative targets represent bona fide targets in vivo, however, requires that they be tested via traditional mutant analysis in a cell-type specific fashion. To investigate the molecular mechanisms whereby ecdysone signaling regulates oogenesis, we used genetic mosaic analysis to screen putative ecdysone-responsive genes for novel roles in the control of the earliest steps of oogenesis. We identified a cohort of genes required for stem cell maintenance, stem and progenitor cell proliferation, and follicle encapsulation, growth, and survival. These genes encode transcription factors, chromatin modulators, and factors required for RNA transport, stability, and ribosome biogenesis, suggesting that ecdysone might control a wide range of molecular processes during oogenesis. Our results suggest that, although ecdysone target genes are known to have cell type-specific roles, many ecdysone response genes that control larval or pupal cell types at developmental transitions are used reiteratively in the adult ovary. These results provide novel insights into the molecular mechanisms by which ecdysone signaling controls oogenesis, laying new ground for future studies.

Functional characterization of CYP71D443, a cytochrome P450 catalyzing C-22 hydroxylation in the 20-hydroxyecdysone biosynthesis of Ajuga hairy roots

20-Hydroxyecdysone (20HE), a molting hormone of insects, is also distributed among a variety of plant families. 20HE is thought to play a role in protecting plants from insect herbivores. In insects, biosynthesis of 20HE from cholesterol proceeds via 7-dehydrocholesterol and 3β,14α-dihydroxy-5β-cholest-7-en-6-one (5β-ketodiol), the latter being converted to 20HE through sequential hydroxylation catalyzed by four P450 enzymes, which have been cloned and identified. In contrast, little is known about plant 20HE biosynthesis, and no biosynthetic 20HE gene has been reported thus far. We recently proposed involvement of 3β-hydroxy-5β-cholestan-6-one (5β-ketone) in 20HE biosynthesis in the hairy roots of Ajuga reptans var. atropurpurea (Lamiaceae). In this study, an Ajuga EST library was generated from the hairy roots and P450 genes were deduced from the library. Five genes with a high expression level (CYP71D443, CYP76AH19, CYP76AH20, CYP76AH21 and CYP716D27) were screened for a possible involvement in 20HE biosynthesis. As a result, CYP71D443 was shown to have C-22 hydroxylation activity for the 5β-ketone substrate using a yeast expression system. The hydroxylated product, 22-hydroxy-5β-ketone, had a 22R configuration in agreement with that of 20HE. Furthermore, labeling experiments indicated that (22R)-22-hydroxy-5β-ketone was converted to 20HE in Ajuga hairy roots. Based on the present results, a possible 20HE biosynthetic pathway in Ajuga plants involved CYP71D443 is proposed.

The effect of silencing 20E biosynthesis relative genes by feeding bacterially expressed dsRNA on the larval development of Chilo suppressalis

RNA interference (RNAi) is a robust tool to study gene functions as well as potential for insect pest control. Finding suitable target genes is the key step in the development of an efficient RNAi-mediated pest control technique. Based on the transcriptome of Chilo suppressalis, 24 unigenes which putatively associated with insect hormone biosynthesis were identified. Amongst these, four genes involved in ecdysteroidogenesis i.e., ptth, torso, spook and nm-g were evaluated as candidate targets for function study. The partial cDNA of these four genes were cloned and their bacterially expressed dsRNA were fed to the insects. Results revealed a significant reduction in mRNA abundance of target genes after 3 days. Furthermore, knocked down of these four genes resulted in abnormal phenotypes and high larval mortality. After 15 days, the survival rates of insects in dsspook, dsptth, dstorso, and dsnm-g groups were significantly reduced by 32%, 38%, 56%, and 67% respectively, compared with control. Moreover, about 80% of surviving larvae showed retarded development in dsRNA-treated groups. These results suggest that oral ingestion of bacterially expressed dsRNA in C. suppressalis could silence ptth, torso, spook and nm-g. Oral delivery of bacterially expressed dsRNA provides a simple and potential management scheme against C. suppressalis.

Transcriptome analysis to identify genes for peptides and proteins involved in immunity and reproduction from male accessory glands and ejaculatory duct of Bactrocera dorsalis

In the male reproductive system of insects, the male accessory glands and ejaculatory duct (MAG/ED) are important organs and their primary function is to enhance the fertility of spermatozoa. Proteins secreted by the MAG/ED are also known to induce post-mating changes and immunity responses in the female insect. To understand the gene expression profile in the MAG/ED of the oriental fruit fly Bactrocera dorsalis (Hendel), that is an important pest in fruits, we performed an Illumina-based deep sequencing of mRNA. This yielded 54,577,630 clean reads corresponding to 4.91Gb total nucleotides that were assembled and clustered to 30,669 unigenes (average 645bp). Among them, 20,419 unigenes were functionally annotated to known proteins/peptides in Gene Orthology, Clusters of Orthologous Groups, Kyoto Encyclopedia of Genes and Genomes pathway databases. Typically, many genes were involved in immunity and these included microbial recognition proteins and antimicrobial peptides. Subsequently, the inducible expression of these immunity-related genes was confirmed by qRT-PCR analysis when insects were challenged with immunity-inducible factors, suggesting their function in guaranteeing fertilization success. Besides, we identified some important reproductive genes such as juvenile hormone- and ecdysteroid-related genes in this de novo assembly. In conclusion, this transcriptomic sequencing of B. dorsalis MAG/ED provides insights to facilitate further functional research of reproduction, immunity and molecular evolution of reproductive proteins in this important agricultural pest.

A biological timer in the fat body comprising Blimp-1, βFtz-f1 and Shade regulates pupation timing in Drosophila melanogaster

During the development of multicellular organisms, many events occur with precise timing. In Drosophila melanogaster, pupation occurs about 12 h after puparium formation and its timing is believed to be determined by the release of a steroid hormone, ecdysone (E), from the prothoracic gland. Here, we demonstrate that the ecdysone-20-monooxygenase Shade determines pupation timing by converting E to 20-hydroxyecdysone (20E) in the fat body, which is the organ that senses nutritional status. The timing of shade expression is determined by its transcriptional activator βFtz-f1. The βftz-f1 gene is activated after a decline in the expression of its transcriptional repressor Blimp-1, which is temporally expressed around puparium formation in response to a high titer of 20E. The expression level and stability of Blimp-1 is critical for the precise timing of pupation. Thus, we propose that Blimp-1 molecules function like sand in an hourglass in this precise developmental timer system. Furthermore, our data suggest that a biological advantage results from both the use of a transcriptional repressor for time determination and the association of developmental timing with nutritional status of the organism.