Fat body lipolysis connects poor nutrition to hypopharyngeal gland degradation in Apis mellifera

The hypopharyngeal glands (HGs) of honey bee nurse workers secrete the major protein fraction of jelly, a protein and lipid rich substance fed to developing larvae, other worker bees, and queens. A hallmark of poorly nourished nurses is their small HGs, which actively degrade due to hormone-induced autophagy. To better connect nutritional stress with HG degradation, we looked to honey bees and other insect systems, where nutrient stress is often accompanied by fat body degradation. The fat body contains stored lipids that are likely a substrate for ecdysteroid synthesis, so we tested whether starvation caused increased fat body lipolysis. Ecdysteroid signaling and response pathways and IIS/TOR are tied to nutrient-dependent autophagy in honey bees and other insects, and so we also tested whether and where genes in these pathways were differentially regulated in the head and fat body. Last, we injected nurse-aged bees with the honey bee ecdysteroid makisterone A to determine whether this hormone influenced HG size and autophagy. We find that starved nurse aged bees exhibited increased fat body lipolysis and increased expression of ecdysteroid production and response genes in the head. Genes in the IIS/TOR pathway were not impacted by starvation in either the head or fat body. Additionally, bees injected with makisterone A had smaller HGs and increased expression of autophagy genes. These data support the hypothesis that nutritional stress induces fat body lipolysis, which may liberate the sterols important for ecdysteroid production, and that increased ecdysteroid levels induce autophagic HG degradation.

Initiation of metamorphosis and control of ecdysteroid biosynthesis in insects: The interplay of absence of Juvenile hormone, PTTH, and Ca(2+)-homeostasis

The paradigm saying that release of the brain neuropeptide big prothoracicotropic hormone (PTTH) initiates metamorphosis by activating the Torso-receptor/ERK pathway in larval prothoracic glands (PGs) is widely accepted nowadays. Upon ligand-receptor interaction Ca(2+) enters the PG cells and acts as a secondary messenger. Ecdysteroidogenesis results, later followed by apoptosis. Yet, some data do not fit in this model. In some species decapitated animals can still molt, even repeatedly, and metamorphose. PTTH does not universally occur in all insect species. PGs may also have other functions; PGs as counterpart of the vertebrate thymus? There are also small PTTHs. Finally, PTTH remains abundantly present in adults and plays a role in control of ecdysteroidogenesis (=sex steroid production) in gonads. This is currently documented only in males. This urges a rethinking of the PTTH-PG paradigm. The key question is: Why does PTTH-induced Ca(2+) entry only result in ecdysteroidogenesis and apoptosis in specific cells/tissues, namely the PGs and gonads? Indeed, numerous other neuropeptides also use Ca(2+) as secondary messenger. The recent rediscovery that in both invertebrates and vertebrates at least some isoforms of Ca(2+)-ATPase need the presence of an endogenous farnesol/juvenile hormone(JH)-like sesquiterpenoid for keeping cytosolic [Ca(2+)]i below the limit of apoptosis-induction, triggered the idea that it is not primarily PTTH, but rather the drop to zero of the JH titer that acts as the primordial initiator of metamorphosis by increasing [Ca(2+)]i. PTTH likely potentiates this effect but only in cells expressing Torso. PTTH: an evolutionarily ancient gonadotropin?

Modulatory effects of bombyxin on ecdysteroidogenesis in Bombyx mori prothoracic glands

In the present study, we investigated the modulatory effects of ecdysteroidogenesis of prothoracic glands (PGs) by bombyxin, an endogenous insulin-like peptide in the silkworm, Bombyx mori. The results showed that bombyxin stimulated ecdysteroidogenesis during a long-term incubation period and in a dose-dependent manner. Moreover, the injection of bombyxin into day 4-last instar larvae increased ecdysteroidogenesis 24h after the injection, indicating its possible in vivo function. Phosphorylation of the insulin receptor and Akt, and the target of rapamycin (TOR) signaling were stimulated by bombyxin, and stimulation of Akt phosphorylation and TOR signaling appeared to be dependent on phosphatidylinositol 3-kinase (PI3K). Bombyxin inhibited the phosphorylation of adenosine 5'-monophosphate-activated protein kinase (AMPK), and the inhibition appeared to be PI3K-independent. Bombyxin-stimulated ecdysteroidogenesis was blocked by either an inhibitor of PI3K (LY294002) or a chemical activator of AMPK (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside, AICAR), indicating involvement of the PI3K/Akt and AMPK signaling pathway. Bombyxin did not stimulate extracellular signal-regulated kinase (ERK) signaling of PGs. Bombyxin, but not prothoracicotropic hormone (PTTH) stimulated cell viability of PGs. In addition, bombyxin treatment also affected mRNA expression levels of insulin receptor, Akt, AMPKα, -β, and -γ in time-dependent manners. These results suggest that bombyxin modulates ecdysteroidogenesis in B. mori PGs during development.

Expression of stress-related genes in the parthenogenetic forms of the pea aphid, Acyrthosiphon pisum

Aphids are an economically important group of insects that have an intricate life cycle with seasonal polyphenism. This study aimed to explore the physiological background of aphid migration from unfavorable nutritional conditions to a new, intact host plant. Specifically, the relative expression of stress/metabolism-related genes and changes in metabolic reserves were determined for the winged and wingless forms of female pea aphids, Acyrthosiphon pisum, under two different nutritional conditions. The expression level was determined for the following sets of genes: the adipokinetic hormone (AKH) and its receptor, enzymes involved in carbohydrate and lipid metabolism, detoxifying enzymes, and genes encoding exoskeleton/cuticular proteins and cytoskeleton proteins. In both forms, the transcription of the adipokinetic hormone was upregulated during nutritional stress, whereas its receptor mRNA levels remained unchanged. Similarly, the expression of genes engaged in glycogen and triglyceride degradation was elevated. Glycogen reserves and phospholipids appeared to be used during stress. In comparison, nutrient rich reproductively active females of both forms appeared to use triglycerides. Moreover, we revealed changes in the mRNA level of the detoxifying genes delta-class glutathione S-transferase (GST-δ) and cytochrome P450 monooxygenase (CYP450), as well as the CP gene (which encodes exoskeleton/cuticular proteins) and the cofilin gene (the products of which influence cytoskeleton organization). These results indicate the possible correlation between nutritional stress, energy content, AKH, and the stress-related enzymes of different metabolic pathways in winged and wingless forms of A. pisum.

Transcriptional control of steroid biosynthesis genes in the Drosophila prothoracic gland by ventral veins lacking and knirps

Specialized endocrine cells produce and release steroid hormones that govern development, metabolism and reproduction. In order to synthesize steroids, all the genes in the biosynthetic pathway must be coordinately turned on in steroidogenic cells. In Drosophila, the steroid producing endocrine cells are located in the prothoracic gland (PG) that releases the steroid hormone ecdysone. The transcriptional regulatory network that specifies the unique PG specific expression pattern of the ecdysone biosynthetic genes remains unknown. Here, we show that two transcription factors, the POU-domain Ventral veins lacking (Vvl) and the nuclear receptor Knirps (Kni), have essential roles in the PG during larval development. Vvl is highly expressed in the PG during embryogenesis and is enriched in the gland during larval development, suggesting that Vvl might function as a master transcriptional regulator in this tissue. Vvl and Kni bind to PG specific cis-regulatory elements that are required for expression of the ecdysone biosynthetic genes. Knock down of either vvl or kni in the PG results in a larval developmental arrest due to failure in ecdysone production. Furthermore, Vvl and Kni are also required for maintenance of TOR/S6K and prothoracicotropic hormone (PTTH) signaling in the PG, two major pathways that control ecdysone biosynthesis and PG cell growth. We also show that the transcriptional regulator, Molting defective (Mld), controls early biosynthetic pathway steps. Our data show that Vvl and Kni directly regulate ecdysone biosynthesis by transcriptional control of biosynthetic gene expression and indirectly by affecting PTTH and TOR/S6K signaling. This provides new insight into the regulatory network of transcription factors involved in the coordinated regulation of steroidogenic cell specific transcription, and identifies a new function of Vvl and Knirps in endocrine cells during post-embryonic development.

Suppression of allatotropin simulates reproductive diapause in the mosquito Culex pipiens

The cessation of juvenile hormone (JH) production is a key endocrine event that halts ovarian development and hence initiates diapause in females of the mosquito, Culex pipiens. The shutdown in endocrine activity of the corpora allata (CA), the source of JH, was manifested in the smaller size of CA in females reared under short daylengths (diapause) compared to those reared under long daylengths (nondiapause), as well as in low expression of the mRNA encoding allatotropin, the neuropeptide that promotes JH biosynthesis in the CA. Genes encoding both allatotropin and allatostatin were identified in C. pipiens, but only expression levels of allatotropin differed in the two types of females. Knockdown of allatotropin mRNA using RNA interference in females programmed for nondiapause resulted in a cessation of ovarian development akin to diapause. This arrest in development could be reversed with an application of JH. Our results thus suggest that suppression of allatotropin is a critical link in regulating the shutdown of the CA during diapause.

Serotonin receptor B may lock the gate of PTTH release/synthesis in the Chinese silk moth, Antheraea pernyi; a diapause initiation/maintenance mechanism?

The release of prothoracicotropic hormone, PTTH, or its blockade is the major endocrine switch regulating the developmental channel either to metamorphosis or to pupal diapause in the Chinese silk moth, Antheraea pernyi. We have cloned cDNAs encoding two types of serotonin receptors (5HTRA and B). 5HTRA-, and 5HTRB-like immunohistochemical reactivities (-ir) were colocalized with PTTH-ir in two pairs of neurosecretory cells at the dorsolateral region of the protocerebrum (DL). Therefore, the causal involvement of these receptors was suspected in PTTH release/synthesis. The level of mRNA(5HTRB) responded to 10 cycles of long-day activation, falling to 40% of the original level before activation, while that of 5HTRA was not affected by long-day activation. Under LD 16:8 and 12:12, the injection of dsRNA(5HTRB) resulted in early diapause termination, whereas that of dsRNA(5HTRA) did not affect the rate of diapause termination. The injection of dsRNA(5HTRB) induced PTTH accumulation, indicating that 5HTRB binding suppresses PTTH synthesis also. This conclusion was supported pharmacologically; the injection of luzindole, a melatonin receptor antagonist, plus 5th inhibited photoperiodic activation under LD 16:8, while that of 5,7-DHT, induced emergence in a dose dependent fashion under LD 12:12. The results suggest that 5HTRB may lock the PTTH release/synthesis, maintaining diapause. This could also work as diapause induction mechanism.

Insulin-like and testis ecdysiotropin neuropeptides are regulated by the circadian timing system in the brain during larval-adult development in the insect Rhodnius prolixus (Hemiptera)

Insulin-like peptides (ILPs) regulate numerous functions in insects including growth, development, carbohydrate metabolism and female reproduction. This paper reports the immunohistochemical localization of ILPs in brain neurons of Rhodnius prolixus and their intimate associations with the brain circadian clock system. In larvae, three groups of neurons in the protocerebrum are ILP-positive, and testis ecdysiotropin (TE) is co-localized in two of them. During adult development, the number of ILP groups increased to four. A blood meal initiates transport and release of ILPs, indicating that release is nutrient dependent. Both production and axonal transport of ILPs continue during adult development with clear cytological evidence of a daily rhythm that closely correlates with the daily rhythm of ILPs release from brains in vitro. The same phenomena were observed with TE previously. Double labeling for ILPs and pigment dispersing factor (PDF) (contained in the brain lateral clock cells, LNs) revealed intimate associations between axons of the ILP/TE cells and PDF-positive axons in both central brain and retrocerebral complex, revealing potential neuronal pathways for circadian regulation of ILPs and TE. Similar close associations were found previously between LN axons and axons of the brain neurons producing the neuropeptide prothoracicotropic hormone. Thus, the brain clock system controls rhythmicity in multiple brain neurohormones. It is suggested that rhythms in circulating ILPs and TE act in concert with known rhythms of circulating ecdysteroids in both larvae and adults to orchestrate the timing of cellular responses in diverse tissues of the animal, thereby generating internal temporal order within it.

In search for non-steroidogenic functions of the prothoracic glands of the desert locust, Schistocerca gregaria: a peptidomic and proteomic approach

The only well established function of the prothoracic glands (PGs) of insects is the production of ecdysteroids. In gregarious locusts, like in most insect species, the PGs degenerate soon after the adult molt. In this way they resemble the thymus of mammals, a gland with an important role in the build up of the immune system in young animals. In adult solitarious locusts the PGs persist much longer, however without producing substantial amounts of ecdysteroids. In the literature the existence of a well developed rough endoplasmic reticulum and Golgi complex system has been repeatedly reported, suggesting an active role in peptide or/and protein synthesis and release. The nature of the secreted products remained unknown. Our pepdidomic analysis of an acidified methanolic extract of PGs of last instar gregarious nymphs did not yield any indication for the presence of known locust or other peptides. The peptide release assay was also negative. For our proteomic analysis, we developed an EST-based identification strategy. We successfully identified 50 protein spots on a two dimensional map. In addition to typical protein synthesis-related proteins, a number of proteins with a role in detoxification processes were found, suggesting some role of the PGs in the defense system.

An FXPRLamide neuropeptide induces seasonal reproductive polyphenism underlying a life-history tradeoff in the tussock moth

The white spotted tussock moth, Orgyia thyellina, is a typical insect that exhibits seasonal polyphenisms in morphological, physiological, and behavioral traits, including a life-history tradeoff known as oogenesis-flight syndrome. However, the developmental processes and molecular mechanisms that mediate developmental plasticity, including life-history tradeoff, remain largely unknown. To analyze the molecular mechanisms involved in reproductive polyphenism, including the diapause induction, we first cloned and characterized the diapause hormone-pheromone biosynthesis activating neuropeptide (DH-PBAN) cDNA encoding the five Phe-X-Pro-Arg-Leu-NH(2) (FXPRLa) neuropeptides: DH, PBAN, and α-, β-, and γ-SGNPs (subesophageal ganglion neuropeptides). This gene is expressed in neurosecretory cells within the subesophageal ganglion whose axonal projections reach the neurohemal organ, the corpus cardiacum, suggesting that the DH neuroendocrine system is conserved in Lepidoptera. By injection of chemically synthetic DH and anti-FXPRLa antibody into female pupae, we revealed that not only does the Orgyia DH induce embryonic diapause, but also that this neuropeptide induces seasonal polyphenism, participating in the hypertrophy of follicles and ovaries. In addition, the other four FXPRLa also induced embryonic diapause in O. thyellina, but not in Bombyx mori. This is the first study showing that a neuropeptide has a pleiotropic effect in seasonal reproductive polyphenism to accomplish seasonal adaptation. We also show that a novel factor (i.e., the DH neuropeptide) acts as an important inducer of seasonal polyphenism underlying a life-history tradeoff. Furthermore, we speculate that there must be evolutionary conservation and diversification in the neuroendocrine systems of two lepidopteran genera, Orgyia and Bombyx, in order to facilitate the evolution of coregulated life-history traits and tradeoffs.

Identification of a cis-regulatory element that directs prothoracicotropic hormone gene expression in the silkworm Bombyx mori

In the silkworm Bombyx mori and other insects, prothoracicotropic hormone (PTTH) plays a central role in controlling molting and metamorphosis by stimulating the prothoracic glands to synthesize and release the molting hormone ecdysone. Using an AcNPV (Autographa californica nucleopolyhedrovirus)-mediated transient gene transfer system, we identified a cis-regulatory element that participates in the decision to switch expression of PTTH on or off in PTTH-producing neurosecretory cells (PTPCs). The nucleotide sequence of this cis-regulatory element is similar to a cis-regulatory element that participates in direction of expression of diapause hormone-pheromone biosynthesis activating neuropeptide gene (DH-PBAN) (Shiomi et al., 2007). Furthermore, we found that B. mori Pitx (BmPitx), a bicoid-like homeobox transcription factor, binds the element and activates PTTH expression. Therefore, we propose that the cell-specific expression of two neuropeptide hormone genes, PTTH and DH-PBAN, is activated by the Pitx transcription factor, which may act as a pan-activator in the insect neuroendocrine system and in vertebrate pituitary cells.

Gene encoding the prothoracicotropic hormone of a moth is expressed in the brain and gut

The molts of lepidopteran insects are typically controlled by the brain-derived prothoracicotropic hormone (PTTH) that stimulates ecdysteroidogenesis in the prothoracic glands (PGs). We report here that the larvae and pupae of the moth Sesamia nonagrioides can molt without brain (PGs must be present), suggesting that there might be a secondary source of PTTH. We addressed this issue by characterizing spatial and temporal expression patterns of the PTTH gene. To this end we identified a major part of the corresponding cDNA. Protein deduced from this cDNA fragment consisted of 128 amino acids and showed 48-85% homology with the matching regions of PTTHs known from other Lepidoptera. Quantification of PTTH expression in major body organs of the last instar larvae revealed high expression in the brain (fading in post-feeding larvae) and considerable expression in the gut (with a maximum in post-feeding larvae). The content of PTTH message in the gut was enhanced after decapitation. It is concluded that the molts of S. nonagrioides larvae are driven by PTTH gene expression in the gut.

Neuropeptide regulators of the juvenile hormone biosynthesis (in vitro) in the beetle, Tenebrio molitor (Coleoptera, Tenebrionidae)

The genome of Tribolium castaneum encodes two allatostatin [AS type B; W(X)(6)Wamide and AS type C; PISCF-OH] and one allatotropin (AT) precursor, but no AS type A (FGLamide) (Tribolium Genome Sequencing Consortium, 2008: Nature 452:949-955). Here we studied the activity (in vitro) of peptides derived from these precursors on the synthesis/release of juvenile hormone (JH) III. The corpora cardiaca-corpora allata (CC-CA) complexes of adult females of another tenebrionid beetle, the mealworm Tenebrio molitor, were used. Incubating the gland complexes in a medium containing Trica-AS B3 peptide, we showed that the peptide has allatostatic function in T. molitor. The activity of the type C AS depended on the age of the test animals and their intrinsic rate of JH III biosynthesis. The Trica-AS C peptide inhibited the JH release from CA of 3-day-old females with a high intrinsic rate of JH synthesis, but activated JH release from the CA of 7-day-old females with a lower intrinsic rate of JH production. The allatotropin peptide (Trica-AT) also activated the JH release from the CA of 7-day-old females in a dose-dependent and reversible manner. Unexpectedly, a type A AS derived from the precursor of the American cockroach Periplaneta americana (Peram-AS A2b) inhibited the JH release from the CA of younger and older females in the concentration range of 10(-8) to 10(-4) M, and the effects were fully reversible in the absence of peptide. These data suggest a complex role of allatoactive neuropeptides in the regulation of JH III biosynthesis in beetles.

The proprotein convertase encoded by amontillado (amon) is required in Drosophila corpora cardiaca endocrine cells producing the glucose regulatory hormone AKH

Peptide hormones are potent signaling molecules that coordinate animal physiology, behavior, and development. A key step in activation of these peptide signals is their proteolytic processing from propeptide precursors by a family of proteases, the subtilisin-like proprotein convertases (PCs). Here, we report the functional dissection of amontillado (amon), which encodes the Drosophila homolog of the mammalian PC2 protein, using cell-type specific inactivation and rescue experiments, and we show that amon is required in the islet-like adipokinetic hormone (AKH)–producing cells that regulate sugar homeostasis. In Drosophila, AKH acts analogously to vertebrate glucagon to increase circulating sugar levels from energy stores, while insulin-like peptides (DILPs) act to decrease sugar levels. amon mutant larvae have significantly reduced hemolymph sugar levels, and thus phenocopy larvae where the AKH–producing cells in the corpora cardiaca have been ablated. Reduction of amon expression in these cells via cell-specific RNA inactivation also results in larvae with reduced sugar levels while expression of amon in AKH cells in an amon mutant background rescues hypoglycemia. Hypoglycemia in larvae resulting from amon RNA inactivation in the AKH cells can be rescued by global expression of the akh gene. Finally, mass spectrometric profiling shows that the production of mature AKH is inhibited in amon mutants. Our data indicate that amon function in the AKH cells is necessary to maintain normal sugar homeostasis, that amon functions upstream of akh, and that loss of mature AKH is correlated with loss of amon activity. These observations indicate that the AKH propeptide is a proteolytic target of the amon proprotein convertase and provide evidence for a conserved role of PC2 in processing metabolic peptide hormones.

Peptide hormones are important signaling molecules that coordinate physiology, behavior, and development. A key step in production of peptide hormones is the proteolytic cleavage of larger inactive precursors by prohormone convertases (PCs). Studies in a variety of organisms, including humans, have shown that deficiencies in PC genes lead to complex and detrimental changes. We used fruitfly genetics to dissect the function of Drosophila PC2, encoded by the amon gene, in the regulation of carbohydrate metabolism. We found that amon is expressed in endocrine cells of the corpora cardiaca that produce the sugar-mobilizing adipokinetic hormone (AKH), a functional analog of vertebrate glucagon. Previous studies suggest that the AKH–producing cells are homologs of the glucagon-producing islet alpha-cells in the pancreas. We found that flies with amon deficiency had significantly reduced hemolymph (insect “blood”) sugar levels. Using cell-type specific inactivation and rescue experiments, we show that amon expression in the AKH cells is necessary and sufficient for normal sugar regulation. We also demonstrate that AKH production is inhibited in amon mutants. Our results indicate that amon is necessary to maintain normal hemolymph sugar levels by activating AKH and suggest a conservation of PC2 function in processing peptide hormones between flies and mammals.

Control of ecdysteroidogenesis in prothoracic glands of insects: a review

The very first step in the study of the endocrine control of insect molting was taken in 1922. Stefan Kopec characterized a factor in the brain of the gypsy moth, Lymantria dispar which appeared to be essential for metamorphosis. This factor was later identified as the neuropeptide prothoracicotropic hormone (PTTH), the first discovery of a series of factors involved in the regulation of ecdysteroid biosynthesis in insects. It is now accepted that PTTH is the most important regulator of prothoracic gland (PG) ecdysteroidogenesis. The periodic increases in ecdysteroid titer necessary for insect development can basically be explained by the episodic activation of the PGs by PTTH. However, since the characterization of the prothoracicostatic hormone (PTSH), it has become clear that in addition to 'tropic factors', also 'static factors', which are responsible for the 'fine-tuning' of the hemolymph ecdysteroid titer, are at play. Many of these regulatory factors are peptides originating from the brain, but also other, extracerebral factors both of peptidic and non-peptidic nature are able to affect PG ecdysteroidogenesis, such as the 'classic' insect hormones, juvenile hormone (JH) and the molting hormone (20E) itself. The complex secretory pattern of ecdysteroids as observed in vivo is the result of the delicate balance and interplay between these ecdysiotropic and ecdysiostatic factors.

QTL analysis of sex pheromone blend differences between two closely related moths: Insights into divergence in biosynthetic pathways

To understand the evolution of premating signals in moths, it is important to know the genetic basis of these signals. We conducted Quantitative Trait Locus (QTL) analysis by hybridizing two noctuid moth species, Heliothis virescens (Hv) and Heliothis subflexa (Hs), and backcrossing the F(1) females to males of both parental species. One of these backcrosses (F(1) x Hs) was a biological replicate of our previous study (Sheck et al., 2006) and served to test the robustness of our previous findings. The backcross to Hv was designed to reveal QTL with recessive inheritance of the Hv character state. This study confirms previously discovered QTL, but also reports new QTL. Most importantly, we found relatively large QTL affecting Z9-16:Ald, the critical sex pheromone component of Hs. For Z9-14:Ald, the critical sex pheromone component of Hv, as well as for the minor pheromone compound 14:Ald, we found QTL in which the change in pheromone ratio was opposite-to-expected. Linking QTL to the biosynthetic pathways of the pheromone compounds of Hv and Hs implicates several candidate genes in the divergence of these premating signals, the most important of which are acetyl transferase, one or more desaturase(s), and a fatty acyl reductase or alcohol oxidase.

Peptides of the adipokinetic hormone/red pigment-concentrating hormone family with special emphasis on Caelifera: primary sequences and functional considerations contrasting grasshoppers and locusts

The presented work is a hybrid of an overview and an original research paper. First, we review briefly the structure, biosynthesis, release, mode of action and function of those peptides that constitute the adipokinetic/red pigment-concentrating family. Second, we collate the data on primary sequences available for caeliferan orthoptera, i.e. grasshoppers and locusts, and add a number of new data from previously unpublished work. The data are interpreted in conjunction with morphological and molecular biology data with respect to phylogenetic relationships of these various taxa. Finally, we discuss the differences between the adipokinetic response of grasshoppers and locusts to corpus cardiacum extract or synthetic adipokinetic hormone with regard to flight ability, phase polymorphism, age, presence of adipokinetic hormones, lipophorin system and other parameters. It appears that the higher hyperlipaemic response is always correlated with pronounced flight ability.

Biochemical, molecular, and functional characterization of PISCF-allatostatin, a regulator of juvenile hormone biosynthesis in the mosquito Aedes aegypti

Aedes aegypti PISCF-allatostatin or allatostatin-C (Ae-AS-C) was isolated using a combination of high performance liquid chromatography and enzyme-linked immunosorbent assay (ELISA). The matrix-assisted laser desorption/ionization time-of-flight (TOF) mass spectrum of positive ELISA fractions revealed a molecular mass of 1919.0 Da, in agreement with the sequence qIRYRQCYFNPISCF, with bridged cysteines. This sequence was confirmed by matrix-assisted laser desorption/ionization tandem TOF/TOF mass spectrometry analysis. The corresponding Ae-AS-C cDNA was amplified by PCR, and the sequence of the peptide was confirmed. An in vitro radiochemical assay was used to study the inhibitory effect of synthetic Ae-AS-C on juvenile hormone biosynthesis by the isolated corpora allata (CA) of adult female A. aegypti. The inhibitory action of synthetic Ae-AS-C was dose-dependent; with a maximum at 10(-9) m. Ae-AS-C showed no inhibitory activity in the presence of farnesoic acid, an immediate precursor of juvenile hormone, indicating that the Ae-AS-C target is located before the formation of farnesoic acid in the pathway. The sensitivity of the CA to inhibition by Ae-AS-C in the in vitro assay varied during the adult life; the CA was most sensitive during periods of low synthetic activity. In addition, the levels of Ae-AS-C in the brain were studied using ELISA and reached a maximum at 3 days after eclosion. These studies suggest that Ae-AS-C is an important regulator of CA activity in A. aegypti.

Regulation of Schistocerca gregaria neuroparsin transcript levels by juvenile hormone and 20-hydroxyecdysone

Neuroparsins (NPs) are small proteins that were originally discovered in the pars intercerebralis-corpus cardiacum neurosecretory complex of the migratory locust brain. From the desert locust, Schistocerca gregaria, we recently cloned four different transcripts, each coding for a distinct NP-related peptide. In addition to the brain, some NP-like precursor (Scg-NPP) transcripts also occur in a number of peripheral tissues, and their expression levels are controlled in a gender- and stage-dependent manner. Previous studies revealed a close correlation between Scg-NPP transcript levels and the gonotrophic cycle. In the present report, we demonstrate that certain Scg-NPP transcript levels are significantly altered upon injection of juvenile hormone (JH) or 20-hydroxyecdysone (20E) in adult gregarious desert locusts (five days after final ecdysis). While Scg-NPP1 transcript levels did not significantly change as a result of hormone treatment (animals were analyzed 24 h after injection), Scg-NPP2, Scg-NPP3, and Scg-NPP4 displayed hormone-dependent regulation in various tissues. Scg-NPP2 and Scg-NPP3 transcript levels significantly increased in the brain of JH-treated locusts. In addition, JH induction of Scg-NPP3 and Scg-NPP4 transcripts was observed in male fat body and in male and female gonads. Furthermore, 20E injection also induced Scg-NPP2, Scg-NPP3, and Scg-NPP4 transcripts in desert locust gonads. This is the first report showing NP-like precursor gene expression in insect ovaries. Our study indicates that the expression levels of some Scg-NPP transcripts are regulated by developmental hormones, suggesting a close correlation between NP expression and the endocrine control of the reproductive cycle.

Adipokinetic hormones in the African malaria mosquito, Anopheles gambiae: identification and expression of genes for two peptides and a putative receptor

Adipokinetic hormones (AKHs) are neuropeptides that mobilize stored fuels for flight in insects, and thus, may regulate flight by mosquitoes that transmit pathogens of human diseases. Our study of AKHs in the African malaria mosquito, Anopheles gambiae, identified and characterized the expression of genes encoding two AKHs, Anoga-AKH-I (pQLFTPAWa) and Anoga-AKH-II (pQVTFSRDWNAa), and a putative homolog for an AKH G-protein coupled receptor. Gene transcripts for both Anoga-AKHs and the AKH receptor were present in eggs, larvae, pupae, and adults of An. gambiae. In females, these transcripts were apparent in heads and thoraces for up to 72 h after blood or sugar feeding, as revealed by RT-PCR. With immunocytochemistry, a cluster of neurosecretory cells posterior to the corpus cardiacum and specific cells in the brain and thoracic ganglia of females were immunostained with an AKH antibody, which recognizes both Anoga-AKHs. Accordingly, Anoga-AKH-I was detected in extracts of female heads and thoraces by HPLC and an AKH radioimmunoassay, whereas Anoga-AKH-II was detected only in heads.

Regulation of insect steroid hormone biosynthesis by innervating peptidergic neurons

In insects, steroid hormones named ecdysteroids elicit molting and metamorphosis. The prothoracic gland (PG) is a predominant source of ecdysteroids, where their biosynthesis (ecdysteroidogenesis) is regulated by several neuropeptides. Here, we report that FMRFamide-related peptides (FaRPs) regulate ecdysteroidogenesis through direct innervation of the PG in the silkworm Bombyx mori. We purified a previously uncharacterized Bombyx FaRP, DPSFIRFamide, and identified the corresponding Bombyx FMRFamide gene (Bommo-FMRFamide, BRFa), which encodes three additional FaRPs. All BRFa peptides suppressed ecdysteroidogenesis in the PG by reducing cAMP production by means of the receptor for Bommo-myosuppressin, another FaRP we have previously shown to act as a prothoracicostatic factor. BRFa is predominantly expressed in neurosecretory cells of thoracic ganglia, and the neurons in the prothoracic ganglion innervate the PG to supply all four peptides to the gland surface. Electrophysiological recordings during development confirmed the increased firing activity of BRFa neurons in stages with low PG activity and decreased ecdysteroid levels in the hemolymph. To our knowledge, this study provides the first report of peptides controlling ecdysteroidogenesis by direct innervation.

Effects of starvation and mating on corpora allata activity and allatotropin (Manse-AT) gene expression in Manduca sexta

The levels of three alternatively spliced mRNAs from the Manduca sexta allatotropin (Manse-AT) gene were determined following physiological manipulations during the larval, pupal and adult stages; starvation of larvae, induction of pupal diapause and adult mating experience. The juvenile hormone biosynthetic activity of the corpora allata (CA) was also determined in starved larvae and in mated and unmated females. Starvation of early fifth instar larvae specifically increased the amount of one Manse-AT mRNA that is predicted to encode Manse-AT and two related peptides, Manse-ATL-I and -II. The normal rapid decrease in the activity of the CA in last instar larvae was not observed in starved insects which maintained a relatively high rate of JH biosynthesis for at least 3 days. Diapause induction resulted in a small increase in one Manse-AT mRNA, but levels were much lower compared to those observed in larvae or adults. During the first 4 days of adult life, Manse-AT mRNA levels were not changed as a result of mating. However, in mated females, the rate of JH biosynthesis gradually increased, in sharp contrast to the relatively low level of CA activity seen in virgin females. These observations suggest the elevated activity of the CA in mated females is not simply due to the increased level of Manse-AT mRNA.

Neuroparsin transcripts as molecular markers in the process of desert locust (Schistocerca gregaria) phase transition

Desert locust swarms occasionally cause severe ecological and economic damage, particularly in countries of northwest Africa. However, the physiological mechanisms underlying locust phase transition, the switch of the solitarious to the gregarious phase, remain elusive. Therefore, identification of molecular changes linked to this phenomenon represents a primary requirement to start unraveling this enigma. The present paper provides novel information on phase-related molecular markers for locust phase transition. We present a detailed quantitative real-time RT-PCR analysis of two distinct neuroparsin precursor transcripts (Scg-NPP3 and Scg-NPP4) in the brain and in abdominal tissues of gregarious and solitarious desert locusts (Schistocerca gregaria). Our data reveal different temporal changes of these transcripts in the fat body during the adult stage of both phases. We, hereby, present novel scientific evidence for a phase-dependent regulation of these particular peptide hormone encoding transcripts and assign them as possible molecular markers in the process of locust phase transition.

Myocyte enhancer factor 2 (MEF2) is a key modulator of the expression of the prothoracicotropic hormone gene in the silkworm, Bombyx mori

Prothoracicotropic hormone (PTTH) plays a central role in controlling molting, metamorphosis, and diapause termination in insects by stimulating the prothoracic glands to synthesize and release the molting hormone, ecdysone. Using Autographa californica nucleopolyhedrovirus (AcNPV)-mediated transient gene transfer into the central nervous sytem (CNS) of the silkworm, Bombyx mori, we identified two cis-regulatory elements that participate in the decision and the enhancement of PTTH gene expression in PTTH-producing neurosecretory cells (PTPCs). The cis-element mediating the enhancement of PTTH gene expression binds the transcription factor Bombyx myocyte enhancer factor 2 (BmMEF2). The BmMEF2 gene was expressed in various tissues including the CNS. In brain, the BmMEF2 gene was expressed at elevated levels in two types of lateral neurosecretory cells, namely PTPCs and corazonin-like immunoreactive lateral neurosecretory cells. Overexpression of BmMEF2 cDNA caused an increase in the transcription of PTTH. Therefore, BmMEF2 appears to be particularly important in the brain where it is responsible for the differentiation of lateral neurosecretory cells, including the enhancement of PTTH gene expression. This is the first report to identify a target gene of MEF2 in the invertebrate nervous system.

Quantitative real-time RT-PCR analysis in desert locusts reveals phase dependent differences in neuroparsin transcript levels

In different parts of the world, locust swarms cause severe ecological and economic damage. However, the physiological mechanisms underlying this gregarization process remain elusive. In this study, we present a detailed quantitative analysis of two neuroparsin precursor (Scg-NPP1 and Scg-NPP2) transcripts in the brain, fat body, gut, gonads and accessory glands of male and female, gregarious and solitarious desert locusts (Schistocerca gregaria). These transcripts are generally more abundant in solitarious than in gregarious animals. In contrast to their gregarious congeners, solitarious locusts contain detectable Scg-NPP1 and Scg-NPP2 transcript levels in the fat body. Moreover, our data reveal temporal changes of neuroparsin mRNA levels in the brains and fat bodies of adult isolated-reared locusts. This paper provides the first scientific evidence for phase-dependent transcriptional regulation of neuropeptide hormone encoding genes.

Aldosterone inhibits uncoupling protein-1, induces insulin resistance, and stimulates proinflammatory adipokines in adipocytes

Aldosterone is a mineralocorticoid hormone that regulates blood pressure and salt/water balance. Increased aldosterone levels are found in states of disturbed energy balance such as the metabolic syndrome. Adipose tissue has been recognized to play a pivotal role in the regulation of energy homeostasis. We investigated direct aldosterone effects on brown adipocyte function. Aldosterone dose-dependently inhibited expression of uncoupling protein-1 (UCP-1) by 30% (p < 0.01). Furthermore, aldosterone dose-dependently impaired insulin-induced glucose uptake by about 25% (p < 0.01). On a transcriptional level, mRNA of the proinflammatory adipokines leptin and monocyte chemoattractant protein-1 (MCP-1) was increased by 5,000% and 40%, respectively, by aldosterone exposure (p < 0.05). This study demonstrates that aldosterone directly impacts on major adipose functions including stimulation of proinflammatory adipokines.

Molecular characterization and expression of prothoracicotropic hormone during development and pupal diapause in the cotton bollworm, Helicoverpa armigera

Using a strategy of rapid amplification of cDNA ends, the cDNA encoding prothoracicotropic hormone (PTTH) was cloned from the brain of Helicoverpa armigera (Hearm). The Hearm-PTTH cDNA contains an open reading frame encoding a 226-amino acid preprohormone, which shows high identity with the closely related noctuid moths, Helicoverpa zea (98%) and Heliothis virescens (94%), and low identity with five species of Bombycoidea: Bombyx mori (57%), Manduca sexta (55%), Hyalophora cecropia (52%), Samia cynthia ricini (49%) and Antheraea peryni (48%). Hearm-PTTH cDNA shares important structural characterization known from other PTTHs, such as seven cysteine residues, proteolytic cleavage site, glycosylation site, and hydrophobic regions within the mature peptides. Northern blot analysis indicated a 0.9kb transcript present only in the brain. Using the more sensitive technique of RT-PCR, PTTH mRNA was also detected in the subesophageal ganglion, thoracic ganglion, abdominal ganglion, midgut and fat body. During the pupal stage, PTTH mRNA in the brain remained at a constant high level in nondiapausing individuals, was low in diapausing pupae, but increased again at diapause termination. The PTTH protein was detected only in the brain by Western blot analysis. Immunocytochemical results revealed that Hearm-PTTH is localized in two pairs of dorsolateral neurosecretory cells within the brain. Recombinant Hearm-PTTH was successfully expressed in E. coli, and purified recombinant-PTTH was effective in breaking pupal diapause. The results are consistent with a role for PTTH in the regulation of diapause in this species.

Immunocytochemical localization of an allatotropin in developmental stages of Heliothis virescens and Apis mellifera

Juvenile hormone biosynthesis by the corpora allata is regulated by stimulatory neuropeptides called allatotropins and inhibitory neuropeptides called allatostatins. This study localized Manduca sexta allatotropin-like material in developmental stages of the noctuid moth Heliothis virescens and the honeybee Apis mellifera. Immunocytochemical methods using both fluorescence-tagged antibodies and enzyme-coupled antibodies were used to stain the central nervous tissue of both species. H. virescens contains M. sexta allatotropin (Manse-AT)-like material consistently throughout larval development. The distribution patterns of Manse-AT immunoreactive cell bodies in the CNS persisted from one larval instar to the next. It will be discussed how larval Manse-AT distribution patterns differed from those in adults. The total number of AT-containing cells in brain and subesophageal ganglion gradually increased during larval development, whereas in the thoracic and abdominal ganglia, the number of AT-containing neurons remained constant. In the honeybee A. mellifera, Manse-AT immunoreactive cells were only found in a few brains from late last instar larvae (prepupae). Manse-AT-like material was present in a group of 6-8 cells in the pars intercerebralis. However, we did not find any Manse-AT-like material in brains of early last instar larvae, whose corpora allata (CA) are more sensitive to in vitro stimulation by Manse-AT than prepupal CA.

Identification of a novel prothoracicostatic hormone and its receptor in the silkworm Bombyx mori

The insect brain regulates the activity of the prothoracic glands to secrete ecdysteroids, which affect growth, molting, and metamorphosis. Here we report the identification of a novel prothoracicostatic factor and its receptor in the silkworm Bombyx mori. The prothoracicostatic factor purified from pupal brains of B. mori is a decapeptide with the conserved structure of an insect myosuppressin and thus named Bommo-myosuppressin. Bommo-myosuppressin dose dependently suppressed the cAMP level and inhibited ecdysteroidogenesis in the larval prothoracic glands at much lower concentrations than the prothoracicostatic peptide, the other prothoracicostatic factor reported previously. In vitro analyses using a prothoracic gland incubation method revealed that Bommo-myosuppressin and prothoracicostatic peptide regulate the prothoracic gland activity via different receptors. In situ hybridization and immunohistochemistry revealed the existence of Bommo-myosuppressin in the brain neurosecretory cells projecting to neurohemal organs in which it is stored. We also identified and functionally characterized a specific receptor for Bommo-myosuppressin and showed its high expression in the prothoracic glands. All these results suggest that Bommo-myosuppressin functions as a prothoracicostatic hormone and plays an important role in controlling insect development.

Coordinated gene expression for pheromone biosynthesis in the pine engraver beetle, Ips pini (Coleoptera: Scolytidae)

In several pine bark beetle species, phloem feeding induces aggregation pheromone production to coordinate a mass attack on the host tree. Male pine engraver beetles, Ips pini (Say) (Coleoptera: Scolytidae), produce the monoterpenoid pheromone component ipsdienol de novo via the mevalonate pathway in the anterior midgut upon feeding. To understand how pheromone production is regulated in this tissue, we used quantitative real-time PCR to examine feeding-induced changes in gene expression of seven mevalonate pathway genes: acetoacetyl-coenzyme A thiolase, 3-hydroxy-3-methylglutaryl coenzyme A synthase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, mevalonate 5-diphosphate decarboxylase, isopentenyl-diphosphate isomerase, geranyl-diphosphate synthase (GPPS), and farnesyl-diphosphate synthase (FPPS). In males, expression of all these genes significantly increased upon feeding. In females, the expression of the early mevalonate pathway genes (up to and including the isomerase) increased significantly, but the expression of the later genes (GPPS and FPPS) was unaffected or decreased upon feeding. Thus, feeding coordinately regulates expression of the mevalonate pathway genes necessary for pheromone biosynthesis in male, but not female, midguts. Furthermore, basal mRNA levels were 5- to 41-fold more abundant in male midguts compared to female midguts. This is the first report of coordinated regulation of mevalonate pathway genes in an invertebrate model consistent with their sex-specific role in de novo pheromone biosynthesis.

Physiological differentiation of DH-PBAN-producing neurosecretory cells in the silkworm embryo

Embryonic diapause of the silkworm, Bombyx mori, is induced by a neuropeptide hormone, the diapause hormone (DH), which is secreted from a limited number of neurosecretory cells in the subesophageal ganglion (SG) at the maternal generation. We examined the developmental fate of the hormone-producing cell (DH-pheromone biosynthesis activating neuropeptide [PBAN]-producing cell) in the embryonic stage at the level of gene expression and cell biology. The DH-PBAN gene expression started at the histogenesis stage and gradually increased toward hatching. DH is an amidated peptide belonging to FXPRLamide family. The immunoreactive somata against anti FXPRLamide antiserum were found in the SG from blastokinesis. Immunoreactive neural processes with varicosites were also found on the corpus cardiacum and the corpus allatum. The implantation of a part of a developing embryo including the SG into the pupae with the SG removed induced diapause eggs in the progeny. These results were obtained from eggs incubated under diapause-averting conditions as well as diapause-inducing conditions. Thus, a neurosecretory system responsible for biosynthesis of FXPRLamide neuropeptides is established as early as histogenesis, although the system to regulate the secretion of neuropeptide hormones has not been fully formed by that time.

[Effect of plants synthesizing biologically active substances-precocenes on insects]

Ntegrated data on the direct and indirect influence of plants synthesizing biologically active substances--precocenes--on phytophagous insects developing and feeding on these plants. The experimental data on individual organs and tissues as well as organ systems in various insect groups are discussed.

Bumble bees alert to food with pheromone from tergal gland

Foragers of Bombus terrestris are able to alert their nestmates to the presence of food sources. It has been supposed that this happens at least partially through the distribution of a pheromone inside the nest. We substantiate this claim using a behavioral test in which an alerting signal is transmitted from one colony to another by long distance air transport, so excluding all other modalities of information exchange. We then investigated the source of the pheromone and were able to show that a hexane extract from tergites V-VII of bumble bee workers elicits higher activity, like a successful forager does. Extracts from other glands, such as the mandibular, labial, hypopharyngeal, and Dufour's gland as well as extracts from other parts of the cuticle had no effect. This suggests that bumble bees possess a pheromone-producing gland, similar to the Nasanov gland in honey bees. Indeed, an extract from the honey bee Nasanov gland also proved to alert bumble bee workers, suggesting a possible homology of the glands.

Coherence between biosynthesis and secretion of insect adipokinetic hormones

The importance of the process of continuous biosynthesis of locust adipokinetic hormones (AKHs) for the availability of these peptide hormones for release was assessed in vitro by inhibiting this biosynthesis followed by secretory stimulation. Inhibition of the biosynthetic activity for AKHs by brefeldin A caused a considerable inhibition of the AKH release induced by the endogenous crustacean cardioactive peptide (CCAP). After brefeldin A treatment followed by potassium depolarization, CCAP-induced AKH release was completely abolished. In vitro pulse-chase labeling experiments indicated that constitutive secretion from the AKH-producing cells does not occur. It is concluded that AKH secretion involves a regulated release from a relatively small pool of newly formed secretory granules, while older AKH-containing granules appear to be unavailable for release.

Cell biology of the adipokinetic hormone-producing neurosecretory cells in the locust corpus cardiacum

The adipokinetic cells are neuron-like unipolar cells, the cell bodies and cell processes of which are intermingled within the glandular part of the corpus cardiacum. In Schistocerca gregaria, they produce two adipokinetic hormones, AKH-I and -II, whereas in Locusta migratoria an additional hormone, AKH-III, is present. The three AKHs are produced by the same cells and are co-localized in secretory granules. The biosynthesis and processing of the AKH prohormones to the bioactive hormones, which has been elucidated in detail for AKH-I and -II in S. gregaria, takes less than 75 min and goes on continuously. In older locusts in particular, the adipokinetic cells contain intracisternal granules, widely dilated cisternae of the rough endoplasmic reticulum, which function as stores of prohormones of AKH-I and -II, not of AKH-III. The adipokinetic cells are subjected to regulation by a number of neural and humoral substances, neural influences coming from secretomotor cells in the lateral part of the protocerebrum. Flight activity is the only natural stimulus unequivocally shown to induce the release of AKHs, which in L. migratoria results in parallel secretion of all three AKHs. During secretory stimulation, young secretory granules containing newly synthesized hormones are preferentially released over older granules. Secretory stimulation is not accompanied by a clear increase in the levels of the AKH mRNAs and the AKH prohormones and in the rate of synthesis of the (pro-)AKHs. Apparently, a coupling between release and biosynthesis of the AKHs in the adipokinetic cells is very loose or does not even exist.

A receptor-type guanylyl cyclase expression is regulated under circadian clock in peripheral tissues of the silk moth. Light-induced shifting of the expression rhythm and correlation with eclosion

The mechanisms by which the circadian clock controls behavior through regulating gene expression in peripheral tissues are largely unknown. Here we demonstrate that the expression of a receptor-type guanylyl cyclase (BmGC-I) from the silk moth Bombyx mori is regulated in the flight muscles in a circadian fashion. BmGC-I mRNA was expressed from the end of the light period through the middle of the dark period. BmGC-I protein expression and cGMP levels were high around the initiation of eclosion events at the beginning of the photoperiod. The rhythm of the BmGC-I and cGMP levels free-ran in constant light and synchronized to the environmental photoperiodic cycle. The circadian regulation of BmGC-I expression was also observed in the legs but not in other tissues examined. BmGC-I therefore represents a circadian output gene that regulates eclosion behavior.

[Fusion expression of cecropin X including the cleavage of FXa in Escherichia coli]

PCR method was used to introduce the code sequence of Factor Xa cleavage site to the 5' end of cecropin CMIV mutant gene X, then the gene was cloned into the expression vector pGEX-KG, and was highly expressed in E. coli BL21 by IPTG induction. The fusion protein was purified by affinity-chromatography and was cleaved by Factor Xa. Cecropin X with antibacterial activity was obtained after purified by ion-exchange chromatography.

Adipokinetic hormones. Coupling between biosynthesis and release

During long-distance flight of migratory locusts, the dramatic energy demand of the flight muscles is controlled by three adipokinetic hormones (AKHs). These peptide hormones regulate the mobilization of lipid and carbohydrate stored in the fat body to serve as energy substrates for the flight muscles. Despite the relatively huge quantities of the three AKHs that are stored in the corpora cardiaca, flight induces a differential 2-4-fold increase in the mRNAs for the three hormones. Moreover, newly synthesized AKHs can be released only during a restricted period of time, suggesting that by far most of the stored hormones are physiologically inactive. This raises the question of how the biosynthetic activity in the AKH-producing cells is coupled to their secretory activity. The present review discusses the potential mechanisms by which generation and release of mixtures of bioactive neurohormones are controlled and how peptidergic neuroendocrine cells cope with variations in physiological stimulation, with the AKH-producing cells serving as a model system.

The neuron-enriched splicing pattern of Drosophila erect wing is dependent on the presence of ELAV protein

Although the Drosophila melanogaster erect wing (ewg) gene is broadly transcribed in adults, an unusual posttranscriptional regulation involving alternative and inefficient splicing generates a 116-kDa EWG protein in neurons, while protein expression elsewhere or of other isoforms is below detection at this stage. This posttranscriptional control is important, as broad expression of EWG can be lethal. In this paper, we show that ELAV, a neuron-specific RNA binding protein, is necessary to regulate EWG protein expression in ELAV-null eye imaginal disc clones and that ELAV is sufficient for EWG expression in wing disc imaginal tissue after ectopic expression. Further, analysis of EWG expression elicited from intron-containing genomic transgenes and cDNA minitransgenes in ELAV-deficient eye discs shows that this regulation is dependent on the presence of ewg introns. Analyses of the ewg splicing patterns in wild-type and ELAV-deficient eye imaginal discs and in wild-type and ectopic ELAV-expressing wing imaginal discs, show that certain neuronal splice isoforms correspond to ELAV levels. The data presented in this paper are consistent with a mechanism in which ELAV increases the splicing efficiency of ewg transcripts in alternatively spliced regions rather than with a mechanism in which stability of specific splice forms is enhanced by ELAV. Additionally, we report that ELAV promotes a neuron-enriched splice isoform of Drosophila armadillo transcript. ELAV, however, is not involved in all neuron-enriched splice events.

Identification of a prothoracicostatic peptide in the larval brain of the silkworm, Bombyx mori

Prothoracicotropic hormone (PTTH) stimulates ecdysteroid biosynthesis in the prothoracic gland (PG) of insects. A peptide inhibiting ecdysteroid biosynthesis in the PG was isolated from the extracts of 2,000 larval brains of the silkworm, Bombyx mori, using a protocol that included four reversed-phase high performance liquid chromatography procedures. The primary structure of this prothoracicostatic peptide (Bom-PTSP) was determined to be H-Ala-Trp-Gln-Asp-Leu-Asn-Ser-Ala-Trp-NH(2). This neuropeptide has the same sequence as Mas-MIP-I, a myoinhibitory peptide previously isolated from the ventral nerve cord of the tobacco hornworm, Manduca sexta, and is highly homologous with the N-terminal portion of vertebrate peptides of the galanin family. This peptide inhibited PTTH-stimulated ecdysteroidogenesis in the PG at both the spinning and feeding stages, which indicates that Bom-PTSP interferes with PTTH-stimulated ecdysteroidogenesis.

The dare gene: steroid hormone production, olfactory behavior, and neural degeneration in Drosophila

Steroid hormones mediate a wide variety of developmental and physiological events in insects, yet little is known about the genetics of insect steroid hormone biosynthesis. Here we describe the Drosophila dare gene, which encodes adrenodoxin reductase (AR). In mammals, AR plays a key role in the synthesis of all steroid hormones. Null mutants of dare undergo developmental arrest during the second larval instar or at the second larval molt, and dare mutants of intermediate severity are delayed in pupariation. These defects are rescued to a high degree by feeding mutant larvae the insect steroid hormone 20-hydroxyecdysone. These data, together with the abundant expression of dare in the two principal steroid biosynthetic tissues, the ring gland and the ovary, argue strongly for a role of dare in steroid hormone production. dare is the first Drosophila gene shown to encode a defined component of the steroid hormone biosynthetic cascade and therefore provides a new tool for the analysis of steroid hormone function. We have explored its role in the adult nervous system and found two striking phenotypes not previously described in mutants affected in steroid hormone signaling. First, we show that mild reductions of dare expression cause abnormal behavioral responses to olfactory stimuli, indicating a requirement for dare in sensory behavior. Then we show that dare mutations of intermediate strength result in rapid, widespread degeneration of the adult nervous system.

Drosophila has several genes for gap junction proteins

The Innexin gene family forms gap junctions in invertebrates. Many genes in this family have been identified in Caenorhabditis elegans, but only two in Drosophila. We have used PCR techniques to identify three new members of this family from Drosophila. These are designated pas-related proteins (prp) 6, 7, and 33. The putative proteins coded by these new genes show 25-35% identity and 39-66% similarity to other Drosophila innexins and share a similar hydrophobicity profile. The genes form two small clusters on the X-chromosome, with three of the genes sitting within 10kb of each other. The closeness in sequence and location suggests an evolutionary origin of these genes via local duplication. In situ hybridization shows expression in the CNS, gut and epidermis. Each gene has a distinct pattern of expression in different tissues at different developmental times. However, parts of the expression patterns overlap, especially for prp33 and ogre which may be expressed from the same transcriptional enhancers. This suggest that the Prp33 and Ogre proteins may join in forming heteromeric gap junction channels.

Expression of the Manduca sexta allatotropin gene in cells of the central and enteric nervous systems

Manduca sexta allatotropin (Mas-AT) was isolated and first characterized as a peptide that stimulated juvenile hormone biosynthesis in adult lepidopteran corpora allata and was subsequently shown to have cardioacceleratory activity in the pharate adult. In this study, we identified the cells in the nervous system of the insect that contain mRNA encoding Mas-AT and immunoreactivity against a polyclonal antiserum to Mas-AT. In larvae, Mas-AT mRNA and immunoreactivity was most abundant in two cells in the frontal ganglion, which project their axons down the recurrent nerve toward the gut, and in cells in the terminal abdominal ganglion. Lower levels of Mas-AT mRNA were detected in the brain and subesophageal ganglion. In the pupal and pharate adult stages, we detected Mas-AT mRNA and immunoreactivity in cells of the abdominal ganglia and in additional cells in the terminal abdominal ganglion. These additional cells in the ventral nerve cord that express Mas-AT during the pupal and pharate adult stages include cells that differentiate during metamorphosis as well as cells that exist in larvae but do not begin to express Mas-AT until these later developmental stages. Some of the cells that exhibit Mas-AT immunoreactivity lack Mas-AT mRNA, suggesting that the antisera used in this and previous studies recognizes other peptides in addition to Mas-AT. This pattern of expression suggests that Mas-AT may mediate multiple physiological functions during the life cycle of the insect, including the larval stage in which no function has yet been described for the peptide.

Angiotensin II and angiotensin-converting enzyme as candidate compounds modulating the effects of testis ecdysiotropin in testes of the gypsy moth, Lymantria dispar1

Lymantria dispar testes synthesize immunodetectable ecdysteroid in vitro in response to the brain peptide, testis ecdysiotropin (TE), acting primarily via a cascade involving Gi protein, diacyl glycerol, and phosphokinase C. However, a component of TE activation also involves the opposite cascade, Gs protein, cAMP, and phosphokinase A. Excess cAMP inhibits the action of TE, acting as a feedback modulator. Here, we show that bovine angiotensin II (AII) and bovine angiotensin converting enzyme (ACE) act like cAMP, inducing synthesis of immunodetectable ecdysteroid by pupal testes in vitro, but are antagonistic to coincubated TE. In addition, an insect ACE antibody clearly stains the spermatogenic cells through all stages of development, as well as testis sheath tissue where ecdysteroid is synthesized. AII induces synthesis of cAMP by pupal testes in vitro. Therefore, insect homologs of mammalian AII and ACE are good candidates for the peptides responsible for the cAMP cascade and as modulators of TE action in lepidopteran testes. Saralasin, an analog of AII that blocks angiotensin receptors in mammals, behaved like AII in inducing ecdysteroid secretion with ecdysteroidogenic effects additive to either angiotensin or ACE. Therefore, the receptors for the insect form of angiotensin on lepidopteran testis cells are probably different from those in mammals. Saralasin also inhibited ecdysteroid synthesis when combined with TE, as did AII.

Evidence for a diazepam-binding inhibitor (DBI) benzodiazepine receptor-like mechanism in ecdysteroidogenesis by the insect prothoracic gland

The diazepam-binding inhibitor (DBI) is a 10-kDa highly evolutionarily conserved multifunctional protein. In mammals, one of DBI's functions is in the activation of steroid hormone biosynthesis via binding to a specific outer mitochondrial membrane receptor (benzodiazepine receptor, BZD) and promoting cholesterol transport to the inner membrane. In this work, a multitiered approach was utilized to study the role of this receptor-like activity in ecdysteroidogenesis by larval insect prothoracic glands (PGs). First, both DBI protein and messenger RNA (mRNA) levels were correlated with peak PG ecdysteroid production. In vitro ecdysteroid production was stimulated by the diazepam analogue FGIN 1-27 and inhibited anti-DBI antibodies. The DBI protein was found distributed throughout PG cells, including regions of dense mitochondria, supposed subcellular sites of ecdysteroid synthesis. Finally, a potential mitochondrial BZD receptor in PG cells was demonstrated by photoaffinity labeling. These results suggest an important role for the insect DBI in the stimulation of steroidogenesis by prothoracic glands and indicate that a pathway for cholesterol mobilization leading to the production of steroid hormones appears to be conserved between arthropods and mammals.

A hydrophobic peptide (VAP-peptide) of the silkworm, Bombyx mori: a unique role for adult activity proposed from gene expression and production at the terminal phase of metamorphosis

A unique hydrophobic peptide (VAP-peptide) isolated from male adult heads of the silkworm, Bombyx mori, has been shown to act as a synergist to the diapause hormone when administered exogenously. Here, we investigated the true role of the endogenous VAP-peptide on differentiation and development of adult organs in the silkworm. By northern blot analyses, the VAP-peptide gene was shown to be exclusively expressed at the terminal phase of adult development in epithelial tissues, especially in the wing and the thoracic integument. In situ hybridization analysis revealed that the gene was highly expressed in the epidermal cells of the wing vein and the thoracic integument. The stage- and tissue-dependent gene expression were clearly correlated to the accumulation profile of VAP-peptide. In the adult thoracic integument, VAP-peptide was predominantly deposited in the cuticle layer. Affinity chromatography indicated the ability of VAP-peptide to bind to chitin. Based on its expression patterns, localization, and chemical properties, VAP-peptide is conceived to be a structural protein that participates in mechanical strengthening of specific cuticle structures, supporting their physical requirements in the adult life of the silkworm.

Effects of social environment and worker mandibular glands on endocrine-mediated behavioral development in honey bees

Previous studies suggest that older honey bee workers possess an inhibitory signal that regulates behavioral development in younger bees. To study how this inhibitor is transmitted, bees were reared for 7 days in double-screen cages, single-screen cages, or unrestricted in a typical colony (control bees). Double-screen cages prevented physical contact with colony members while single-screen cages allowed only antennation and food exchange. Bees reared in double-screen cages showed accelerated endocrine and behavioral development; they had significantly higher rates of juvenile hormone biosynthesis and juvenile hormone titers than did control bees and also were more likely to become precocious foragers. Relative to the other two groups, bees reared in single-screen cages showed intermediate juvenile hormone biosynthesis rates and titers, and intermediate rates of behavioral development. These results indicate that physical contact is required for total inhibition. We also began to test the hypothesis that worker mandibular glands are the sources of an inhibitory signal. Old bees with mandibular glands removed were significantly less inhibitory towards young bees than were sham-operated and unoperated bees. These results suggest that an inhibitor is produced by the worker mandibular glands.

In situ hybridization analysis of leucomyosuppressin mRNA expression in the cockroach, Diploptera punctata

In the cockroach Diploptera punctata, sequencing of the cDNA for the insect myoinhibitory neuropeptide, leucomyosuppressin (LMS), has demonstrated that LMS is the only Phe-Met-Arg-Phe-amide (NH2) (FMRFamide)-related peptide to be encoded by this gene (Donly et al. [1996] Insect Biochem. Mol. Biol. 26:627-637). However, in the present study, high performance liquid chromatography analysis of brain extracts showed six discrete FMRFamide-like immunoreactive fractions, one of which co-eluted with LMS. This study compared the distribution of FMRFamide-related peptides visualized by immunohistochemistry with LMS mRNA expression demonstrated by in situ hybridization in D. punctata. Immunohistochemistry with a polyclonal antiserum generated against FMRFamide, but which recognizes extended RFamide peptides, demonstrated numerous RFamide-like immunoreactive cells and processes in both nervous and nonnervous tissues. RFamide-like immunoreactivity was found in cells and processes of the brain and optic lobes, the stomatogastric nervous system, including the frontal and ingluvial ganglia, and the suboesophageal ganglion. Immunoreactivity was also present in all ganglia of the ventral nerve cord and in the alimentary canal. Within the alimentary canal, positively stained processes were found in the crop, midgut, and hindgut, and immunoreactive endocrinelike cells were located in the midgut. In situ hybridization with a digoxigenin-labeled RNA probe spanning the entire LMS coding region showed cell bodies containing LMS mRNA in all ganglia studied, other than the ingluvial ganglion. Expression was most abundant in the brain and optic lobes and in the frontal and suboesophageal ganglia. LMS mRNA was also apparent, although less intensely, in all other ganglia of the ventral nerve cord. Within the alimentary canal, LMS mRNA-positive cells were only visible in the anterior portion of the midgut, in the endocrinelike cells. The appearance of LMS mRNA in the central nervous system, stomatogastric nervous system, and midgut suggests that LMS may play a central role in Diploptera and may be associated with feeding and digestion.

The Ceratitis capitata homologue of the Drosophila sex-determining gene sex-lethal is structurally conserved, but not sex-specifically regulated

In Drosophila, Sxl functions as a binary switch in sex determination. Under the control of the primary sex-determining signal, it produces functional protein only in XX animals to implement female development. Here we report that, in contrast to Drosophila, the Sxl homologue in the Medfly, Ceratitis capitata, expresses the same mRNAs and protein isoforms in both XX and XY animals irrespective of the primary sex-determining signal. Also, experiments with two inducible transgenes demonstrate that the corresponding Ceratitis SXL product has no significant sex-transforming effects when expressed in Drosophila. Similar results have been obtained for the Sxl homologue of Musca domestica (Meise, M., Hilfiker-Kleiner, D., Brunner, C., DLbendorfer, A., N?thiger, R. and Bopp, D. (1998) Development 125, 1487–1494). Our findings suggest that Sxl acquired its master regulatory role in sex determination during evolution of the Acalyptratae group, most probably after phylogenetic divergence of the genus Drosophila from other genera of this group.

virilizer regulates Sex-lethal in the germline of Drosophila melanogaster

In Drosophila, the gene Sex-lethal (Sxl) is required for female development. It controls sexual differentiation in the soma, dosage compensation and oogenesis. The continuous production of SXL proteins in XX animals is maintained by autoregulation and depends on virilizer (vir). This gene is required in somatic cells for the female-specific splicing of Sxl primary transcripts and for an unknown vital process in both sexes. In the soma, clones of XX cells lacking Sxl or vir are sexually transformed and form male structures; in the germline, XX cells mutant for Sxl extensively proliferate, but are unable to differentiate. We now studied the role of vir in the germline by generating germline chimeras. We found that XX germ cells mutant for vir, in contrast to cells mutant for Sxl, perform oogenesis. We show that the early production of SXL in undifferentiated germ cells is independent of vir while, later in oogenesis, expression of Sxl becomes dependent on vir. We conclude that the early SXL proteins are sufficient for the production of eggs whereas the later SXL proteins are dispensable for this process. However, vir must be active in the female germline to allow normal embryonic development because maternal products of vir are required for the early post-transcriptional regulation of Sxl in XX embryos and for a vital process in embryos of both sexes.