Molecular characterization of a cDNA from the true armyworm Pseudaletia unipuncta encoding Manduca sexta allatotropin peptide(1)

Prevention of tick-borne diseases: challenge to recent medicine

Abstract

Ticks represent important vectors and reservoirs of pathogens, causing a number of diseases in humans and animals, and significant damage to livestock every year. Modern research into protection against ticks and tick-borne diseases focuses mainly on the feeding stage, i.e. the period when ticks take their blood meal from their hosts during which pathogens are transmitted. Physiological functions in ticks, such as food intake, saliva production, reproduction, development, and others are under control of neuropeptides and peptide hormones which may be involved in pathogen transmission that cause Lyme borreliosis or tick-borne encephalitis. According to current knowledge, ticks are not reservoirs or vectors for the spread of COVID-19 disease. The search for new vaccination methods to protect against ticks and their transmissible pathogens is a challenge for current science in view of global changes, including the increasing migration of the human population.

Highlights

• Tick-borne diseases have an increasing incidence due to climate change and increased human migration

• To date, there is no evidence of transmission of coronavirus COVID-19 by tick as a vector

• To date, there are only a few modern, effective, and actively- used vaccines against ticks or tick-borne diseases

• Neuropeptides and their receptors expressed in ticks may be potentially used for vaccine design

Larval feeding status regulates the transcript levels of genes encoding PTTH and allatoregulatory peptides in silkworm Bombyx mori

In Bombyx mori, two dorsolateral neurosecretory cells (NSCs) in each of the two brain lobes have been identified as prothoracicotropic hormone (PTTH) producing cells. This neuropeptide in insects stimulates the prothoracic gland for the synthesis and release of ecdysone, responsible for the molting events. Allatotropin (AT) and allatostatin (AST) are allatoregulatory neuropeptides that regulate juvenile hormone biosynthesis. Here, by using RT-qPCR, we showed that in B. mori, nutritional stress modulates the mRNA expression of AT and AST-C (allatostain type C) in the central nervous system consisting of the brain lobes and all the associated ganglia. Using whole-mount in situ hybridization, we showed that the feeding status of Bombyx larvae also influences the expression of PTTH in the NSCs of the brain. Food deprivation significantly decreased the mRNA expression levels of PTTH in larvae at active or terminal growth period. Further, we showed that insulin modulates the expression level of PTTH. However, its action was dependent on the feeding status of the larvae. At feeding, the insulin decreased the PTTH expression level, while at food deprivation, the insulin increased the PTTH expression level. The data thus indicates that larval feeding status plays an important role in altering the mRNA expression levels of allatoregulatory peptide genes and PTTH.

Neuropeptide and microRNA regulators of juvenile hormone production

The sesquiterpenoid juvenile hormone(s) (JHs) of insects are the primary regulators of growth, metamorphosis, and reproduction in most insect species. As a consequence, it is essential that JH production be precisely regulated so that it is present only during appropriate periods necessary for the control of these processes. The presence of JH at inappropriate times results in disruption to metamorphosis and development and, in some cases, to disturbances in female reproduction. Neuropeptides regulate the timing and production of JH by the corpora allata. Allatostatin and allatotropin were the names coined for neuropeptides that serve as inhibitors or stimulators of JH biosynthesis, respectively. Three different allatostatin neuropeptide families are capable of inhibiting juvenile hormone but only one family is utilized for that purpose dependent on the insect studied. The function of allatotropin also varies in different insects. These neuropeptides are pleiotropic in function acting on diverse physiological processes in different insects such as muscle contraction, sleep and neuromodulation. Genome projects and expression studies have assigned individual neuropeptide families to their respective receptors. An understanding of the localization of these receptors is providing clues as to how numerous peptide families might be integrated in regulating physiological functions. In recent years microRNAs have been identified that down-regulate enzymes and transcription factors that are involved in the biosynthesis and action of juvenile hormone.

Isolation functional characterization of allatotropin receptor from the cotton bollworm, Helicoverpa armigera

Insect allatotropin (AT) plays multi-functions including regulation of juvenile hormone synthesis, growth, development and reproduction. In the present study, the full-length cDNA encoding the AT receptor was cloned from the brain of Helicoverpa armigera (Helar-ATR). The ORF of Helar-ATR exhibited the characteristic seven transmembrane domains of the G protein-coupled receptor (GPCR) and was close to the ATR of Manduca sexta in the phylogenetic tree. The Helar-ATR expressed in vertebrate cell lines can be activated by Helar-AT and each Helar-ATL in a dose-responsive manner, in the following order: Helar-ATLI > Helar-ATLII > Helar-AT > Helar-ATLIII. Helar-ATLI and Helar-ATLII represented the functional ligands to Helar-ATR in vitro, while Helar-AT and Helar-ATLIII behaved as partial agonists. The in vitro functional analysis suggested that the Helar-ATR signal was mainly coupled with elevated levels of Ca²⁺ and independent of cAMP levels. Helar-ATR mRNA in larvae showed the highest level in the brain, followed by the thorax ganglion, abdomen ganglion, fat body and midgut. Helar-ATR mRNA levels in the complex of the brain-thoracic-abdomen ganglion on the 2nd day of the larval stage and during later pupal stages were observed to be relatively higher than in the wandering and early pupal stages.

Multiple neuropeptides produced by sex-specific neurons control activity of the male accessory glands and gonoducts in the silkworm Bombyx mori

The male accessory glands (AG) and gonoducts of moths develop during metamorphosis and are essential for successful fertilization of females. We found that these reproductive organs are innervated by a sex-specific cluster of peptidergic neurons in the posterior 9^th neuromere of the terminal abdominal ganglion (TAG). This cluster of ~20 neurons differentiate during metamorphosis to innervate the accessory glands and sperm ducts. Using immunohistochemistry and in situ hybridization (ISH) we showed that these neurons express four neuropeptide precursors encoding calcitonin-like diuretic hormone (CT-DH), allatotropin (AT) and AT-like peptides (ATLI-III), allatostatin C (AST-C), and myoinhibitory peptides (MIPs). We used contraction bioassay in vitro to determine roles of these neuropeptides in the gonoduct and accessory gland activity. Spontaneous contractions of the seminal vesicle and AG were stimulated in a dose depended manner by CT-DH and AT, whereas AST-C and MIP elicited dose dependent inhibition. Using quantitative RT-PCR we confirmed expression of receptors for these neuropeptides in organs innervated by the male specific cluster of neurons. Our results suggest a role of these neuropeptides in regulation of seminal fluid movements during copulation.

Developmental and sex-specific differences in expression of neuropeptides derived from allatotropin gene in the silkmoth Bombyx mori

Allatotropin (AT) and related neuropeptides are widespread bioactive molecules that regulate development, food intake and muscle contractions in insects and other invertebrates. In moths, alternative splicing of the at gene generates three mRNA precursors encoding AT with different combinations of three structurally similar AT-like peptides (ATLI-III). We used in situ hybridization and immunohistochemistry to map the differential expression of these transcripts during the postembryonic development of Bombyx mori. Transcript encoding AT alone was expressed in numerous neurons of the central nervous system and frontal ganglion, whereas transcripts encoding AT with ATLs were produced by smaller specific subgroups of neurons in larval stages. Metamorphosis was associated with considerable developmental changes and sex-specific differences in the expression of all transcripts. The most notable was the appearance of AT/ATL transcripts (1) in the brain lateral neurosecretory cells producing prothoracicotropic hormone; (2) in the male-specific cluster of about 20 neurons in the posterior region of the terminal abdominal ganglion; (3) in the female-specific medial neurons in the abdominal ganglia AG2-7. Immunohistochemical staining showed that these neurons produced a mixture of various neuropeptides and innervated diverse peripheral organs. Our data suggest that AT/ATL neuropeptides are involved in multiple stage- and sex-specific functions during the development of B. mori.

Allatotropin inhibits juvenile hormone biosynthesis by the corpora allata of adult Bombyx mori

Juvenile hormone (JH) synthesis by the corpora allata (CA) does not occur during the pupal stage in both male and female Bombyx mori but begins shortly before adult ecdysis and thereafter only in females. JH biosynthesis in female adults was prevented by allatotropin (AT) through the corpora cardiaca (CC) and the tightly attached oesophagus before adult ecdysis, but after ecdysis, removal of the CC had little effect and only the oesophagus was necessary for AT to prevent JH synthesis. AT could not prevent JH synthesis by the CA alone in either stage. Short neuropeptide F (sNPF) acted directly on the CA, preventing JH biosynthesis without preventing the JH biosynthetic enzymes before adult ecdysis, but had little effect after ecdysis, indicating that the action of AT was not via sNPF. The inhibition of JH synthesis by AT was indirect. Both AT and a factor(s) from the AT-stimulated oesophagus through the CC were necessary for the inhibitory action, which was due to the prevention of some of the JH biosynthetic enzymes. These results clearly show that AT prevents JH synthesis in adult CA in B. mori, although AT stimulates JH biosynthesis by the CA in several insect species.

Molecular characterization and possible biological roles of allatotropin in Rhodnius prolixus

Allatotropins (ATs) are a family of neuropeptides that have been shown to stimulate the biosynthesis of juvenile hormone in certain insect species, and to have stimulatory activity on some visceral muscles. Here, we have examined the AT in Rhodnius prolixus. Molecular analysis revealed a cDNA fragment of 973 bp encoding one mature amidated AT (Rhopr-AT) with transcript levels observed in the central nervous system (CNS) and pool of fat body, trachea and associated peripheral nerves. AT-like immunoreactive neurons were found throughout the CNS and AT-like immunoreactive processes were present on some peripheral tissues. Bioassays based upon changes in hindgut and dorsal vessel contractions failed to demonstrate any myotropic effects of Rhopr-AT on these tissues; however Rhopr-AT stimulated contractions of muscles surrounding the salivary glands and secretion of saliva, as judged by the reduction in content of the cherry red saliva from the salivary glands. Serotonin stimulated an increase in peristaltic contractions of the gland though no secretion was observed. Co-application of Rhopr-AT and serotonin resulted in a more rapid secretion than either chemical alone.

Allatotropin: an ancestral myotropic neuropeptide involved in feeding

Background

Cell-cell interactions are a basic principle for the organization of tissues and organs allowing them to perform integrated functions and to organize themselves spatially and temporally. Peptidic molecules secreted by neurons and epithelial cells play fundamental roles in cell-cell interactions, acting as local neuromodulators, neurohormones, as well as endocrine and paracrine messengers. Allatotropin (AT) is a neuropeptide originally described as a regulator of Juvenile Hormone synthesis, which plays multiple neural, endocrine and myoactive roles in insects and other organisms.

Methods

A combination of immunohistochemistry using AT-antibodies and AT-Qdot nanocrystal conjugates was used to identify immunoreactive nerve cells containing the peptide and epithelial-muscular cells targeted by AT in Hydraplagiodesmica. Physiological assays using AT and AT- antibodies revealed that while AT stimulated the extrusion of the hypostome in a dose-response fashion in starved hydroids, the activity of hypostome in hydroids challenged with food was blocked by treatments with different doses of AT-antibodies.

Conclusions

AT antibodies immunolabeled nerve cells in the stalk, pedal disc, tentacles and hypostome. AT-Qdot conjugates recognized epithelial-muscular cell in the same tissues, suggesting the existence of anatomical and functional relationships between these two cell populations. Physiological assays indicated that the AT-like peptide is facilitating food ingestion.

Significance

Immunochemical, physiological and bioinformatics evidence advocates that AT is an ancestral neuropeptide involved in myoregulatory activities associated with meal ingestion and digestion.

Neuropeptides in insect mushroom bodies

Owing to their experimental amenability, insect nervous systems continue to be in the foreground of investigations into information processing in - ostensibly - simple neuronal networks. Among the cerebral neuropil regions that hold a particular fascination for neurobiologists are the paired mushroom bodies, which, despite their function in other behavioral contexts, are most renowned for their role in learning and memory. The quest to understand the processes that underlie these capacities has been furthered by research focusing on unraveling neuroanatomical connections of the mushroom bodies and identifying key players that characterize the molecular machinery of mushroom body neurons. However, on a cellular level, communication between intrinsic and extrinsic mushroom body neurons still remains elusive. The present account aims to provide an overview on the repertoire of neuropeptides expressed in and utilized by mushroom body neurons. Existing data for a number of insect representatives is compiled and some open gaps in the record are filled by presenting additional original data.

Families of allatoregulator sequences: a 2011 perspective1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

Three different peptide families have been named “allatostatins” (ASTs), based on their initial purifications which were based on their ability to inhibit juvenile hormone (JH) biosynthesis. These include (i) a family of peptides that have a consensus C-terminal sequence Y/FXFGL-NH2; (ii) a family of peptides with a conserved C-terminal sequence W(X)6W-NH2; and(iii) a family of peptides with C-terminal sequence PISCF, some of which are C-terminally-amidated. Each allatostatin family has functions distinct and apart from the inhibition of JH biosynthesis. A peptide family known as the “allatotropins” serve to stimulate JH biosynthesis. This family of peptides also has been proven to exert multiple effects dependent on the species in question. Genome and peptidome projects are uncovering new members of these families and it is clear that these structures are not just confined to Insecta but are found in a range of invertebrates. The receptors for these neuropeptides have been identified and tested experimentally for specific ligand binding. The Y/FXFGLa-ASTs exert their action through galanin-like receptors, W(X)6Wa-ASTs through a sex peptide-binding receptor, and PISCF-ASTs through somatostatin-like receptors. These receptors are conserved through evolutionary time and are being identified in numerous invertebrates by way of genome projects.

Regulation of migration in Mythimna separata (Walker) in China: a review integrating environmental, physiological, hormonal, genetic, and molecular factors

Each year the Mythimna separate (Walker), undertakes a seasonal, long-distance, multigeneration roundtrip migration between southern and northern China. Despite its regularity, the decision to migrate is facultative, and is controlled by environmental, physiological, hormonal, genetic, and molecular factors. Migrants take off on days 1 or 2 after eclosion, although the preoviposition period lasts ≈7 d. The trade-offs among the competing physiological demands of migration and reproduction are coordinated in M. separata by the "oogenesis-flight syndrome." Larvae that experience temperatures above or below certain thresholds accompanied by appropriate humidity, short photoperiod, poor nutrition, and moderate density tend to develop into migrants. However, there is a short window of sensitivity within 24 h after adult eclosion when migrants can be induced to switch to reproductive residents if they encounter extreme environmental factors including starvation, low temperature and long photoperiod. Juvenile hormone (JH) titer is low before migration but high titers are associated with termination of migratory behavior and the switch to reproduction. Early release of JH by the corpora allata in environmentally stressed 1-d old adults, otherwise destined by larval conditions to be migrants, switches them to residents. Offspring inherit parental additive genetic effects governing migratory behavior. However, they also retain flexibility in expression of both flight and reproductive life history traits. The insect neuropeptide, allatotropin, which activates corpora allata to synthesize JH, controls adult flight and reproduction. Future research directions to better understand regulation of migration in this species are discussed.

Neuropeptide physiology in insects

In a search for more environmentally benign alternatives to chemical pesticides, insect neuropeptides have been suggested as ideal candidates. Neuropeptides are neuromodulators and/or neurohormones that regulate most major physiological and behavioral processes in insects. The major neuropeptide structures have been identified through peptide purification in insects (peptidomics) and insect genome projects. Neuropeptide receptors have been identified and characterized in Drosophila and similar receptors are being targeted in other insects considered to be economically detrimental pests in agriculture and forestry. Defining neuropeptide action in different insect systems has been more challenging and as a consequence, identifying unique targets for potential pest control is also a challenge. In this chapter, neuropeptide biosynthesis as well as select physiological processes are examined with a view to pest control targets. The application of molecular techniques to transform insects with neuropeptide or neuropeptide receptor genes, or knockout genes to identify potential pest control targets, is a relatively new area that offers promise to insect control. Insect immune systems may also be manipulated through neuropeptides which may aid in compromising the insects ability to defend against foreign invasion.

Allatotropin-related peptide in cockroaches: identification via mass spectrometric analysis of single identified neurons

The first insect allatotropin-related peptide (ATRP) was isolated from head extracts of the adult sphinx moth Manduca sexta [Kataoka H, Toschi A, Li JP, Carney RL, Schooley DA, Kramer SJ. Identification of an allatotropin from adult Manduca sexta. Science 1989;243:1481-3.]. Meanwhile ATRPs are known from different holometabolous insects but only a single ATRP could be identified from hemimetabolous insects [Paemen L, Tips A, Schoofs L, Proost P, Van Damme J, De Loof A. Lom-AG-myotropin: a novel myotropic peptide from the male accessory glands of Locusta migratoria. Peptides 1991;12:7-10.]. This means that the extensive analysis of neuropeptides from Leucophaea maderae and Periplaneta americana, which led to the discovery of many novel insect neuropeptides, did not result in the detection of any ATRP. In this study, we used another approach to find a cockroach ATRP by first identifying Manse-AT immunoreactive neurons in the terminal ganglion that can be stained by retrograde labeling and are suitable for dissection and subsequent mass spectrometric analysis. The peptidomic analysis of these putative ATRP neurons paved the way for the identification of the first cockroach ATRP. MALDI-TOF/TOF tandem mass spectrometry revealed a sequence identity with Locmi-AG-MT-1 which classifies this ATRP as a highly conserved neuropeptide. A mass spectrometric screening of the nervous system allowed the detection of ATRP-ion signals in different parts of the CNS of P. americana as well as L. maderae. The data obtained in this study will be incorporated in a map of peptidergic neurons from the CNS of the American cockroach, P. americana.

Allatotropin-like peptide in Malpighian tubules: insect renal tubules as an autonomous endocrine organ

Malpighian tubules (MTs) are recognised as the main excretory organ in insects, ensuring water and mineral balance. Haematophagous insects incorporate with each meal a large quantity of blood, producing a particularly large volume of urine in a few hours. In the present study, we report the presence of an allatotropin-like (AT-like) peptide in MTs of Triatoma infestans (Klug). The AT-like content in MTs decreased during the first hours after blood-intake, correlating with the post-prandial diuresis. In vivo artificial dilution of haemolymph showed a similar effect. Isolated MTs challenged with a diluted saline solution resulted in an autonomous and reversible response of the organ regulating the quantity of peptide released to the medium, and suggesting that MTs synthesise the AT-like peptide. While MTs are recognised as the target for several hormones, our results corroborate that they also have the ability to produce and secrete a hormone in an autonomous way.

Starvation influences allatotropin gene expression and juvenile hormone titer in the female adult oriental armyworm, Mythimna separata

The first day of adult life is the sensitive stage for shifting migrants into the resident morphs of the oriental armyworm (OAW), Mythimna separata (Walker). The juvenile hormone (JH) titer, expression of the allatotropin (AT) gene, and their relationship were investigated in adult female migrants starved in the sensitive stage, to understand the underlying mechanism of changing migrants into resident OAWs. Haemolymph JH titers of the starved female adults were mostly elevated earlier than in controls, although not all differences were statistically significant. JH I titers in the starved moths were significantly higher than those in the controls on 1, 2, and 5 days after treatment (DAT), respectively. JH II titers in the starved moths were significantly higher than the controls through the period tested except on 5 DAT. JH II is the most likely regulator in changing migrants into resident morphs. The relative quantities of AT expression in the starved moths were higher through the period tested except on 5 DAT. AT expression and JH titers appear to be positively correlated, especially for those in earlier days of the adult life. We infer that AT is the important regulator of JH levels. A model for the shifting of migrants into resident morphs in the OAW is proposed.

RNA interference with the allatoregulating neuropeptide genes from the fall armyworm Spodoptera frugiperda and its effects on the JH titer in the hemolymph

The juvenile hormone (JH) titer was measured by liquid chromatography-mass spectrometry (LC-MS) with electrospray ionization (ESI). Three JH homologs, the JH I-III were detected in various amounts in larvae, prepupae and virgin adult females of Spodoptera frugiperda. In penultimate larvae, the JH II and III titers were relatively high, but decreased continuously during the 3 days of that stage, whereas JH I was detectable at low amounts only on the first 2 days. At the beginning of the last larval stage almost no JH could be detected but thereafter, a consistent low amount of JH III was present until the prepupal stage. In adult virgins, the JH titer peaked on the 2nd and 6th day after the imaginal molt. The measured hormone titers well agree with general lepidopteran physiology, because in larvae the JH titer should be high to prevent premature metamorphosis, but decrease in last instar larvae before pupation, whereas in adults JH returns to control various aspects of reproduction. JH biosynthesis is thought to be the main factor influencing the JH titer in the hemolymph and there is evidence that neuropeptides either act stimulatory (allatotropins) or inhibitory (allatostatins) on this process. After silencing of either the allatostatin AS-C-type (Spofr/Manse-AS) or the allatotropin AT 2 (Spofr-AT 2) gene the transcript level was reduced in brain and gut of last instar larvae as well as of adult S. frugiperda. This suppression led to an increased JH titer in larvae, suggesting an allatostatic activity of both the peptides in this stage. As a result of the elevated hormone titer, the last larval stage was prolonged. In prepupae, the JH titer was decreased, but the animals pupated and molted normally. In adult female virgin moths the effect on the JH titer was inversely dependent on the age of the moths and varied among the JH homologs, indicating that the peptides act either allatostatic or allatotropic. For both peptides, gene silencing clearly reduced the oviposition rates of adult females.

Allatoregulatory peptides in Lepidoptera, structures, distribution and functions

Allatoregulatory peptides either inhibit (allatostatins) or stimulate (allatotropins) juvenile hormone (JH) synthesis by the corpora allata (CA) of insects. However, these peptides are pleitropic, the regulation of JH biosynthesis is not their only function. There are currently three allatostatin families (A-, B-, and C-type allatostatins) that inhibit JH biosynthesis, and two structurally unrelated allatotropins. The C-type allatostatin, characterised by its blocked N-terminus and a disulphide bridge between its two cysteine residues, was originally isolated from Manduca sexta. This peptide exists only in a single from in Lepidoptera and is the only peptide that has been shown to inhibit JH synthesis by the CA in vitro in this group of insects. The C-type allatostatin also inhibits spontaneous contractions of the foregut. The A-type allatostatins, which exist in multiple forms in a single insect, have also been characterised from Lepidoptera. This family of peptides does not appear to have any regulatory effect on JH biosynthesis, but does inhibit foregut muscle contractions. Two structurally unrelated allatotropins stimulate JH biosynthesis in Lepidoptera. The first was identified in M. sexta (Manse-AT) and occurs in other moths. The second (Spofr AT2) has only been identified in Spodoptera frugiperda. Manduca sexta allatotropin also stimulates heart muscle contractions and gut peristalsis, and inhibits ion transport across the midgut of larval M. sexta. The C-terminal (amide) pentapeptide of Manse-AT is important for JH biosynthesis activity. The most active conformation of Manse-AS requires the disulphide bridge, although the aromatic residues also have a significant effect on biological activity. Both A- and C-type allatostatins and Manse-AT are localised in neurosecretory cells of the brain and are present in the corpora cardiaca, CA and ventral nerve cord, although variations in localisation exist in different moths and at different stages of development. The presence of Manse-AS and Manse-AT in the CA correlates with the biological activity of these peptides on JH biosynthesis. There is currently no explanation for the presence of A-type allatostatins in the CA. The three peptide types are also co-localised in neurosecretory cells of the frontal ganglion, and are present in the recurrent nerve that supplies the muscles of the gut, particularly the crop and stomodeal valve, in agreement with their role in the regulation of gut peristalsis. There is also evidence that they are expressed in the midgut and reproductive tissues.

Allatotropin-like peptide in Heliothis virescens: tissue localization and quantification

The mating-induced increase in juvenile hormone (JH) biosynthesis in Heliothis virescens females may be stimulated by production and/or release of stimulatory neuropeptides such as allatotropins (AT). Although there is evidence that H. virescens allatotropin may be structurally related to Manduca sexta allatotropin (Manse-AT), little is known of its occurrence and distribution in H. virescens. An enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody against Manse-AT was used to quantify concentrations of Manse-AT immunoreactivity in tissue extracts of H. virescens. In mated females, the highest concentrations of Manse-AT-like material occurred in the brain. The ventral nervous system and the accessory glands also contained considerable amounts of Manse-AT-like material, whereas concentrations were very low in ovaries, fat body, and flight muscle. The Manse-AT antibody was used for whole-mount immunocytochemistry to localize Manse-AT-immunoreactivity in the central nervous system. Several groups of Manse-AT-immunoreactive cells were discovered in the brain, subesophageal ganglion, and thoracic and abdominal ganglia of H. virescens females and males. Strong immunoreactivity was detected in axons going through the corpora cardiaca and branching out over the surface of the corpora allata. The presence of Manse-AT-like material in various locations in the central nervous system suggests that these peptides may have other as yet unknown functions. At the posterior margin of the terminal ganglion of males, a group of large immunoreactive cells was observed that was not present in females. Other than that, there were no obvious differences between virgin and mated females or males. The lack of differences in AT distribution in mated and virgin females suggests that mating-induced differences in female JH biosynthesis rates may be caused by changes in cellular response to AT at the level of the CA, rather than by changes in the amounts of AT acting on the CA.

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.

Structural organization and expression analysis of the cDNA encoding allatotropin in the cotton bollworm, Helicoverpa armigera

The cDNA encoding allatotropin (AT), which stimulates juvenile hormone (JH) biosynthesis by the adult corpora allata (CA) of Lepidoptera, was cloned from Helicoverpa armigera (Har). Har-AT cDNA encodes a 135-amino acid polypeptide precursor containing a 13-amino acid AT sequence identical to Manduca sexta AT (Mas-AT). Three other H. armigera AT cDNAs encoding 172, 213, and 246 amino acids were also cloned. The four isoforms were produced by alternative splicing and termed Har-AT1, -AT2, -AT3, and -AT4, respectively. The basic organization of the Har-AT1 polypeptide precursor is similar to that of known ATs from other Lepidoptera with 80-97% identity at amino acid level. From the processing of the polypeptide precursor, three AT-like peptides named Har-ATL-I, -II, and -III were predicted. However, functions of the three AT-like peptides remain to be further elucidated. The evidence of Northern blots showed that a 0.7-kb Har-AT1 transcript is present in the brain and 0.7-kb Har-AT1 and 1.0-kb Har-AT4 transcripts are present in the abdominal ganglion (AG). Using quantitative RT-PCR, Har-AT mRNAs were detectable at much lower levels in other neural tissues, such as suboesophageal ganglion (SG) and thoracic ganglion (TG), but not in non-neural tissue, such as the epidermis, midgut, and fat body. We investigated the spatial and temporal expression of Har-AT gene in the central nervous system, and showed that expression patterns of four isoforms are distinct from each other. The results from immunocytochemistry showed that Har-AT transcript is located in the central nervous system, mainly in the brain and terminal abdominal ganglion (TAG). Thus, the AT gene products, besides affecting JH biosynthesis, might have broad influence on many biological processes in H. armigera.

Effects of Manduca allatotropin and localization of Manduca allatotropin-immunoreactive cells in earwigs

Manduca sexta allatotropin (Manse-AT) was first isolated on the basis of its ability to stimulate production of juvenile hormone in that insect. We examined whether this neuropeptide affects corpus allatum activity and visceral muscle contraction in adult females of the earwig, Euborellia annulipes. We also assessed the presence of allatotropin-like material in tissues using immunocytochemistry. Manse-AT at 1 nM to 10 muM stimulated juvenile hormone production in vitro by glands of low activity from 2-day virgin females. In glands of high activity from 12-day mated females, 1 and 100 nM allatotropin were effective, but 10 muM was not. Similarly, hindguts of 2-day and 12-day females significantly increased in motility in vitro in response to Manse-AT. A monoclonal antibody to Manse-AT was used to demonstrate allatotropin-like material throughout the nervous system of 2-day, virgin females. Immunoreactivity was most pronounced within varicosities of the corpora cardiaca and perisympathetic organs. No immunofluorescence was observed in gut tissue. Lastly, we showed that extract of retrocerebral complexes also enhanced in vitro hindgut motility from 2-day virgin females, in a dose-dependent manner. These results indicate material similar to M. sexta allatotropin in female earwigs and that such peptides may modulate juvenile hormone biosynthesis and visceral muscle contractions. Sensitivity to the peptides may change with physiological stage.

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.

Manduca sexta allatotropin and the in vitro biosynthesis of juvenile hormone by moth corpora allata: a comparison of Pseudaletia unipuncta females from two natural populations and two selected lines

We compared the effects of Manduca sexta allatotropin (Manse-AT) on the rate of in vitro juvenile hormone (JH) biosynthesis by the corpora allata (CA) of different-aged virgin females from migrant (Quebec) and non-migrant (Azores) populations of the armyworm, Pseudaletia unipuncta, as well as from early- and late-calling lines selected from the Quebec population. There was a significant age x strain interaction, with the observed rates of JH biosynthesis in early adult life closely reflecting strain-specific differences in the age at onset of calling. In considering data for all ages combined, treatment of CA with Manse-AT resulted in a significant increase in the rate of JH biosynthesis for all but the Late strain, although significant differences for this strain were detected at certain ages. The CA of females from the Azores strain showed the strongest stimulation, with those of 0- and 1-day-old individuals displaying a singularly high degree of sensitivity. Selection for early- and late-calling lines resulted in significant differences in the temporal patterns of JH biosynthesis but did not markedly affect the sensitivity of the CA to Manse-AT. These findings are discussed within the context of the age-related differences observed in the rates of in vitro JH biosynthesis and JH haemolymph titers previously reported in comparisons of the Quebec and Azorean strains of the true armyworm.

Allatotropin regulation of juvenile hormone synthesis by the corpora allata from the lubber grasshopper, Romalea microptera

The in vitro synthesis of juvenile hormone (JH) by corpora allata (CA) from the lubber grasshopper (Romalea microptera) was stimulated by low concentrations of brain extract and this effect was reduced at higher concentrations, suggesting the presence of allatotropin (AT) and allatostatin (AST) factors in the brain. The AT activity of brain extracts caused a rapid and reversible stimulation and appeared to be a peptide(s). Reversed phase (C18) HPLC analysis of brain extracts disclosed two peaks of AT activity but no significant AST activity. Manse-AT, Schgr-NPF, and Locmi-FLRF had no effect on JH synthesis by lubber CA, indicating that the Rommi-AT factors are distinct from these peptides. High concentrations of Dippu-AST-7 and Grybi-AST-1 inhibited JH synthesis, implying that AST factors might be present in lubber grasshoppers. CA response to AT activity of brain extracts varied during the oviposition cycle ( approximately 35 days), with the maximum response occurring on days 16-18. AT activity of brain extracts also varied during the cycle, being highest on day 25. Our data suggest that the lubber CA is largely regulated by AT activity, and that JH synthesis reflects both CA response to AT activity and the level of AT activity in the brain.

Mas-allatotropin/Lom-AG-myotropin I immunostaining in the brain of the locust, Schistocerca gregaria

Mas-allatotropin (Mas-AT) and Lom-accessory gland-myotropin I (Lom-AG-MTI) are two members of a conserved family of insect neuropeptides, collectively termed allatotropins, which have diverse functions, ranging from stimulation of juvenile hormone secretion to myotropic effects on heart and hindgut. In addition, allatotropins appear to be abundant within the nervous system, suggesting neuroactive roles. To identify neurons in the insect brain suitable for a neurophysiological analysis of the roles of allatotropins, we used antisera against Mas-AT and Lom-AG-MTI to map allatotropin-immunoreactive neurons in the brain of a suitable insect, the locust Schistocerca gregaria. Both antisera revealed basically identical staining patterns throughout the locust brain with more than 12,500 immunostained interneurons per brain hemisphere. Neurosecretory cells were not labeled, and the retrocerebral complex was devoid of immunostaining. Prominent immunoreactive cell types include about 9,600 lamina monopolar neurons, medulla to lobula interneurons, local neurons of the antennal lobe, a giant interneuron of the mushroom body, projection neurons of the glomerular lobe to the mushroom body, and three systems of tangential neurons of the central complex. Several groups of neurons showed colocalization of Mas-AT- and gamma-aminobutyric acid immunostaining. Mass spectrometric analysis identified a peptide with a molecular mass identical to Lom-AG-MTI in all major parts of the locust brain but not in the retrocerebral complex. This study strongly suggests that Lom-AG-MTI is highly abundant in the locust brain, and is likely to play a neuroactive role in many brain circuits including all stages of sensory processing, learning and memory, and higher levels of motor control.

Characterization of a novel peptide with allatotropic activity in the fall armyworm Spodoptera frugiperda

A cDNA that encodes 53 amino acids, including one copy of the RVRGNPISCF-OH peptide, was cloned from Spodoptera frugiperda. This peptide strongly stimulates the synthesis and release of juvenile hormone (JH) in vitro by the corpora allata (CA) of S. frugiperda and was code-named Spofr-AT 2. Northern blotting and reverse transcriptase polymerase chain reaction (RT-PCR) analyses revealed that the preprohormone is expressed as one transcript in the brain, midgut (Mg) and ovary (Ov) in a tissue- and developmental-specific manner. Whole-mount in situ hybridization confirmed the gene expression in the suboesophageal ganglion (SOG) and in the ovary of adult females. Treating the CA with the synthetic peptide caused an up to tenfold increase in the release of JH. The stimulation was dose-dependent with an apparent EC(50) of ca. 10(-7) M. CA that were activated with Spofr-AT 2 could be inhibited by the addition of synthetic allatostatin type-C from Manduca sexta (Manse-AS). This is the first report on the presence and function of two different peptides with allatotropic activity in an insect species.

Regulation of juvenile hormone biosynthesis in Heliothis virescens by Manduca sexta allatotropin

In Heliothis virescens, reproduction is strictly dependent on juvenile hormone (JH). In females, mating induces a sharp increase in JH titers, which stimulates increased vitellogenin biosynthesis and higher rates of egg production. JH biosynthesis is presumably stimulated by production and/or release of stimulatory neuropeptides such as allatotropins. There is evidence that allatotropin of H. virescens may be structurally related to Manduca sexta allatotropin (Manse-AT). In a radiochemical in vitro assay, synthetic Manse-AT stimulated JH biosynthesis by corpora allata (CA) of virgin H. virescens females in a dose-dependent manner, but had no effect on CA activity in H. virescens males. In females, the CA showed a transient increase in sensitivity to Manse-AT shortly after mating. Several structurally related peptides stimulated CA activity to a similar extent as Manse-AT. Corpora allata activity was stimulated by a Ca2+ ionophore, A23187. A membrane-permeable Ca2+ chelator, BAPTA/AM, antagonized the stimulatory effects of Manse-AT, suggesting that Manse-AT may enhance CA activity by increasing intracellular Ca2+ concentration.

Insect allatotropins belong to a family of structurally-related myoactive peptides present in several invertebrate phyla

Originally named for its ability to stimulate juvenile hormone production by lepidopteran corpora allata, allatotropin has emerged as a neuropeptide with multiple neural, endocrine and myoactive roles. This paper describes the experimental evidence for allatotropin action, its localization in several species of insects, and its multiple effects on a variety of different tissues that lead to increased hemolymph circulation and gut motility. The overall physiological effects may also include species-specific effects such as the regulation of nutrient absorption, modulation of the circadian cycle and migratory preparedness. In addition, we present evidence suggesting that allatotropins are members of a family of myoactive peptides found in several invertebrate phyla. Finally, we speculate that the myoactive properties of allatotropins are basal and it is likely that the stimulatory action of allatotropins on juvenile hormone synthesis evolved secondarily.

Stimulation of JH biosynthesis by the corpora allata of adult female Aedes aegypti in vitro: effect of farnesoic acid and Aedes allatotropin

Previous studies have demonstrated that the synthesis of juvenile hormone (JH) by the isolated corpora allata (CA) complex in vitro as well as the JH titer in the yellow fever mosquito Aedes aegypti are elevated before feeding and low after a blood meal. In the present study, we used an in vitro radiochemical assay to analyze the effect of farnesoic acid (FA) and Aedes allatotropin (Aedes-AT) on the biosynthesis of JH and methyl farnesoate (MF) by the isolated CA complex of A. aegypti adult female. CA complex from day-0 females (0-1 h after emergence) exhibited a low basal juvenile hormone III (JH III) biosynthetic activity and did not respond to either allatotropic or FA stimulation. However, incubation of CA complexes from newly emerged females with Aedes-AT plus FA resulted in very high production of JH III. This is the first report suggesting that allatotropin makes corpora allata in newly emerged females capable for JH biosynthesis. When we studied CA complexes dissected from females 1 day after emergence, the stimulatory action of Aedes-AT was strong and dose-dependent, with maximum stimulation in the range of 10(-8)-10(-9) mol l(-1), suggesting that Aedes-AT is indeed a true allatotropin (a molecule with allatotropic activity) in A. aegypti. The addition to the culture medium of 40 micro mol l(-1) FA, a JH precursor, resulted in a 9-fold increase in JH III biosynthesis in 2-, 4- and 6-day-old sugar-fed females. The two major labeled products synthesized by the stimulated CA complex were identified as JH III and MF by RP-HPLC and GC-MS. Treatment of CA complexes with FA, but not Aedes-AT, resulted in an increase in MF. Application of both Aedes-AT and FA to the CA complexes of 2-, 4- and 6-day-old females resulted in the same effects as FA alone. These data suggest that in sugar-fed females, FA and Aedes-AT exert different effects on the terminal steps in JH biosynthesis.

Molecular characterisation of cDNAs from the fall armyworm Spodoptera frugiperda encoding Manduca sexta allatotropin and allatostatin preprohormone peptides

Allatotropin (AT) is a 13-residue amidated neuropeptide, first isolated from pharate adult heads of the tobacco hornworm, Manduca sexta (Manse-AT), which strongly stimulates the biosynthesis of juvenile hormones (JH) in the corpora allata (CA) of adult moths. In Spodoptera frugiperda, a cDNA that encodes 134 amino acids, including an AT peptide, has been cloned. The S. frugiperda allatotropin mature peptide (Spofr-AT) [GFKNVEMMTARGFa] is identical to that isolated from M. sexta. The basic organization of the Spofr-AT precursor is similar to that of Agrius convolvuli, M. sexta, Pseudaletia unipuncta, and Bombyx mori with 83-93% amino acid sequence identity. The Spofr-AT gene is expressed in at least three mRNA isoforms with 134, 171 and 200 amino acids, differing from each other by alternative splicing. All allatostatins (AS) have an inhibitory action on the JH biosynthesis in the CA. A cDNA that encodes 125 amino acid residues including one copy of the Manse-AS peptide has been cloned from S. frugiperda (Spofr-AS; QVRFRQCYFNPISCF). The basic organization of the Spofr-AS precursor is similar to that of P. unipuncta with 85% amino acid sequence identity. Using one step RT-PCR for semi-quantification of the gene expression, we showed that the three mRNAs of the Spofr-AT gene and the Spofr-AS gene are expressed in brains of last instar larvae, prepupae, pupae, and adults of both sexes of S. frugiperda with variable intensity.

Enhanced haemolymph circulation by insect ventral nerve cord: hormonal control byPseudaletia unipunctaallatotropin and serotonin

The ventral diaphragm (VD) in many insects is a muscular membrane that essentially partitions a perineural sinus from the rest of the abdomen. In the true armyworm moth Pseudaletia unipuncta (Lepidoptera: Noctuidae) we describe how the VD is characterized by a series of aliform muscles inserted into a tissue matrix that is fused to the dorsal surface of the ventral nerve cord (VNC) itself. Because of this arrangement, the abdominal VNC can attain high rates of lateral oscillation, and is capable of directing haemolymph flow. We have previously demonstrated Manduca sexta allatotropin(Manse-AT)-like immunoreactivity throughout the central nervous system (CNS)in P. unipuncta, and that both Manse-AT and serotonin (5-HT) are dose-dependent stimulators of the dorsal vessel. Here we describe both Manse-AT- and 5-HT-like immunoreactivity associated with the VD. Furthermore,both Manse-AT and 5-HT are dose-dependent stimulators of the rates of VNC oscillation, and together are capable of maintaining highly elevated rates of VNC oscillation for extended periods of time. These data indicate that both the dorsal vessel and the VD/VNC are similarly modulated by both Manse-AT and 5-HT, and that VNC oscillations play a more active role in overall haemolymph circulation than previously recognized.

Molecular characterization and cell-specific expression of a Manduca sexta FLRFamide gene

FMRFamide-related peptides (FaRPs) are a large group of neuropeptides containing a common RFamide C-terminus; they have been identified in vertebrates and invertebrates. We have isolated the cDNA that encodes three FaRPs in the tobacco hornworm, Manduca sexta, including the amidated decapeptide F10. The larger FaRPs are the partially processed precursors of F10, a neuropeptide belonging to the myosuppressin family of peptides. The presence of all three FaRPs in different tissues suggests differential utilization of typical dibasic processing sites and atypical processing sites C-terminal to leucine residues. F10 mRNA was detected in the brain, nerve cord, and midgut, and the mRNA levels in the nervous system are dynamically regulated during development. In situ hybridization analysis localized the F10 mRNA to a variety of cell types within the central nervous system (CNS), a peripheral neurosecretory cell (L1), and midgut endocrine cells, which suggests diverse functions. Distribution of the F10-containing neurons within the central nervous system is segment-specific, and the developmental profile suggests that the F10 gene products may have stage-specific functions. Molecular characterization of the F10 gene has provided insights into its regulation and cell-specific distribution that will enhance our understanding of how these FaRPs modulate different physiological systems and ultimately behavior.

Cardioacceleratory effects of Manduca sexta allatotropin in the true armyworm moth, Pseudaletia unipuncta

Manduca sexta allatotropin (Manse-AT), a peptide originally isolated on the basis of its ability to stimulate juvenile hormone (JH) biosynthesis in the tobacco hornworm, is a potent in vitro stimulator of the corpora allata (CA) in Pseudaletia unipuncta (Lepidoptera: Noctuidae). At 10(-6)M, Manse-AT stimulated in vitro rates of JH biosynthesis by CA of day 0 and 6 adult females 15- and 10-fold respectively. Both Manse-AT and serotonin were also shown to be dose-dependent stimulators of heart rate in day 0, 3 and 6 adult males and females. Furthermore, analysis suggests that there are differences in both resting and Manse-AT-stimulated heart rates depending on age and rearing conditions.

Molecular characterization of a cDNA from the silk moth Bombyx mori encoding Manduca sexta allatotropin peptide

Allatotropin is a 13-residue amidated neuropeptide isolated from pharate adult heads of the tobacco hornworm, Manduca sexta and strongly stimulates biosynthesis of juvenile hormones in adults, but not larval, lepidopteran corpora allata. From a Bombyx mori midgut cDNA library, a cDNA that encodes a 130-amino-acid polypeptide containing M. sexta allatotropin sequence was isolated. The B. mori allatotropin cDNA consists of 1196 nucleotides. The encoded allatotropin peptide is identical to that isolated from M. sexta and that predicted from Pseudaletia unipuncta, with 84% and 81% identity in the amino acid sequence of the allatotropin peptide precursor, respectively. M. sexta allatotropin is flanked by two different endoproteolytic cleavage sites within the precursor of the B. mori allatotropin peptide. Evidence from northern blotting of B. mori tissues showed that the allatotropin gene is expressed in the cells of midgut, head and integument with different transcription amount, but not in the fat body and silk gland. Midgut has also a number of allatotropin-immunoreactive cells and nerve fibers. These results will provide valuable information in understanding the AT gene of insects.

Flights of fancy: possible roles of allatostatin and allatotropin in migration and reproductive success of Pseudaletia unipuncta

Many invertebrate neuropeptides have recently been identified and there is evidence that the same compound may serve different roles in different species and/or multiple functions within a given species. However, until the relevant receptors or 'knock out' animals, lacking the neuropeptide of interest, become available it will be difficult to clarify the precise inter- and intraspecific functions of these neuropeptides. In the present paper, we argue that until these tools are available a more meaningful understanding of the roles of neuropeptides could be obtained by carrying out experiments within an ecological context. Furthermore, this approach would allow us to generate hypotheses that could be rigorously tested when more sophisticated techniques are developed. We discuss these ideas using our interdisciplinary research on the reproductive biology of the true armyworm, Pseudaletia unipuncta, as a case study.