Insect neuropeptides-identification, establishment of functional roles and novel target sites for pesticides

Dynamic transcriptome analysis of Bombyx mori embryonic development

Bombyx mori has been extensively studied but the gene expression control of its embryonic development is unclear. In this study, we performed transcriptome profiling of six stages of B. mori embryonic development using RNA sequencing (RNA-seq). A total of 12 894 transcripts were obtained from the embryos. Of these, 12 456 transcripts were shared among the six stages, namely, fertilized egg, blastoderm, germ-band, organogenesis, reversal period, and youth period stages. There were 111, 48, 41, 54, 77, and 107 transcripts specifically expressed during the six stages, respectively. By analyzing weighted gene correlation networks and differently expressed genes, we found that during embryonic development, many genes related to DNA replication, transcription, protein synthesis, and epigenetic modifications were upregulated in the early embryos. Genes of cuticle proteins, chitin synthesis-related proteins, and neuropeptides were more abundant in the late embryos. Although pathways of juvenile hormone and the ecdysteroid 20-hydroxyecdysone, and transcription factors were expressed throughout the embryonic development stages, more regulatory pathways were highly expressed around the organogenesis stage, suggesting more gene expression for organogenesis. The results of RNA-seq were confirmed by quantitative real-time polymerase chain reaction of 16 genes of different pathways. Nucleic acid methylation and seven sites in histone H3 modifications were confirmed by dot blot and western blot. This study increases the understanding of the molecular mechanisms of the embryonic developmental process and information on the regulation of B. mori development.

3D-QSAR based optimization of insect neuropeptide allatostatin analogs

Allatostatins (AST) are neuropeptides originally described as inhibitors of juvenile hormone (JH) synthesis in insects. Consequently, they have been considered as potential lead compounds for the discovery of new insect growth regulators (IGRs). In the present work, receptor-based three-dimensional quantitative structure-activity relationship (3D-QSAR) was studied with 48 AST analogs, and a general approach for novel potent bioactive AST analogs is proposed. Hence, six novel AST analogs were designed and synthesized. Bioassays indicated that the majority novel analogs exhibited potent JH inhibitory activity, especially analog A6 (IC₅₀: 3.79 nmol/L), which can be used as lead compound to develop new IGRs.

A potential insect growth regulator for cockroach control: design, synthesis and bioactivity of N-terminal-modified allatostatin analogues

BACKGROUND

The FGLa-allatostatins (ASTs) are a family of neuropeptides that can inhibit juvenile hormone biosynthesis by the corpora allata (CA) in vitro, and therefore they are regarded as insect growth regulator (IGR) candidates for pest control. In our previous studies, an AST mimic, H17, was found to have a significant effect on JH biosynthesis by cockroach CA, both in vitro and in vivo. To discover new potential mimics and explore the substituent effect on the inhibition of JH biosynthesis, 30 analogues, modified with various substituents on the benzene ring at the N-terminus of lead compound H17, were designed and synthesised. Their bioactivity in inhibiting JH biosynthesis by the CA of Diploptera punctata and the potency of M9, M10 and M11 in activation of Dippu-AstR were evaluated.

RESULTS

All the analogues showed an effect on JH biosynthesis by CA in vitro. M9, M10 and M11 can activate the Dippu-AstR, albeit with much lower potency than that of AST 1. M11 also exhibited improved in vitro activity (IC₅₀ 6.98 nm) in comparison with the lead compound H17 (IC₅₀ 29.5 nm). In particular, M11 displayed good in vivo activity in inhibiting JH biosynthesis and basal oocyte growth.

CONCLUSION

The structure-activity relationship studies suggest that different positions of substituents on the benzene ring of the cinnamic acid can lead to different activities. The para-substitution on the benzene ring plays an important role in inhibiting JH biosynthesis in vitro. Moreover, M11 is considered to be a potential IGR for cockroach control. © 2016 Society of Chemical Industry.

The discovery of a novel antagonist - Manduca sexta allatotropin analogue - as an insect midgut active ion transport inhibitor

BACKGROUND

The midgut is an important site for both nutrient absorption and ionic regulation in lepidopteran larvae, major pests in agriculture. The larval lepidopteran midgut has become a potent insecticide target over the past few decades. Recent studies have shown that an insect neuropeptide, Manduca sexta allatotropin (Manse-AT), exhibits inhibition of active ion transport (AIT) across the larval midgut epithelium. The full characteristic of the AIT inhibition capacity of Manse-AT is essential to assay. In this study, AIT inhibition across the M. sexta midgut by Manse-AT and its analogues in a range of concentrations was assayed. The structure-activity relationship of Manse-AT was also studied by truncated and alanine-replacement strategies.

RESULTS

Our results identified three residues, Thr4, Arg6 and Phe8, as the most important components for activity on the midgut. Replacement of Glu1, Met2 and Met3 reduced the potency of the analogues. The conservative substitution of Gly7 with alanine had little effect on the potency of the analogues. We demonstrated for the first time that Manse-AT (10-13) behaves as a potent antagonist in vitro on active ion transport across the epithelium of the posterior midgut in M. sexta.

CONCLUSION

Structure-activity studies of Manse-AT are useful in developing lead compounds for the design and testing of synthetic antagonists, ultimately to develop potent and specific pest control strategies. Manse-AT (10-13) has been discovered as the first Manse-AT antagonist, with a significant effect and a short sequence compared with other insect neuropeptides. It may be a new potential pest control agent in the future. © 2016 Society of Chemical Industry.

Development of antiparasitic drugs in the 21st century

Prospects for discovering new antiparasitic drugs for veterinary medicine in the coming century will be determined by economic, social and scientific factors. Consolidation in the pharmaceutical industry in general, and the animal health industry in particular, changes the business conditions in which drug discovery for veterinary medicine occurs. Social pressures on traditional animal agriculture and companion animal ownership have shifted the interest of animal companies primarily to pet medicine. Antiparasitic drug discovery is more than ever targeted to the most lucrative market segments, but the excellence of available drugs, and the apparent lack of resistance in important parasites, reduces industrial motivation to invest in parasitology. Veterinary parasitologists in academia will still have the chance to interact with their industrial counterparts in the traditional ways of supporting drug discovery and development. Nonetheless, there are many new opportunities to expand the research horizons of veterinary parasitology to strengthen the case for retaining a significant presence in the animal health industry.

The range and biological activity of FMRFamide-related peptides and classical neurotransmitters in nematodes

Nematodes include both major parasites of humans, livestock and plants in addition to free-living species such as Caenorhabditis elegans. The nematode nervous system (especially in C. elegans) is exceptionally well defined in terms of the number, location and projections of the small number of neurons in the nervous system and their integration into circuits involved in regulatory behaviours vital to their survival. This review will summarize what is known about the biological activity of neurotransmitters in nematodes: the biosynthetic pathways and genes involved, their receptors, inactivation mechanisms and secondary messenger signalling systems. It will cover the 'classical' transmitters, such as acetylcholine (ACh), GABA, glutamate, serotonin, dopamine, octopamine, noradrenaline and nitric oxide. The localization of peptides throughout the nematode nervous system is summarized, in addition to the isolation of nematode neuropeptides by both traditional biochemical techniques and more modern genetic means. The major contribution of the completion of the C. elegans genome-sequencing program is highlighted throughout. Efforts to unravel neurotransmitter action in various physiological actions such as locomotion, feeding and reproduction are detailed as well as the various inactivation mechanisms for the current complement of nematode transmitters.

Led-NPF-1 stimulates ovarian development in locusts

For more than a decade, immunohistochemical results on FMRFamide related peptides (FaRP's) have been reported extensively, suggesting many possible roles for these peptides associated with behavioural and physiological events as well as reproduction. This study provides a clear effect in vivo of members of this family of insect neuropeptides. The effect of two neuropeptide F-related peptides from the Colorado potato beetle, Leptinotarsa decemlineata, Led-NPF-1 and Led-NPF-2 as well as the locusts myotropins, Lom-PK-1, Lom-PK-2 and Lom-SK, was screened in an ovarian development assay in the African migratory locust and the grey fleshfly, Neobellieria bullata. Led-NPF-1 (Ala-Arg-Gly-Pro-Gln-Leu-Arg-Leu-Arg-Phe-NH2) was shown to be a potent gonadostimulin in Locusta migratoria, but not in Neobellieria bullata. A minimal dose of 0.05 microg of Led-NPF-1 per animal, every 12 h, during 5 consecutive injections into 6 day old virgin females, could accelerate egg development. Higher doses of prolonged injections were demonstrated to be even more potent in the ovarian development assay. Led-NPF-2 (Ala-Pro-Ser-Leu-Arg-Leu-Arg-Phe-NH2) was far less active. The other tested peptides scored no reproducible effect what so ever on ovarian growth, in locusts, nor in flies. The gonadotropic action of a NPF-like peptide on oocyte growth implies a complex regulation of oogenesis in the locust and adds to our knowledge of insect neuroendocrinology in general. The results also suggest that a peptide of similar sequence also resides in the locust.

Distribution of myomodulin-like immunoreactivity in the brain and retrocerebral complex of the locust, Schistocerca gregaria

The distribution of myomodulin-like immunoreactivity is described for the brain and retrocerebral complex of an insect, the locust, Schistocerca gregaria. The locust brain contains 70-100 neuronal cell bodies and numerous neuropilar processes exhibiting myomodulin-like immunoreactivity. The most marked feature of the staining is a group of lateral tritocerebral neurones that form a highly immunoreactive tract that gives rise to a complex neuropile of stained processes in the dorsal tritocerebrum. This tract continues dorsally and bifurcates into a major branch that exists the brain via nervi corpora cardiaca 1 (NCC1) to innervate the corpora cardiaca and the corpora allata. A minor branch, consisting of several individual axons, combines with immunoreactive processes from the ventral nerve cord and generates a complex immunoreactive neuropile in the anterior and posterior regions of the protocerebrum. Immunoreactive processes are also found in the structured neuropile of the central body complex. Immunoreactive cell bodies are also found in the antennal lobes, in the lateral margins of the protocerebrum, in the optic lobes, and in a few cells in the pars intercerebralis. The results suggest that myomodulin-like neuropeptides may play roles as central neurotransmitters or neuromodulators in insects as well as being released into the circulation as neurohormones or acting as releasing agents for neurohormones in neurohaemal areas. They also further strengthen the idea that myomodulins, which were first identified in molluscs, may represent another interphyletic family of neuropeptides.

Distribution of myomodulin-like immunoreactivity in the adult and developing ventral nervous system of the locust Schistocerca gregaria

The distribution of myomodulin-like immunoreactivity in the ventral nervous system of an insect, the locust Schistocerca gregaria, both in the adult and during development, is described. The results suggest the presence of a novel modulatory system in insects which uses myomodulin-like neuropeptides. The study also indicates that the myomodulins, which were first identified in mollusks, may represent another interphyletic family of neuropeptides. In the suboesophageal ganglion, immunoreactive cells occur in five groups. The processes from the two anterior ventral midline groups of cells project to the corpora allata via nervi corpora allata II. Thus myomodulin-like neuropeptides may be involved in the control of the release of juvenile hormone from the corpora allata. The thoracic ganglia contain three groups of immunoreactive cells, including a bilaterally symmetrical group of 12-15 posterior lateral cells, which project to the median nerve and its neurohaemal organs, suggesting a possible neurohaemal role for myomodulin-like peptides. Each thoracic neuromere also contains a single, intensely stained, dorsal unpaired median (DUM) cell that may correspond to the so-called H cell. In the abdominal ganglia, the staining shows sexual dimorphism, both in terms of the number of dorsal and ventral midline cells stained and in terms of the distribution of their immunoreactive processes. Myomodulin-like immunoreactivity is one of the earliest neurotransmitter/neurohormone phenotypes detectable during the development of the locust nervous system. It first appears in the single DUM cells in each of the thoracic neuromeres at 50% development, and the complete adult pattern of staining is present at 85-90% of development.

Isolation, sequence, and bioactivity of FMRFamide-related peptides from the locust ventral nerve cord

The ventral nerve cord of the locust, Locusta migratoria, was examined for the presence of FMRFamide-related peptides (FaRPs). RP-HPLC coupled to an RIA specific for extended -RFamides revealed the presence of several FaRPs eluting at different percentages of acetonitrile. The sequences of five of these peptides were determined. Two sequences are identical to the two peptides previously sequenced from brain and retrocerebral complex of Locusta. These two peptides (PDVDHVFLRFamide and ADVGHVFLRFamide) were inhibitory when tested on locust oviduct contractions. The other peptides are novel with sequences of GQERNFLRFamide, AXXRNFIRFamide, and AFIRFamide. The synthesized peptides were stimulatory when tested on locust oviduct contractions, increasing the frequency and amplitude of spontaneous contractions and resulting in a basal contraction.

Isolation, sequence, and bioactivity of PDVDHVFLRFamide and ADVGHVFLRFamide peptides from the locust central nervous system

The brain and the retrocerebral complex of the locust, Locusta migratoria, were examined for the presence of FMRFamide-related peptides (FaRPs) using an RIA specific for -RFamide. RP-HPLC of these extracts using both C18 and phenyl columns revealed the presence of several FaRPs eluting at different percentages of acetonitrile. The sequences of two peptides were determined. One sequence is identical to the previously described SchistoFLRFamide (PDVDHVFLRFamide), whereas a second peptide is novel and differs from SchistoFLRFamide in positions 1 and 4 (ADVGHVFLRFamide). The bioactivity of these native and synthetic FaRPs on locust oviduct contractions has been examined. Both peptides showed inhibitory activity on the locust oviduct. Truncated versions of PDVDHVFLRFamide revealed that the essential features for inhibition lay in the sequence HVFLRFamide.

Peptide amidation in an invertebrate: purification, characterization, and inhibition of peptidylglycine alpha-hydroxylating monooxygenase from the heads of honeybees (Apis mellifera)

Peptidylglycine alpha-hydroxylating monooxygenase (PHM), an enzyme involved in formation of neuropeptides with a C-terminal amide functionality in mammals and amphibians, was isolated from the head of an invertebrate, the honeybee, Apis mellifera, and purified 220-fold in 1% overall yield. The bee PHM has a molecular weight of 71,000, is membrane associated but can be solubilized with a detergent (n-octyl-beta-D-glucopyranoside), and cross-reacts with rabbit antibodies generated toward bacterially expressed rat PHM. In the presence of copper, oxygen, and ascorbic acid, the enzyme hydroxylates model tripeptides such as dansyl-L-Phe-L-Phe-Gly on the methylene carbon of the glycine residue with retention of configuration. Using this tripeptide as substrate, the Km is 1.7 microM and the Vmax is 2.3 nmol.micrograms-1.h-1. Treatment of the insect PHM with D-Phe-L-Phe-D-vinylglycine, a substrate analogue and mechanism-based inactivator of PHM from pig pituitary, results in irreversible loss of activity. The diastereomeric analogue, D-Phe-L-Phe-L-vinylglycine, is only a competitive inhibitor (IC50 = 320 microM).

FMRFamide-like activity in the female locust during vitellogenesis

The control of oviposition in the locust involves the expulsion of eggs from the lateral oviducts, a process believed to be under neurohormonal control. In this paper we have attempted to identify this putative hormone. Immunohistochemical staining of the brain retrocerebral complex and suboesophageal ganglion of Locusta migratoria with antiserum against FMRFamide revealed a number of FMRFamide-immunopositive cells. FMRFamide-like immunoreactivity was present in median neurosecretory cells and lateral neurosecretory cells of the protocerebrum. Other FMRFamide-immunoreactive cells were detected in the deutocerebrum and tritocerebrum. Immunoreactive cell processes were observed in the mushroom bodies, the central body, the optic lobes, and in the axon tracts leaving the pars intercerebralis and tritocerebrum. FMRFamide-like material was also seen in the circumoesophageal commissures. Further FMRFamide-like material was present in cell bodies of the suboesophageal ganglion. FMRFamide-like staining activity changed dramatically during the oviposition cycle in mature adult females. The median neurosecretory cells stained lightly immediately after oviposition and remained pale until the third day, when staining of perikarya and axon tracts increased. The staining intensity decreased on days 4 and 5. The titre of FMRFamide-like material in the hemolymph increased during the vitellogenic cycle but plummeted after oviposition. A single band of FMRFamide-like material was evident on immunoblot following sodium dodecyl sulphate-polyacrylamide gel electrophoresis of adult female hemolymph. The approximate molecular weight of this molecule was 8,000. Gel permeation chromatography of hemolymph revealed a FMRFamide-immunoreactive fraction with a molecular weight of 8,000. This fraction possessed myotropic activity when applied to the locust oviduct.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of FMRFamide-related peptides and morphine on the isolated foregut of the locust schistocerca gregaria

1. Morphine and YAGFMamide were the most effective potentiators of 5-hydroxytryptamine (5-HT)-induced relaxation of the isolated foregut. 2. Morphine had no effect on proctolin-induced tissue contraction which was inhibited by YGGFMamide and YFMRFamide. 3. The differing potency of FaRPs and morphine to potentiate 5-HT effects and reduce proctolin responses suggests that there are two separate FaRP receptor sub types. 4. This proposal is supported by the observation that, while naloxone (10(-5) M) is a relatively potent antagonist of FaRP induced inhibition of proctolin contraction, it has less effect on FaRP-induced potentiation of 5-HT-induced relaxation.

Neurobiology of arthropod parasites

Many medically important diseases of man are caused by blood-sucking arthropods which serve as vectors for a wide range of viral, bacterial, protozoal and nematode infections (Table 1). Furthermore, serious economic losses are caused by the numerous arthropod parasites which infect domesticated animals (for examples, see Table 2). Among these the ixodid hard ticks are particularly important and it has been estimated that the global cost of hard tick infections is $7000 million per annum (F.A.O., 1984). Not surprisingly, there have been strenuous efforts to control infections caused by arthropods.