Pheromone biosynthesis activating neuropeptides: functions and chemistry

The regulation of Δ11-desaturase gene expression in the pheromone gland of Mamestra brassicae (Lepidoptera; Noctuidae) during pheromonogenesis

Cabbage moth (Mamestra brassicae) females produce sex pheromones to attract conspecific males. In our M. brassicae colony, the pheromone blend is composed of Z11-hexadecenyl acetate (Z11-16Ac) and hexadecyl acetate (16Ac) in a 93:7 ratio. A fatty acyl Δ11-desaturase is involved in the production of the main pheromone component. The release of Pheromone Biosynthesis Activating Neuropeptide (PBAN) regulates the pheromone production in the pheromone gland (PG). We cloned a cDNA encoding the MambrΔ11-desaturase and analyzed its expression profile over time in M. brassicae tissues. Transcript levels of the Δ11-desaturase in larvae, pupal PGs, fat body, brain and muscle tissues were <0.1% of that in female PGs, whereas expression in male genitalia was 2%. In the PGs of virgin females the expression level increased continuously from eclosion to the end of the 1st day when it reached a plateau without further significant fluctuation up to the 8th day. In contrast, we recorded a characteristic daily rhythmicity in pheromone production with a maximum around 200 ng Z11-16Ac/PG. In some experiments, females were decapitated to prevent PBAN release and thereby inhibit pheromone production, which remarkably increased after treatment with Mambr-Pheromonotropin. Further experiments revealed that mating resulted in a significant suppression of pheromone production. However, expression of the Δ11-desaturase was not affected by any of these interventions, suggesting that it's not regulated by PBAN. Fluorescent microscopy was used to study the potential role of lipid droplets during pheromone production, however, no lipid droplets were identified indicating that pheromonogenesis is regulated via de novo fatty acid synthesis.

Pyrokinin β-neuropeptide affects necrophoretic behavior in fire ants (S. invicta), and expression of β-NP in a mycoinsecticide increases its virulence

Fire ants are one of the world's most damaging invasive pests, with few means for their effective control. Although ecologically friendly alternatives to chemical pesticides such as the insecticidal fungus Beauveria bassiana have been suggested for the control of fire ant populations, their use has been limited due to the low virulence of the fungus and the length of time it takes to kill its target. We present a means of increasing the virulence of the fungal agent by expressing a fire ant neuropeptide. Expression of the fire ant (Solenopsis invicta) pyrokinin β-neuropeptide (β-NP) by B. bassiana increased fungal virulence six-fold towards fire ants, decreased the LT(50), but did not affect virulence towards the lepidopteran, Galleria mellonella. Intriguingly, ants killed by the β-NP expressing fungus were disrupted in the removal of dead colony members, i.e. necrophoretic behavior. Furthermore, synthetic C-terminal amidated β-NP but not the non-amidated peptide had a dramatic effect on necrophoretic behavior. These data link chemical sensing of a specific peptide to a complex social behavior. Our results also confirm a new approach to insect control in which expression of host molecules in an insect pathogen can by exploited for target specific augmentation of virulence. The minimization of the development of potential insect resistance by our approach is discussed.

Family of CNP neuropeptides: common morphology in various invertebrates

Neuropeptides expressed in the command neurons for withdrawal behavior were originally detected in the the central nervous system (CNS) of the terrestrial snail Helix (command neurons peptides, CNP). The family of CNP-like neuropeptides bears a C-terminal signature sequence Tyr-Pro-Arg-X. Using antisera against two of them, we have studied the CNS of various invertebrates belonging to the phyla of mollusks, annelids and insects. The immunoreactive neurons were detected in all studied species. Stained neurons were either interneurons projecting along the CNS ganglia chain, or sensory neurons, or neurohormonal cells. Beyond common morphological features, the immunoreactive cells had another similarity: the level of CNP expression depended on the functional state of the animal. Thus, the homologous neuropeptides in evolutionary distant invertebrate species possess some common morphological and functional features.

FXPRL-amide peptides induce ecdysteroidogenesis through a G-protein coupled receptor expressed in the prothoracic gland of Bombyx mori

The FXPRL-amide peptide family (pyrokinin/PBAN family) consists of insect peptides that function broadly in insect life processes and are characterized by a conserved C-terminal motif. In the silkworm, Bombyx mori, sex pheromone biosynthesis and induction of embryonic diapause are regulated by peptides from this family. To elucidate other functions of Bombyx FXPRL-amide peptides, we analyzed the tissue expression patterns of two known Bombyx G-protein coupled receptors for these peptides. We found that the Bombyx diapause hormone receptor (BmDHR), is expressed in the prothoracic gland (PG), the organ which synthesizes and releases the insect molting hormones, ecdysteroids. Furthermore, diapause hormone (DH), a member of the Bombyx FXPRL-amide peptides, increases both intracellular Ca(2+) and cAMP concentrations and induces ecdysteroidogenesis in late fifth instar PGs coincident with BmDHR expression in the PGs. DH also has the highest prothoracicotropic activity among the FXPRL-amide peptides, which corresponds well to the ligand specificity of heterologously expressed BmDHR. These results demonstrate that FXPRL-amide peptides can function as prothoracicotropic factors through the activation of BmDHR and may play an important role in controlling molting and metamorphosis.

Distribution, activity and evidence for the release of an anti-diuretic peptide in the kissing bug Rhodnius prolixus

In the haematophagous insect Rhodnius prolixus, diuresis is accomplished through the combined actions of peptidergic diuretic hormones and 5-HT released from neurohaemal sites on the abdominal nerves. Preliminary work on anti-diuresis in this blood-feeder, previously believed to occur through a decrease in the levels of the diuretic factors, indicates that an anti-diuretic hormone, with properties similar to CAP2b (pELYAFPRVamide; recently renamed Mas-CAPA-1), might also be present in R. prolixus. Here, we present evidence from immunohistochemical analysis that suggests a PRXamide-like neuropeptide may be released from the abdominal neurohaemal sites beginning 3-4 h following feeding; a time that coincides with the cessation of diuresis. We also show evidence for an endogenous factor, isolated from the central nervous system using reversed-phase high performance liquid chromatography, which mimics the effects of Mas-CAPA-1. Specifically, this endogenous anti-diuretic factor inhibits rates of 5-HT-stimulated secretion in a dose-dependent manner and elevates intracellular cGMP levels of Malpighian tubules stimulated with 5-HT.

Role of neuropeptides in sex pheromone production in moths

Sex pheromone biosynthesis in many moth species is controlled by a cerebral neuropeptide, termed pheromone biosynthesis activating neuropeptide (PBAN). PBAN is a 33 amino acid C-terminally amidated neuropeptide that is produced by neuroendocrine cells of the subesophageal ganglion (SEG). Studies of the regulation of sex pheromone biosynthesis in moths have revealed that this function can be elicited by additional neuropeptides all of which share the common C-terminal pentapeptide FXPRL-amide (X = S, T, G, V). In the past two decades extensive studies were carried out on the chemical, cellular and molecular aspects of PBAN and the other peptides (termed the pyrokinin (PK)/PBAN family) aiming to understand the mode of their action on sex pheromone biosynthesis. In the present review we focus on a few of these aspects, specifically on the: (i) structure-activity relationship (SAR) of the PK/PBAN family, (ii) characterization of the PK/PBAN receptor and (iii) development of a novel strategy for the generation of PK/PBAN antagonists and their employment in studying the mode of action of the PK/PBAN peptides.

Insect neuropeptide antagonists

The development of a new integrated approach to the generation of a novel type of insect neuropeptide (Np) antagonists and putative insect control agents based on backbone cyclic compounds is described. The approach, termed the backbone cyclic neuropeptide-based antagonist (BBC-NBA), was applied to the insect pyrokinin (PK)/pheromone biosynthesis activating neuropeptide (PBAN) family as a model, and led to the discovery of a potent linear lead antagonist and several highly potent, metabolically stable BBC antagonists, devoid of agonistic activity, which inhibited PBAN-mediated activities in moths in vivo. This review briefly summarizes our knowledge of insect Nps, describes the PK/PBAN Np family, presents the basic concepts behind the BBC-NBA approach, and introduces the advantages of this method for generation of Np agonists, antagonists and insecticide prototype molecules.

Neuropeptides in the nervous system of Drosophila and other insects: multiple roles as neuromodulators and neurohormones

Neuropeptides in insects act as neuromodulators in the central and peripheral nervous system and as regulatory hormones released into the circulation. The functional roles of insect neuropeptides encompass regulation of homeostasis, organization of behaviors, initiation and coordination of developmental processes and modulation of neuronal and muscular activity. With the completion of the sequencing of the Drosophila genome we have obtained a fairly good estimate of the total number of genes encoding neuropeptide precursors and thus the total number of neuropeptides in an insect. At present there are 23 identified genes that encode predicted neuropeptides and an additional seven encoding insulin-like peptides in Drosophila. Since the number of G-protein-coupled neuropeptide receptors in Drosophila is estimated to be around 40, the total number of neuropeptide genes in this insect will probably not exceed three dozen. The neuropeptides can be grouped into families, and it is suggested here that related peptides encoded on a Drosophila gene constitute a family and that peptides from related genes (orthologs) in other species belong to the same family. Some peptides are encoded as multiple related isoforms on a precursor and it is possible that many of these isoforms are functionally redundant. The distribution and possible functions of members of the 23 neuropeptide families and the insulin-like peptides are discussed. It is clear that each of the distinct neuropeptides are present in specific small sets of neurons and/or neurosecretory cells and in some cases in cells of the intestine or certain peripheral sites. The distribution patterns vary extensively between types of neuropeptides. Another feature emerging for many insect neuropeptides is that they appear to be multifunctional. One and the same peptide may act both in the CNS and as a circulating hormone and play different functional roles at different central and peripheral targets. A neuropeptide can, for instance, act as a coreleased signal that modulates the action of a classical transmitter and the peptide action depends on the cotransmitter and the specific circuit where it is released. Some peptides, however, may work as molecular switches and trigger specific global responses at a given time. Drosophila, in spite of its small size, is now emerging as a very favorable organism for the studies of neuropeptide function due to the arsenal of molecular genetics methods available.

Endogenous control of circadian rhythms of pheromone production in the turnip moth, Agrotis segetum

The circadian variation of pheromone production in the turnip moth, Agrotis segetum, was characterized by quantifying (Z)-7-dodecenyl acetate (Z7-12:OAc), the most abundant pheromone component produced by female turnip moth, at different times of day. Under 17:7 h light-dark cycle (LD), the peak of Z7-12:OAc production occurred around 4 h into the scotophase, while there was very little pheromone production during the photophase. When females were maintained under constant darkness (DD), the periodicity of pheromone production was sustained for 3 consecutive days. Furthermore, the rhythm in pheromone production could be entrained to a shifted LD. These results demonstrate that the pheromone production in the turnip moth is regulated endogenously by a circadian clock. To understand how the circadian rhythm of pheromone production is generated, circadian variation of pheromone- biosynthesis-activating neuropeptide (PBAN)-like activity in the brain-suboesophageal ganglion complexes (Br-SOG), hemolymph, and ventral nerve cord (VNC) was also examined. Under both LD and DD, only the VNC displayed a circadian variation in the PBAN-like activity, which was significantly higher during the late-photophase than that in the scotophase. In addition, the present study showed that removal of VNC in isolated abdomen did not affect PBAN stimulation of pheromone production, while severing the VNC impaired normal pheromone production. The role of Br-SOG, VNC, and hemolymph in the regulation of the periodicity of pheromone production is discussed.

A brominated-fluorene insect neuropeptide analog exhibits pyrokinin/PBAN-specific toxicity for adult females of the tobacco budworm moth

An analog of the insect pyrokinin/PBAN class of neuropeptides, which features a 2-amino7-bromofluorene attached to the carboxy-terminal bioactive core of the insect pyrokinin/PBAN class of neuropeptides (Phe-Thr-Pro-Arg-Leu-NH(2)), via a succinnic acid linker, was tested in adult H. virescens moths. This analog was found to induce pheromone production when injected into or applied topically to moths. Topical application of as much as 1 nmol of the analog to moths induced production of significant amounts of pheromone for only 1-2 h, whereas injection of 500 pmol induced pheromone production for up to 20 h. All insects died within 24 h after injection of 500 pmol of the analog. Mortality studies indicated that the LD(50) for the analog was 0.7 pmol when injected. A non-pyrokinin/PBAN peptide analog formed by attachment of 2-amino-7-bromofluorene to Ala-Ala-Arg-Ala-Ala-NH(2) (via the succinnic acid linker) did not induce mortality when injected at 1 nmol. Similarly no mortality was found when up to 2 nmol of an analog containing a non-brominated fluorene ring, formed by attachment of 9-fluoreneacetic acid to Phe-Thr-Pro-Arg-Leu-NH(2,) was injected into moths. The data indicated that both the bromine and active core of the pyrokinin neuropeptides (Phe-Thr-Pro-Arg-Leu-NH(2)) were critical for a specific toxic action and suggested that the brominated analog poisoned the moths by interacting with pyrokinin receptors.

Discovery of a linear lead antagonist to the insect pheromone biosynthesis activating neuropeptide (PBAN)

We report the discovery of a linear lead antagonist for the insect pheromone biosynthesis activating neuropeptide (PBAN) which inhibits sex pheromone biosynthesis in the female moth Heliothis peltigera. Two approaches have been used in attempting to convert PBAN agonists into antagonists. The first involved omission of the C-terminal amide and reduction of the sequence from the N-terminus in a linear library based on PBAN 1-33NH(2.) The second involved replacement of L amino-acids by the D hydrophobic amino acid D-Phe in a linear library based on PBAN28-33NH(2.) Screening of the two libraries for pheromonotropic antagonists resulted in the disclosure of one compound out of the D-Phe library (Arg-Tyr-Phe-D-Phe-Pro-Arg-Leu-NH(2)) which inhibited sex pheromone production by 79 and 64% at 100 pmol in two moth colonies and exhibited low agonistic activity. Omission of the C-terminal amide in PBAN 1-33NH(2) and its shorter analogs did not lead to the discovery of an antagonistic compound.

Insect pheromones--an overview of biosynthesis and endocrine regulation

This overview describes, compares, and attempts to unify major themes related to the biosynthetic pathways and endocrine regulation of insect pheromone production. Rather than developing and dedicating an entirely unique set of enzymes for pheromone biosynthesis, insects appear to have evolved to add one or a few tissue-specific auxiliary or modified enzymes that transform the products of "normal" metabolism to pheromone compounds of high stereochemical and quantitative specificity. This general understanding is derived from research on model species from one exopterygote insect order (Blattodea) and three endopterygote insect orders (Coleoptera, Diptera, and Lepidoptera). For instance, the ketone hydrocarbon contact sex pheromone of the female German cockroach, Blattella germanica, derives its origins from fatty acid biosynthesis, arising from elongation of a methyl-branched fatty acyl-CoA moiety followed by decarboxylation, hydroxylation, and oxidation. Coleopteran sex and aggregation pheromones also arise from modifications of fatty acid biosynthesis or other biosynthetic pathways, such as the isoprenoid pathway (e.g. Cucujidae, Curculionidae, and Scolytidae), or from simple transformations of amino acids or other highly elaborated host precursors (e.g. Scarabaeidae and Scolytidae). Like the sex pheromone of B. germanica, female-produced dipteran (e.g. Drosophilidae and Muscidae) sex pheromone components originate from elongation of fatty acyl-CoA moieties followed by loss of the carbonyl carbon and the formation of the corresponding hydrocarbon. Female-produced lepidopteran sex pheromones are also derived from fatty acids, but many moths utilize a species-specific combination of desaturation and chain-shortening reactions followed by reductive modification of the carbonyl carbon. Carbon skeletons derived from amino acids can also be used as chain initiating units and elongated to lepidopteran pheromones by this pathway (e.g. Arctiidae and Noctuidae). Insects utilize at least three hormonal messengers to regulate pheromone biosynthesis. Blattodean and coleopteran pheromone production is induced by juvenile hormone III (JH III). In the female common house fly, Musca domestica, and possibly other species of Diptera, it appears that during hydrocarbon sex pheromone biosynthesis, ovarian-produced ecdysteroids regulate synthesis by affecting the activities of one or more fatty acyl-CoA elongation enzyme(s) (elongases). Lepidopteran sex pheromone biosynthesis is often mediated by a 33 or 34 amino acid pheromone biosynthesis activating neuropeptide (PBAN) through alteration of enzyme activities at one or more steps prior to or during fatty acid synthesis or during modification of the carbonyl group. Although a molecular level understanding of the regulation of insect pheromone biosynthesis is in its infancy, in the male California fivespined ips, Ips paraconfusus (Coleoptera: Scolytidae), JH III acts at the transcriptional level by increasing the abundance of mRNA for 3-hydroxy-3-methylglutaryl-CoA reductase, a key enzyme in de novo isoprenoid aggregation pheromone biosynthesis.

FMRFamide neuropeptides and neuropeptide-associated enzymes in Drosophila

To review the histochemistry of neuropeptide transmitters system in insects, this chapter focuses on the biology of FMRFamide-related neuropeptides in Drosophila. dFMRFamide expression is limited to a small number of neurons that present a complex spatial pattern and whose functions appear heterogeneous. The neuropeptide is first expressed by a few neurons in late stage embryos, then dynamically in as many as 44 neurons in the larval CNS. This review describes histochemical procedures to evaluate this neuronal phenotype and its regulation, including descriptions of promoter activity, and RNA and peptide distributions. To evaluate the use of peptidergic transmitters on a broad scale, I also review experiments in Drosophila studying enzymes necessary for neuropeptide biosynthesis, and in particular, histochemical studies of an enzyme responsible for peptide alpha-amidation.

The pheromone biosynthesis activating neuropeptide (PBAN) of the black cutworm moth, Agrotis ipsilon: immunohistochemistry, molecular characterization and bioassay of its peptide sequence

PBAN-like immunoreactivity has been detected in the suboesophageal ganglion and the brain (Br-SOG) of larvae and adult males and females of Agrotis ipsilon, using an antiserum against Helicoverpa zea PBAN (Hez-PBAN). The amino acid sequence of A. ipsilon PBAN (Agi-PBAN) was deduced from the cDNA sequence, using both Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) and 5' Rapid Amplification of cDNA Ends (RACE). The primers were degenerate sets of oligonucleotides derived from known amino acid sequences of the PBAN precursor. The final cloned fragment contained the complete DNA sequence coding for the putative Agi-PBAN. Based on a comparison with known PBAN processing from the polypeptide precursor, we propose that Agi-PBAN is a 33-amino acid peptide. Agi-PBAN exhibits high sequence homology with Hez-PBAN (88%), Lymantria dispar PBAN (Lyd-PBAN, 88%) and Bombyx mori PBAN (Bom-PBAN, 73%). Agi-PBAN shares the C-terminal hexapeptide sequence (Tyr-Phe-Ser-Pro-Arg-LeuNH2) with all identified PBANs but has only one methionine residue instead of two in Hez-PBAN and Lyd-PBAN, and three in Bom-PBAN. Based on predicted a.a. sequence, Agi-PBAN, with Leu-NH2 as C-terminal motif, has been synthesized and assayed for its ability to promote pheromone production in decapitated females of A. ipsilon. Synthetic Agi-PBAN induced pheromone production in decapitated females as evaluated by the male responsiveness to the pheromonal blend in a wind tunnel.

Activity patterns of neurosecretory cells releasing pheromonotropic neuropeptides in the moth Bombyx mori

Short- and long-term firing patterns of neurosecretory cells releasing pheromonotropic neuropeptides in the silkworm moth Bombyx mori were examined. The cells showed three types of rhythmic changes in firing activity. Bursting activities with an interval of several seconds were synchronized with rhythmic abdominal motions for calling behavior. A slow fluctuation in firing activity over a period of several minutes depended on cyclic alternations of the flow of hemolymph. The electrical activity displayed a diel rhythm that related to light/dark cycles of the environment and sex pheromone titers in the pheromone gland. In addition to a transient inhibition of firing caused by a tactile or light stimulus, a long-term permanent inhibition was induced by mating with a fertile male. Thus, the insect neurosecretory system is highly coordinated with physiology and behavior in Bombyx mori and is influenced by external stimuli.

Immunocytochemical distribution of angiotensin I-converting enzyme-like immunoreactivity in the brain and testis of insects

Angiotensin converting enzyme (ACE) is Zn2+ metallopeptidase which plays an important role in blood pressure homeostasis in mammals and other vertebrates. Homologues of ACE involved in the biosynthesis of mammalian peptide hormones have also been identified in the insects, Musca domestica, Drosophila melanogaster and Haematobia irritans exigua. In the pursuit of the biological role of insect ACE, this work focused on the tissue and cellular distribution of ACE in several insect species. The localisation of ACE in the central nervous system and reproductive tissues from a number of insect species suggests that ACE is of physiological importance in these tissues. By means of an antiserum to housefly ACE, we found that ACE-like immunoreactivity was abundantly present in the neuropil areas of the brain of all insects investigated, suggesting a role for ACE in the metabolic inactivation of peptide neurotransmitters. Especially in the fleshfly, Neobellieria bullata neuropile staining is abundant. In the cockroach Leucophaea maderae, immunoreactive staining was abundant in the neuronal perikarya as well as in the neuropilar regions. Staining in neurosecretory cells was also observed in the brains of the lepidopteran species, Bombyx mori and Mamestra brassica. The localisation of ACE in neurosecretory cells is consistent with the role as a processing hormone, involved in the generation of active peptide hormones. ACE was found to be co-localised with peptides of the FXPRLamide family in M. brassica and in B. mori, suggesting a role for the biosynthesis of these hormones. Finally, we found ACE-like immunoreactivity in the testis of Locusta migratoria, N. bullata and Leptinotarsa decemlineata, providing additional evidence for its important role in insect reproduction.

Phe-X-Pro-Arg-Leu-NH(2) peptide producing cells in the central nervous system of the silkworm, Bombyx mori

Members of the neuropeptide family having Phe-X-Pro-Arg-Leu-NH(2) (FXPRLamide; X=Ser, Thr, Val, or Gly) at the C-terminus serve as regulators of oviduct and visceral muscle contraction, sex pheromone production, and diapause induction. Antibody raised against Bombyx mori diapause hormone recognized a variety of FXPRLamide peptides. Using this antibody, the antigen was immunocytochemically localized in the central nervous system (CNS) of the silkworm, Bombyx mori. Immunoreactive somata were observed in all ganglia of the CNS including the brain. Twelve somata localized at the midline of the suboesophageal ganglion (SG) were most intensely stained, and their neurite projections reached the retrocerebral complex. Thus, these cells in the SG exhibited typical features of neuroendocrine neurons. Marked reduction in immunoreactivity was observed in a pair of neurosecretory cells in the labial neuromere in SG of diapause type pupae, which indicates an active release of FXPRLamide peptides from these cells. No clear connection to neurohemal sites were observed in immunoreactive cells in the brain, thoracic or abdominal ganglia, suggesting that the immunoreactive peptides in these organs are likely to serve as neurotransmitters or neuromodulators.

A novel peptide-processing activity of insect peptidyl-dipeptidase A (angiotensin I-converting enzyme): the hydrolysis of lysyl-arginine and arginyl-arginine from the C-terminus of an insect prohormone peptide

Insect peptidyl-dipeptidase A [angiotensin I-converting enzyme (ACE)] is a soluble single-domain peptidyl-dipeptidase that has many properties in common with the C-domain of mammalian somatic ACE and with the single-domain mammalian germinal ACE. Mammalian somatic ACE is important in blood homoeostasis, but the role of ACE in insects is not known. Immunocytochemistry has been used to localize ACE in the neuroendocrine system of the locust, Locusta migratoria. Staining was observed in five groups of neurosecretory cells in the brain and suboesophageal ganglion, in the nervi corpori cardiaci, the storage part of the corpora cardiaca and in the nervi corpori allati. In three groups of neurosecretory cells, ACE co-localized with locustamyotropins, suggesting a possible role for the enzyme in the metabolism of these neuropeptides. We demonstrate in vitro a novel activity of ACE that removes pairs of basic amino acid residues from a locustamyotropin peptide extended at the C-terminus with either Gly-Lys-Arg or Gly-Arg-Arg, corresponding to a consensus recognition sequence for endoproteolysis of prohormone proteins by prohormone convertases. The low Km and high kcat values (Km 7.3 and 5.0 microM, kcat 226 and 207 s-1 for the hydrolysis of Phe-Ser-Pro-Arg-Leu-Gly-Lys-Arg and Phe-Ser-Pro-Arg-Leu-Gly-Arg-Arg, respectively) obtained for the hydrolysis of these two peptides by insect ACE means that these peptides, along with mammalian bradykinin, are the most favoured in vitro ACE substrates so far identified. The discovery of this in vitro prohormone-processing activity of insect ACE provides a possible explanation for the intracellular co-localization of the enzyme with locustamyotropin peptides, and provides evidence for a new role for ACE in the biosynthesis of peptide hormones and transmitters.

Structure-function analysis of Lymantria testis ecdysiotropin: a search for the active core

A structure-function study was performed on the synthetic 21 residue neuropeptide, Lymantria testis ecdysiotropin (LTE), originally isolated from brains of Lymantria dispar pupae. The peptide induces ecdysteroid synthesis by testis sheaths of various lepidopteran species. LTE, as well as synthetic LTE 1-11, 11-21, and 11-15, stimulated synthesis in larval and pupal testes of Lymantria dispar at concentrations of 10(-9) to 10(-15) M; LTE 16-21 was weakly active, and an elongated LEU-LTE was inhibitory to synthesis at all but extremely low concentrations (10(-15) M). Since the sequence and polarity of residues in LTE 1-11, 11-15, and 11-21 are quite different, several parts of the molecule must activate receptors which initiate the cascade, resulting in ecdysiogenesis in Lepidopteran testes.

Prolonged pheromonotropic activity of pseudopeptide mimics of insect pyrokinin neuropeptides after topical application or injection into a moth

Amphiphilic pseudopeptide analogs of Phe-Thr-Pro-Arg-Leu-NH2, representing the active C-terminal core pentapeptide of the pyrokinin class of insect neuropeptides, were synthesized by replacement of phenylalanine with hydrocinnamic acid (Hca-Thr-Pro-Arg-Leu-NH2), or addition of 1-pyrenebutyric acid (Pba-Phe-Thr-Pro-Arg-Leu-NH2) or 9-fluoreneacetic acid (Fla-Phe-Thr-Pro-Arg-Leu-NH2). The pseudopeptides were found to stimulate sex pheromone biosynthesis when injected into females of the moth Heliothis virescens. Optimal pheromonotropic responses were obtained by injection of 0.25 pmol of Hca-Thr-Pro-Arg-Leu-NH2, 2.5 pmol of Pba-Thr-Pro-Arg-Leu-NH2 and 0.5 pmol of Fla-Thr-Pro-Arg-Leu-NH2. Topical application of each of the pseudopeptides in water to the cuticle of moths stimulated significant production of pheromone at a dose of 50 pmol with optimal stimulation occurring when 500 pmol were applied. The parent peptide, Phe-Thr-Pro-Arg-Leu-NH2, failed to stimulate significant production of pheromone when applied topically at a dose as high as 2000 pmol. Temporal studies indicated that Hca-Thr-Pro-Arg-Leu-NH2 stimulated significant production of pheromone for only 4 h after application where as continuous pheromone production for 18 h was observed when either Pba-Phe-Thr-Pro-Arg-Leu-NH2 or Fla-Phe-Thr-Pro-Arg-Leu-NH2 were applied to the abdomen. The results show that modification of the C-terminal active core of the insect pyrokinins, by addition of hydrophobic moieties, can result in production of pseudopeptides which effectively penetrate the insect cuticle and have prolonged physiological effects making them favorable candidates for use in development of alternative strategies for pest insect control.

Induction of pheromone production in a moth by topical application of a pseudopeptide mimic of a pheromonotropic neuropeptide

An amphiphilic analog of Locusta myotropin II (Lom-MT-II), Glu-Gly-Asp-Phe-Thr-Pro-Arg-Leu-amide, was synthesized by addition of 6-phenylhexanoic acid (6-Pha) linked through alanine to the amino terminus. This pseudopeptide, [6-Pha-Ala0]Lom-MT-II, was found to have pheromonotropic activity equivalent to pheromone biosynthesis activating neuropeptide when injected into females of Heliothis virescens. Topical application of [6-Pha-Ala0]Lom-MT-II or Helicoverpa zea-pheromone biosynthesis activating neuropeptide (PBAN), dissolved in dimethyl sulfoxide, to the descaled abdomen of females induced production of pheromone, although more Hez-PBAN than [6-Pha-Ala0]Lom-MT-II was required to obtain significant production of pheromone. Application of [6-Pha-Ala0]Lom-MT-II, dissolved in water, to the abdomen induced production of pheromone, but neither Hez-PBAN nor Lom-MT-II dissolved in water stimulated production of significant amounts of pheromone. Dose- and time-response studies indicated that application of the amphiphilic mimetic in water induced pheromone production in as little as 15 min after application and that the effects were maintained for prolonged periods. These findings show that amphiphilic pseudopeptide mimics of insect neuropeptides will penetrate the insect cuticle when applied topically in water and induce an endogenous response.

Neuroanatomy and immunocytochemistry of the median neuroendocrine cells of the subesophageal ganglion of the tobacco hawkmoth, Manduca sexta: immunoreactivities to PBAN and other neuropeptides

The median neuroendocrine cells of the subesophageal ganglion, important components of the neuroendocrine system of the tobacco hawkmoth, Manduca sexta, have not been well investigated. Therefore, we studied the anatomy of these cells by axonal backfills and characterized their peptide immunoreactivities. Both larvae and adults were examined, and developmental changes in these neuroendocrine cells were followed. Processes of the median neuroendocrine cells project to terminations in the corpora cardiaca via the third and the ventral nerves of this neurohemal organ, but the ventral nerve of the corpus cardiacum is the principal neurohemal surface for this system. Cobalt backfills of the third cardiacal nerves revealed lateral cells in the maxillary neuromere and a ventro-median pair in the labial neuromere. Backfills of the ventral cardiacal nerves revealed two ventro-median pairs of cells in the mandibular neuromere and two ventro-median triplets in the maxillary neuromere. The efferent projections of these cells are contralateral. The anatomy of the system is basically the same in larvae and adults. The three sets of median neuroendocrine cells are PBAN- and FMRFamide-immunoreactive, but only the mandibular and maxillary cells are proctolin-immunoreactive. During metamorphosis, the mandibular and maxillary cells also acquire CCK-like immunoreactivity and the labial cells become SCP- and sulfakinin-immunoreactive. Characteristics of FMRFamide-like immunostaining suggest that the median neuroendocrine cells may contain one or more of the FLRFamides that have been identified in M. sexta. The mandibular and maxillary neuroendocrine cells appear to produce the same set of hormones, and a somewhat different set of hormones is produced by the labial neuroendocrine cells. Two pairs of interneurons immunologically related to the neurosecretory cells are associated with the median maxillary neuroendocrine cells. These cells are PBAN-, FMRFamide-, SCP-, and sulfakinin-immunoreactive and project to arborizations in the brain and all ventral ganglia. These interneurons appear to have extensive modulatory functions in the CNS.