The significance of Manduca sexta allatostatin in the tomato moth Lacanobia oleracea

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.

Defining the contribution of select neuropeptides and their receptors in regulating sesquiterpenoid biosynthesis by Drosophila melanogaster ring gland/corpus allatum through RNAi analysis

The larval ring gland and adult corpus allatum (CA) of Drosophila melanogaster produce at least three sesquiterpenoid products: methyl farnesoate (MF), juvenile hormone III (JHIII), and JHIII bisepoxide (JHB(3)). Our understanding of neuropeptide regulation of sesquiterpenoid biosynthesis in D. melanogaster has been hampered by uncertainty over the biosynthetic pathway and the sites of action of regulators. As an approach to defining the neuropeptide regulators, we have used in vivo gene-specific silencing (RNAi). D. melanogaster strains containing an inducible UAS-RNAi construct made to either PheGlyLeu-NH(2)-allatostatin (FGLa/AST) and its cognate receptors Dar-1 and Dar-2 or PISCF-allatostatin (PISCF/AST) or its cognate receptors Drostar-1 or Drostar-2 were expressed in vivo. MF, JHIII and JHB(3) production was measured in ring glands of 3rd instars or corpora allata (CA) of adult females using the radiochemical assay. Reduction in FGLa/AST and Dar-1 or Dar-2 mRNA levels had no effect on MF, JHIII, or JHB(3) production in larvae or adults. Inhibition of Drostar-1 expression resulted in a significant decrease in MF and JHB(3) production in 3rd instars with little effect on JHIII biosynthesis. In contrast, inhibition of Drostar-1 in adult females led to a significant increase in MF and JHIII production. Inhibition of Drostar-2 also reduced MF biosynthesis in 3rd instars. In adults, inhibition of Drostar-2 led to a significant increase in MF and JHIII production but showed no effect on JHB(3). PISCF/AST had no effect on sesquiterpenoid biosynthesis when incubated with 3rd instar ring glands but was stimulatory when incubated with adult glands. Inhibition of short neuropeptide F (sNPF) expression by RNAi or application of sNPF to ring glands had no effect on MF, JHIII, or JHB3 biosynthesis in larvae or adults. Reduction in the neuropeptide Y receptor (NepYr) or neuropeptide F receptor (NPF-R) inhibited JHIII and JHB(3) production in 3rd instars but only reduction in NepYr resulted in JHB(3) reduction in adults.

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.

Identification of cDNAs encoding allatotropin and allatotropin-like peptides from the silkworm, Bombyx mori

The cDNAs encoding allatotropin (AT) and allatotropin-like peptides (ATLPs) were isolated from the silkworm, Bombyx mori. Similar to those of the tobacco hornworm, Manduca sexta, four peptides (AT, ATLP1, ATLP2, and ATLP3) are present in three different variants generated by alternative splicing. RT-PCR analyses showed that these splice variants are expressed in the central nervous system with differing expression patterns in each ganglion. Immunohistochemistry using an anti-AT antibody confirmed that AT-expressing cells were located in these central nervous ganglia as well as in two large anterior cells of the frontal ganglia. Injection of synthetic AT and ATLP-1 into B. mori larvae increased the latency to feed, indicating that AT and ATLP might function in the regulation of feeding behavior in B. mori.

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.

Allatostatin C and its paralog allatostatin double C: the arthropod somatostatins

Arthropods do not have one, but two genes encoding an allatostatin C-like peptide. The newly discovered paralog gene was called Ast-CC, and the peptide which it is predicted to make was called allatostatin double C (ASTCC). Genes for both allatostatin C (ASTC) and its paralog were found in the tick Ixodes scapularis as well as dipteran, lepidopteran, coleopteran, aphidoidean and phthirapteran insect species. In addition partial or complete cDNAs derived from Ast-CCs were found in a number of species, including Drosophila melanogaster, Bombyx mori and Rhodnius prolixus. The ASTCC precursors have a second conserved peptide sequence suggesting that they may produce two biologically active peptides. The predicted precursors encoded by the Ast-CCs have some unusual features, particularly in Drosophila, where they lack a signal peptide, and have instead a peptide anchor. These unusual structural features suggest that they are perhaps expressed by cells that are not specialized in neuropeptide synthesis and that in Drosophila ASTCC may be a juxtacrine. Data from the Fly Atlas project show that in Drosophila Ast-CC is little expressed. Nevertheless a P-element insertion in this gene is embryonic lethal, suggesting that it is an essential gene. Similarity between the precursors and receptors of ASTC/ASTCC and somatostatin suggests that ASTC/ASTCC and somatostatin have a common ancestor.

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.

Degradation of Manduca sexta allatostatin and allatotropin by proteases associated with the foregut of Lacanobia oleracea larvae

The degradation of synthetic Manduca sexta allatostatin (Manse-AS) and allatotropin (Manse-AT), by enzymes of the foregut of larvae of the tomato moth, Lacanobia oleracea was investigated using reversed-phase high performance liquid chromatography (RP-HPLC) together with matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and Edman sequencing. Metabolism of 1nmol Manse-AS by foregut extract (1microg protein) was rapid, t(1/2) approximately 5min, with two major products produced. Mass spectrometry of HPLC fractions identified cleavage products Manse-AS-(4-15) and Manse-AS-(6-15), which indicates enzymatic cleavage at the C-terminal side of arginine residues (R(3) and R(5)). This degradation of Manse-AS could be inhibited by up to 80% by the serine protease inhibitor aprotinin, but not PMSF, pepstatin, E64, EDTA, or 1,10-phenanthroline.M. sexta allatotropin was also rapidly degraded when incubated with foregut extract, t(1/2) approximately 8min, producing two metabolic products, one of which was identified as Manse-AT-(1-11), showing enzymatic cleavage at the C-terminal side of arginine (R(11)). The second product was identified as Manse-AT-(1-8). Hydrolysis of Manse-AT could only be partially inhibited by high doses of aprotinin (30%).

Drosophila melanogaster myotropins have unique functions and signaling pathways

Drosophila melanogaster TDVDHVFLRFamide (DMS), SDNFMRFamide, and pEVRFRQCYFNPISCF (FLT) represent three structurally distinct peptide families. Each peptide decreases heart rate albeit with different magnitudes and time-dependent responses. DMS and FLT are expressed in the crop and decrease crop motility; however, SDNFMRFamide expression and effect on the crop has not been reported. These data suggest the peptides have different physiological roles. The peptides have non-overlapping expression patterns in neural tissue, which suggests different mechanisms regulate their synthesis and release. The structures, expression patterns, and activities of the myotropins suggest they have important but different roles in biology and different signaling pathways.

Metabolism of Manduca sexta allatostatin by hemolymph of larvae of the tomato moth, Lacanobia oleracea

The degradation of synthetic Manduca sexta allatostatin (Manse-AS) by hemolymph from larvae of the tomato moth, Lacanobia oleracea was investigated using reversed phase-high performance liquid chromatography (RP-HPLC), and matrix assisted laser desorption ionisation-time of flight mass spectrometry. Metabolism of 1 nmole Manse-AS in diluted hemolymph was rapid, t(1/2) = 3.5 min, with a number of products produced. Mass spectrometry of HPLC fractions identified cleavage products, which indicated a sequential degradation of Manse-AS from the N-terminal to Manse-AS (7-15). The most abundant products identified were Manse-AS (5-15), (6-15), and (7-15). These metabolites were synthesized and assayed for biological activity on juvenile hormone (JH) biosynthesis in vitro. All three of the above deletion peptides showed allatostatin activity, but were not as potent as Manse-AS (1-15).

Morphological and physiological comparisons of two types of allatostatin in the brain and retrocerebral complex of the tomato moth, Lacanobia oleracea (Lepidoptera: Noctuidae)

The cellular localisation of two types of allatostatin in the brain and retrocerebral complex has been studied in larvae of Lacanobia oleracea (Noctuidae) using antisera against Manduca sexta allatostatin (Mas-AS) and two members of the Y/FXFGL-NH(2) allatostatin family. The axons of two groups of Mas-AS-immunoreactive neurosecretory cells in the pars lateralis form part of the nervi corporis cardiaci (NCC 1). They exit the brain as the combined NCC 1 and NCC 2 and pass through the corpora cardiaca (CC), where they divide to innervate the corpora allata (CA) and the mandibular (salivary) gland. The presence of Mas-AS immunoreactivity in the CA is consistent with the inhibitory action of this peptide on juvenile hormone (JH) biosynthesis in L. oleracea. Immunoreactivity in the mandibular gland nerve suggests an additional, as yet unidentified role for this peptide. Cells of the pars intermedialis, the main contributors to NCC 2, do not show Mas-AS immunoreactivity. The distribution of Y/FXFGL-NH(2) immunoreactivity is different from that of Mas-AS. Although there are fewer cells in the pars lateralis, immunoreactivity is observed in certain neurones of the pars intermedialis and the tritocerebrum. Axons of these latter neurones contribute to NCC 2 and NCC 3, respectively, and, combined with those from NCC 1, result in the prominent occurrence of Y/FXFGL-NH(2) immunoreactivity in the CC, particularly in the storage lobe. The CA has far less Y/FXFGL-NH(2) immunoreactivity compared with Mas-AS. In bioassays, the Y/FXFGL-NH(2) allatostatins did not inhibit JH synthesis by CA of L. oleracea.

A review of the role of neurosecretion in the control of juvenile hormone synthesis: a tribute to Berta Scharrer

In the 1950s, Berta Scharrer predicted that neurosecretions from the brain regulated corpus allatum activity based upon the observation of the change in localization of neurosecretory material in the brain and change in gland activity after severance of nerves between the brain and corpus allatum. Isolation and characterization of neuropeptide regulators of juvenile hormone production by the corpora allata in the late 1980s has confirmed this prediction. Both a stimulatory allatotropin and an inhibitory allatostatin have been isolated from moth brains. Two families of allatostatins, both quite different from each other and that of moths, have been isolated from cockroaches and crickets. The wide distribution of these peptides in the nervous system, in nerves to visceral muscle, in endocrine cells of the midgut and in blood cells, indicate multifunctions in the insects in which they are allatoregulatory. Some of these other functions have been demonstrated in these insects and in insects in which these neuropeptides occur but do not act as corpus allatum regulators. For the latter group, the neuropeptide regulators of the corpora allata have yet to be isolated. The families of neurosecretory regulators will continue to grow.