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

Role of peptide hormones in insect gut physiology

Nutrient uptake and digestion are essential for optimal growth and development. In insects, these processes are regulated by the gut-brain axis, which is a neurohumoral communication system for maintaining gut homeostasis. The insect gut is a complex organ consisting of three distinct structures, denominated foregut, midgut and hindgut, each with their specific specializations. These specializations are tightly regulated by the interplay of several neuropeptides: a versatile group of signalling molecules involved in a multitude of processes including gut physiology. Neuropeptides take part in the regulation of gut processes ranging from digestive enzyme release to muscle activity and satiety. Some neuropeptide mimetics are a promising strategy for ecological pest management. This review focuses on a selection of neuropeptides that are well-known for their role in gut physiology, and neuropeptides for which the mode of action is yet to be unravelled.

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.

bHLH proneural genes as cell fate determinants of entero-endocrine cells, an evolutionarily conserved lineage sharing a common root with sensory neurons

Entero-endocrine cells involved in the regulation of digestive function form a large and diverse cell population within the intestinal epithelium of all animals. Together with absorptive enterocytes and secretory gland cells, entero-endocrine cells are generated by the embryonic endoderm and, in the mature animal, from a pool of endoderm derived, self-renewing stem cells. Entero-endocrine cells share many structural/functional and developmental properties with sensory neurons, which hints at the possibility of an ancient evolutionary relationship between these two cell types. We will survey in this article recent findings that emphasize the similarities between entero-endocrine cells and sensory neurons in vertebrates and insects, for which a substantial volume of data pertaining to the entero-endocrine system has been compiled. We will then report new findings that shed light on the specification and morphogenesis of entero-endocrine cells in Drosophila. In this system, presumptive intestinal stem cells (pISCs), generated during early metamorphosis, undergo several rounds of mitosis that produce the endocrine cells and stem cells (ISCs) with which the fly is born. Clonal analysis demonstrated that individual pISCs can give rise to endocrine cells expressing different types of peptides. Immature endocrine cells start out as unpolarized cells located basally of the gut epithelium; they each extend an apical process into the epithelium which establishes a junctional complex and apical membrane specializations contacting the lumen of the gut. Finally, we show that the Drosophila homolog of ngn3, a bHLH gene that defines the entero-endocrine lineage in mammals, is expressed and required for the differentiation of this cell type in the fly gut.

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.

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.

Neuropeptides associated with the regulation of feeding in insects

The stomatogastric nervous system plays a pivotal role in feeding behaviour. Central to this system is the frontal ganglion, which is responsible for foregut motor activity, and hence the passage of food through the gut. Many insect peptides, which exhibit myoactivity on the visceral muscles of the gut in vitro, have been detected in the stomatogastric nervous system by immunochemical or mass spectrometric techniques. This localisation of myoactive peptides, particularly in the frontal ganglion, implies roles for these peptides in the neural control and modulation of feeding in insects. Insect sulfakinins, tachykinins, allatotropin and proctolin have all been shown to stimulate the foregut muscles, whereas myosuppressins, myoinhibitory peptides and allatostatins all inhibited spontaneous contractions of the foregut in a variety of insects. Some of these peptides, when injected, inhibited feeding in vivo. Both the A-type and B-type allatostatins suppressed feeding activity when injected into the cockroach, Blattella germanica and the Manduca sexta C-type allatostatin and allatotropin inhibited feeding when injected into the larvae of two noctuid moths, Lacanobia oleracea and Spodoptera frugiperda, respectively. Injection of sulfakinins into the fly Phormia regina, the locust Schistocera gregaria and the cockroach B. germanica also suppressed feeding, whereas silencing the sulfakinin gene through the injection of double stranded RNA resulted in an increase in food consumption in the cricket Gryllus bimaculatus. The regulation of feeding in insects is clearly very complex, and involves the interaction of a number of mechanisms, one of which is the release, either centrally or locally, of neuropeptides. However, the role of neuropeptides, their mechanisms of action, interactions with each other, and their release are still poorly understood. It is also unclear why insects possess such a number of different peptides, some with multiples copies or homologues, which stimulate or inhibit gut motility, and how their release, sometimes from the same neurone, is regulated. These neuropeptides may also act at sites other than visceral muscles, such as centrally through the brain or on gut stretch receptors.

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.

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.

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.

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.

Neuropeptides associated with the frontal ganglion of larval Lepidoptera

The occurrence of neuropeptides in the frontal ganglia of larvae of the tobacco hawkmoth, Manduca sexta, the tomato moth, Lacanobia oleracea and the cotton leafworm, Spodoptera littoralis was investigated using reversed-phase high performance liquid chromatography (RP-HPLC), matrix-assisted laser desorption time of flight mass spectrometry (MALDI-TOF MS) and enzyme-linked immunosorbent assay (ELISA). Only three types of peptides could be identified or assigned from frontal ganglion extracts; M. sexta allatostatin (Manse-AS), M. sexta allatotropin (Manse-AT), and F/YXFGL-NH2 allatostatins. The peptide profiles of frontal ganglion of L. oleracea and S. littoralis were similar, with ten identical [M+H]+ ions, seven of which could be assigned to known lepidopteran peptides (Manse-AT, cydiastatin 2, 3, 4 and helicostatin 1, 5, 9). In addition, mass ions corresponding to helicostatin 7 (which was confirmed by MALDI-post source decay analysis) and Manse-AS were present in frontal ganglia of L. oleracea and helicostatin 6 in frontal ganglia of S. littoralis. Only four mass ions from M. sexta frontal ganglia corresponded to known peptides, cydiastatin 3 and 4, helicostatin 1, and Manse-AT. The only difference between the profiles of frontal ganglia from different stages of L. oleracea were mass ions which could not be assigned, and no differences were observed in the allatoregulatory peptides present. In HPLC fractions of M. sexta frontal ganglia, F/YXFGL-NH2 allatostatin-like immunoreactivity was widespread suggesting that more allatostatins were present than were identified.

Endopeptidase activity of larval Lacanobia oleracea corpus allatum: metabolism of Manduca sexta allatostatin and allatotropin

The degradation of synthetic Manduca sexta allatostatin (Manse-AS) and allatotropin (Manse-AT) by enzymes associated with the corpus allatum (CA) of larvae of the tomato moth, Lacanobia oleracea, was investigated using reversed-phase high performance liquid chromatography and matrix-assisted laser desorption ionisation-time of flight mass spectrometry. Manduca sexta allatostatin was metabolised by CA extract to Manse-AS5-15, Manse-AS6-15, and Manse-AS7-15, which indicates enzymic cleavage at the C-terminal side of arginine residues R3 and R5 and the N-terminal side of R5, suggesting this is due to a trypsin-like enzyme. In support of this, the same degradation products were identified after Manse-AS was incubated with trypsin, and CA enzymic activity could be inhibited up to 79% by aprotinin. Degradation of Manse-AT by CA extract was also trypsin-like, cleaving at the C-terminal side of the basic residues K3 and R11 to produce Manse-AT4-13 and Manse-AT1-11. Metabolism by trypsin produced the same deletion peptides, but the major product due to this enzyme was Manse-AT4-11. Hydrolysis of Manse-AT by CA could only be partially inhibited by high doses of aprotinin (36%), and the CA extract also cleaved Manse-AT between M8 and T9 to produce Manse-AT1-8. A trypsin-like peptidase appears to be the major enzyme present in the CA of larval L. oleracea that acts to metabolise Manse-AS and Manse-AT. In addition, an unidentified enzyme that cleaves between M and T residues degraded Manse-AT.

Expression and localization of the Spodoptera frugiperda allatotropin (Spofr-AT) and allatostatin (Spofr-AS) genes

Manduca sexta allatotropin and allatostatin were the first corpora allata (CA) regulating neuropeptides identified from Lepidoptera. Recently, we cloned the allatotropin (Spofr-AT) and the allatostatin (Spofr-AS) genes from the fall armyworm Spodoptera frugiperda. Using one-step RT-PCR for semi-quantification of the gene expression, we now demonstrate that three mRNA isoforms of the Spofr-AT gene and the Spofr-AS gene are expressed in brain, digestive tract, and reproductive organs of larvae, pupae, and adults in a time- and tissue-specific manner. Expression rates in the brain and in various parts of the digestive tract prove the dual role of the peptides as brain/gut (neuro)peptides. The functional meaning of ovarian and testes expression of the genes is not yet clear, although myoregulatory properties of the peptides are probable. The tissue-specific localization of the prohormone expression, as demonstrated by whole mount in situ hybridization, confirms the overall distribution of the prohormones as shown by RT-PCR and supports the pleiotropic functions of the peptides.

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.

Biological activity of Manduca sexta allatotropin-like peptides, predicted products of tissue-specific and developmentally regulated alternatively spliced mRNAs

The insect neuropeptide, allatotropin (Manse-AT), exerts multiple functions including the stimulation of juvenile hormone (JH) biosynthesis in adults and the inhibition of active ion transport across the midgut epithelium of feeding larvae. The Manse-AT gene is expressed in multiple regions of the nervous system as three mRNAs that differ by alternative splicing. The specific mRNA isoform present differs in a tissue- and developmental-specific manner thus providing a mechanism for the regulated production of peptides specific to each isoform. These peptides are predicted to include three allatotropin-like (Manse-ATL) peptides that exhibit limited structural identity to Manse-AT and overlapping biological activities.

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%).

Restriction of nutrient intake results in the increase of a specific Manduca sexta allatotropin (Manse-AT) mRNA in the larval nerve cord

The Manduca allatotropin (Manse-AT) gene is expressed as three mRNAs that differ from each other by alternative splicing. The level of one of these mRNAs (RNA-3) is specifically increased in the nerve cord of last instar larvae that were starved, parasitized, or fed the ecdysteroid agonist RH-5992. Each of these treatments results in reduction of feeding and increased levels of juvenile hormone (JH). The normal decline in JH biosynthesis by the corpora allata does not occur in starved or RH-5992-fed larvae. The increase in RNA-3 levels has the capacity to increase the production of Manse-AT and two related peptides that may be part of the complex response of larvae to nutrient deprivation.

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.

Alternative splicing of transcripts expressed by the Manduca sexta allatotropin (Mas-AT) gene is regulated in a tissue-specific manner

The Manduca allatotropin (Mas-AT) gene is expressed as at least three mRNA isoforms that differ from each other by alternative splicing. The location at which the alternative exons are included in the mature mRNAs occur within the open reading frame, so that three different propeptides are predicted as translation products. In the pharate adult insect, the major mRNA isoform expressed in the brain and frontal ganglion differs from that expressed in the nerve cord. Examination of the deduced translations of the alternative exons reveals the presence of three additional Mas-AT-like sequences that are flanked by basic amino acid residues. Therefore, the Mas-AT-like sequences present within the gene may be derived from a duplication of an ancestral Mas-AT-like sequence followed by divergence.

Allatotropin-like neuropeptide in the cockroach abdominal nervous system: myotropic actions, sexually dimorphic distribution and colocalization with serotonin

Allatotropin (AT) was isolated from the moth Manduca sexta as a peptide stimulating biosynthesis of juvenile hormone in the corpora allata, but has also been shown to be cardioactive in the same species. Here, we have investigated the presence and biological activity of AT-like peptide in the cockroaches Leucophaea maderae and Periplaneta americana with focus on abdominal ganglia and their target tissues. An antiserum to M. sexta AT was used for immunocytochemical mapping of neurons in the abdominal ganglia. A small number of interneurons and efferent neurons were found AT-like immunoreactive (AT-LI) in each of the abdominal ganglia. A prominent sexual dimorphism was detected in the terminal abdominal ganglion: in L. maderae the male ganglion there are approximately 18 AT-LI neurons with cell bodies posteriorly and efferent axons in the genital nerves; in the female ganglion 4-5 AT-LI cell bodies (with efferent axons) were found in the same region. Correlated with the extra efferents in males, the male accessory glands are richly supplied by AT-LI fibers and in females a less prominent innervation was seen in oviduct muscle. A similar dimorphism was seen in abdominal ganglia of P. americana. A sexual dimorphism was also detected in the abdominal ganglia A4-A6 of L. maderae. In each of these ganglia, approximately 8-10 large AT-LI neuronal cell bodies were found along the midline; in females these neurons have significantly larger cell bodies than in males. In both sexes, and both cockroach species, two large dorsal midline neurons were detected in A-5 and 6, which seem to send axons to the hindgut: the rectal pads of the hindgut are supplied by arborizing AT-LI axons. In males and females of both species, efferent AT-LI axons from midline neurons in A3-A6 supply the lateral heart nerves and other neurohemal release sites with arborizations. The efferent midline neurons of females contain colocalized serotonin-immunoreactivity. We tested the in vitro actions of M. sexta AT on muscle contractions in the L. maderae hindgut and the abdominal heart of both species. The frequency of contractions in the hindgut increased dose dependently when applying AT at 5 x 10(-8) to 5 x 10(-6) M (maximal response at 5 x 10(-7) M). Also the frequency of contractions of the heart increased by application of AT (threshold response at 5 x 10(-9) M). This effect was more prominent in males of both species (maximal response was a 35-40% increase in males and 10-20% in females). In conclusion, an AT-like peptide is present in neurons and neurosecretory cells of cockroach abdominal ganglia and seems to play a role in control of contractions in the hindgut and heart and also to have some function in male accessory glands and oviduct.

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

Allatotropin (AT) is an insect neuropeptide isolated from the tobacco hornworm, Manduca sexta, stimulates juvenile hormone (JH) biosynthesis by the corpora allata. A cDNA isolated from the true armyworm, Pseudaletia unipuncta, encodes a 135 amino acid AT precursor peptide which contains the AT peptide, with processing sites necessary for its endoproteolytic cleavage and amidation, plus two additional peptides of unknown function. The encoded AT peptide is identical to that isolated from M. sexta and Agrius convolvuli. Southern blot analysis indicated that AT is a single copy gene per haploid genome and is present in two allelic forms. A single transcript of approximately 1.5 kilobases was detected by northern blot analysis. The expression of the AT gene was analyzed during development from sixth instar larvae to five day-old moths. Initial expression was observed in late pupae and this expression was maintained throughout the adult stages in both sexes. In one day-old moths, expression was at its lowest level of the stages that express AT mRNA but levels increased in day 3 and day 5 adults. This pattern of AT expression in adult P. unipuncta moths mirrors that of JH biosynthesis and supports the notion that AT may act in the adult stages. Immunohistochemistry and in situ hybridization revealed that AT expression was localized to numerous structures of the nervous system, suggesting that AT may have functions distinct from regulation of JH biosynthesis.

Juvenile hormone biosynthesis by corpora allata of larval tomato moth, Lacanobia oleracea, and regulation by Manduca sexta allatostatin and allatotropin

Juvenile hormone (JH) biosynthesis and the effects of synthetic Manduca sexta allatostatin (Mas-AS) and M. sexta allatotropin (Mas-AT) were investigated in isolated corpora allata (CA) of Vth stadium larvae of the tomato moth, Lacanobia oleracea. Reversed-phase high-performance liquid chromatography (RP-HPLC) of JH extracted from CA shows that larvae produce predominantly JH II and its corresponding acid. It appears that the acid homologue is a result of JH esterase activity in the CA (and other tissues) rather than the lack of JH acid methyltransferase. Mean rates of synthesis (100-200fmol/pr/h) were inhibited ca. 70% by Mas-AS and stimulated in a dose-dependent manner up to three times by Mas-AT. However, Mas-AS had no significant effect on Mas-AT-stimulated rates of JH biosynthesis. Using RP-HPLC and an enzyme-linked immunosorbent assay (ELISA) to Mas-AT, a peak of Mas-AT-like immunoreactivity was detected in larval L. oleracea brain homogenates. Co-elution of this immunoreactive peak with synthetic Mas-AT suggests that this neuropeptide is also present in 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.