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PubMed1994

Dynamics and metamorphosis of an identifiable peptidergic neuron in an insect.

Eclosion hormone (EH) is a 7000 Da peptide that triggers ecdysis behavior in insects. In the moth, Manduca sexta, EH is found in two pairs of ventromedial (VM) cells in the brain which send their axons down the ventral nerve cord to a neurohemal site in the proctodeal nerve in the larva and pupa. During adult development, these cells send axon collaterals to the corpora cardiaca where they form a new release site used for adult eclosion. Studies of bioassayable peptide during the 5th larval instar and the larval-pupal transformation revealed that after depletion at ecdysis, the VM cells showed a transient increase in EH found in their cell bodies and axons. By contrast, their terminals in the proctodeal nerve showed a gradual accumulation of peptide followed by a release of over 90% of the stored material at pupal ecdysis. In situ hybridization analysis on whole mounts of the brains showed that the VM cells always contained EH mRNA with increased accumulation during the larval and pupal molting periods with a slight decline just before ecdysis. High levels of EH mRNA were found in brains of diapausing pupae. During the first two-thirds of adult development, mRNA accumulated to high levels, then slowly declined until ecdysis. EH mRNA levels then increased and remained at intermediate levels up to 3 days after adult eclosion. At no time was EH mRNA found in the lateral neurosecretory cell cluster previously reported to produce EH for adult eclosion.

Animals↗
PubMed1982

The action of peptides and cyclic nucleotides on the nervous system of an insect.

Eclosion hormone (EH) is a moderate-sized peptide that acts on the insect nervous system to release the stereotyped behaviors involved in shedding the old skin (eclosion) as well as to activate new reflex pathways. The action of the peptide has been studied by using two preparations. The first preparation involves the preeclosion and eclosion motor programs that can be released from the isolated abdominal central nervous system (CNS) in response to EH. The target sites associated with the release of these programs are scattered throughout the CNS, each apparently being associated with a segmental component of one of the programs. A fully coordinated behavioral response requires that all these segmental elements be exposed to the peptide. The second preparation has allowed the cellular analysis of a simple multisegmental reflex that is turned on by EH. The data indicate that the reflex pathway is activated by the peptide through the selective action on a key synaptic junction. In the case of both of these preparations, the action of EH appears to involve an increase in cyclic GMP levels in the CNS. The manner by which these increases result in altered neuronal activity remains unknown.

Action Potentials↗
PubMed1971

Practical aspects of insect control by juvenile hormone.

The development of juvenile hormone (JH) analogues for insect control, and their laboratory and field testing, are now being carried out on an industrial scale. Studies of the hormone action at the cellular level, and of the many implications of JH applications on various stages of the insect life-cycle, are lagging because such studies require long-term scientific involvement. Although many analogues have little specificity for particular insects, the ultimate effects may be very different. Various considerations that may influence the commercial development of JH are discussed.

Insect Control↗
PubMed2002

A novel putative insect chitinase with multiple catalytic domains: hormonal regulation during metamorphosis.

We have used differential display to identify genes that are regulated by juvenile hormone in the epidermis of the beetle Tenebrio molitor. One of the genes encodes T. molitor chitinase 5 (TmChit5), a chitinase possessing an unusual structure. Sequence analysis of TmChit5 identified five 'chitinase units' of approx. 480 amino acids with similarity to chitinase family 18. These units are separated by less conserved regions containing putative PEST (rich in proline, glutamic acid, serine and threonine) sequences, putative chitin-binding domains and mucin domains. Northern-blot analysis identified a single transcript of approx. 9 kb, whose abundance correlated with that of 20-hydroxyecdysone during metamorphosis. Injection of pupae with 20-hydroxyecdysone alone, or in combination with cycloheximide, indicated that TmChit5 expression is directly induced by the hormone. Further experiments indicated that methoprene (a juvenile hormone analogue) indirectly induced TmChit5 mRNA expression. On the basis of the present results and previous studies, we propose a molecular mechanism for cuticle digestion during the moulting process.

Amino Acid Sequence↗
PubMed1995

Stimulation of glycogenolysis by three locust adipokinetic hormones involves Gs and cAMP.

Insect adipokinetic hormones (AKHs) have been shown to mobilize fat body carbohydrate by glycogen phosphorylase activation. In this study, the signal transduction pathways of AKH-I, -II and -III from the migratory locust are further elucidated. We show that the AKHs enhance fat body cAMP levels in vitro. For all hormones, maximal levels are reached after 1 min and correspond to a 200% increase compared to resting levels. Although cAMP levels induced by massive doses of AKH-I, -II and -III are equal, AKH-III is the most potent when applied in a physiological dose. This difference in potency also applies to glycogen phosphorylase activation. Cholera toxin (CTX) likewise ennhaces cAMP levels and phosphorylase activity, however pertussis toxin (PTX) has no effect. Increases induced by CTX and AKH are not additive, suggesting that they share the same pathway. Phosphorylase activation by the AKHs is strongly attenuated by guanosine-5'-O-(2-thiodiphosphate) (GDP beta S). These results demonstrate a role for cAMP in AKH signal transduction and indicate that the AKH receptor(s) are coupled to cAMP formation and glycogen phosphorylase activation via the stimulatory guanine nucleotide-binding protein (Gs).

Animals↗
PubMed1977

Ultrastructural localization of juvenile hormone biosynthesis by insect corpora allata.

The conversion of exogenous 3H-farnesenic acid to 3H-methyl farnesoate and 3H-C16 juvenile hormone (JH) has been followed in the corpus allatum (CA) cells of the desert locust Schistocerca gregaria by means of electron microscopic autoradiography. Aerobic and anaerobic 'chase' incubations have been used to modify the quantities of these three compounds within the CA cells. Under all incubation conditions, radiolabel is found associated almost exclusively with the subcellular membrane systems - smooth endoplasmic reticulum (SER) and Golgi elements - and with the mitochondria. CA cells are probably similar to vertebrate steriod-synthesizing cells in that the secretory product is synthesized in the SER and mitochondria. Radiolabel was found to be present in all cells of the CA suggesting that all cells are capable of at least the final two stages of JH biosynthesis (the esterification and epoxidation of 3H-farnesenic aid). This indicates that JH biosynthesis may be regulated through changes in the biosynthetic capabilities of individual cells rather than through changes in the total number of cells engaged in biosynthesis. Radiolabel was not observed to be associated with any distinctive cellular product, a result which provides additional evidence for the suggestion that the release of JH from the CA is governed by laws of simple physical diffusion.

Animals↗
PubMed2000

Cloning and sequence analysis of cDNA for diuretic hormone receptor from the Bombyx mori.

The insect diuretic hormone (DH) binds to their receptor in malpighian tubules, and stimulates water secretion and cAMP synthesis. Complementary DNA encoding a diuretic hormone receptor was cloned from the malpighian tubules of Bombyx mori. The cloned cDNA encodes a protein consisting of 391 amino acid residues with the seven transmembrane domains. The receptor protein is homologous with that of other insects, and is structurally related to G-protein coupled receptors such as corticotropin relating factor (CRF), secretin, and vasoactive intestinal peptide.

Amino Acid Sequence↗
PubMed1989

Expansion of the central arborizations of persistent sensory neurons during insect metamorphosis: the role of the steroid hormone, 20-hydroxyecdysone.

During insect metamorphosis many larval neurons persist but are modified to serve new behavioral roles at later stages of life. For example, certain larval mechanosensory neurons expand their central arborizations during pupal development and evoke a different behavioral response, the gin trap reflex. The role of the insect steroid hormone, 20-hydroxyecdysone (20-HE) in this developmental change was investigated by removing the normal source of the hormone, followed by topical application of 20-HE to the peripheral somata of the sensory neurons. In prepupal animals that were ligated between the abdomen and thorax to remove the source of ecdysteroids the sensory neurons retained a larval arborization pattern. Topical application of 20-HE to the peripheral sensory neuron somata caused the treated neurons to undergo terminal arbor expansion within the CNS. The treated sensory neurons were not able to evoke the normal pupal behavioral response, but instead caused a larval-like reflex response. In a previous study, sensory neurons that were treated peripherally with a juvenile hormone analog during the commitment peak of ecdysteroids were shown to retain a larval arborization pattern at pupation and to not evoke the gin trap reflex (Levine et al., 1986). Within 4 d of pupation, however, these neurons belatedly developed expanded terminal arbors and evoked the pupal reflex. In the present study, similarly treated animals were ligated at pupation to block the surge in ecdysteroids that normally occurs at this time. This treatment prevented both the delayed expansion and the reflex, whereas topical 20-HE application induced growth and allowed the treated sensory neurons to evoke the gin trap reflex. It is concluded that both 20-HE and juvenile hormone act directly on the cell bodies of the sensory neurons to regulate the growth of their central processes. This growth is necessary but not sufficient for the development of the gin trap reflex, suggesting that other steroid-dependent changes must also occur within the CNS. Thus, as in the vertebrates, steroid hormones direct important developmental events within the insect nervous system.

Animals↗
PubMed2006

Structural studies of a potent insect maturation inhibitor bound to the juvenile hormone esterase of Manduca sexta.

Juvenile hormone (JH) is an insect hormone containing an alpha,beta-unsaturated ester consisting of a small alcohol and long, hydrophobic acid. JH degradation is required for proper insect development. One pathway of this degradation is through juvenile hormone esterase (JHE), which cleaves the JH ester bond to produce methanol and JH acid. JHE is a member of the functionally divergent alpha/beta-hydrolase family of enzymes and is a highly efficient enzyme that cleaves JH at very low in vivo concentrations. We present here a 2.7 A crystal structure of JHE from the tobacco hornworm Manduca sexta (MsJHE) in complex with the transition state analogue inhibitor 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP) covalently bound to the active site. This crystal structure, the first JHE structure reported, contains a long, hydrophobic binding pocket with the solvent-inaccessible catalytic triad located at the end. The structure explains many of the interactions observed between JHE and its substrates and inhibitors, such as the preference for small alcohol groups and long hydrophobic backbones. The most potent JHE inhibitors identified to date contain a trifluoromethyl ketone (TFK) moiety and have a sulfur atom beta to the ketone. In this study, sulfur-aromatic interactions were observed between the sulfur atom of OTFP and a conserved aromatic residue in the crystal structure. Mutational analysis supported the hypothesis that these interactions contribute to the potency of sulfur-containing TFK inhibitors. Together, these results clarify the binding mechanism of JHE inhibitors and provide useful observations for the development of additional enzyme inhibitors for a variety of enzymes.

Acetone↗
PubMed1996

Molecular cloning and function expression of a diuretic hormone receptor from the house cricket, Acheta domesticus.

Insect diuretic hormones regulate fluid and ion secretion and the receptors with which they interact are attractive targets for new insect control agents. Recently, a diuretic hormone receptor from the moth Manduca sexta was isolated by expression cloning and found to be a member of the calcitonin/secretin/corticotropin releasing factor family of G-protein coupled receptors [Reagan J. D. (1994) J. Biol. Chem. 269, 9-12]. Degenerate oligonucleotides were designed based upon conserved regions in this receptor family and used to isolate a diuretic hormone receptor from the house cricket, Acheta domesticus. The complementary DNA isolated encodes a protein consisting of 441 amino acids with seven putative membrane spanning regions. Interestingly, unlike the M. sexta diuretic hormone receptor, the cricket diuretic hormone receptor contains a putative signal sequence. The receptor shares 53% and 38% sequence identity with the M. sexta diuretic hormone and human corticotropin releasing factor receptors respectively. When expressed in COS-7 cells, the receptor binds A. domesticus diuretic hormone with high affinity and stimulates adenylate cyclase with high potency. Four other insect diuretic hormones are considerably less effective at stimulating adenylate cyclase in COS-7 cells transfected with the receptor. This is in contrast to the M. sexta diuretic hormone receptor which is stimulated by all five insect diuretic hormones with high potency.

Amino Acid Sequence↗
PubMedDate not supplied

Effects of a fat body extract on larval midgut cells and growth of lepidoptera.

Treatment with fat body extract (FBX) from pupae of the tobacco hornworm, Manduca sexta, caused mortality in larvae of two pest lepidopterans, the gypsy moth, Lymantria dispar, and the cotton leafworm, Spodoptera littoralis. In FBX-treated larvae, the feeding rate was depressed, causing reduced weight gain and then larval death. Their midgut showed formation of multicellular layers of midgut epidermis, indicating stem-cell hyperplasia. Hence, the integument of FBX-treated larvae had a double cuticle, indicating induction of premature molting. But radioimmunoassay measurements confirmed that the amount of ecdysteroids in FBX was too low to be responsible for the molt-inducing effects observed after treatment with FBX. With midgut stem cell cultures in vitro, addition of FBX to the culture medium stimulated cell proliferation and differentiation in a concentration-dependent manner. This effect was compared with those of insect molting hormones, ecdysone and 20-hydroxyecdysone; an ecdysteroid agonist, RH-2485; and a purified protein from FBX (multiplication factor). This article describes the mode of action of FBX and possible interplay between fat body factor(s) and insect hormones in the development and metamorphosis of the insect midgut.

Animals↗