Biochemical aspects of juvenile hormone action in insects.
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Amino Acids↗
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Juvenile hormone acid methyltransferase: a key regulatory enzyme for insect metamorphosis.
Juvenile hormone (JH) acid methyltransferase (JHAMT) is an enzyme that converts JH acids or inactive precursors of JHs to active JHs at the final step of JH biosynthesis pathway in insects. By fluorescent mRNA differential display, we have cloned a cDNA encoding JHAMT from the corpora allata (CA) of the silkworm, Bombyx mori (BmJHAMT). The BmJHAMT cDNA encodes an ORF of 278 aa with a calculated molecular mass of 32,544 Da. The predicted amino acid sequence contains a conserved S-adenosyl-l-methionine (SAM) binding motif found in the family of SAM-dependent methyltransferases. Purified N-terminal 6xHis-tagged recombinant BmJHAMT protein expressed in Escherichia coli catalyzed conversion of farnesoic acid and JH acids I, II, and III to their cognate methyl esters in the presence of SAM, confirming that this cDNA encodes a functional JHAMT. Putative orthologs, DmJHAMT and AgJHAMT, were identified from the genome sequence of the fruit fly Drosophila melanogaster, and a malaria vector, Anopheles gambiae, respectively. Northern blot and quantitative RT-PCR analyses revealed that the BmJHAMT gene was expressed specifically in the CA throughout the third and fourth instar. At the beginning of the last (fifth) instar, the expression level of BmJHAMT declined rapidly and became undetectable by day 4 and remained so until pupation. Correlation of the BmJHAMT gene expression and the JH biosynthetic activity in the CA suggests that the transcriptional suppression of the BmJHAMT gene is crucial for the termination of JH biosynthesis in the CA, which is a prerequisite for the initiation of metamorphosis.
Amino Acid Sequence↗
Peptide hormones, steroid hormones, and puffs: mechanisms and models in insect development.
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Amino Acid Sequence↗
Recent advances in hormonal regulation of water metabolism in terrestrial insects.
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Animals↗
Expression of a 26S proteasome ATPase subunit, MS73, in muscles that undergo developmentally programmed cell death, and its control by ecdysteroid hormones in the insect Manduca sexta.
MS73, an ATPase regulatory subunit of the 26S proteasome in the moth Manduca sexta, is shown to be expressed at a high level only in muscles that are undergoing developmentally programmed cell death, or which are destined to do so. The amount of MS73 is increased by more than two-fold just before death in each of three different muscles that die at different times, under different developmental controls. An ecdysteroid (moulting hormone) agonist, RH-5849, that prevents the occurrence of programmed cell death in two of these muscles also prevents the normally occurring rise in level of MS73 in these muscles. This evidence is consistent with a role for MS73 in programmed cell death.
Adenosine Triphosphatases↗
Enhanced haemolymph circulation by insect ventral nerve cord: hormonal control by Pseudaletia unipuncta allatotropin and serotonin.
The ventral diaphragm (VD) in many insects is a muscular membrane that essentially partitions a perineural sinus from the rest of the abdomen. In the true armyworm moth Pseudaletia unipuncta (Lepidoptera: Noctuidae) we describe how the VD is characterized by a series of aliform muscles inserted into a tissue matrix that is fused to the dorsal surface of the ventral nerve cord (VNC) itself. Because of this arrangement, the abdominal VNC can attain high rates of lateral oscillation, and is capable of directing haemolymph flow. We have previously demonstrated Manduca sexta allatotropin (Manse-AT)-like immunoreactivity throughout the central nervous system (CNS) in P. unipuncta, and that both Manse-AT and serotonin (5-HT) are dose-dependent stimulators of the dorsal vessel. Here we describe both Manse-AT- and 5-HT-like immunoreactivity associated with the VD. Furthermore, both Manse-AT and 5-HT are dose-dependent stimulators of the rates of VNC oscillation, and together are capable of maintaining highly elevated rates of VNC oscillation for extended periods of time. These data indicate that both the dorsal vessel and the VD/VNC are similarly modulated by both Manse-AT and 5-HT, and that VNC oscillations play a more active role in overall haemolymph circulation than previously recognized.
Animals↗
The effect of insecticide on adipokinetic hormone titre in the insect body.
The effect of an insecticide, permethrin (Ambush 25 EC), on the titre of two adipokinetic hormones in the central nervous system (CNS) and haemolymph of the firebug Pyrrhocoris apterus (L) was tested. Doses of 2.5, 12.5 and 25 ng of the insecticide elicited no significant effect on the titre of the adipokinetic peptides in CNS, but caused their dramatic elevation in the haemolymph of both macropterous and reproductive brachypterous bugs. Changes in diapausing brachypterous bugs were minimal and not significant. Using high-performance liquid chromatography (HPLC) and competitive ELISA, both adipokinetic peptides of P apterus (Pyrap-AKH and Peram-CAH-II) were identified and quantified in the CNS of all experimental groups. The ratios of the two peptides in the CNS of the bugs used were affected by insecticide treatment, but in all three groups of bugs the Pyrap-AKH level remained dominant. The insecticide-treated bugs were compared with those exposed to forced running (shaking) and dark shock. Both factors also acted as stressors and enhanced the titre of adipokinetic peptides in the haemolymph but had no effect on hormone titre in CNS. The results indicate an involvement of adipokinetic peptides in the response of insect to various stressors including insecticides.
Animals↗
Use and role of invertebrate models in endocrine disruptor research and testing.
Historically, invertebrates have been excellent models for studying endocrine systems and for testing toxic chemicals. Some invertebrate endocrine systems are well suited for testing chemicals and environmental media because of the ease of using certain species, their sensitivity to toxic chemicals, and the broad choice of models from which to choose. Such assays will be useful in identifying endocrine disruptors to protect invertebrate populations and as screening systems for vertebrates. Hormone systems are found in all animal phyla, although the most simple animals may have only rudimentary endocrine systems. Invertebrate endocrine systems use a variety of types of hormones, including steroids, peptides, simple amides, and terpenes. The most well-studied hormone systems are the molting and juvenile hormones in insects, the molting hormones in crustaceans, and several of the neurohormones in molluscs and arthropods. These groups offer several options for assays that may be useful for predicting endocrine disruption in invertebrates. A few invertebrate phyla offer predictive capabilities for understanding vertebrate endocrine-disrupting chemicals. The echinoderms, and to a lesser extent molluscs, have closer evolutionary relationships with the vertebrates than the arthropods and these phyla. The recently identified estrogen receptor structure within the genome of the marine gastropod, Aplysia, indicates that the estrogens, and probably the basic steroid receptor, are quite old evolutionarily. This review of the recent literature confirms the effects of some endocrine-disrupting chemicals on invertebrates--tributyltin on snails, pesticides on insects and crustaceans, and industrial compounds on marine animals.
Animals↗
Do thyroid hormones function in insects?
Earlier work demonstrated that phenoxy-phenyl compounds such as fenoxycarb and thyroxine mimicked the effects of JH III in causing a reduction in volume of the follicle cells of Locusta migratoria. While these compounds were only moderately effective, a derivative of thyroxine, 3,3',5-triiodothyronine (T3) was as effective as JH III, and T3 has been shown to bind to the same membrane receptor and activate the same pathway as JH III. The current paper shows that other thyroxine derivatives vary in activity. 3,3', 5'-Triiodothyronine (reverse T3) is inactive. 3,5-Diiodothyronine (T2) is more active than JH III, while its relatives (iodines at 3', 5' or at 3,3') are inactive. When follicles are exposed in vitro to rhodamine conjugated T3, the fluorescent compound can be seen to enter the cells and accumulate there: this process is inhibited by cycloheximide or by a temperature of 0 degrees C. The accumulation is antagonised by JH III but not JH I (which does not bind to the JH III membrane receptor) and by an antiserum raised against the putative membrane receptor protein. The action of T3, but not T2, is inhibited by 6-n-propyl-2-thiouracil or by aurothioglucose, both known to inhibit deiodinases. The activity of T3, but not of T2, increases with time of exposure to the follicle cells. These facts suggest that T3 enters the cells by receptor mediated endocytosis and is converted to a more active compound. Immunoreactivity to T3, but not thyroxine, can be detected in the haemolymph of locusts, and the titre varies slightly with the gonotrophic cycle. The food shows immunoreactivity for both thyroxine and T3. These findings suggest that thyroid hormones are ingested by locusts and have the potential to be used as hormonal signals in the control of egg production.
Animals↗
Detection and microsequencing of juvenile hormone-binding proteins of an insect by the use of an iodinated juvenile hormone analog.
An [125I]iodinated juvenile hormone (JH) analog can be used as a sensitive and highly selective probe for the visualization of high-affinity, (JH)-specific binding proteins from insect hemolymph samples. The proteins can be detected in their native form using a two-dimensional (isoelectric focusing then native gradipore gel) separation of the crude protein mixture containing the 125I-labeled iodinated JH analog. The proteins can be transferred to activated glass fiber paper by electroblotting, and the location of the bound gamma-emitter can be found by exposure of the dried gel or the electroblot to X-ray film. The radiolabeled protein spot can be excised from the Coomassie-stained glass fiber paper and subjected directly to gas-phase N-terminal amino acid sequencing. This non-destructive, non-denaturing technique may have wide applicability in identifying and sequencing ligand-specific binding proteins in complex mixtures.
Amino Acid Sequence↗
Systemic activity of a juvenile hormone analog.
The peptidic analog of insect juvenile hormone, ethyl pivaloyl-L-alanyl-p-aminobenzoate with enormous biological activity on the red cotton bug, Dysdercus cingulatus, has pronounced systemic effect in sunflower plants. The compound is absorbed by the plant tissues and appears to be translocated throughout the plant system in active form. There is some evidence that juvenile hormone analogs of other types also have similar systemic effects. The discovery of systemic action should aid in the possible utilization of juvenile hormone analogs in insect control programs.
Animals↗
Bombyx and Manduca prothoracicotropic hormones: an immunologic test for relatedness.
Prothoracicotropic hormone (PTTH) controls the synthesis of ecdysteroids (molting hormones) by the insect prothoracic gland and thereby plays a critical role in insect growth, molting, and metamorphosis. PTTH has been purified, and cDNA clones obtained, from only one insect, the silkmoth Bombyx mon. Recently, a partial amino acid sequence was obtained for-a putative PTTH from the tobacco hornworm, Manduca sexta, and the data suggested an unexpected homology to a vertebrate retinoid binding protein rather than to the Bombyx PTTH. In this study, a monoclonal antibody against the Bombyx PTTH was added to in vitro assays that assess the ability of partially purified Manduca PTTH to stimulate prothoracic gland ecdysteroid and protein synthesis. The results indicate that Bombyx and Manduca PTTHs are indeed members of the same protein family that have likely diverged in the PTTH receptor-binding region.
Adsorption↗
Prothoracicotropic hormone activity in the embryonic brain of the tobacco hornworm, Manduca sexta.
Head segments and brains were extirpated from embryos of the tobacco hornworm, Manduca sexta, extracted and the resulting extracts assayed for prothoracicotropic hormone (PTTH) activity on prothoracic glands from day 3 fifth instar larvae and day 0 pupae. Dose-response curves were generated and indicated the presence of PTTH activity in embryonic brains and head segments, suggesting a role(s) for this neurohormone during embryogenesis. Maximal PTTH activity was found in brains from embryos 117 h post-oviposition, just prior to hatching, but activity was also noted in head segments as early as 24 h post-oviposition. These data on PTTH and those on ecdysteroids and juvenile hormones in embryos suggest that these 3 classes of hormones which control insect post-embryonic development, may also be involved in the regulation of developmental processes in the embryo.
Animals↗
Preventing insect diapause with hormones and cholera toxin.
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Animals↗
Crystallization of the 'brain' hormone of an insect.
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Animals↗
Structure of locust adipokinetic hormone, a neurohormone that regulates lipid utilisation during flight.
Adipokinetic hormone, isolated from locust corpora cardiaca, has been identified as a blocked peptide: PCA-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2. The detailed structure is based on mass spectrometric data, substantiated in part by dansyl-Edman and carboxypeptidase data on thermolytic fragments. This is the first peptide hormone from an insect neuroendocrine organ to be fully characterised.
Amino Acid Sequence↗
Isolation and identification of ecdysteroid phosphates and acetylecdysteroid phosphates from developing eggs of the locust, Schistocerca gregaria.
Maturing eggs of the desert locust, Schistocerca gregaria, contain a variety of ecdysteroid (insect moulting hormone) conjugates and metabolites, four of which have been previously isolated from polar extracts and identified as ecdysonoic acid, 20-hydroxyecdysonoic acid, 3-acetylecdysone 2-phosphate and ecdysone 2-phosphate. In the present study we have isolated eight additional ecdysteroids from similar late-stage eggs by high-performance liquid chromatography. The 22-phosphate esters of ecdysone, 2-deoxyecdysone, 20-hydroxyecdysone and 2-deoxy-20-hydroxyecdysone, all of which were first identified as ecdysteroid components of newly-laid eggs of S. gregaria, were identified by co-chromatography with authentic compounds and by physicochemical techniques. The remaining compounds were identified as 3-acetyl-20-hydroxyecdysone 2-phosphate, 3-epi-2-deoxyecdysone 3-phosphate, 3-acetylecdysone 22-phosphate and 2-acetylecdysone 22-phosphate by fast atom bombardment mass spectrometry, p.m.r. spectroscopy and analysis of the steroid moieties after enzymic hydrolysis. The latter two compounds, after isolation, are susceptible to nonenzymic acetyl migration and deacetylation to give mixtures of ecdysone 22-phosphate and its 2- and 3-acetate derivatives. The possible role and significance of these ecdysteroid conjugates with respect to the control of hormone titres in insect eggs is discussed.
Animals↗
Structure and significance of mandibular organ-inhibiting hormone in the crab, Cancer pagurus. Involvement in multihormonal regulation of growth and reproduction.
Current evidence indicates that methyl farnesoate is the crustacean equivalent of the juvenile hormones of insects. This putative hormone is produced by the mandibular organs and is negatively regulated by a neuropeptide produced and secreted by the X-organ-sinus gland complex of the eyestalk. To identify this neuropeptide, a bioassay was developed which measures the inhibition of methyl farnesoate synthesis by mandibular organs exposed to fractionated sinus gland extracts from the crab, Cancer pagurus. Two neuropeptides, named mandibular organ-inhibiting hormones (MOIH-1 and -2) repressed methyl farnesoate synthesis. MOIH-1 was fully sequenced by automated Edman degradation of endoproteinase-derived fragments and further characterized by mass spectrometry. This peptide consisted of 78 residues (Mr 9235.6), with unblocked termini and three intrachain disulfide bridges. MOIH-2 appeared to be almost identical to MOIH-1 with the exception of a Gln for Lys substitution at position 33. Comparison with previously sequenced crustacean neuropeptides shows that these MOIHs are members of the ever expanding crustacean hyperglycemic hormone family, with significant sequence similarity to molt-inhibiting hormones (MIHs). It is possible that these two structurally similar peptides (MIH, MOIH) may control mutually exclusive physiological phenomena (somatic and gonadal growth), suggesting a complex hormonal integration of these processes in crustaceans.
Amino Acid Sequence↗