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PubMedDate not supplied

Naturally occurring insect growth regulators. II. Screening of insect and plant extracts as insect juvenile hormone mimics.

Ethereal extracts prepared from the larvae, pupae, or eggs of 10 species of insects and from various parts of 343 species of higher plants were screened for juvenilizing effects against Tenebrio molitor and Oncopeltus fasciatus. Activity in both species was shown by an extract of the larvae of the stable fly, Stomoxys calcitrans, whereas an extract of the pupae was active in O. fasiatus only. Extracts of two plant species (Echinacea angustifolia roots and Chamaecyparis lawsoniana seeds) showed high juvenilizing activity in T. MOLITOR, AND EXtracts of five plant species (Clethra alnifolia stems, leaves, and fruits, Sassafras albidum roots and root bark, Eucalyptus camaldulensis stems and bark, Pinus rigida twigs and leaves, and Iris douglasiana roots, stems, and fruits) were highly active in O. fasciatus an extract of Tsuga canadensis leaves showed lower activity in this insect. Extracts of 16 species of plants showed high insecticidal activity (mortality) in O. fasciatus but lacked juvenilizing properties in both species of test insects.

Animals↗
PubMed1993

Ligand binding by a recombinant insect juvenile hormone binding protein.

A cDNA for the hemolymph juvenile hormone binding protein (JHBP) of larval Manduca sexta has been isolated, sequenced, and expressed in an insect cell line. A recombinant baculovirus, containing the JHBP cDNA fused to the p10 promoter of Autographa californica nuclear polyhedrosis virus, was constructed. Insect cells (Sf9) infected with this virus secreted recombinant JHBP (rJHBP) into the medium (> 50 micrograms/mL), and cotranslational removal of an 18 amino acid leader sequence was observed. rJHBP was cross-reactive with an antiserum prepared to the hemolymph JHBP and was specifically labeled by [3H]EHDA, a photoaffinity analog of JH II, demonstrating that rJHBP was an isoform of the previously reported 32-kDa JHBP [Lerro, K. A., & Prestwich, G.D. (1990) J. Biol. Chem. 265, 19800-19806]. rJHBP was purified from insect cell medium to homogeneity by ion-exchange and gel-filtration chromatography. The purified rJHBP had a higher affinity (KD = 11 nM for JH I and KD = 42 nM for JH II) than that reported for crude hemolymph JHBP (KD = 80 nM for JH I). The circular dichroism (CD) spectrum of purified rJHBP indicated 34% alpha-helix and 23% beta-sheet. The CD spectra of rJHBP in the presence and absence of JH II were the same, indicating no change in secondary structure induced by ligand binding. Thus, the rJHBP expressed in insect cells binds JHs and is suitable for structural and functional analysis.

Amino Acid Sequence↗
PubMed1996

Cell culture approaches to understanding the actions of steroid hormones on the insect nervous system.

During metamorphosis of the hawkmoth, Manduca sexta, ecdysteroids regulate the dendritic remodeling and programmed death of identified motoneurons. These changes contribute to the dramatic reorganization of behavior that accompanies metamorphosis. As a step toward elucidating cellular and molecular mechanisms by which ecdysteroids affect neuronal phenotype, we have investigated the responses of Manduca motoneurons to ecdysteroids in vitro. Following dendritic regression at the end of larval life, thoracic leg motoneurons placed in culture respond to ecdysteroids by an increase in branching complexity, similar to events in vivo. Growth cone structure is affected markedly by ecdysteroids. At pupation, a rise in ecdysteroids triggers the segment-specific death of proleg motoneurons: the same segmental pattern of death is observed when motoneurons from different segments are removed from the nervous system and exposed to ecdysteroids in vitro. These studies provide strong evidence that Manduca motoneurons are direct targets of steroid action and set the stage for further studies of the specific mechanisms involved.

Animals↗
PubMed1998

Insect juvenile hormone resistance gene homology with the bHLH-PAS family of transcriptional regulators.

Juvenile hormone analog (JHA) insecticides are relatively nontoxic to vertebrates and offer effective control of certain insect pests. Recent reports of resistance in whiteflies and mosquitoes demonstrate the need to identify and understand genes for resistance to this class of insect growth regulators. Mutants of the Methoprene-tolerant (Met) gene in Drosophila melanogaster show resistance to both JHAs and JH, and previous biochemical studies have demonstrated a mechanism of resistance involving an intracellular JH binding-protein that has reduced ligand affinity in Met flies. We cloned the Met+ gene by transposable P-element tagging and found reduced transcript level in several mutant alleles, showing that underproduction of the normal gene product can lead to insecticide resistance. Transformation of Met flies with a Met+ cDNA resulted in susceptibility to methoprene, indicating that the cDNA encodes a functional Met+ protein. MET shows homology to the basic helix-loop-helix (bHLH)-PAS family of transcriptional regulators, implicating MET in the action of JH at the gene level in insects. This family also includes the vertebrate dioxin receptor, a transcriptional regulator known to bind a variety of environmental toxicants. Because JHAs include a diverse array of chemicals with JH activity, a mechanism whereby they can exert effects in insects through a common pathway is suggested.

Amino Acid Sequence↗
PubMed1981

Is octopamine a transmitter mediating hormone release in insects?

The release of hyperlipemic hormone from the glandular cells of the corpus cardiacum (CC) of Locusta migratoria is under the synaptic control of axons in nervus corpus cardiacum II (NCC II). The effects of aminergic agonists and antagonists on the release of the hyperlipemic hormone induced by electrical stimulation of NCC II have been examined. CC isolated from reserpine-injected locusts did not release hormone when subjected to electrical stimulation of NCC II but continued to release hormone in response to high-potassium saline. The electrically stimulated release of hormone from isolated CC was abolished by the alpha-adrenergic blocking agent, phenoxybenzamine, but potentiated by the beta-adrenergic blocking agent, propranolol. Phenoxybenzamine did not interfere with release induced by high-potassium saline. It is suggested that the postsynaptic receptors on the glandular cells are similar to the alpha-adrenergic receptors of vertebrates. Octopamine was found to be present in the glandular lobe of the CC at concentrations of 0.62 pmole per gland pair. Reserpine depleted the content to 0.3 pmole per pair. Bathing the CC in 10(-7) M octopamine resulted in the release of hyperlipemic hormone, and this release was blocked by phenoxybenzamine. It is concluded that the neurotransmitter involved in the synapse between axons of NCC II and the cells releasing hyperlipemic hormone is aminergic, possibly octopaminergic. Octopamine may well be a transmitter mediating hormone release in insects.

Animals↗
PubMed1986

Transition state analogs as ligands for affinity purification of juvenile hormone esterase.

Insect juvenile hormones are metabolized in numerous species of caterpillars by low abundance, highly specific esterases. Because of their role in regulating and possibly disrupting juvenile hormone titer and thus insect metamorphosis, they are of interest to developmental biologists as well as scientists interested in selective insect control. However, the enzymes have defied attempts to purify and characterize them. Juvenile hormone esterase activity can be inhibited by a variety of 3-substituted 1,1,1-trifluoropropanone sulfides. These apparent transition state analogs were used as ligands and eluting agents to purify juvenile hormone esterase from four insect species from 500-fold to over 1000-fold in high yield. After elution from the affinity column, the enzymes were radiolabeled with paraoxon and analyzed by electrophoresis, and the results demonstrate a high degree of purity. Transition state analogs may be useful for the affinity purification of other enzymes.

Acetone↗
PubMed2000

Programmed cell death triggered by insect steroid hormone, 20-hydroxyecdysone, in the anterior silk gland of the silkworm, Bombyx mori.

Silk gland is a larval specific tissue of lepidopteran insects and begins to degenerate shortly before pupation. Programmed cell death (PCD) of the anterior silk gland of Bombyx mori last instar larvae was studied in vivo and in vitro, focusing on the effects of 20- hydroxyecdysone (20E). The glands began to exhibit signs of PCD in vivo 2 days after gut purge and completed PCD by 48 h. In vitro, 20E prematurely induced PCD, and its completion took 144 h (6 days). An oligo-nucleosomal ladder pattern was observed in DNA extracted at the end of PCD. Caspase 3 inhibitor inhibited attainment of full PCD, but it did not block chromatin condensation as revealed by acridine orange staining. alpha-Amanitin inhibited the PCD induced by 20E in vitro if added to the culture in the first 8 h. Similarly, cycloheximide and emetine completely blocked PCD when applied in the first 18 h of culture with 20E. These results indicate that 20E-stimulated transcription and protein synthesis for PCD are completed in 8 h and 18 h, respectively. Nevertheless, withdrawal of 20E from the medium at different times showed that 20E must be present in vitro for 42 h to elicit full PCD. Current results indicate that the effects of 20E on the progression of PCD are mediated by two distinct processes - one through nuclear hormone receptors, and the other independent from de novo gene expression.

Animals↗
PubMed2005

Quantitative structure-activity relationship modeling of insect juvenile hormone activity of 2,4-dienoates using computed molecular descriptors.

Juvenile hormone (JH) activity of one hundred and eighty 2,4-dienoates reported for the larvae/pupae of six insect species was modeled using 915 atom pairs and 258 global molecular descriptors (topological and geometrical). Ridge regression, principal component regression and partial least square regression methods were used to model each of the JH activities. The use of all of the available parameters did not yield any good models, and extensive predictor trimming was necessary to improve the models. Ridge regression was found to give the best results among the three statistical tools used. The top ten molecular descriptors selected based on the t-statistic for each of the six models were found to be mostly atom pairs containing heteroatoms and topochemical descriptors. This suggests the importance of the chemical nature of the ligand rather than mere space-filling as the basis of the JH bioactivity. The residual plots indicate the existence of some non-linear relations, and recursive partitioning was used to capture any nonlinear relation between the bioassays and the molecular descriptors.

Alkenes↗