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PubMed1996

The intranuclear site of excision of each intron in Balbiani ring 3 pre-mRNA is influenced by the time remaining to transcription termination and different excision efficiencies for the various introns.

The 10.9-kb Balbiani ring 3 (BR3) gene contains 38 constitutively excised introns. Both nascent and nucleoplasmic, released BR3 gene pre-mRNA can be isolated by microdissection of the polytene salivary gland nuclei in which the gene is transcribed. Here we analyze the order of intron excision in relation to transcription and to intranuclear transport. We demonstrate that the introns are excised with an overall 5' to 3' polarity that is established during transcription and maintained during transport. In contrast, we also show that individual introns are excised at very different rates and that neighboring introns are removed in a preferred order that is not necessarily 5' to 3'. Splicing factors are, in addition, shown to associate with the nascent BR3 pre-mRNA. Our data argue that functional spliceosomes assemble rapidly as introns appear in the pre-mRNA, but that intron-specific properties influence the kinetics of spliceosome assembly and/or function, resulting in cotranscriptional excision of some introns, preferentially those located in the 5' part of the pre-mRNA, and posttranscriptional excision of other introns, preferentially those located in the 3' part of the pre-mRNA.

Animals↗
PubMedDate not supplied

Regioselective formation of the three disulfide bonds of a 35-residue insect peptide.

PMP-D2, a 35-residue peptide containing three disulfide bonds, was synthesized on solid-phase using 9-fluorenylmethoxy-carbonyl (Fmoc) as alpha-NH2 protection and simultaneous air oxidation of the six cysteines for formation of its disulfide bonds. The overall yield was 13%. As very little research has been done on the regioselective formation of three disulfide bonds, we decided to investigate different strategies using either trityl (Trt), acetamidomethyl (Acm) and methoxybenzyl (Mob), or methoxytrityl (Mmt), trityl and acetamidomethyl, as cysteine-protecting groups and Fmoc as alpha-NH2 protection. In the first strategy, the first disulfide bond was formed by air oxidation and the second was formed by iodine oxidation of the Cys(Acm). Then, the Cys (Mob) was deprotected using TFMSA/TFA treatment for formation of the third disulfide bond. This last step was poorly reproducible on a large scale. The overall yield was 2.5%. In the second strategy, the first disulfide was formed on the resin after removal of the methoxytrityl group, and the two remaining disulfide bonds were formed classically in solution. The overall yield was 2%. From the overall yields using these strategies, it appears clear that simultaneous oxidation of the six cysteines is particularly appropriate for the synthesis of PMP-D2.

Acetamides↗
PubMed1996

In vivo interactions of the Drosophila Hairy and Runt transcriptional repressors with target promoters.

The Hairy and Runt pair-rule proteins regulate Drosophila segmentation by repressing transcription. To explore the ability of these proteins to function as promoter-bound regulators in vivo, we examined the effects of Hairy and Runt derivatives containing heterologous transcriptional activation domains (HairyAct and RunAct). Using this approach, we find that Hairy and Runt efficiently target such activation domains to specific segmentation gene promoters, leading to rapid induction of transcription. Our results strongly suggest that Hairy normally acts as a promoter-bound repressor of fushi tarazu, runt and odd-skipped, and that Runt directly represses even-skipped. We also show that expressing HairyAct in early blastoderm embryos causes ectopic Sex-lethal expression and male-specific lethality, implying that the Hairy-related denominator element Deadpan represses Sex-lethal during sex determination by directly recognizing the early Sex-lethal promoter.

Animals↗
PubMed1998

The lethal effects of Cyperus iria on Aedes aegypti.

The sedge Cyperus iria, a common weed in rice, contains large amounts of the insect hormone (10R) juvenile hormone III (JH III). Given its widespread distribution in Asia and Africa, we examined the possibility that C. iria could be used as a safe, inexpensive, and readily available mosquito larvicide. Plants of varying ages were harvested and leaves tested for lethal effects on larvae of the yellow fever mosquito, Aedes aegypti. The median lethal doses (LD50s) for frozen leaves from 1- and 2-month-old plants were 267 and 427 mg/100 ml of water, respectively. Leaves from 1-month-old C. iria contained 193 micrograms JH III/g fresh weight, whereas leaves from 2-month-old plants contained 143 micrograms JH III/g fresh weight. Larval sensitivity to the plant differed with age; 4-day-old larvae displayed the greatest mortality followed in decreasing sensitivity by larvae 5, 6, 3, and 2 days old. Six Cyperus species (C. albostriatus, C. alternifolius, C. esculentus, C. iria, C. miliifolius, and C. papyrus) of similar developmental stage were assayed for JH III content. Only C. iria was found to contain significant levels of JH III.

Aedes↗
PubMed1996

Involvement of microtubules in prothoracicotropic hormone-stimulated ecdysteroidogenesis by insect (Manduca sexta) prothoracic glands.

Secretion of ecdysteroid molting hormones by insect prothoracic glands is stimulated by neuropeptide prothoracicotropic hormones (PTTH). Studies reported here were conducted to assess the effects of microfilament and microtubule inhibitors on in vitro ecdysteroidogenesis by prothoracic glands of Manduca sexta. Microfilament inhibitors (cytochalasins B and D) had no effect on basal or big PTTH-stimulated ecdysteroidogenesis. Microtubule inhibitors (colchicine, podophyllotoxin, nocodazole) had no effect on basal ecdysteroid secretion, but suppressed PTTH-stimulated secretion in a concentration-dependent manner. The effect of nocodazole was partially reversible, suggesting it was not due to nonspecific toxicity. Colchicine had no effect on glandular ecdysteroid levels, indicating that inhibition was not due solely to blockage of secretion. The combined results are consistent with the hypothesis that microtubule-mediated transport of ecdysteroid precursors plays a critical role in stimulation of ecdysteroidogenesis by PTTH.

Actin Cytoskeleton↗
PubMed1989

Do insects really have a homeostatic hypotrehalosaemic hormone?

Since trehalose in insects, in contrast to glucose in mammals, does not enter the haemolymph directly from the digestive tract, but is all synthesized by the insect itself, and furthermore an increased trehalose synthesis during stress and flight does not lead to significant increases in haemolymph trehalose, there seems to be no physiological need for an insect homeostatic hypotrehalosaemic hormone. Experiments in which tissue extractions were found to lower haemolymph trehalose can not prove the existence of such a hormone, while all insect species which so far have been submitted to a trehalose-tolerance test, decrease their haemolymph trehalose concentrations at a rate which can be accounted for by the metabolic use of trehalose. These results therefore indicate the absence, and not the presence, of a homeostatic hypotrehalosaemic hormone. This is also true for blowflies, from which an insulin-like immunoreactive peptide has been isolated. It seems therefore unlikely that this insulin-like peptide is a homeostatic hypotrehalosaemic hormone. The physiological mechanism by which this insulin-like peptide would have to act to function as a hypotrehalosaemic hormone is also an unlikely one. It therefore seems justified to conclude that so far, homeostatic hypotrehalosaemic hormones have not been demonstrated in insects. Furthermore, it may well be that they do not exist.

Animals↗
PubMed2000

Inhibition of vitellogenin synthesis in Apis mellifera workers by a juvenile hormone analogue, pyriproxyfen.

Insect juvenile hormone (JH) has been related to modulation of vitellogenin (Vg) synthesis, a protein produced by fat body cells, secreted in haemolymph and sequestered by developing oocytes. A stimulatory JH action has been described for the majority of species studied thus far. In some insects, however, Vg synthesis has been inhibited or unaffected by JH. The aim of this study was to re-examine the action of JH on Vg synthesis in Apis mellifera workers, since contrasting effects of this hormone were described. Newly emerged worker bees were treated with different doses of pyriproxyfen (PPN), a potent JH analogue. Vg and total protein were quantified in haemolymph samples of newly emerged up to 6-day-old worker bees. Protein synthesis activity of fat body cultured in vitro and ultrastructure of fat body cells were also examined. High doses (1.25, 2.5, 5 and 10 &mgr;g) of PPN inhibited the onset and accumulation of Vg in the haemolymph of young worker bees in a dose-dependent fashion. This inhibition was not a result of fat body cell degeneration or death, as illustrated by fat body cells ultrastructure analysis, but by impairing Vg synthesis, as demonstrated by in vitro culture of fat body cells. Low doses (0.001, 0.01 and 0.1 &mgr;g) neither affected the normal synthesis and secretion of Vg into the haemolymph nor caused an early onset of Vg in treated bees (which could be interpreted as a JH-activating effect), as shown by Vg quantification at 24-h intervals. The results suggest that a low JH titre in honey bee workers permits the onset and accumulation of Vg in haemolymph, whereas high JH levels turn off Vg synthesis.

Journal Article↗
PubMed1987

Identification and purification of two precursors of the insect neuropeptide adipokinetic hormone.

Our objective was to establish a system for the investigation of neuropeptide biosynthesis in an insect. To achieve this we developed an in vitro organ culture system for the corpora cardiaca (CC) of the locust (Schistocerca gregaria). The CC are the neurosecretory structures containing the adipokinetic hormones AKH I and AKH II. Tritiated amino acids were added to the glands, and we studied the development of label in newly made proteins using size-exclusion and reverse-phase liquid chromatography. We performed pulse-chase and pulse-translation block experiments using 3H-tryptophan as tracer. We also raised an antiserum to a synthetic AKH analog and used this in combination with liquid chromatography to identify 2 precursor polypeptides, P1 and P2. Size-exclusion chromatography indicated the presence of a major component of the CC of about 8 kDa that incorporates 3H-tryptophan before AKH I and II. Moreover, in both pulse-chase and pulse-translation block experiments we showed that label is transferred from this 8 kDa component into AKH I. We call this component proAKH; it is recognized by anti-AKH serum in a radioimmunoassay (RIA). Further fractionation of tritium-labeled proAKH by reverse-phase chromatography yielded 2 polypeptides, P1 and P2. Both are AKH-immunoreactive and contain 3H-tryptophan after in vitro pulse labeling, and both are proposed precursors of AKH I. The in vitro system we have developed may be a model system for the study of the processes of neuropeptide biosynthesis and its regulation in an intact neurosecretory tissue of an insect.

Animals↗
PubMed1976

Glucagon-like and insulin-like hormones of the insect neurosecretory system.

Aqueous extracts of corpus cardiacum-corpus allatum complexes of the adult tobacco hornworm Manduca sexta produced both glycogenolysis and hypoglycaemia when injected into the larval form of the same species. Application of specific radioimmuno assays to similar extracts showed also that these gland complexes contain both glucagon-like and insulin-like peptides. Further, the partially purified immunoreactive peptides had the expected biological activities. The former decreased the glycogen content of the fatbody and the latter the circulating trehalose levels in recipient animals. These results suggest the existence of hormones in these invertebrates having both biological and structural similarities to vertebrate insulin and glucagon.

Animals↗
PubMed1998

"Insects do not have sex hormones": a myth?

Mammals have two genes (SRY and DMT1) for testis formation-androgenesis, an anti-testis gene, DAX1, an anti-Müllerian duct hormone, and steroid sex hormones. Drosophila uses the sex-lethal, transformer, and doublesex genes for sexual differentation and is supposed to lack sex hormones. However, the statement that insects do not have sex hormones loses much of its credibility if one considers (1) the classical endocrinological work on sexual differentiation in the firefly Lampyris and in the hevea tussock moth Orgyia; (2) the recent identification of an androgenic hormone and its role in sex determination in the isopod Armadillidium; (3) the similarity between steroidogenic factor 1 (SF-1) of mammals and fushi tarazu factor 1 (FTZ-F1) of Drosophila; and (4) the steroidogenic effect of gonadotropins secreted by the brain of female locusts and mosquitoes and of male gypsy moth. In our model, based on data from the literature, ecdysone, when present in high concentrations, might function as an androgenic sex steroid. It is also the precursor of 20-OH-ecdysone, which is the moulting hormone of insects, and in vitellogenic females of many species, the counterpart of estrogens as well. Other gender-specific hormones are likely to exist in the brain-gonad axis.

Amino Acid Sequence↗
PubMed2005

Bursicon, the insect cuticle-hardening hormone, is a heterodimeric cystine knot protein that activates G protein-coupled receptor LGR2.

All arthropods periodically molt to replace their exoskeleton (cuticle). Immediately after shedding the old cuticle, the neurohormone bursicon causes the hardening and darkening of the new cuticle. Here we show that bursicon, to our knowledge the first heterodimeric cystine knot hormone found in insects, consists of two proteins encoded by the genes burs and pburs (partner of burs). The pburs/burs heterodimer from Drosophila melanogaster binds with high affinity and specificity to activate the G protein-coupled receptor DLGR2, leading to the stimulation of cAMP signaling in vitro and tanning in neck-ligated blowflies. Native bursicon from Periplaneta americana is also a heterodimer. In D. melanogaster the levels of pburs, burs, and DLGR2 transcripts are increased before ecdysis, consistent with their role in postecdysial cuticle changes. Immunohistochemical analyses in diverse insect species revealed the colocalization of pburs- and burs-immunoreactivity in some of the neurosecretory neurons that also express crustacean cardioactive peptide. Forty-three years after its initial description, the elucidation of the molecular identity of bursicon and the verification of its receptor allow for studies of bursicon actions in regulating cuticle tanning, wing expansion, and as yet unknown functions. Because bursicon subunit genes are homologous to the vertebrate bone morphogenetic protein antagonists, our findings also facilitate investigation on the function of these proteins during vertebrate development.

Amino Acid Sequence↗
PubMed1991

Hormonal effects on insects and other endoparasites in vitro.

Metamorphic and reproductive events in vertebrates and invertebrates are under endocrine control and are often correlated with developmental, behavioral, or reproductive changes in the parasites living in or on these hosts. This paper reviews selected examples of a) host hormone mediated influences on endoparasites in vivo, b) host hormone effects in vitro on protozoan, helminth, and insect endoparasites, and c) identifies possible relationships in hormone effects across parasite taxa. The significance of studies on endoparasites in vitro in relation to the impact of host hormones, antihelminthic, and prophylactic drugs on parasite growth and proliferation will also be addressed. A review of the literature indicates only limited studies have been done in vitro in an attempt to elucidate the bases of reported host hormone influences on endoparasites in vivo. Steroid hormones of hosts seem to stimulate growth, molting or encystment or both of helminth, insect, and protozoan parasites. Vertebrate steroids such as estrogen, testosterone, and progesterone had primarily reproduction- or growth-promoting effects or both on protozoan and nematode parasites. Insect ecdysteroids such as ecdysone, 20-hydroxyecdysone, and makisterone were the most widely studied steroids in vitro and induced growth or molting or both of cestode, nematode, and insect parasite larvae. Although juvenile hormone (JH III) stimulated growth in the protozoan and nematode parasites tested, the analogue methoprene and JH precursors, farnesal, farnesol, and farnesol methyl ether had various effects. Biogenic amines also varied in their effects on the nematode parasites tested, while the peptide hormone, insulin, stimulated growth in the protozoans tested. The evidence for in vitro effects of host hormones on their natural endoparasites is patchy at best. Additional studies are needed to identify the biochemical bases for the numerous host hormone mediated effects on parasites.

Animals↗
PubMed1997

Specific requirement of putrescine for the mitogenic action of juvenile hormone on adult insect neuroblasts.

Persistent neurogenesis in an adult insect brain was recently shown to be stimulated by juvenile hormone (JH). This morphogenetic hormone was also shown to act on polyamine biosynthesis. To analyze the possible involvement of polyamines in the neurogenic action of JH, two series of experiments were carried out with adult female crickets, Acheta domesticus: (i) inhibition of the first key enzyme in polyamine biosynthesis, ornithine decarboxylase, with alpha-difluoromethylornithine (alpha-DFMO), and examination of the effects of this treatment on the neuroblast proliferation response to JH; and (ii) examination of the effects of putrescine supplementation on the mitotic index of JH-deprived and alpha-DFMO-treated females. In control females, alpha-DFMO treatment, as well as JH deprivation, greatly reduced neuroblast proliferation. Putrescine supplementation in alpha-DFMO-treated insects overcame the effects of alpha-DFMO, and allowed for detection of putrescine in the neural tissue and stimulation of brain neurogenesis. In JH-deprived females, alpha-DFMO treatment completely prevented the stimulatory action of JH on neuroblast proliferation and on brain putrescine levels. By contrast, putrescine feeding of JH-deprived animals was able to mimic the stimulatory effect of JH: brain putrescine levels increased and neuroblast proliferation was restored. To our knowledge, this report demonstrates for the first time that in vivo administration of putrescine can mimic the effects of a morphogenetic hormone on adult neuroblast proliferation, and shows the importance of polyamines, especially putrescine, in the transduction of JH message in neural tissue.

Animals↗
PubMed1985

Gas chromatography-mass spectroscopy analysis of juvenile hormone released by insect corpora allata.

Corpora allata incubated in appropriate medium release several compounds including juvenile hormones. Juvenile hormones (14C labeled or unlabeled) were extracted with hexane and directly analyzed by gas chromatography-mass spectroscopy. This method allowed the qualitative and quantitative analysis of total released juvenile hormone. It could also be used as a routine assay for evaluation of corpus allatum activity. Data obtained by this method were compared to those obtained by radiochemical assay.

Animals↗
PubMed2000

Distinctive structural and kinetic properties of an unusual juvenile hormone-hydrolyzing esterase.

The insect juvenile hormone specific esterases (JHEs), related to acetylcholinesterases but exhibiting substrate specificity for juvenile hormone (JH), are essential enzymes for normal insect development, making them attractive targets for biorationally designed, environmentally safe pesticides. We examine here a new enzyme, JHER, related to, but yet structurally, biochemically, and kinetically distinct from, the classical JHE. Both classical JHE and baculovirus-expressed JHER hydrolyze JH show disproportionately higher catalytic rates at higher substrate concentrations (in contrast to substrate inhibition reported for acetylcholinesterase) and are similarly inhibited by an organophosphate. However, JHER, which possesses an unusual cysteine residue at +1 to the catalytic serine, is less sensitive to trifluoromethyl ketone transition state analogs designed around the structure of JH. We propose a model in which JHER is expressed just prior to metamorphosis for hydrolysis of a JH-like substrate with hydrophobic backbone, a proximal ester, and a terminal expoxide or related substitution.

Amino Acid Sequence↗
PubMed1990

Juvenile hormone receptors in insect larval epidermis: identification by photoaffinity labeling.

Tritiated photoaffinity analogs of the natural lepidopteran juvenile hormones, JH I and II [epoxy[3H]bishomofarnesyl diazoacetate ([3H]EBDA) and epoxy[3H]homofarnesyl diazoacetate ([3H]EHDA)], and of the JH analog methoprene [[3H]methoprene diazoketone ([3H]MDK)] were synthesized and used to identify specific JH binding proteins in the larval epidermis of the tobacco hornworm (Manduca sexta). EBDA and EHDA specifically photolabeled a 29-kDa nuclear protein (pI 5.8). This protein and a second 29-kDa protein (pI 6.0) were labeled by MDK, but excess unlabeled methoprene or MDK only prevented binding to the latter. These 29-kDa proteins are also present in larval fat body but not in epidermis from either wandering stage or allatectomized larvae, which lack high-affinity JH binding sites. A 29-kDa nuclear protein with the same developmental specificity as this JH binder bound the DNA of two larval endocuticle genes. A 38-kDa cytosolic protein was also specifically photolabeled by these photoaffinity analogs. The 29-kDa nuclear protein is likely the high-affinity receptor for JH that mediates its genomic action, whereas the 38-kDa cytosolic protein may serve as an intracellular carrier for these highly lipophilic hormones and hormone analogs.

Journal Article↗