Mass spectrum of glycosides of ecdysteroids and their peracetatesEcdysteroids bind to their intracellular receptors, ecdysone receptors EcRsthat migrate to the nucleus and transactivate the genes with the collaboration of ultraspiracle Ecdysteroid glycosides . The F domains of most EcRs except for that of Diptera are very short. DNA binding domains are highly homologous among insect species, but ligand-binding domains are varied among insect orders. Three-dimensional structures ecdysteroid glycosides the ligand binding domains of ecdysteroid glycosides EcRs have been solved by X-ray crystal structure analysis. Recently, in insects and crustaceans, it has been suggested that ecdysteroids may interact with transmembrane receptors, G protein-coupled receptors GPCRs ecdysteroid glycosides, and take part in the activation of various second messenger pathways.
Ecdysteroid glycosides from Sida rhombifolia L. - PubMed - NCBI
Ecdysteroids bind to their intracellular receptors, ecdysone receptors EcRs , that migrate to the nucleus and transactivate the genes with the collaboration of ultraspiracle USP .
The F domains of most EcRs except for that of Diptera are very short. DNA binding domains are highly homologous among insect species, but ligand-binding domains are varied among insect orders. Three-dimensional structures of the ligand binding domains of some EcRs have been solved by X-ray crystal structure analysis. Recently, in insects and crustaceans, it has been suggested that ecdysteroids may interact with transmembrane receptors, G protein-coupled receptors GPCRs , and take part in the activation of various second messenger pathways.
The ecdysteroids are polar, polyhydroxylated steroids that function as the moulting hormones of insects and crustaceans. Ecdysteroids are also found in plants, often in high concentration, where it is thought they contribute to insect deterrence by acting as antifeedants, interfering in ecdysteroid metabolism or mode of action on ingestion by phytophagous insects. The chromatographic behavior of ecdysteroid glycosides is characteristic, as they appear much more polar than their corresponding free aglycones when analyzed by normal-phase HPLC, whereas the presence of glycosidic moieties has a very limited if any impact on polarity when using reversed-phase HPLC.
These authors used an analytical 4. This study also explored the application of HPLC—NMR spectroscopy and HPLC—NMR spectroscopy—MS to these ecdysteroid -containing plant extracts, showing the advantages and limitations of the use of complex multiply hyphenated detection systems, which incorporate detectors of differing sensitivities. Table 7 lists studies that are representative of the approaches that have been used for the high-resolution chromatographic separation of ecdysteroids.
Chang, in Encyclopedia of Animal Behavior , Ecdysteroids also appear to have neuromodulatory activities. With in vitro neuromuscular preparations, increased amplitudes and frequency of the excitatory potentials were observed in the opener muscle of the lobster claw in the presence of 20E. In abdominal muscle, these potentials were significantly smaller in the presence of 20E compared to control abdominal muscle. These observations were consistent with the changes observed in vivo in which premolt lobsters with high circulating levels of ecdysteroids had increased aggressiveness relative to other molt stages.
In support of these observations on alterations in neuromuscular activity, experiments were conducted on lobsters using 20E injections. Intermolt females injected with 20E displayed increased aggressiveness relative to saline-injected controls. Ecdysteroids and juvenile hormones JHs are key hormones that are responsible for insect molting and metamorphosis. JH maintains the larval state and the decline of its level in the hemolymph is crucial to elicit transformation to the pupal stage; therefore, the precise control of JH biosynthesis is necessary for normal development and the initiation of metamorphosis.
This chapter summarizes mechanisms of the regulation of JH biosynthesis by the corpora allata and shows that several factors such as ecdysteroids , neurotransmitters, and peptides act together in the stage-specific manner to guarantee the accurate production of JH in each stage, in particular, in the last larval stage when metamorphosis is initiated with the transformation of the larva to the pupa.
In addition, recent progress in understanding the JH signaling pathway is briefly discussed, including the identification of a long elusive JH receptor. Ecdysteroid hormones are the primary regulators of insect development, molting, and metamorphosis.
In the larval stages, ECDs are synthesized from dietary cholesterol in the prothoracic glands PG and released into the hemolymph for circulation to target tissues. Several neuropeptides stimulate or inhibit ECD production. Two other native ILPs stimulated the pupal—adult molt of a related silkmoth, Sa. Cross species activity was shown for a synthetic B.
Ecdysteroids coordinate an entire network of physiological and developmental activities that are initially triggered by EcR and USP, and, in turn, act through a variety of nuclear receptor partners and gene targets. The aforementioned activity of ecdysone, other ecdysteroids , and 20E metabolites has special importance for DHR38, which together with USP can regulate transcriptional activity, though its interaction with these agonists does not involve a cognate ligand interaction with the DHR38 ligand binding pocket .
DHR38 is expressed throughout development, though the phenotypes generated by its mutation are subtle by Drosophila standards—DHR38 mutations inhibit the normal formation of the adult cuticle. In epidermal tissues, DHR38 normally represses the transcription of dopa decarboxylase ddc , an early—late ecdysteroid responsive gene whose enzymatic product plays an essential role in the formation of cuticle. DHR38 acts as a positive regulator of the same ddc gene in neural tissues .
DHR3, for instance, appears as an early—late puff, whose upregulation is targeted directly by the ecdysteroid receptor. DHR3 forms a dimer with a nuclear receptor isoform, E75B, which lacks one of its zinc fingers.
E75 is an early ecdysteroid inducible gene, and is also the second Drosophila nuclear receptor that indisputably interacts with a cognate ligand via its ligand binding pocket. When the heme iron is oxidized, its interaction with E75 is altered, and, in turn, E75 can no longer dimerize with DHR3 .
Both nitric oxide and carbon monoxide molecules also bind to the heme, and thereby reduce the dimerization efficiency of E Mutants of the E75A isoform one of three E75 isoforms in D. Genes that are normally specific to the third instar are expressed and mutants prematurely enter the puparial prepupal stage, suggesting that E75 plays a role in ecdysteroidogenesis .
E75A has also been implicated in the JH signaling pathway . The orphan receptor DHR4 is also expressed in response to 20E. Similar to the case with E75 mutants, mutational disruption of DHR4 results in undersized larvae that pupariate prematurely, again suggesting the failure of a normally repressive mechanism.
In DHR4 mutants, many early ecdysteroid inducible genes are repressed. DHR4 itself is normally expressed in the fat body and in neuroendocrine cells. The fat body of mutant larvae undergo a premature autophagy and the larvae cease feeding prematurely, though pupariation occurs. The possible role of DHR4 in neuroendocrine cells is less clear, though these cells normally produce prothoracicotropic hormone, which, in turn, normally stimulates ecdysteroid production, and therefore, might be abnormally active at this developmental time .
As noted, DHR78 is also induced by ecdysteroids , and its action has been inextricably tied to a corepressor, Moses Middleman for Seventy-Eight Signaling. Further, the ectopic expression of DHR78 in wild-type flies evokes no phenotypic effect, inferring that the receptor by itself has no biological effect.
The level of Moses protein in the cell depends upon the level of DHR78, indicating that the receptor stabilizes the Moses protein. Genetic evidence also establishes the codependence of Moses and DHR Tissues that are homozygous for the mutant corepressor develop an overgrowth phenotype, and DHR78 null mutants also develop growth defects at the onset of metamorphosis .
Does this paradigm offer any insight into a similar mechanism in mammals? Finally, DHR96 is ecdysteroid inducible and has been linked to xenobiotic responses.
Mutants of this receptor are sensitive to the effects of phenobarbitol and DDT and are resemblant of the activity found in its mammalian orthologs . Alain Strambi, in International Review of Cytology , They are also produced in adults, in which they are involved in reproductive functions Hagedorn, , Wyatt and Davey, Ecdysone, extracted from silkworm pupae, was isolated in a crystalline pure form by Butenandt and Karlson and recognized as a steroid.
Among them, a homolog of ecdysone, makisterone A, was recognized as the molting hormone in Heter-optera and the major ecdysteroid in Hymenoptera and some Diptera Feldlaufer et al. In larval insects, ecdysone biosynthesis takes place in ecdysial glands, and it occurs in ventral glands in apterygotes, the ring gland in Diptera, and the prothoracic gland in most insect groups Herman, In adult insects, the presence of ecdysteroids in the ovaries was recognized more than 20 years ago Onishi et al.
However, in some Lepidoptera, male gonads incubated in vitro release in the medium large amounts of ecdysteroids produced by the follicular sheath of the testes Loeb et al. Secreted by two cephalic endocrine glands, the corpora allata, juvenile hormone JH was first discovered by Wigglesworth Although mainly secreted by the corpora allata, other sources of JH have been found. In Cecropia silkmoth, JH is synthesized in the male accessory glands and then transfered to the female during mating Shirk et al.
The functions of JH in the control of adult reproduction are fairly well-known Wyatt and Davey, In adult female, the hormone stimulates oocyte growth, vitellogenin synthesis in the fat body, and absorption of vitellogenin by the oocytes. By contrast, fewer reports concern the role of ecdysteroids in adult insects Hagedorn, , Moreover, although much evidence indicates that hormones affect adult behavior, only a few data focus on hormone actions on the nervous tissue.
Two kinds of action were recognized for JH: The control of a function in a dose-dependent and immediate way is referred as to regulation Truman and Riddiford, or releasing Wyatt and Davey, The primer or modifier effect is slow to appear and prepares the tissue to change its responsiveness to a stimulus. Direct actions of JH at the cell membrane have been recognized in ovarian follicle cells and in male accessory glands; JH also modulates nuclear gene expression and recent reviews summarize the current knowledge of the mechanisms of action of JH Riddiford, ; Jones, ; Wyatt and Davey, Despite numerous attempts, JH receptors have not been clearly identified; however, recent data suggest that USP can bind specifically to ligands of the JH family and could be a JH receptor Jones and Sharp, Although rapid actions of ecdysteroids at the cell membrane level have been observed Robert et al.
Recently isolated and cloned, the ecdysone receptor codes for three protein isoforms Koelle et al. EcR proteins are activated to form heterodimers with another steroid receptor encoded by the Drosophila gene ultraspiracle usp Yao et al.
Because hormone actions on the nervous system have been especially studied in the honeybee and in the cricket, we shall briefly review the life and changes in hormone titers occurring in these two models.
Among social insects comprising bees, ants, wasps, and termites, honeybees represent one of the best studied species. The colony usually consists of a reproductive queen which can live for several years, unreproductive worker bees having a 1- or 2-month life in summer, and drones having a short life and dying after mating. During their adult life, a clear division of labor exists among worker honeybees that was defined as age polyethism by Winston In brief, young worker bees take care of the brood and are considered nurse bees during the first week of their life, then they perform different tasks in the hive, and finally, at the age of about 3 weeks, they start to forage outside the hive, becoming foragers.
Studies using bioassay indicated that JH titers were increasing during worker honeybee life Fluri et al. Whereas JH levels Fig. By contrast to workers, queens present a peak of JH on their first day of adult life Fig. Circulating levels of JH in the drones Fig. Determination of ecdysteroid hemolymph titers demonstrated that in a queenright colony there were no measurable ecdysteroid titers in newborn workers, nurses, and foragers.
Only in egg-laying workers from a queenless colony were ecdysteroids detectable. Queens had significantly higher levels of ecdysteroids than did laying workers, and among ecdysteroids makisterone A was the major compound Feldlaufer et al.
The adult crickets live for about 2 months. The panoistic ovaries contain about ovarioles per ovary; the maturing terminal ovocytes are stored in the genital chamber before being laid in the soil in groups of 10— Because terminal ovocytes do not mature in a completely synchronous way, the waves of maturing ovocytes rapidly overlap.
Thus, the first ovarian cycle is the most convenient period in which to analyze the titers of the two hormones involved in ovarian development. As seen Figure 4a , after a weak elevation of JH titer, 1 day after emergence, two increases of JH levels occur, which are respectively related to previtellogenesis for the small increase and to vitellogenesis for the large increase Renucci and Strambi, ; Renucci et al.
During ovarian maturation, the follicular cells surrounding the follicles enlarge and secrete ecdysteroids Fig. In the house cricket, allatectomy performed during the last larval instar completely suppressed JH production and ovarian development; similarly, in females ovariectomized before emergence there was no trace of circulating ecdysteroids Renucci and Strambi, ; Renucci et al.
In insects, major reactions contributing to the inactivation of ecdysteroids ecdysone and hydroxyecdysone are 1 epimerization, 2 ecdysonic acid formation, 3 phosphorylation, 4 fatty acylation, and 5 glucosylation, summarized below. The molecular cloning and characterization of the cDNAs encoding the three enzymes mentioned above have been reported [11—13]. Ecdysonic acid oic acid is formed via the following inactivation pathway: Properties of enzymes that catalyze these three reactions remain to be elucidated .