Conversion of alpha ecdysone to beta ecdysone by crustaceans and insects

On gonads and gadflies: the estrus angle

The first sex steroid to be crystallized was the vertebrate ovarian hormone, estrone - a less potent metabolite of 17β-estradiol, which in mammals stimulates the female urge to mate (estrus). The gadfly (Greek oistros) lent its name to the process of estrus, as an insect that bites and torments in classical Greek mythology. With the purification and crystallization of a moult-inducing steroid (ecdysone) from insects, an interesting parallel emerged between mating and moulting in lower mammals and arthropods. Ecdysterone (potent ecdysone metabolite) has anabolic effects in mammalian muscle cells that can be blocked by selective estrogen receptor antagonists. Insects utilize ecdysteroids in similar ways that vertebrates use estrogens, including stimulation of oocyte growth and maturation. Ecdysteroids also modify precopulatory insect mating behaviour, further reinforcing the gonad-gadfly/mate-moult analogy.

Contextual cross-referencing of species names for fiddler crabs (genus Uca): an experiment in cyber-taxonomy

Cyber-taxonomy of name usage has focused primarily on producing authoritative lists of names or cross-linking names and data across disparate databases. A feature missing from much of this work is the recording and analysis of the context in which a name was used—context which can be critical for understanding not only what name an author used, but to which currently recognized species they actually refer. An experiment on recording contextual information associated with name usage was conducted for the fiddler crabs (genus Uca). Data from approximately one quarter of all publications that mention fiddler crabs, including 95% of those published prior to 1924 and 67% of those published prior to 1976, have currently been recorded in a database. Approaches and difficulties in recording and analyzing the context of name use are discussed. These results are not meant to be a full solution, rather to highlight problems which have not been previously investigated and may act as a springboard for broader approaches and discussion. Some data on the accessibility of the literature, including in particular electronic forms of publication, are also presented. The resulting data has been integrated for general browsing into the website http://www.fiddlercrab.info; the raw data and code used to construct the website is available at https://github.com/msrosenberg/fiddlercrab.info.

Desenvolvimento e produção de seda do Bombyx mori L. exposto a análogos do hormônio juvenil

O crescimento dos insetos é regulado por um complexo hormonal que inclui o hormônio juvenil, que assegura ao inseto a retenção de suas características larvais, prevenindo a maturação. A aplicação de análogos do hormônio juvenil em Bombyx mori tem promovido o incremento da produção de seda; entretanto, altas doses podem provocar efeitos deletérios sobre a biologia do inseto. Este estudo avaliou a pulverização de diferentes análogos do hormônio juvenil sobre o bicho-da-seda e seus efeitos sobre o desenvolvimento larval e a produção de seda. Lagartas foram expostas a piriproxifeno, metopreno e fenoxicarbe a doses de 20, 2 e 0,02 ppb de ingrediente ativo, respectivamente, através da pulverização dos insetos e do alimento a 48 horas após a quarta ecdise. A administração de análogos do hormônio juvenil promoveu aumentos no período larval, massa de glândulas sericígenas, peso de casulos e de pupas. Os produtos testados afetaram negativamente a taxa de encasulamento. Metopreno promoveu o maior incremento na produção de seda e menor taxa de mortalidade, podendo seu uso ser recomendado na sericicultura.

Roles of ecdysone in Drosophila development

A temperature-sensitive lethal mutant of Drosophila melanogaster called ecd(1) becomes deficient in ecdysone, as measured by a radioimmunoassay, when there is a shift in temperature from 20 degrees to 29 degrees at various stages of development. Associated with the ecdysone deficiency at 29 degrees , there are abnormalities in larval and imaginal development and the adult functions. When the shift occurs early in third-instar stage, the mutant larvae grow to full size but fail to pupariate, and instead remain living larvae for as long as 3 weeks. These larvae, which have only about 5% as much ecdysone as the wild-type at the time of pupariation, can be induced to pupariate at 29 degrees by ecdysone in their food, indicating that the pupariation block results from an ecdysone deficiency. A shift to 29 degrees later in the third-instar stage does not prevent pupariation of the mutant, but the imaginal discs fail to complete differentiation, although the discs can differentiate at 29 degrees after transplantation to the normal environment of a wild-type host. A shift to 29 degrees early in the first-instar stage blocks a subsequent rise in ecdysone titer and results in extensive developmental defects. Mutant adults become sterile at 29 degrees , and the ecdysone titer in the females concomitantly decreases to 13% of the wild-type value. Mutant larval ovaries transplanted to wild-type female hosts continue to develop and produce competent eggs at 20 degrees , but when the adult hosts are put at 29 degrees the transplanted ovaries become sterile, suggesting that the ecdysone needed for female fertility is synthesized autonomously by ovarian tissue. In contrast to these effects of a shift to 29 degrees during larval, pupal, and adult stages, there is a normal increase in ecdysone titer and normal development in mutant embryos grown at 29 degrees . The insensitivity of the embryo to the ecd(1) mutation might be due to a maternal contribution of components needed for ecdysone synthesis during the embryonic stage.

Overt and covert effects of endogenous and exogenous ecdysone in puparium formation of flies

Mature larvae of Sarcophaga argyrostoma fail to form puparia when kept in contact with water, but pupariate after having been subsequently exposed to dryness for 30 hr. They become increasingly more sensitive to injected ecdysone the longer the exposure to dry conditions. A second wet treatment halts the production of hormone that had occurred during the dry period, and reduces a sensitization to injected ecdysone during the intervening dry treatment. Apparently, injected ecdysone had cumulative effects not with the endogenous or exogenous hormone, but with its covert effects which had arisen during the dry period and persisted throughout the second wet period. The hind parts of larvae ligated at the end of a wet period pupariate when injected with either one massive dose of ecdysone, or a far smaller total of several subsequent doses. In the case of two unequal doses, the effect was greater when the smaller dose was injected first. In order to get pupariation with minimal effective doses, a continuous supply of the hormone during a certain period is required. It is suggested that the inhibition of pupariation by moisture has arisen as an adaptation to unfavorable conditions.

The Secretion of alpha-Ecdysone by the Prothoracic Glands of Manduca sexta In Vitro

Prothoracic glands of tobacco hornworm larvae cultured in vitro secrete into the culture medium a substance which was active in ecdysone bioassays and determined to be ecdysone-like by radioimmunoassay. The prothoracic glands appear to be the sole source of this substance. The material was identified as alpha-ecdysone by thin-layer, gas-liquid, and high-resolution liquid chromatography and mass spectrometry. No other active moulting principles were present in the medium. It appears that the prothoracic gland secretes a prohormone, alpha-ecdysone, which is subsequently converted into the active moulting hormone, beta-ecdysone, in other insect tissues.

Ecdysteroid concentrations through various life-stages of the meiobenthic harpacticoid copepod, Amphiascus tenuiremis and the benthic estuarine amphipod, Leptocheirus plumulosus

Endocrine function in arthropods has principally been characterized in insects and malacostracan crustaceans. However, meiofauna represent the most abundant metazoan marine taxa, with harpacticoid copepods comprising the second most abundant taxon. In addition, their diminutive biomass has made characterization of endocrine components difficult, so little is known about endocrine control of reproduction, molting, and growth in meiofauna. In this study, a sensitive fluorometric enzyme immunoassay (EIA) was utilized to quantify and compare the arthropod molting hormone, 20-hydroxyecdysone (20E), in various life-cycle and developmental stages of a laboratory reared meiobenthic copepod, Amphiascus tenuiremis, and in an amphipod, Leptocheirus plumulosus. In copepods, gravid females carrying late stage pre-hatch embryos contained significantly more 20E (390+/-252 fmol/female) than gravids carrying early (Stage-I) embryos (172+/-83 fmol/female). In contrast, ecdysteroid levels in Stage-I L. plumulosus gravid females (277+/-83 fmol/female) was greater than pre-hatch gravid females (146+/-42). Stage-I embryos of both copepods (19+/-10) and amphipods (11+/-5 fmol/embryo) possessed lower ecdysteroid content than copepod (35+/-15) and amphipod (43+/-33 fmol/embryo) pre-hatch embryos. Ecdysteroid levels were also assessed in naupliar, juvenile, adult male and non-gravid female copepod life-stages. In addition, ecdysteroids measured in field collected copepod species indicated gravid females possessed ecdysteroid levels similar to gravid A. tenuiremis. However, upon normalization of egg sac 20E content by brood size, embryos from larger broods contained lower levels of ecdysteroids when compared to embryos from smaller clutch sizes-indicating an inverse embryo/ecdysteroid relationship may exist across species.

Role of the head in the ultrastructural midgut organization in Rhodnius prolixus larvae: evidence from head transplantation experiments and ecdysone therapy

Studies on the effects of decapitation, head transplantation and ecdysone therapy on the ultrastructural organization of the midgut in 5th-instar larvae of Rhodnius prolixus, were carried out. Control insects had a typical and significant organization of the epithelial cells (mainly microvilli, extracellular membrane layers and basal portion of the epithelial cells) of the midgut (stomach and intestine) during the entire period of the experiment. However, the host larvae, when decapitated 1 day after feeding, demonstrated significant changes in the ultrastructural organization of the epithelial cells of these compartments. In converse experiments, head transplantations from untreated donors 4-5 days after feeding into headless larvae sustained the ultrastructural organization of the epithelial cells in the midgut. Oral therapy with ecdysone (5 &mgr;g/mL of blood meal) in decapitated insects significantly reversed the altered organization of the stomach and intestine. These results point to a brain factor, possibly the prothoracicotropic hormone (PTTH) which stimulates ecdysteroid production in the prothoracic glands, may be a factor responsible, directly or indirectly, for the midgut cell organization in R. prolixus.

Role of the midgut gland in metabolism and excretion of ecdysteroids by lobsters, Homarus americanus

The chromatographic profile of ecdysteroids (Ecds) from the midgut gland (MG) of juvenile female lobsters, Homarus americanus, was examined using high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA) over four stages of the molt cycle. Upon initial examination, highly polar Ecd conjugates appeared to be the principal metabolites found in all molt stages. HPLC fractions containing apolar Ecds initially exhibited low RIA activity. Upon hydrolysis with a Helix pomatia enzyme preparation and reanalysis, significant amounts of other Ecds were released. Amounts of apolar Ecd conjugates were estimated, at their highest levels, to be at least 50% of the total Ecds in MGs of molt stage D3 lobsters. Only the MG formed significant amounts of apolar Ecds upon in vitro culture with [3H]ecdysone ([3H]E). Epidermis and antennal gland significantly increased their rates of [3H]E metabolism in vitro between molt stages C4 and D1. This result further supports the idea that regulation of ecdysteroid metabolism, at least in selected tissues, may be important in the molt cycle regulation of hormone titers. Using gel filtration column chromatography and sucrose density gradient centrifugation analyses, evidence was found for association of apolar Ecds with a protein(s) from MG cytosol. The protein was estimated to have a molecular weight of 180,000-200,000 and specifically bound apolar Ecds.

Ecdysteroid titers and Y-organ activity during late anecdysis and proecdysis in the fiddler crab, Uca pugilator

The titer of ecdysone in hemolymph and the ratio of ecdysone to other radioimmunoassay(RIA)-active hemolymph ecdysteroids were compared to in vitro secretion of ecdysone in Y-organs removed from eyestalkless fiddler crabs at various times following eyestalk ablation. Using high-pressure liquid chromatography (HPLC) and RIA it was established that ecdysone, 20-hydroxyecdysone, and RIA-active metabolites are present in the hemolymph at the end of anecdysis and throughout proecdysis. There was little correlation between in vitro secretory activity and total ecdysone in circulation. Ratios of ecdysone and 20-hydroxyecdysone changed during proecdysis as did the percentage of total RIA activity attributable to both. Positive correlations were observed between in vitro Y-organ secretion rates and amounts of ecdysteroids extracted from hemolymph and added to incubation media.

Ecdysteroid metabolism in a crab: Carcinus maenas L

Ponasterone A (25-deoxy-20-hydroxyecdysone) and 20-hydroxyecdysone were the major ecdysteroids detected in crab hemolymph, although some ecdysone was also present. The metabolism of ponasterone A was examined in intermolt and premolt crabs either by injecting the radiolabeled hormone or by incubating tissues in its presence. Metabolites were extracted from the surrounding seawater and from tissues and separated by high-performance liquid chromatography. Ponasterone A metabolism proceeds through (1) C-25 and C-26 hydroxylation, followed by formation of inactivation products via oxidation of the terminal alcoholic group to a carboxylic residue, (2) conjugation, (3) "binding" to very polar compounds and (4) side-chain scission. The conversion of ponasterone A into 20-hydroxyecdysone, inokosterone (25-deoxy-20, 26-dihydroxyecdysone), 20, 26-dihydroxyecdysone and ecdysonoic acids, as well as the formation of conjugates and of very polar compounds, occurs in various tissues. These metabolites were excreted by both intermolt and premolt crabs.

Patterns of serum ecdysteroids during induced and uninduced proecdysis in the fiddler crab, Uca pugilator

Eyestalk-intact and eyestalkless fiddler crabs, Uca pugilator, have similar temporal patterns of circulating serum ecdysteroids during proecdysis. Both groups of animals showed two distinct transient peaks of radioimmunoassay (RIA)-active ecdysteroids. Peak 1 occurred 3 weeks prior to ecdysis and preceded the onset of rapid proecdysial limb bud growth. Peak 2 was a larger peak that occurred a few days prior to ecdysis. Thin-layer chromatography profiles of the two peaks showed at least seven RIA-active compounds common to both peaks. The relative abundance of these compounds differed between the two peaks. The role of the eyestalks in control of circulating ecdysteroids was limited to maintenance of intermolt conditions. During proecdysis, the control of circulating ecdysteroid levels was located outside of the eyestalks. There was no correlation between limb bud growth rates and serum ecdysteroid levels during proecdysis.

Ecdysone 20-monooxygenase activity during larval-pupal development of Manduca sexta

Profiles of ecdysone 20-monooxygenase (E-20-M) activity in the fat body and midgut of Manduca sexta were determined during larval-pupal development. The E-20-M activities for both tissues were found to exhibit a single major fluctuation during this 10-day period of development: fat body, a 10-fold fluctuation with peak activity on day 4; midgut, a 60-fold fluctuation with peak activity on day 5. Substrate kinetics revealed that the apparent Km values of fat body and midgut monooxygenases for ecdysone were fairly constant during the instar, 2.42 X 10(-7) M and 4.67 X 10(-7) M, respectively. By contrast, the monooxygenase Vmax values in each tissue fluctuated in a manner both quantitatively and temporally coincident with the fluctuations in enzyme activity. These findings suggest that changes in E-20-M activity are a function of changes in the titer of the enzyme. The possible developmental significance of the fluctuations in E-20-M activity are discussed.

Development of microsomal cytochrome P-450 monooxygenases during the last larval instar of the locust, Locusta migratoria: correlation with the hemolymph 20-hydroxyecdysone titer

Several enzyme activities were measured in microsomes from Malpighian tubules and from fat body of the locust, Locusta migratoria, during the last larval instar and the 20-hydroxyecdysone titer was determined in the hemolymph. Ecdysone 20-monooxygenase, the cytochrome P-450 dependent monooxygenase which converts ecdysone to the active molting hormone 20-hydroxyecdysone had a low activity in the beginning of the instar, but showed a peak in both Malpighian tubules and fat body which coincided with the peak of 20-hydroxyecdysone in the hemolymph. The varying ratios of ecdysone and 20-hydroxyecdysone in L. migratoria hemolymph may therefore be accounted for by these changes in ecdysone 20-monooxygenase activity. The amounts of cytochrome P-450 and the activity of NADPH-cytochrome c reductase also showed a peak on day 5 of the instar, as did the activity of cytochrome P-450 linked lauric acid omega-hydroxylase in fat body microsomes. In larvae experimentally deprived of molting hormone, the activities of the cytochrome P-450 monooxygenases were low. The possible role of ecdysteroids in the control of developmental changes of cytochrome P-450 monooxygenases is discussed.

Differences in inducibility by glucocorticoids of rat liver TO and TAT

The modulation of tryptophan-oxygenase (TO) and tyrosine amino-transferase (TAT) in the rat liver after a single dose of hydrocortisone has been studied under various physiological conditions. Differences in the induction behavior of the two enzymes have been observed dependent on sex, age, amount of administered hormone, and presence or absence of the adrenals. Some of the results observed are the following: 1) TO reached its maximum induction level 3 h prior to TAT in normal male rats. This difference disappeared when adrenalectomized male rats or when female animals were tested. 2) The maximal induction values of both enzymes were 50--80% higher in adrenalectomized rats than in normal rats. This effect was independent of sex. 3) Higher doses of hydrocortisone were necessary for optimal induction of TO and TAT in normal than in adrenalectomized rats. 4) The minimum dose of hydrocortisone necessary for enzyme induction was significantly lower for TO than for TAT. 5) Actinomycin D caused a complete inhibition of the induction of TO and TAT when given simultaneously with the glucocorticoid. The inhibition was less complete the longer the interval between hormone and actinomycin D administration. The activity of TAT was suppressed to a larger extent than TO.

Ecdysterone biosynthesis: a microsomal cytochrome-P-450-linked ecdysone 20-monooxygenase from tissues of the African migratory locust

Ecdysone 20-monooxygenase, an enzyme which converts ecdysone to ecdysterone (the major moulting hormone of insects) has been characterized in cell-free preparations of tissues from African migratory locust. The product of the reaction has been identified as ecdysterone on the basis of several microchemical derivatization and chromatographic methods. Ecdysone 20-monooxygenase activity is located primarily in the microsomal fraction which also carries NADPH cytochrome c reductase and cytochrome P-450, as shown by sucrose density gradient centrifugation. Optimal conditions for the ecdysone 20-monooxygenase assay have been determined. The enzyme has a Km for ecdysone of 2.7 x 10(-7) M and is competitvely inhibited by ecdysterone (Ki = 7.5 x 10(-7) M). Ecdysone 20-monooxygenase is a typical cytochrome P-450 linked monooxygenase: the reaction requires O2 and is inhibited by CO, an effect partially reversed by white light. The enzyme is effectively inhibited by several specific monooxygenase inhibitors and by sulfhydryl reagents, but not by cyanide ions. Ecdysone elicits a type I difference spectrum when added to oxidized microsomes. NADPH acts as preferential electron donor. The transfer of reducing equivalents proceeds through NADPH cytochrome c (P-450) reductase: ecdysone 20-monooxygenase is inhibited by cytochrome c. Both NADPH cytochrome c reductase and ecdysone 20-monooxygenase are inhibited by NADP+ and show a similar Km for NADPH. The Malpighian tubules have the highest specific activity of ecdysone 20-monooxygenase, while fat body contain most of the cytochrome P-450 and NADPH cytochrome c reductase.

The successful induction of molting in the adult male lobster (Homarus americanus) with a slow-release form of ecdysterone

In an initial, and then a confirmatory experiment, adult, male lobsters were injected with solvent, ecdysterone (E, 2.0 mug/g live weight) or ecdysterone acetate (EAc, 2.5 or 5.0 mug/g live weight) emulsions in Freund's incomplete adjuvant (FIA). Control lobsters underwent no molts and only one death in the two cases. The E treated animals all died (average: exp. 1, 19.2 +/-2.1 days; exp. 2, 25.3 +/- 8 days). After the lobsters were treated twice with 2.5 mug EAc/g live weight, in the first experiment, four out of five molted and one died; in the second experiment six out of eight molted, one died and one remained refractory. The high EAc dose resulted in five deaths, one molt and two pseudomolts after one treatment. It is concluded that the use of the oil emulsion and EAc sufficiently slowed the release of free ecdysterone to allow complete premolt development in the lobster.

The in vitro synthesis and secretion of alpha-ecdysone by the ring glands of the fly, Sarcophaga bullata

The in vitro secretory product of larval Sarcophage bullata ring glands has been identified as 2beta, 3beta, 14alpha, 22R, 25-pentahydroxy-5beta-cholest-7-en-6-one (alpha-ecdysone). Mid to late 3rd instar larval ecdysones were isolated and identified as 2beta, 3beta, 14alpha, 20R, 22R, 25-hexahydroxy-5beta-cholest-7-en-6-one (beta-ecdysone) and alpha-ecdysone at a ratio of 27:1. The low level of alpha-ecdysone in vivo, relative to its exclusive in vitro synthesis and secretion by the ring glands, is a function of the very active C20 hydroxylation mechanism in tissues peripheral to the ring gland. The role of alpha-ecdysone as a prohormone in dipteran metamorphosis is discussed.

Ecdysone-mediated stimulation of DOPA decarboxylase activity and its relationship to ovarian development in Aedes aegypti

Very little dopa decarboxylase activity is detectable in adult female mosquitoes Aedes aegypti which have not been allowed to engorge blood. However, when such females are injected with the molting hormone beta-ecdysone a marked stimulation of this enzyme's activity is observable. No stimulation is observed in males similarly injected, nor in females injected with cholesterol or a juvenile hormone mimic. In addition, ecdysone injection initiates ovarian development in these anautogenous non-blood-fed mosquitoes. The extent of stimulation in both cases is dependent upon the amount of beta-ecdysone administered. These results suggested that ecdysone may play a role in ovarian development in Aedes and led us to hypothesize that a normal blood meal may trigger the synthesis, activation, or release of this hormone endogenously. Using the radioimmune assay for ecdysone developed by Borst and O'Connor (Science [Wash. D. C.] 178:4-18.), we found that the titer of an antigenic-positive material, presumably ecdysone or a closely related analogue, substantially increased 24 h after blood feeding, thereby supporting our postulation.

Biosynthesis of agr-Ecdysone by Prothoracic Glands in vitro

An in vitro study in which isolated prothoracic glands of the Bombyx silkworm were cultured has provided definite evidence that the prothoracic gland is the site where molting hormone is synthesized. The hormone behaved very similarly to free ecdysone on thin-layer chromatography. Analysis by liquid chromatography and mass fragmentography revealed that the hormone is identical with alpha-ecdysone.