Radioimmunossay of ecdysone. An application to Drosophila larvae and pupae

Respiratory metabolism of salivary glands during the late larval and prepupal development of Drosophila melanogaster

During the late larval period, the salivary glands (SG) of Drosophila show a cascade of cytological changes associated with exocytosis and the expectoration of the proteinaceous glue that is used to affix the pupariating larva to a substrate. After puparium formation (APF), SG undergo extensive cytoplasmic vacuolation due to endocytosis, vacuole consolidation and massive apocrine secretion. Here we investigated possible correlations between cytological changes, the puffing pattern in polytene chromosomes and respiratory metabolism of the SG. The carefully staged SG were explanted into small amounts (1 or 2μl) of tissue culture medium. The respiratory metabolism of single or up to 3 pairs of glands was evaluated by recording the rate of O2 consumption using a scanning microrespirographic technique sensitive to subnanoliter volumes of the respiratory O2 or CO2. The recordings were carried out at times between 8h before pupariation (BPF), until 16h APF, at which point the SG completely disintegrate. At the early wandering larval stage (8h BPF), the glands consume 2nl of O2/gland/min (=2500μl O2/g/h). This relatively high metabolic rate decreases down to 1.2-1.3nl of O2 during the endogenous peak in ecdysteroid concentration that culminates around pupariation. The metabolic decline coincides with the exocytosis of the proteinaceous glue. During and shortly after puparium formation, which is accompanied cytologically by intense vacuolation, O2 consumption in the SG temporarily increases to 1.6nl O2/gland/min. After this time, the metabolic rate of the SG decreases downward steadily until 16h APF, when the glands disintegrate and cease to consume oxygen. The SG we analyzed from Drosophila larvae were composed of 134 intrinsic cells, with the average volume of one lobe being 37nl. Therefore, a single SG cell of the wandering larva (with O2 consumption of 2nl/gland/min), consumes each about 16pl of O2/cell/min. A simultaneous analysis of the rate of protein and RNA synthesis in the SG shows a course similar to that found in respiratory metabolism.

Ecdysteroid biosynthesis and embryonic development are disturbed in insects (Locusta migratoria) reared on plant diet (Triticum sativum) with a selectively modified sterol profile

Wheat seedlings germinating in the presence of the systemic fungicide fenpropimorph accumulate 9beta,19-cyclopropylsterols (95% of total sterols) in place of Delta(5)-sterols, which are normally produced in these plants. Adult females of the phytophagous insect Locusta migratoria show a dramatic decrease in their cholesterol content when reared on fenpropimorph-treated wheat. These females lay eggs with the ecdysteroid concentration reduced by up to 80% as compared to controls. Injection of fenpropimorph to the insects or feeding them on wheat coated with the fungicide (normal sterol composition) does not affect their sterol or ecdysteroid profiles; addition of cholesterol to fenpropimorph-treated wheat prior to feeding restores normal ecdysteroid titers in the insects. The severe reduction of the ecdysteroid content in eggs laid by females reared on fenpropimorph-treated wheat is associated with a series of developmental arrests and/or abnormalities. The results show that the dietary 9beta,19-cyclopropylsterols cannot be used by Locusta in place of Delta(5)-sterols for ecdysteroid biosynthesis. They suggest that the selective inhibition of specific enzymes in the sterol biosynthetic pathway of the plants can be used as a strategy to control insect development.

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.

The Drosophila 63F early puff contains E63-1, an ecdysone-inducible gene that encodes a novel Ca(2+)-binding protein

Pulses of ecdysone at the end of Drosophila larval development dramatically reprogram gene expression as they signal the onset of metamorphosis. Ecdysone directly induces several early puffs in the salivary gland polytene chromosomes that, in turn, activate many late puffs. Three early puffs, at 2B5, 74EF, and 75B, have been studied at the molecular level. Each contains a single ecdysone primary-response gene that encodes a family of widely expressed transcription factors. We report here a molecular characterization of the 63F early puff. Unexpectedly, we have found this locus to be significantly different from the previously characterized early puff loci. First, the 63F puff contains a pair of ecdysone-inducible genes that are transcribed in the larval salivary glands: E63-1 and E63-2. Second, E63-1 induction in late third instar larvae appears to be highly tissue-specific, restricted to the salivary gland. Third, E63-1 encodes a novel Ca(2+)-binding protein related to calmodulin. The discovery of an ecdysone-inducible Ca(2+)-binding protein provides a foundation for integrating steroid hormone and calcium second messenger signaling pathways and generates an additional level for potential regulation of the ecdysone response.

Ecdysteroid titre and metabolism and cuticle deposition during embryogenesis of the ixodid tick Amblyomma hebraeum (Koch)

Three embryonic cuticles are formed before larval cuticle deposition during embryonic development of Amblyomma hebraeum. The quantity of radioimmunoassay-positive material varied between 50 and 200 pg ecdysone equivalents per mg, but no significant peaks were detected. Maternally incorporated [3H]-20-hydroxyecdysone and [3H]-ecdysone contained in freshly laid eggs appear to be conjugated to C-22 fatty acid esters and 3 alpha epimers of those esters, and, thus, appear doubly inactivated. In addition, ecdysone is converted to an unknown product called 2'. The role of these maternally derived ecdysteroids is unknown.

[Inhibition of ecdysone biosynthesis by synthetic molecules]

We studied the putative inhibitory activity of about 50 synthetic molecules on the biosynthesis of ecdysone. Most of these molecules had been synthesized according to the conceptual framework of suicide substrate type inhibitors. They potentially react either with well-known catalytic mechanisms (hydroxylations at C-22 and C-25) or with more hypothetic ones (introduction of the keto group at C-6 and the hydroxylation at C-14). The two hydroxylations which take place on the side chain at C-22 and C-25 in the last steps of the ecdysone biosynthetic pathway, and which are catalysed by cytochrome P-450 dependent monooxygenases, can be effectively affected. The essential chemical arrangement which produced a consequent inhibitory effect included an acteylenic or an allenic inhibitory function, near the hydroxylation to inhibit, with a hydroxyl group, preferably grafted in C-20. In order to increase the inhibitory effect, several characteristics gradually appeared: shortness of the side chain, hydroxyl group in position (R) at C-20 and at C-22, if necessary; in the proximal shortening side chain molecules, hydroxyl group at C-17 in position beta; lowering steric hindrance at C-20. It seemed that a molecule bearing a side chain in a relative position behind the midplan of the steroid nucleus induced a more important inhibitory effect. On the contrary, the form of the steroid nucleus itself (as in cholesterol, 7-dehydrocholesterol, 3-dehydrocholesterol, or in a molecule with a saturated B cycle) did not play a deciding part in the activity of the compound. Only the molecules with a typical ecdysteroid nucleus showed a poor inhibitory effect. Molecules acting as suicide substrate type inhibitors on the ecdysone biosynthesis should produce an irreversible inactivation of the enzyme and show a biosynthetic inhibition specifically linked to ecdysteroid. It was not the case of all the tested molecules. Some of them induced a very important inhibition without possessing the other characteristics of a suicide substrate type compound. Other derived chemicals, which were not synthesized according to the framework of the suicide substrate type molecules, showed all the characteristics of this type of molecules. In the course of this work, it has been possible to point out several molecules showing an important inhibitory effect on ecdysone biosynthesis.

Ecdysone coordinates the timing and amounts of E74A and E74B transcription in Drosophila

Pulses of the steroid hormone ecdysone function as temporal signals to coordinate the development of both larval and adult tissues in Drosophila. Ecdysone acts by triggering a genetic regulatory hierarchy that can be visualized as puffs in the larval polytene chromosomes. In an effort to understand how the ecdysone signal is transduced to result in sequential gene activation, we are studying the transcriptional control of E74, an early gene that appears to play a regulatory role in the hierarchy. Northern blot analysis of RNA isolated from staged animals or cultured organs was used to characterize the effects of ecdysone on E74 transcription. Ecdysone directly activates both E74A and E74B promoters. E74B mRNA precedes that of E74A, each mRNA appearing with delay times that agree with their primary transcript lengths and our previous transcription elongation rate measurement of approximately 1.1 kb/min. The earlier appearance of E74B transcripts is enhanced by its activation at an approximately 25-fold lower ecdysone concentration than E74A. E74B is further distinguished from E74A by its repression at a significantly higher ecdysone concentration than that required for its induction, close to the concentration required for E74A activation. These regulatory properties lead to an ecdysone-induced switch in E74 expression, with an initial burst of E74B transcription followed by a burst of E74A transcription. We also show that the patterns of ecdysone-induced E74A and E74B transcription vary in four ecdysone target tissues. These studies provide a means to translate the profile of a hormone pulse into different amounts and times of regulatory gene expression that, in turn, could direct different developmental responses in a temporally and spatially regulated manner.

Cuticle deposition and ecdysteroid titers during embryonic and larval development of the argasid tick Ornithodoros moubata (Murray, 1877, sensu Walton, 1962) (Ixodoidea:Argasidae)

Timing of embryonic and larval molts at the ultrastructural level and presence of ecdysteroids (ES) during embryonic and larval development of the argasid tick Ornithodoros moubata were studied. Embryonic "cuticles" A, B, and C were deposited 24-30 hr, 48-56 hr, and 6 days after oviposition, respectively. Deposition of the larval cuticulin layer started on Day 8 of embryonic development and procuticle deposition continued after hatching until apolysis of the larval cuticle 40 hr posthatch. Plaques of cuticulin formed on tips of microvilli 48-56 hr after hatching and procuticle was deposited until after ecdysis. Radioimmunoassay (RIA) was used to determine the ES titer in methanolic extracts of various ages of embryos and larvae. No peaks of RIA-positive material were detected during deposition of envelopes A, B, and C. However two peaks of ES were observed during embryonic development, one which coincided with the shortening of the germ band and a second which coincided with the deposition of the larval epicuticle on Day 8. During larval development, a peak of ES was observed on Day 3 (48-56 hr posthatch) and was correlated with nymphal epicuticle deposition. HPLC-RIA revealed that these last two peaks consisted mainly of 20-hydroxyecdysone together with a small quantity of ecdysone. Conjugated RIA positive material was present in freshly laid eggs and an augmentation of this esterase hydrolysable material was noted at the appearance of each ES peak. Thus the embryos did not appear to be hydrolyzing the maternal apolar conjugates to release ES during embryonic development; on the contrary, they appeared to be conjugating the newly synthesized hormones.

Caste and metamorphosis: hemolymph titers of juvenile hormone and ecdysteroids in last instar honeybee larvae

Juvenile hormone (JH) and ecdysteroid titers are critical factors for caste development and metamorphosis in the last larval instar of the honeybee, Apis mellifera. Two highly sensitive radioimmunoassays were used for the determination of these hormones in the hemolymph. For juvenile hormone, which is of prime importance for the control of caste development in honeybees, our data show a caste-specific peak in queen larvae of the early fifth instar. A second peak appears in prepupae of both castes which probably is responsible for the regulation of the pupal moult. A single peak of ecdysteroids was observed in prepupae of both castes. In queens, however, the titer increases distinctly earlier than in worker larvae. The ecdysteroid composition of this prepupal peak was determined by high-performance liquid chromatography separation followed by radioimmunoassay. Makisterone A proved to be the main ecdysteroid compound, but 20-hydroxyecdysone was also found in significant amounts.

Effects of an imidazole derivative (KK-42) on development and ecdysteroid production in Locusta migratoria (Insecta, Orthoptera)

The imidazole derivative KK-42 was applied in various experimental conditions to larvae and adult females of Locusta migratoria. The effect of this compound was monitored on the development of larvae, on oocyte growth in adult females and on the development of eggs laid by these females. KK-42 had only minor effects on postembryonic development; anticipation of imaginal moult was never observed. In contrast oocyte and egg development were markedly affected by KK-42: this effect is however not related to modifications of the synthesis of ecdysteroids in the ovaries.

Stage-specific effects of diflubenzuron on ecdysteroid titers during the development of Tenebrio molitor: evidence for a change in hormonal source

The effects of the insect growth regulator diflubenzuron (DFB) were observed on the larval-larval and larval-pupal moulting cycles of Tenebrio molitor, after treatment at ecdysis. In both cases, the first parts of the cycles, from ecdysis to apolysis, were apparently not affected, but the pharate periods were lengthened; treated animals were generally unable to perform ecdysis and died at this step. The ecdysteroid titers in the hemolymph of treated animals were measured with a radioimmunoassay and compared to controls. During larval-larval cycles, the single ecdysteroid increase was not affected by DFB treatment. On the contrary, during larval-pupal development, a significant modification was observed; whereas two ecdysteroid peaks occurred in controls, the second peak of treated animals was significantly reduced and slightly delayed; however, the first peak was not modified. Taking into account that previous observations demonstrated a complete inhibition of the ecdysteroid peak in Tenebrio pupae, these stage-specific differences could reveal either a change in the DFB sensitivity of a sole endocrine source (i.e., prothoracic gland) or a change in hormone origin during metamorphosis. Ligation experiments during the last larval stage, in combination or not with DFB applications, clearly demonstrated the change in the moulting hormone source at the end of larval development in Tenebrio.

A competitive enzyme-linked immunosorbent assay: applications in the assay of peptides, steroids, and cyclic nucleotides

Indirect competitive enzyme-linked immunosorbent assays (ELISAs) that can be used to quantify several types of small, bioactive molecules, including peptides, steroids, and cyclic nucleotides, are described. The assays require no special expertise to perform, and the sensitivities are very high, equally or exceeding what is commonly achieved in radioimmunoassay (RIA). The molecule to be assayed or a synthetic derivative is coupled to a protein carrier (= conjugate). The conjugate is adsorbed to the wells of a microtiter plate where it is bound by antibody in inverse proportion to free hapten in a sample or standard. Bound antibody is then quantified with enzyme-labeled anti-immunoglobulin and appropriate substrate. The assay of peptides is illustrated for the sulfated cholecystokinin octapeptide, in which an ED50 of 20 fmol (2 x 10(-10) M in 100 microliters assay volume) is attained. The ED50's and slopes of the dose-response curves in the steroid and cyclic nucleotide ELISAs are compared with those parameters obtained earlier by RIA using the same antisera. This comparison indicates that a steroid, ecdysone, can be quantified with no apparent participation of the bridging group of the conjugate in the competitive assay. Furthermore, the ED50's in the ecdysone assays (ecdysone 2 beta, 3 beta, 14 alpha, 22R, 25-pentahydroxy-5 beta-cholest-7-en-6-one, 7.7 fmol; 20-hydroxyecdysone, 16 fmol) are 19- to 38-fold lower for ELISA than for RIA. In the cyclic nucleotide assay, the bridge of a cAMP conjugate (homologous with the bridge of the immunogen) decreases the slope of the dose-response curve. This effect is minimized by the use of short incubations with anti-cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypogonadism and ecdysteroid production in Loa loa and Mansonella perstans filariasis

Possible endocrinological repercussions of infection with Loa loa and Mansonella perstans filariae were studied in Gabonese subjects. Microfilaremic males were compared with amicrofilaremic controls. In the infected group 13/105 subjects (12%) presented only abnormally low serum levels of testosterone (less than 4 ng/ml), 25/105 (24%) only abnormally high serum levels of gonadotrophins, FSH (greater than 15 mIU/ml) and LH (greater than 20 mIU/ml), and 22/105 (21%) presented anomalies in both testosterone and gonadotrophin levels. One out of 68 control subjects had 3.6 ng/ml seric testosterone and all had normal levels of gonadotrophins. Ecdysteroids were detected (greater than 0.025 ng/ml) in the serum of 87/97 (90%) microfilaremic subjects (GM 0.123 ng/ml) compared to 12/64 (19%) controls (GM 0.030 ng/ml). Ecdysteroids were detected in the urine of all subjects, infected (GM 8.468 ng/ml) as well as control (GM 1.245 ng/ml). The hormonal perturbations were correlated with the levels of Loa loa microfilaremia but not with those of serum and urinary ecdysteroids. These results demonstrate that microfilaremic subjects often show endocrinal signs of hypogonadism and present appreciable levels of ecdysteroids in serum and urine. A direct role for parasitic ecdysteroids in hypogonadism remains to be demonstrated.

Hemolymph ecdysteroids and molt cycle in males and females of Siriella armata M-Edw. (Crustacea: Mysidacea): possible control by the MI-ME X-organ of the eyestalk

Hemolymph ecdysteroids were quantified by radioimmunoassay (RIA) at successive stages of the molt cycle in the mysid Siriella armata. Profiles showed a single peak during premolt, at stage D1 for males, and D2 for reproducing females who displayed ecdysteroid levels 10 times higher than males. Titers were also measured for individuals which had been molt inhibited by early electrocauterization of the eyestalk MI-ME X-organ. In the case of total inhibition of molt preparation, the ecdysteroid peak was suppressed. It was displaced toward the end of the cycle when only ecdysis was inhibited. Ecdysone and 20-hydroxyecdysone were characterized in the hemolymph of both sexes using high-pressure liquid chromatography followed by RIA. High-polarity products, abundant in the female hemolymph, were resolved into 20-hydroxyecdysone and ecdysone by enzymatic hydrolysis and thin-layer chromatography. The quantitative and qualitative variations of ecdysteroid in the different situations (male or female, normal or inhibited cycles) are presented in relation to apolysis, epidermic activity, ecdysis, and secondary vitellogenesis in females, emphasizing the importance not only of ecdysteroids, but also of the MI-ME X-organ in monitoring molt and blood preparation in mysids.

Further experimental evidence for the involvement of ecdysone in the control of meiotic reinitiation in oocytes of Locusta migratoria (Insecta, Orthoptera)

Ecdysone has recently been shown to be able to trigger meiotic reinitiation in vitro in submature oocytes of Locusta. In the present study we have experimentally depressed (by 60-70%) ecdysone biosynthesis in the ovaries of adult females by rearing them on a diet with a modified sterol profile. Mature oocytes from such females fail to undergo normal reinitiation, but when incubated in vitro, can be induced to break their meiotic arrest by the addition of exogenous ecdysone. These results lend further support to the hypothesis that in Locusta, ovarian ecdysone is involved in the control of meiotic reinitiation.

Ecdysteroid titers during the molt cycle of Orchestia cavimana (Crustacea, Amphipoda)

Ecdysteroids were analyzed during a molt cycle in adult males of the crustacean Orchestia cavimana; levels were determined in the hemolymph and in whole bodies, using radioimmunoassay. Results show a single and sharp peak at the end of D1 stage, reaching 810 pg eq/microliter in the hemolymph (a 230-fold increase compared to the middle of intermolt). From B stage to the beginning of D1, levels are very low but increase regularly and significantly. The amplitude and the temporal position of the peak are discussed in detail, in relation to the precision of the staging (17 different stages can be easily made in Orchestia) and to the cuticle cycle (the hormonal peak occurs ca. 10 hr before the beginning of cuticle synthesis at D2). Preliminary experiments, using monoclonal antibodies during the period of low ecdysteroid titers or high-performance liquid chromatography followed by polyclonal RIA during the peak period, suggest that the immunoreactive hormone in O. cavimana behaves like 20-hydroxyecdysone. However, other minor compounds have been detected (some unknown, others migrating like ecdysone and ponasterone A in HPLC).

Normal and experimentally induced changes in hormonal hemolymph titers during parental behavior of the earwig Labidura riparia

The reproductive cycle of Labidura riparia includes two distinct phases of behavior: a feeding and sexual phase followed by a parental and fasting phase. These phases correspond to two contrasting physiological phases (vitellogenesis, followed by ovarian inactivity). These correlations have been verified by correlating radioimmunoassay (RIA) measurements of the levels of circulating juvenile hormones (JH) and ecdysteroids with ovarian state during the first reproductive cycle. Similar studies were also made after experimentally suppressing parental activity (care of eggs) either by depriving females of their eggs or by force-feeding during the egg-care phase. Taking eggs away without feeding caused the disappearance of parental behavior and a short lived period of vitellogenesis. Likewise, feeding in the presence of eggs resulted in vitellogenesis and disappearance of egg-care behavior. Thus, it appears that in order for the parental phase to develop normally it is necessary to preserve the proper external conditions (the presence of eggs) and physiological conditions (fasting).

Changes in ecdysteroid and juvenile hormone titers in the hemolymph of Galleria mellonella larvae and pupae

The variations in circulating ecdysteroids and juvenile hormones (JH) in Galleria, from the end of the antepenultimate larval stage until emergence of adults, have been determined. The two hormonal families were extracted separately from the same hemolymph sample and quantified by two radioimmunoassays. Juvenile hormone RIA activity was about 35 nM in larvae of the antepenultimate and penultimate stages. It dropped before each molt and increased thereafter. Moreover, it gradually decreased during the last larval instar. In pupae, it was generally low, but it rose drastically during the late pupal development and in young adults. This rise was very much higher in females than in males. Three different RIA-active compounds were found; they were assumed to be JH-I, JH-II, and JH-III according to their retention times in HPLC. The three compounds were present in almost equal concentration in larvae of the penultimate stage: JH-I predominated, however, during the last larval instar. In late pupae, the main hormone was JH-III both in males and in females. There is no clear relationship between ecdysteroid and juvenile hormone changes, except for a female-specific ecdysteroid rise which coincides with the juvenile hormone release in late pupae. This double hormonal stimulation can be involved in the regulation of vitellogenin synthesis and deposition in oocytes.

Metabolism of ecdysteroids during the vitellogenesis of the tick Ornithodoros moubata (Ixodoidea, Argasidae): accumulation of apolar metabolites in the eggs

The fate of injected [3H]ecdysone [( 3H]E) and 20-hydroxy-[3H]ecdysone [( 3H]20E) has been investigated in the female tick Ornithodoros moubata (Murray, 1877; sensu Walton, 1962). When injected into fed mated vitellogenic females, [3H]E is converted into [3H]20E and two apolar classes of metabolites, AP1 and AP2. Injected [3H]20E is directly converted into AP1 and AP2. AP2 is incorporated into the ovaries in a high proportion and at the end of the vitellogenic cycle represents about 25% of the total label recovered from the animal. The fate of labeled hormones injected into virgin females which perform an abortive vitellogenic cycle is quite similar. However, the ovaries incorporated less of the AP2 products. Ovaries of mated females cultured in vitro in the presence of [3H]E are able to produce [3H]20E and AP2. AP2 is incorporated, while [3H]20E is mainly found in the medium. Ovaries of virgin females presented a slower rate of transformation and of incorporation of the label. Labeled AP2 is recovered in freshly laid eggs and AP1 in the females after oviposition. AP1 and AP2 can produce [3H]20E, [3H]E, and other minor polar peaks when submitted to hydrolysis by esterase. It is concluded that the female O. moubata possesses a special enzymatic mechanism for transformation of ecdysteroids into apolar products and for selective incorporation of AP2 into the ovaries. These products are present in the freshly laid eggs and could play a role during embryogenesis.