Changes in ecdysone content during postembryonic development of the wax moth, Galleria mellonella: the role of the ovary

Comprehensive physiology and toxicology of ecdysogens--The metabolically activated porphyrin-ecdysteroid complexes in insects

The polyhydroxylated derivatives of 6-keto,7-dehydrocholesterol (ecdysone, ecdysteroids, Ecd) are natural compounds widely distributed in plants. They exhibit strong anabolic, vitamin D-like, pharmacological effects in vertebrate animals and in the human body. In the larval stages of insects, injections of pure Ecd cause serious pathophysiological, "hyperecdysonic" syndromes associated with neuromuscular paralysis, premature cuticular apolysis and complete inhibition of ecdysis. Ecds do not penetrate insect cuticle. For this reason, all previous attempts to induce ecdysone responses by topical applications of Ecd failed. In this work, we tried to induce the topical effects of Ecd by preparation of more lipophilic complexes, with 2 or 4 molecules of 20-hydroxyecdysone (E20) attached to a relatively large nucleus of the porphyrin. The resulting porphyrin-E20 complexes (ecdysogens) have been subjected to standardised assays for ecdysone activity in the ligatured larvae ("dauerlarvae") of the greater waxmoth (Galleria mellonella). Similarly like the free E20 alone, porphyrin-E20 complexes had no effect when applied on the body surface or administered in the larval diet. When injected, however, they exhibited delayed effects, but the adverse ("hyperecdysonic") pathophysiological syndromes were reduced or abolished. It is concluded, therefore, that the replacement of pathophysiological, precocious or "hyperecdysonic" moults by the larval-pupal transformation, was due to successive metabolic liberation of the biologically active, free E20 from the porphyrin-E20 complex. The biological status of Ecd does not agree with their definition as the prothoracic gland (PG) hormone of insects, nor with the assumptions about a growth hormone of plants. A possibility that the most important status of Ecd may depend on the pharmacological properties of a sterolic D6 vitamin has been discussed.

Larval testes of the tobacco budworm: a new source of insect ecdysteroids

Testes of last-instar larvae of the tobacco budworm release five times more ecdysteroid into incubation medium (judged by radioimmunoassay) in 2.5 hours than is found in testis homogenates. Incubation of testicular components indicates that the testis sheath may be the site of ecdysteroid synthesis. Fractionation of hemalymph, testis homogenate, and incubation medium by high-performance liquid chromatography produces a distinct ecdysteroid pattern in each case. Thus, released testis ecdysteroids are probably converted to other forms for use, sequestration, or general circulation. Their functions are unknown.

Role of ecdysone 20-monooxygenase in regulation of 20-hydroxyecdysone levels by juvenile hormone and biogenic amines in Drosophila

The effects of increased levels of dopamine (feeding flies with dopamine precursor, L: -dihydroxyphenylalanine) and octopamine (feeding flies with octopamine) on ecdysone 20-monooxygenase activity in young (2 days old) wild type females (the strain wt) of Drosophila virilis have been studied. L: -dihydroxyphenylalanine and octopamine feeding increases ecdysone 20-monooxygenase activity by a factor of 1.6 and 1.7, respectively. Ecdysone 20-monooxygenase activity in the young (1 day old) octopamineless females of the strain Tbetah ( nM18 ), in females of the strain P845 (precursor of Tbetah ( nM18 ) strain) and in wild type females (Canton S) of Drosophila melanogaster have been measured. The absence of octopamine leads to a considerable decrease in the enzyme activity. We have also studied the effects of juvenile hormone application on ecdysone 20-monooxygenase activity in 2-day-old wt females of D. virilis and demonstrated that an increase in juvenile hormone titre leads to an increase in the enzyme activity. We discuss the supposition that ecdysone 20-monooxygenase occupies a key position in the regulation of 20-hydroxyecdysone titre under the conditions that lead to changes in juvenile hormone titre and biogenic amine levels.

Nucleotide sequence, structure and developmental regulation of LHP82, a juvenile hormone-suppressible hexamerin gene from the waxmoth, Galleria mellonella

We cloned and sequenced a composite cDNA corresponding to the 2.6 kb last instar-specific, juvenile hormone-suppressible Lhp82 mRNA from Galleria mellonella. The identity of the cDNA was confirmed by N-terminal amino acid sequencing of the purified Lhp82 subunit. In addition, we sequenced all coding regions and most of the intronic DNA as well as 1300 nucleotides of 5' flanking DNA from the Lhp82 gene. The eight exons of the Lhp82 gene specify a pre-protein of 706 residues, including the signal peptide of 18 amino acids. The deduced amino acid sequence of Lhp82 contains four potential N-glycosylation sites, and the calculated isoelectric point and molecular weight of secreted Lhp82 are pI = 6.43 and 79.9 kDa, respectively. Inspection of the 5' flanking and intronic regions of Lhp82 DNA revealed a 301 nucleotide cassette in intron 6 that appears to be a recently inserted repetitive element. We also performed Northern blot and nuclear run-off transcription experiments in order to determine the basis for Lhp82 gene inactivity after day 2 of the pupal stage. The results of these studies indicate that Lhp82 transcription is permanently shut off by the ecdysteroid pulse which occurs in the absence of juvenile hormone beginning 24 h post-pupation.

Sex differences in the profiles of prothoracic gland synthetic activity and of hemolymph ecdysteroid titers during development in the last larval instar of Rhodnius prolixus (Hemiptera)

The synthesis of ecdysteroids by prothoracic glands (PGs) of Rhodnius prolixus was measured in vitro by radioimmunoassay in both male and female larvae following initiation of development in the last larval instar by a blood meal. Neither ecdysteroid synthesis nor hemolymph titer differ between the sexes during the first few days following a blood meal. However, on Day 4 the PGs of female larvae commence a surge of increased synthesis, while in males this surge does not commence until Day 5. This 1 day difference is attributed to different times of activation of the PGs by prothoracicotropic hormone in male and female larvae. From Day 4 onward, differences between male and female larvae are described for both ecdysteroid synthesis and titer, both of which are more complex than a 1-day displacement of duplicate profiles. Both temporal and quantitative differences are detailed between males and females during Days 4-16 of development; ecdysteroid synthesis by PGs varies between males and females by up to fourfold on the same day. The hemolymph ecdysteroid titer profile closely follows that of PG synthesis for each sex. Both PG activity and titer in females decline 1 day ahead of males. The declining titer is known to influence the timing of ecdysis, and it was found that the median ecdysis time of females occurs 1 day before that of males even when males and females are synchronized with each other using a developmental marker on Day 14. We conclude that male and female PGs possess the intrinsic ability to synthesize ecdysteroids in a sex-specific pattern during development.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of hormones in starvation-induced delay in larval hemolymph protein gene expression in Galleria mellonella

Developmental Northern analysis of larval hemolymph protein gene transcripts in Galleria mellonella showed that Lhp76 is expressed all through the larval life, while Lhp82 is expressed only during the last larval stadium. Neither transcript was detectable in pharate adults and adult moths. In addition, these transcripts were not detectable during the first 48 h of the last larval stadium. Experimental analyses of the effects of the nutritional state and the hormonal levels of the last instar larvae on LHP gene expression suggests that the nutritional state of the larva has no direct effect, but nutrition acts through its effect on the hormone titers. Larvae starved after the first 24 h of the stadium and those fed on a non-protein diet produced both the transcripts on schedule on day 3. However, starvation during the first 24 or 48 h or feeding them on agar caused a marked delay in activation of Lhp82. These starved larvae pupated 4 to 12 days later than controls. Furthermore, JH titers in the starved larvae remain high even 5 days after ecdysis into the last instar. Prothorax-ligation of the starved and the starved-refed larvae accelerated production of the transcripts, thereby suggesting that the nutritional state does not directly affect LHP gene expression. Application of JH 1 to the ligated preparations resulted in selective blocking of Lhp82, while 20-OH ecdysone affected both the genes, thereby supporting the view that the insect hormones play an important role in stage-specific expression of LHP genes.

Developmental regulation of the larval hemolymph protein genes in Galleria mellonella

The role of juvenile hormone (JH) and 20-hydroxyecdysone (20-HE) in the stage-specific expression of the larval hemolymph protein (LHP) genes, Lhp82 and Lhp76, was investigated in the waxmoth, Galleria mellonella, larvae. Northern blot and dot hybridization analyses of total RNA in larvae that were undergoing an extralarval molt, induced either by cold shock or by application of JH to day-0 last instar larvae, showed that the last instar-specific Lhp82 transcripts were not present during this molt cycle. Lhp76 transcripts were, however, present transiently. During the course of an extralarval molt induced by JH in day-3 larvae both the transcripts were present but they were relatively less abundant than in the controls. JH had no effect on the relative abundance of the Lhp transcripts when applied to ligated day-3 or older larvae. By contrast, application of 20-HE either to intact or prothorax-ligated larvae of different developmental stages as well as to fat body in vitro resulted in a rapid decrease in the relative abundance of the Lhp transcripts. The natural decrease in the Lhp transcript levels that occurs in wandering and spinning last instar larvae was blocked in ligated larvae, probably due to deprivation of the source of the endogenous ecdysteroids. These observations suggest that ecdysteroids serve as the natural cue to turn off the Lhp genes at each molt and that JH blocks activation of only the last instar-specific Lhp82 gene.

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.

Hormonal regulation of ovarian ecdysteroid production in the autogenous mosquito, Aedes atropalpus

The effects of juvenile hormone (JH) and egg development neurosecretory hormone (EDNH) on ovarian ecdysteroid production during vitellogenesis in the autogenous mosquito, Aedes atropalpus, were investigated using in vitro techniques coupled with radioimmunoassay (RIA) and high-pressure liquid chromatography (HPLC). Normal females were characterized by quantitative, qualitative, and temporal patterns of in vitro ovarian ecdysteroid production. Females decapitated at emergence showed little ovarian ecdysteroid production and did not undergo vitellogenesis. A 500-ng dose of JH-I applied topically to decapitated females restored normal patterns of ecdysteroid production. In both normal and experimental females, ecdysone constituted the major portion of the ecdysteroids secreted by the ovaries in vitro. However, significant amounts of other RIA-active materials were detected, one of which was probably 20-OH-ecdysone. Fat body incubations indicated that these tissues produce little RIA-active material during the peak of vitellogenesis. During that period, the ovaries were the major source of ecdysteroid. Various doses of JH-I, applied to abdomens isolated at emergence, enhanced ovarian responsiveness to subsequent applications of head extracts containing EDNH both in vivo and in vitro. A 500-ng dose of JH-I, applied topically to blood-fed, decapitated Aedes aegypti, stimulated a significant increase in in vitro ovarian ecdysteroid production. Similarities between these data and those demonstrating prothoracicotropic effects of JH in the Lepidoptera are discussed.

Ecdysteroids during the third larval instar in 1(3)ecd-1ts, a temperature-sensitive mutant of Drosophila melanogaster

The temperature-sensitive 1(3)ecd-1ts mutation (A. Garen, L. Kauvar, and J.A. Lepesant (1977). Proc. Natl. Acad. Sci USA 74, 5099-5103.) has been used in several laboratories to obtain Drosophila larvae deprived of moulting hormone. The development of mutants and controls during the third larval instar at permissive (20 degrees C) and restrictive temperatures (29 degrees C) was compared. Pupariation was inhibited when larvae were shifted to the restrictive temperature immediately at the second moult. The permanent larvae obtained remained active, did not leave the food, and reached a maximum weight superior to the weight of controls. Ecdysteroids were studied during the third larval instar by HPLC analysis and radioimmunoassays. A careful synchronization of the larvae at the second moult enabled the confirmation that at least one ecdysteroid peak occurs during the third larval instar, prior to the wandering stage in controls (20 or 29 degrees C). Ecdysone was then the predominant moulting hormone, whereas 20-hydroxyecdysone was the main ecdysteroid at the time of pupariation. Low levels of ecdysteroid were measured in mutant larvae shifted to 29 degrees C immediately at the second moult but larvae completely deprived of immunoreactive material were never observed. Nearly normal levels of ecdysteroids appeared at 27.5 degrees C. Feeding ecd-1 larvae maintained at restrictive temperature on 20-hydroxyecdysone-yeast mixture for 16 hr triggered abortive pupariation. Ecdysteroid levels were measured after the return of the larvae to the standard medium; normal levels were restored 24 hr later. The mutant ecd-1 appears to present interesting opportunities for the detailed study of the hormonal induction of a developmental process during the third larval instar.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlations between endocrine gland ultrastructure and hormone titers in the fifth larval instar of Manduca sexta

Correlations were made between endocrine gland ultrastructure and circulating hormone titers of Manduca sexta to investigate the mechanisms of hormone biosynthesis and secretion. Both the prothoracic glands (PTG), which secrete ecdysone, and the corpora allata (CA), which secrete juvenile hormone (JH), were studied. In the prothoracic glands, the intracellular spaces increase in area and reach their maximum size following the major ecdysteroid peak in the fourth and fifth larval instars. Within the intercellular spaces are multivesicular sacs (MVS), structures which are clusters of vesicles bounded by another membrane. Since these sacs are largely depleted of their internal vesicles after the second cycle of tropic hormone stimulates the PTG to secrete ecdysone, the MVS probably release a gland cell product at this time. In the CA, concentric whorls of smooth endoplasmic reticulum are present in larval glands, when the JH titer is high, but are absent from pupal CA when the JH titer is low. The peak of JH at Days 6-8 of the fifth larval instar occurs after an increase is seen in the neurosecretory cell axon diameters suggesting that the CA are stimulated by a brain hormone to release JH. The number of Golgi complexes increases in pupal CA and dense bodies are present in pupal but not larval glands. These Golgi complexes may be involved in the manufacture of lysosomal enzymes which degrade JH within the gland itself.

Cyclic AMP in the fat body of Mamestra brassicae during the last instar and its possible involvement in the cellular autophagocytosis induced by 20-Hydroxyecdysone

The amount of cAMP was assayed by a competitive protein binding method in fat body cells of Mamestra brassicae, during the last larval stage and after administration of 20-hydroxyecdysone. When expressed as picomoles of cAMP per milligram fresh weight of tissue, two increases in its concentration were observed on the 3rd and on the 6th days. However, only the first peak appeared on the curve when cAMP concentration was expressed as picomoles cAMP per milligram of protein of tissue homogenate. Electron microscopical examination of the tissue showed that the first increase of cAMP level coincided with the beginning of the formation of autophagic vacuoles and revealed a heavy accumulation of protein storage granules in the cells, starting on the 4th day. This process might mask the second rise of cAMP level when tissue protein content is taken as the basis for calculation. 20-Hydroxyecdysone (5 micrograms/g body wt) administered to 48-hr-old larvae induced premature autophagocytosis in the fat body cells and a sharp rise in their cAMP content, reaching within 3 hr a level as high as observed in the 3-day-old untreated larvae. Autophagy was also enhanced in the cells exposed to dibutyryl cAMP or theophylline either in vivo or in vitro. Based on these data we think that cAMP content of the fat body is controlled by ecdysone and that cAMP plays a significant role in the regulation of autophagocytosis in this tissue during metamorphosis.

Induction of Follicle Separation in the Mosquito by Physiological Amounts of Ecdysterone

Physiological quantities of the molting hormone, ecdysterone, injected into female Aedes aegypti prematurely induced separation of incipient follicles in the ovarioles, an event that normally occurs only in blood-fed females. It was possible to stimulate this morphological event with physiological amounts of hormone by mimicking, with two injections, the timing of normal increases in endogenous hormone of blood-fed females.

Graded inhibition of cell disintegration of juvenile hormone

The proventriculus of Galleria mellonella larvae consists of 260-300 polyploid cells. The cells grow throughout larval development and at each ecdysis produce a new cuticular lining of the proventriculus. Each cell secretes a large sclerotized plaque covered with thorns. At the end of the last larval instar, the cells disintegrate unless the larvae is treated with juvenile hormone or implanted with active corpora allata. Depending on the time of treatment and the hormone dose, these insects preserve their proventricular cells to graded degrees. In some cases, the cells continue to grow or at least preserve their full function, in other instances they secrete but small plaques with fewer thorns or a smooth cuticle without any thorns. Very late treatments preserve healthy cells incapable of secreting the cuticle.

The follicle cell epithelium of maturing ovaries of Locusta migratoria: a new biosynthetic tissue for ecdysone

Follicle cells of maturing ovaries of Locusta migratoria are demonstrated to synthesize the moulting hormone ecdysone (2beta,3beta,14alpha,22R,25-pentahydroxy-5beta-cholest-7-en-6-one). Studies of secretory kinetics under in vitro conditions show that the intensity of hormone secretion is strictly dependent on the stage of maturation of the excised ovaries.