Inhibition of <Emphasis Type="Italic">DD2R</Emphasis> gene expression in the corpus allatum activates alkaline phosphatase in female <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Tissue-specific inhibition of the expression of the D2-like dopamine receptor gene (DD2R) in the corpus allatum (CA), which is a gland that synthesizes the juvenile hormone (JH), was tested for effect on alkaline phosphatase (ALP) activity and the intensity of the ALP response to heat stress (stress reactivity) in female Drosophila melanogaster. ALP activity and ALP stress reactivity in transgenic females with lower DD2R expression in the CA were higher than in control flies. A pharmacological elevation in JH increased ALP activity in females of the control strains. DD2R was assumed to mediate the inhibitory effect of dopamine of JH synthesis in the CA of D. melanogaster.     

Mutation in the <Emphasis Type="Italic">Drosophila</Emphasis> insulin-like receptor substrate, <Emphasis Type="Italic">chico</Emphasis>, affects the neuroendocrine stress-reaction development

It is shown for the first time that the insulin receptor substrate gene chico controls the functioning of the systems of metabolism of dopamine and juvenile hormone in Drosophila melanogaster females under normal conditions and in thermal stress.     

InR gene expression and octopamine metabolism in Drosophila melanogaster females

The influence of suppression of the expression of the Drosophila insulin-like receptor gene (InR) in corpus allatum (the gland-synthesizing juvenile hormone) on octopamine (OA) and juvenile hormone metabolism and on the development of the stress-reaction in Drosophila melanogaster females was studied. It was demonstrated that the suppression of InR gene expression in corpus allatum induces in D. melanogaster females an increase in the activity of the enzyme that limits the rate of octopamine synthesis (tyrosine decarboxylase), as well as in the level of juvenile hormone degradation and the intensity of the response of octopamine and juvenile hormone metabolism systems to heat stress. It was mentioned that a decrease in InR gene expression in corpus allatum does not influence the activity of OA-dependent N-acetyltransferase (the enzyme that degrades octopamine). It was established that the influence of suppression of the InR gene expression in corpus allatum on octopamine metabolism is mediated by juvenile hormone, since the treatment of flies by exogenous juvenile hormone restores the activity of tyrosine decarboxylase in flies with decreased InR expression in corpus allatum up to the normal level.     

The DD2R gene expression level in the corpus allatum affects the fitness of female Drosophila melanogaster

The effect of tissue-specific suppression of the dopamine D2-like receptor gene (DD2R) in the corpus allatum (CA), the gland that synthesizes juvenile hormone (JH) on the Drosophila melanogaster resistance to heat stress has been studied. A decreased expression of the DD2R gene in the CA has been found to substantially decrease the heat stress resistance of adult transgenic female, but not male, D. melanogaster compared to the control group, this phenomenon being weakly pronounced in juvenile flies. The effect of DD2R activation on the D. melanogaster reproductive function has been estimated. It has been shown that treatment of D. melanogaster with a synthetic specific agonist of DD2R decreases the fertility, the effect being considerably stronger in adult flies than in juvenile ones. It is concluded that the change in the number of DD2Rs in CA or their activation decreases the fitness of Drosophila.     

An ultrastructural and developmental analysis of the corpus allatum of juvenile hormone deficient mutants ofDrosophila melanogaster

Summary The ultrastructure of the corpus allatum of theapterous mutantsap ⁴ andap ^56f ofDrosophila melanogaster during larval-pupal-adult metamorphosis and adult life was correlated with the gland's ability to synthesize juvenile hormone in vitro. During the early wandering period of the third instar of both mutants, a high concentration of smooth endoplasmic reticulum, mitochondria and mitochondrion-scalariform junction complexes are typical features of an active corpus allatum cell. Juvenile hormone biosynthesis by the glands is high at that time and, in fact, only slightly lower than that of wild type glands. In contrast to the wild type gland, the cells of the pupal and pharate adult corpus allatum of both mutants contains highly electron dense mitochondria with tubular cristae but no whorls of smooth endoplasmic reticulum nor glycogen clusters. The frequency and size of the lipid droplets, putatives depots of the juvenile hormone precursors, in cells of theap ^56f gland is a function of the insect's age, but both are lower than in wild type gland cells. Juvenile hormone biosynthesis by both mutant glands remains at the basal level when compared to increased synthesis by the wild type gland. The frequency and density of lipid droplets in cells of theap ⁴ corpus allatum are much lower than in theap ^56f glands. During adult life, the ultrastructural profile of theap ^56f corpus allatum is similar to that of the wild type gland although the in vitro production of juvenile hormone by the former is much lower than that of the wild type gland. The ultrastructural features of the adult corpus allatum ofap ⁴ homozygotes reveal precocious degeneration and support the view that this non-vitellogenic mutant is a juvenile hormone deficient mutation.     

Insulin‐like receptor substrate gene chico regulates octopamine metabolism in Drosophila melanogaster

Octopamine, one of the main insect biogenic amines, plays an important role in the control of fitness in Drosophila melanogaster Meigen. The present study examines the effects of a null mutation of the gene of the insulin‐like receptor substrate (chico), in the heterozygous state, on octopamine metabolism, heat stress resistance and fecundity of D. melanogaster. A rise in the activity of one of the key enzymes of octopamine synthesis, tyrosine decarboxylase, as well as that of an enzyme of its degradation, octopamine‐dependent N‐acetyl transferase, is observed in chico^1/+ females. It is also found that the resistance to heat stress is decreased and fecundity is reduced dramatically in chico^1/+ flies. Such changes in these parameters in D. melanogaster females result from a rise in octopamine titre, which suggests that chico affects the octopamine level by regulating the activity of tyrosine decarboxylase.     

Inhibition of DD2R gene expression in the corpus allatum activates alkaline phosphatase in female Drosophila melanogaster

Tissue-specific inhibition of the expression of the D2-like dopamine receptor gene (DD2R) in the corpus allatum (CA), which is a gland that synthesizes the juvenile hormone (JH), was tested for effect on alkaline phosphatase (AP) activity and the intensity of the AP response to heat stress (stress reactivity) in female Drosophila melanogaster. AP activity and AP stress reactivity in transgenic females with lower DD2R expression in the CA were higher than in control flies. A pharmacological elevation in JH increased AP activity in females of the control strains. DD2R was assumed to mediate the inhibitory effect of dopamine of JH synthesis in the CA of D. melanogaster.     

Humidity affects genetic architecture of heat resistance in Drosophila melanogaster

Laboratory experiments on Drosophila have often demonstrated increased heritability for morphological and life‐history traits under environmental stress. We used parent–offspring comparisons to examine the impact of humidity levels on the heritability of a physiological trait, resistance to heat, measured as knockdown time at constant temperature. Drosophila melanogaster were reared under standard nonstressful conditions and heat‐shocked as adults at extreme high or low humidity. Mean knockdown time was decreased in the stressful dry environment, but there was a significant sex‐by‐treatment interaction: at low humidity, females were more heat resistant than males, whereas at high humidity, the situation was reversed. Phenotypic variability of knockdown time was also lower in the dry environment. The magnitude of genetic correlation between the sexes at high humidity indicated genetic variation for sexual dimorphism in heat resistance. Heritability estimates based on one‐parent–offspring regressions tended to be higher under desiccation stress, and this could be explained by decreased environmental variance of heat resistance at low humidity. There was no indication that the additive genetic variance and evolvability of heat resistance differed between the environments. The pattern of heritability estimates suggests that populations of D. melanogaster may have a greater potential for evolving higher thermal tolerance under arid conditions.     

Ubiquitous downregulation of InR gene expression affects stress associated hormone metabolism in Drosophila females

The effect of the ubiquitous downregulation of insulin receptor (InR) gene expression on the metabolism of juvenile hormone (JH) and dopamine (DA) in young females of D. melanogaster under normal conditions and heat stress is studied. The level of JH degradation and alkaline phosphatase activity (ALP, an enzyme regulating DA synthesis) were used as indicators of JH and DA levels, respectively. We demonstrated that, under normal conditions, the ubiquitous inhibition of the InR gene expression in D. melanogaster females induced an increase in the JH degradation and ALP activity. As we have already shown, this is indicative of the decrease in the concentration of the above hormones. It was also found that the total inactivation of InR does not affect the initiation of JH and DA metabolic system response to heat stress; however, it does affect its intensity. Thus, the involvement of the insulin signaling pathway in the regulation of the JH and DA metabolism in Drosophila females was demonstrated in vivo under normal and stress conditions.     

The effect of mild heat stress of different frequencies on the adaptability of Drosophila melanogaster females

In natural populations, insects regularly face an adverse impact of different natures: harsh weather swings, lack of food resources, the insecticidal treatment. We studied the effect of repeated episodes of mild heat stress of different frequencies on stress resistance of Drosophila melanogaster females. We found out that the mild heat stress (38°С, 1 hr) repeated daily within 2 weeks resulted in (a) an increased activity of the dopamine (DA) metabolism enzymes, DA‐dependent arylalkylamine N‐acetyltransferase and alkaline phosphatase, which suggested a decrease in DA level, and (b) an increased survival rate under acute heat stress (38°С, 4 hr). The same mild heat stress repeated weekly had no effect on these parameters.     

The Effects of Stress-Related Hormones on the Stress Resistance in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> Carrying Mutation in the <Emphasis Type="Italic">Dilp6</Emphasis> Gene

The heat stress resistance of Drosophila melanogaster females carrying a hypomorphic mutation of the DILP6 insulin-like protein gene (dilp6 ⁴¹ ) under a change in the level of stress-related hormones (juvenile hormone and octopamine) is studied. It is revealed that the dilp6 ⁴¹ mutation decreases the heat stress resistance of mature D. melanogaster females. An experimental decrease in the level of juvenile hormone is shown to restore the stress resistance of mutant females to the level of stress resistance observed in wild type Canton S females. These data suggest that the effects of the dilp6 ⁴¹ mutation on the stress resistance of females are mediated by an increased level of juvenile hormone. An experimental increase in the octopamine level that causes an increase in juvenile hormone level supports this hypothesis: the resistance to heat stress decreases in females of both lines and this decrease is more significant in mutant females than in the control line. Thus, it is established for the first time that the effect of the hypomorphic dilp6 gene mutation on the heat stress resistance of D. melanogaster females is mediated by juvenile hormone.     

Altered juvenile hormone metabolism, reproduction and stress response in Drosophila adults with genetic ablation of the corpus allatum cells

Juvenile hormone (JH), which controls many developmental and physiological processes in Drosophila melanogaster, is synthesized de novo in the specialized endocrine glands, corpus allatum (CA). The present study concerns JH metabolism, reproduction and stress resistance in Drosophila with genetic ablation of a part of CA cells. The correlated regulation of JH biosynthesis and degradation in Drosophila adults has been found: ablation of CA cells led to (1) a dramatic decrease in activity of the key regulatory enzyme of JH biosynthesis, juvenile hormone acid methyl transferase and (2) a considerable increase in JH-hydrolyzing activity. It has been also shown that ablation of CA cells caused three significant physiological changes: (1) an increase in the intensity of response of JH degradation system to heat stress; (2) a disturbance of reproduction; (3) a decrease in stress resistance. Pharmacological rise of JH level rescued JH-hydrolyzing activity, fecundity and stress resistance in CA-ablated females. Pronouncedly, all the physiological effects caused by CA ablation were significant in females but not in males indicating a sexual dimorphism of JH physiological roles in Drosophila adults.     

Precocene I and II inhibition of vitellogenic oöcyte development in Drosophila melanogaster

Adult female Drosophila melanogaster were exposed to precocene I and II, antiallatropin compounds which result in juvenile hormone deficiency in many insects. The presence of juvenile hormone in Drosophila adults was evaluated by examining vitellogenic oöcyte development, a process regulated by juvenile hormone in these flies. Both precocenes reduced the number of vitellogenic oöcytes present 43 hr after exposure in a dose-dependent manner. Precocene I was effective when applied to either newly eclosed females prior to vitellogenic oöcyte development or to gravid females. Precocene I was also effective in decapitated females, indicating that the action of the compound is not mediated by the brain. Corpus allatum volume, presumably a reflection of secretory activity, increased between 0 and 24 hr after eclosion in control females but not in precocene-treated females even after 48 hr. However, when females were removed from precocene medium, gland volumes increased within 48 hr to approximately those of control flies. This result is consistent with the reversibility of the precocene effect on Drosophila adults. These results suggest that precocene acts on the corpus allatum of Drosophila adult females to produce juvenile hormone deficiency.     

A pharmacological and endocrinological study of female insemination inPhormia regina (Diptera: Calliphoridae)

Injections of octopamine, dopamine, and the octopaminergic agonists, clonidine and naphazoline, into the thoracic hemocoel enhanced female insemination in sugar-fed (sexually unreceptive)Phormia regina. Topical applications of the juvenile hormone (JH) analogue, methoprene, also enhanced female insemination in sugar-fed (sexually unreceptive)P. regina. Since JH plays a role in receptivity in protein-fed females, it was originally hypothesized that one agonist, clonidine, enhanced female insemination by acting on the corpus allatum (CA) to increase JH biosynthesis. Two or three doses of the antiallatal agent, precocene II, prior to administration of clonidine, did not inhibit clonidine-enhanced female insemination. Removal of the corpus allatum also did not have a significant effect on clonidine-enhanced female insemination. Measurement of juvenile hormone (JH) biosynthesis/release in corpora allata, which were removed at 1, 3, 5, and 7 h postinjection, revealed that clonidine does not affect JH biosynthesis/release. Our study reveals a possible role for the biogenic amines in female insemination in insects. We suggest that the octopaminergic agonist, clonidine, acts downstream from the corpus allatum on the regulatory mechanisms involved in female insemination.     

Juvenile Hormone and Insulin Regulate Trehalose Homeostasis in the Red Flour Beetle,Tribolium castaneum

Insulin/IGF-1 signaling (IIS) has been well studied for its role in the control of life span extension and resistance to a variety of stresses. The Drosophila melanogaster insulin-like receptor (InR) mutant showed extended life span due to reduced juvenile hormone (JH) levels. However, little is known about the mechanism of cross talk between IIS and JH in regulation of life span extension and resistance to starvation. In the current study, we investigated the role of IIS and JH signaling in regulation of resistance to starvation. Reduction in JH biosynthesis, JH action, or insulin-like peptide 2 (ILP2) syntheses by RNA interference (RNAi)-aided knockdown in the expression of genes coding for juvenile hormone acid methyltransferase (JHAMT), methoprene-tolerant (Met), or ILP2 respectively decreased lipid and carbohydrate metabolism and extended the survival of starved beetles. Interestingly, the extension of life span could be restored by injection of bovine insulin into JHAMT RNAi beetles but not by application of JH III to ILP2 RNAi beetles. These data suggest that JH controls starvation resistance by regulating synthesis of ILP2. More importantly, JH regulates trehalose homeostasis, including trehalose transport and metabolism, and controls utilization of stored nutrients in starved adults.     

The role of endocrines in flight-muscle degeneration in Dysdercus cingulatus (Heteroptera: Pyrrhocoridae)

In Dysdercus cingulatus, extirpation of the median neurosecretory cells inhibits flight-muscle breakdown. However, implantation of median neurosecretory cells or corpus allatum into females lacking these neurosecretory cells induces muscle histolysis. Median neurosecretory cells stimulate the corpus allatum to produce juvenile hormone which in turn induces muscle degeneration. Topical application of kinoprene induces muscle breakdown, even in males and starved virgin females. The direct participation of juvenile hormone in muscle degeneration is further confirmed by observations on the effect of precocene II which inhibits muscle histolysis in many individuals. The endocrine basis of vitellogenesis and flight-muscle degeneration could be identical; vitellogenesis however appears to require a higher threshold concentration of juvenile hormone.     

Histophysiological studies on the corpus allatum during prepupal diapause in Monema flavescens (Lepidoptera)

The appearance of the corpus allatum, the central endocrine gland of diapause, was examined histologically in the slug moth prepupae, Monema flavescens (Lepidoptera) Before beginning of diapause, the secretory cells of the corpus allatum increase in size with the enrichment of the cytoplasm in quantity and in number of organelles, while RNA synthesis also starts. As diapause progresses, the secretory cells have many large unstained vacuoles in the cytoplasm, which were demonstrated to contain some substances of lipoidal nature. It is not clear that the substance is juvenile hormone itself or a material related to juvenile hormone. Agranular ER is the most characteristic organelle connected with mitochondria and situated around the vacuoles during diapause. Electron micrographs show that agranular ER and mitochondria have an essential role for the production of juvenile hormone. The function of the corpus allatum during diapause and the relationship between juvenile hormone and diapause are discussed.     

Biosynthesis and release of juvenile hormone during the reproductive cycle of the ring-legged earwig

Corpora allata of adult female Euborellia annulipes, incubated in medium containing ³H-methionine, synthesized and released juvenile hormone III. Labelled material co-migrating with methyl farnesoate was also found, suggesting this as an intermediate in the pathway of juvenile hormone III production. Juvenile hormone was not appreciably stored in the glands, but was released into the medium. In normal medium, 93.6 ± 1.6% of the total juvenile hormone III synthesized was released and 96.5% ± 0.3 in medium supplemented with 60 μM farnesoic acid. The rate of juvenile hormone III biosynthesis/release in vitro remained constant for at least 8 hr for glands of different activities. The rate of juvenile hormone production was closely correlated with the gonadotrophic cycle. In females with previtellogenic ovarian follicles (0.26 ± 0.004 mm), hormone production was only 0.59 ± 0.13 fmol hr⁻/corpus allatum; production increased to 1.52 ± 0.25 fmol hr⁻¹/corpus allatum when basal follicles were growing rapidly, and remained high during the period of oviposition. By 3 days following oviposition when females were brooding clutches, hormone production had declined to 0.46 ± 0.13 fmol hr⁻¹/corpus allatum. The addition of 60 μM farnesoic acid to the medium enhanced juvenile hormone biosynthesis at each stage examined. Lastly, elevating the level of l-methionine in the medium also enhanced hormone biosynthesis. Maximal hormone production was 32.8 ± 10.9 fmol hr⁻¹/corpus allatum, at an l-methionine concentration of 51 μM.