[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 activity ofJH degradation and alkaline phosphatase (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 ofJ H 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.

[Role of DopR in the molecular mechanism of the dopamine control of juvenile hormone metabolism in female Drosophila]

The effect of a decreased availability of the D1-like dopamine receptor (DopR) in Drosophila (caused by DopR antagonist added into food) on the juvenile hormone (JH) synthesis rate in young female D. melanogaster has been studied. The JH degradation rate and the alkaline phosphatase (ALP) and tyrosine decarboxylase (TDC) activities were used as indicators of the JH synthesis rate. Treatment of the flies with butaclamol, a specific DopR antagonist, has been demonstrated to increase the JH degradation rate, and the stress reactivity of the system of JH metabolism and decrease the ALP activity and stress reactivity, and increase the TDC activity and stress reactivity. As shown earlier, all this indicates a decrease in the JH synthesis rate in young female drosophila with a decreased DopR availability. It is concluded that the activating effect of dopamine on JH synthesis in Drosophila is mediated by D1-like receptors.

[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.

Decrease in juvenile hormone level as a result of genetic ablation of the corpus allatum cells affects the synthesis and metabolism of stress related hormones in Drosophila

Previous studies have shown that juvenile hormone (JH) regulates dopamine (DA) and octopamine (OA) content in Drosophila, and we have shown the influence of an increase in JH level on DA and OA metabolism in young females of Drosophila virilis and Drosophila melanogaster. Here we investigate the effects of genetic ablation of a subset of cells in the Corpusallatum (CA, endocrine gland synthesizing JH) on the DA levels and activities of alkaline phosphatase (ALP), tyrosine hydroxylase (TH), DA-dependent arylalkylamine N-acetyltransferase (DAT) and tyrosine decarboxylase (TDC) in young D. melanogaster females under normal conditions and upon heat stress (38°С). We show that ablation of СА cells causes: (1) a decrease in ALP, TH and DAT activities, (2) an increase in DA level and (3) an increase in TDC activity in young females. The CA ablation was also found to modulate ALP, TH and TDC responses to heat stress. Mechanisms of regulation of DA and OA levels by JH in Drosophila females are discussed.

[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.

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.

Mechanisms of age-specific regulation of dopamine metabolism by juvenile hormone and 20-hydroxyecdysone in Drosophila females

20-hydroxyecdysone (20E) and the juvenile hormone (JH) have an age-specific effect on total dopamine (DA) content in Drosophila (Gruntenko and Rauschenbach 2008). Earlier we studied the mechanism of influence of 20E and JH on DA metabolism in young females (Rauschenbach et al. in J Insect Physiol 53:587-591, 2007a: Arch Insect Biochem Physiol 65:95-102, 2008a; Gruntenko et al. in Arch Insect Biochem Physiol 72:263-269, 2009). Here we investigate the effects of 20E and JH on the activities of the alkaline phosphatase (ALP), tyrosine hydroxylase (TH) and DA-dependent arylalkylamine N-acetyltransferase (AANAT) in mature females of wild type D. virilis under normal conditions and under heat stress (38°C). 20E feeding of the flies led to a substantial decrease in ALP and TH activities and to an increase in AANAT activity in mature females. JH application resulted in an increasing of ALP and TH activities, but did not influence AANAT activity in mature females. A rise in JH and 20E levels was found to change ALP and TH stress reactivities. Mechanisms of age-specific regulation of DA level by 20E and JH in Drosophila females are discussed.

Dopamine down-regulates activity of alkaline phosphatase in Drosophila: the role of D2-like receptors

The effect of a rise in dopamine (DA) level as a result of a mutation, stress or pharmacological treatment on the activity of the enzyme of its synthesis, alkaline phosphatase (ALP) in females of Drosophila virilis and Drosophila melanogaster has been studied. It has been found that regardless of its nature, a rise in DA level has a negative effect on ALP activity, which indicates that DA down-regulates activity of the enzyme. The effects of bromocriptine (an agonist of Drosophila dopamine 2-like receptor (DD2R)) on ALP activity have been studied. ALP activity was found to drop in response to bromocriptine in flies. Conversely ALP activity was increased in flies with reduced DD2R expression (i.e. Actin5C-Gal4>UAS-ds-DD2R RNA-interference flies) vs. corresponding controls (i.e. Actin5C-Gal4>w1118 flies). Bromocriptine treatment of RNAi flies rescues ALP activity to the level typical of Actin5C-Gal4>w1118 flies. A change in DD2R number or availability was found not to prevent the response of ALP to heat stress, but to change the intensity of its response to the stress exposure. The role of D2-like receptors in down-regulation of ALP activity by DA and in ALP response to stressor in Drosophila is discussed.

20-hydroxyecdysone and juvenile hormone influence tyrosine hydroxylase activity in Drosophila females under normal and heat stress conditions

The effects of exogenous 20-hydroxyecdysone (20E) and the juvenile hormone (JH) on the activity of the tyrosine hydroxylase (TH), the first and rate-limiting DA biosynthetic enzyme, has been studied in young females of wild type D. virilis and D. melanogaster under normal conditions and under heat stress (38 degrees C). Both 20E feeding of the flies and JH application led to a substantial rise in TH activity. A rise in JH and 20E levels was found not to prevent the response of TH to heat stress, but to change the intensity of its response to the stress exposure. Putative mechanisms of regulation of DA level by 20E and JH in Drosophila females are discussed.

Effects of 20-hydroxyecdysone and juvenile hormone on octopamine metabolism in females of Drosophila

The effect of exogenous 20-hydroxyecdysone (20E) and juvenile hormone (JH) on the activities of the tyrosine decarboxylase (TDC), the first enzyme in octopamine (OA) synthesis, has been studied in young females of wild type D. virilis and D. melanogaster under normal and heat stress (38 degrees C) conditions. Flies fed 20E expressed increased TDC activity in both species. JH application decreased TDC activity in both species. A rise in JH and 20E levels did not prevent a TDC response to heat stress, but changed the response intensity. A long-term increase in JH titre had no effect on the activity of main OA catabolyzing enzyme, arylalkylamine N-acetyltransferase, in females of both species. A possible mechanism of regulation of OA levels by 20E and JH in Drosophila females is discussed.

Interplay of JH, 20E and biogenic amines under normal and stress conditions and its effect on reproduction

Juvenile hormone (JH) and 20-hydroxyecdysone (20E) are well known to play a gonadotropic role in adult insects. In Drosophila the mechanism of reciprocal regulation of JH and 20E is shown to be responsible for their proper balance. Dopamine is a mediator in this JH and 20E interplay. A proper balance between JH and 20E is crucial for the normal progress of oogenesis. An imbalance of gonadotropins leads to reproductive defects: a rise in JH titre leads to oviposition arrest, a rise in 20E level, to the degradation of vitellogenic oocytes. Upon a change in the level of one of the gonadotropins, the balance is restored owing to the relative change in the titre of the other.

[Effect of the apterous56f mutation on N-acetyltransferase and alkaline phosphatase activities in Drosophila melanogaster females]

Alkaline phosphatase (AP) and N-acetyltransferase (NAT) activities were studied in 1-day-old Drosophila melanogaster females of the apterous56f (ap56f) strain, having an elevated level of the juvenile hormone (JH) and a decreased level of dopamine as a result of the mutation, and in the Canton S ancestral wild-type strain in the normal conditions and upon an experimental increase in JH titer. The AP and NAT activities in ap56f females were significantly lower than in Canton S females in the norm. JH application increased the AP activity of mutant females to the level characteristic to JH-treated wild-type females.

Role of arylalkylamine N-acetyltransferase in regulation of biogenic amines levels by gonadotropins in Drosophila

The effect of 20-hydroxyecdysone (20E) and the juvenile hormone (JH) on the activity of the arylalkylamine N-acetyltransferase (AANAT) was studied in young females of wild-type D. virilis and D. melanogaster. 20E feeding of the flies led to a decrease in AANAT activity in both species when dopamine (DA) was used as substrate, but did not affect the enzyme activity when octopamine (OA) was used as substrate. JH application increased AANAT activity with DA as substrate in both species, but did not change it with OA as substrate. AANAT activity was also measured in young females of a JH-deficient strain of D. melanogaster, apterous ( 56f ). A decrease in the enzyme activity was observed in the mutant females as compared to wild-type. Mechanisms of regulation of DA level by gonadotropins in Drosophila are discussed.

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.

[Ecdysone 20-monooxygenase activity in Drosophila virilis strains varying in ecdysteroid response to heat stress]

The effect of various duration of heat stress (38 degrees C) on the activity of ecdysone 20-monooxygenase converting ecdysone into 20-hydroxyecdysone has been studied in D. virilis of wild type and mutant strain females, which differ by the mode of heat stress response of ecdysone and 20-hydroxyecdysone. We are the first to show that heat stress induces activity of ecdysone 20-monooxygenase in Drosophila females and enzyme activity correlates with the level of 20-hydroxyecdysone.