Effects of juvenile hormone and 20-hydroxyecdysone on alkaline phosphatase activity in Drosophila under normal and heat stress conditions

Impact of Exposure to Leaves From Metal-Polluted Sites on the Developmental Parameters of Larvae of the Dark Sword-Grass, Agrotis ipsilon (Lepidoptera: Noctuidae)

Insects are impacted by pollutants in their environments and food sources. Herein, we set out a semi-field study to assess the impact of environmental heavy metal contamination on developmental parameters, energy reserves, and acidic and alkaline phosphatases in the larval Agrotis ipsilon (Lepidoptera: Noctuidae). Castor leaves from contaminated and uncontaminated (reference site) areas were fed to A. ipsilon larvae in all treatments. The heavy metal concentrations in the plant from different areas (contaminated and reference sites) and in the larvae were analyzed. Toxic effects were observed in the larvae feeding on the leaves from the metal contaminated areas. Larval and pupal weights, growth indices, and larval fitness were all significantly lower than in the reference group. Likewise, in the third and fourth instars, there was a significant decrease in both the survival and moth emergence rates. In contrast, the pupation duration was significantly longer. Total protein, lipid, and glycogen content showed significant reductions in treated larvae. Larval homogenate samples contaminated with heavy metals showed a significant increase in acid- and alkaline- phosphatase levels. The results obtained could provide a basis for a long-term evaluation of the risk associated with heavy metals and their impact on plant populations and important agricultural pests.

Bioactivity of aqueous extract of Jacaranda spp. (Bignoniaceae) on Plutella xylostella L. 1758 (Lepidoptera: Plutellidae)

Abstract The high consumption rate of vegetables stimulates the cultivation and increases the demand regarding the adequacy of the production processes. The attack of the pest Plutella xylostella causes high losses by reducing product quality, typifying a phytosanitary problem. This study aimed to verify the bioactivity of aqueous extracts of leaves of Jacaranda decurrens and Jacaranda mimosifolia at concentrations of 5, 10, and 15% on the insect. The choice test was carried out at the laboratory to determine the food effect of plant extracts and evaluate changes in the life cycle of insects exposed to active compounds through the analysis of biological parameters. Plant extracts of J. decurrens and J. mimosifolia presented with phagodeterrent classification in the choice experiments. The three J. decurrens extract concentrations promoted a prolongation of larval and pupal duration, while the duration of individuals treated with J. mimosifolia at 10% was significantly reduced. Occurred reduction in larval survival of individuals treated with aqueous extracts of J. decurrens and J. mimosifolia. Eggs from treatments with aqueous extract of J. decurrens and J. mimosifolia had reduced survival. Pupal survival of individuals treated with extract at 15% showed a significant reduction compared to the treatments at 5% and 10%. Pupae from the treatment with aqueous extract of Jacaranda mimosifolia showed a reduction in biomass in the treatment at 15% differing from the control e 5%. Thus, the aqueous extracts of the species J. decurrens and J. mimosifolia show insecticidal potential in the tests performed on P. xylostella.

Sensitivity of midgut physiological parameters of Lymantria dispar L. larvae to benzo[a]pyrene in populations with different multigeneration contact to environmental pollutants

Accumulation of organic pollutants in the environment calls for sensing physiological parameters adequate to indicate the presence of contaminants and their effects on ecosystems. Evidence points to the importance of insect adaptations in their habitats for the assessment of sensitive biomarkers so we examined the influence of origin and multigenerational adaptations of the Lymantria dispar larvae to chronic benzo[a]pyrene (B[a]P) treatment under laboratory conditions. The main aim was to compare reactions of larvae from unpolluted and polluted forests using alkaline phosphatase (ALP), acid phosphatase (ACP), and carboxylesterase (CE) specific activities in the midgut, including electrophoretic isoform patterns; midgut expression levels of Hsp70, larval development time (DT), and midgut mass (MM), after chronic exposure to 5 and 50 ng of B[a]P/g dry food weight. The biomarker potential of these parameters regarding larval pre-exposure history to pollution was estimated by principal component analysis (PCA). B[a]P treatment resulted in inhibition of ALP activity, a rise of CE activity, and reduction of MM in larvae from the unpolluted forest, while the population from the polluted forest showed significant elevation of Hsp70 expression in the midgut, prolonged DT, and reduction of MM. PCA confirmed variations in responses of the selected parameters regarding population origin. The obtained results provide insight into insect population variability concerning physiological responses to pollutants. It is indicative that all investigated physiological parameters of L. dispar larvae showed origin-dependent responses to long-term presence of B[a]P, which may be of great importance in ecotoxicological research.

Functional Analysis of Alkaline Phosphatase in Whitefly Bemisia tabaci (Middle East Asia Minor 1 and Mediterranean) on Different Host Plants

Alkaline phosphatases (ALPs: EC 3.1.3.1) are ubiquitous enzymes and play crucial roles in the fundamental phosphate uptake and secretory processes. Although insects are regarded as the most diverse group of organisms, the current understanding of ALP roles in insects is limited. As one type of destructive agricultural pest, whitefly Bemisia tabaci, a phloem feeder and invasive species, can cause extensive crop damage through feeding and transmitting plant diseases. In this study, we retrieved five ALP genes in MEAM1 whitefly, nine ALP genes in MED whitefly via comparative genomics approaches. Compared with nine other insects, whiteflies' ALP gene family members did not undergo significant expansion during insect evolution, and whiteflies' ALP genes were dispersed. Moreover, whiteflies' ALP gene family was conserved among insects and emerged before speciation via phylogenetic analysis. Whiteflies' ALP gene expression profiles presented that most ALP genes have different expression patterns after feeding on cotton or tobacco plants. Female/male MED whiteflies possessed higher ALP activities on both cotton and tobacco plants irrespective of sex, relative to MEAM1 whiteflies. Meanwhile, adult MED whiteflies possessed higher ALP activity in both whole insect and salivary samples, relative to MEAM1 whiteflies. We also found that both MED and MEAM1 whiteflies could upregulate ALP activities after feeding on cotton compared with feeding on tobacco plants. These findings demonstrated the functions of whiteflies ALPs and will assist the further study of the genomic evolution of insect ALPs.

Significance of DopEcR, a G-protein coupled dopamine/ecdysteroid receptor, in physiological and behavioral response to stressors

Organisms respond to various environmental stressors by modulating physiology and behavior to maintain homeostasis. Steroids and catecholamines are involved in the highly conserved signaling pathways crucial for mounting molecular and cellular events that ensure immediate or long-term survival under stress conditions. The insect dopamine/ecdysteroid receptor (DopEcR) is a dual G-protein coupled receptor for the catecholamine dopamine and the steroid hormone ecdysone. DopEcR acts in a ligand-dependent manner, mediating dopaminergic signaling and unconventional "nongenomic" ecdysteroid actions through various intracellular signaling pathways. This unique feature of DopEcR raises the interesting possibility that DopEcR may serve as an integrative hub for complex molecular cascades activated under stress conditions. Here, we review previously published studies of Drosophila DopEcR in the context of stress response and also present newly discovered DopEcR loss-of-function phenotypes under different stress conditions. These findings provide corroborating evidence that DopEcR plays vital roles in responses to various stressors, including heat, starvation, alcohol, courtship rejection, and repeated neuronal stimulation in Drosophila. We further discuss what is known about DopEcR in other insects and DopEcR orthologs in mammals, implicating their roles in stress responses. Overall, this review highlights the importance of dual GPCRs for catecholamines and steroids in modulating physiology and behavior under stress conditions. Further multidisciplinary studies of Drosophila DopEcR will contribute to our basic understanding of the functional roles and underlying mechanisms of this class of GPCRs.

Insect responses to heat: physiological mechanisms, evolution and ecological implications in a warming world

Surviving changing climate conditions is particularly difficult for organisms such as insects that depend on environmental temperature to regulate their physiological functions. Insects are extremely threatened by global warming, since many do not have enough physiological tolerance even to survive continuous exposure to the current maximum temperatures experienced in their habitats. Here, we review literature on the physiological mechanisms that regulate responses to heat and provide heat tolerance in insects: (i) neuronal mechanisms to detect and respond to heat; (ii) metabolic responses to heat; (iii) thermoregulation; (iv) stress responses to tolerate heat; and (v) hormones that coordinate developmental and behavioural responses at warm temperatures. Our review shows that, apart from the stress response mediated by heat shock proteins, the physiological mechanisms of heat tolerance in insects remain poorly studied. Based on life-history theory, we discuss the costs of heat tolerance and the potential evolutionary mechanisms driving insect adaptations to high temperatures. Some insects may deal with ongoing global warming by the joint action of phenotypic plasticity and genetic adaptation. Plastic responses are limited and may not be by themselves enough to withstand ongoing warming trends. Although the evidence is still scarce and deserves further research in different insect taxa, genetic adaptation to high temperatures may result from rapid evolution. Finally, we emphasize the importance of incorporating physiological information for modelling species distributions and ecological interactions under global warming scenarios. This review identifies several open questions to improve our understanding of how insects respond physiologically to heat and the evolutionary and ecological consequences of those responses. Further lines of research are suggested at the species, order and class levels, with experimental and analytical approaches such as artificial selection, quantitative genetics and comparative analyses.

Azadirachtin acting as a hazardous compound to induce multiple detrimental effects in Drosophila melanogaster

Azadirachtin, a tetranortriterpenoid botanical insecticide, has varied sub-lethal effects against many insect pests, including antifeedant, repellent, and growth regulatory. Despite extensive studies of the mechanisms that underline these physiological effects, little attention has been given to multiple toxic effects of azadirachtin under a coherent concentration, and there is no definitive overarching consensus on its toxicity. Here, we investigated multiple sub-lethal effects induced by 4 mg L^-1 of azadirachtin, which did not elicit antifeedant behavior in Drosophila melanogaster, on metrics of longevity, development, compound eyes and reproduction. Exposure to <20 mg L^-1 azadirachtin did not induce mortality, and 4 mg L^-1 of azadirachtin could shorten lifespan, expression of detoxification genes and activities of related detoxification enzymes were higher. The lower activity of chitinase and higher content of chitin in fruit fly exposed to 4 mg L^-1 azadirachtin could be important in developmental inhibition effects, and ovarian abnormalities and lower fecundity could have resulted from azadirachtin-mediated influences on juvenile hormone and ecdysone that disrupted the endocrine system. Caspase-3, head involution defective and reaper-dependent apoptosis genes may have been responsible for compound eye abnormalities in flies exposed to azadirachtin. Our findings provide important insights to the potential mechanisms of sub-lethal effects of azadirachtin.

Insulin-like peptide DILP6 regulates juvenile hormone and dopamine metabolism in Drosophila females

Insulin-like peptide DILP6 is a component of the insulin/insulin-like growth factor signalling pathway of Drosophila. Juvenile hormone (JH) and dopamine (DA) are involved in the stress response and in the control of reproduction. In this study, we investigate whether DILP6 regulates the JH and DA levels by studying the effect of a strong hypomorphic mutation dilp6⁴¹ on JH and DA metabolism in D. melanogaster females. We show that DILP6 regulates JH and DA metabolism: the mutation dilp6⁴¹ results in a reduction in JH-hydrolysing activity and an increase in the activities of DA synthesis enzymes (alkaline phosphatase (ALP) and tyrosine hydroxylase (TH)). In the mutant females, we also found increased fecundity in addition to the intensity of the response (stress reactivity) of ALP and TH to heat stress. As we showed previously, this suggests an increased level of JH synthesis. We confirm this suggestion by treating the mutant females with the JH inhibitor, precocene, which restors the activity and stress reactivity of ALP and TH as well as fecundity to levels similar to those in the control flies. The data suggest a feedback system in the interaction between JH and DILP6 in which DILP6 negatively regulates the JH titre via an increase in the hormone degradation and a decrease in its synthesis.

The impact of FOXO on dopamine and octopamine metabolism in Drosophila under normal and heat stress conditions

The forkhead boxO transcription factor (FOXO) is a component of the insulin signalling pathway and plays a role in responding to adverse conditions, such as oxidative stress and starvation. In stressful conditions, FOXO moves from the cytosol to the nucleus where it activates gene expression programmes. Here, we show that FOXO in Drosophila melanogaster responds to heat stress as it does to other stressors. The catecholamine signalling pathway is another component of the stress response. In Drosophila, dopamine and octopamine levels rise steeply under heat, nutrition and mechanical stresses, which are followed by a decrease in the activity of synthesis enzymes. We demonstrate that the nearly twofold decline of FOXO expression in foxo^BG01018 mutants results in dramatic changes in the metabolism of dopamine and octopamine and the overall response to stress. The absence of FOXO increases tyrosine decarboxylase activity, the first enzyme in octopamine synthesis, and decreases the enzymatic activity of enzymes in dopamine synthesis, alkaline phosphatase and tyrosine hydroxylase, in young Drosophila females. We identified the juvenile hormone as a mediator of FOXO regulation of catecholamine metabolism. Our findings suggest that FOXO is a possible trigger for endocrinological stress reactions.

Summary: The transcription factor FOXO affects catecholamine metabolism under normal and heat stress conditions in D. melanogaster, and juvenile hormone (JH) is a mediator of this effect.

Disruption of insulin signalling affects the neuroendocrine stress reaction in Drosophila females

Juvenile hormone (JH) and dopamine are involved in the stress response in insects. The insulin/insulin-like growth factor signalling pathway has also recently been found to be involved in the regulation of various processes, including stress tolerance. However, the relationships between the JH, dopamine and insulin signalling pathways remain unclear. Here, we study the role of insulin signalling in the regulation of JH and dopamine metabolism under normal and heat stress conditions in Drosophila melanogaster females. We show that suppression of the insulin-like receptor (InR) in the corpus allatum, a specialised endocrine gland that synthesises JH, causes an increase in dopamine level and JH-hydrolysing activity and alters the activities of enzymes that produce as well as those that degrade dopamine [alkaline phosphatase (ALP), tyrosine hydroxylase (TH) and dopamine-dependent arylalkylamine N-acetyltransferase (DAT)]. We also found that InR suppression in the corpus allatum modulates dopamine, ALP, TH and JH-hydrolysing activity in response to heat stress and that it decreases the fecundity of the flies. JH application restores dopamine metabolism and fecundity in females with decreased InR expression in the corpus allatum. Our data provide evidence that the insulin/insulin-like growth factor signalling pathway regulates dopamine metabolism in females of D. melanogaster via the system of JH metabolism and that it affects the development of the neuroendocrine stress reaction and interacts with JH in the control of reproduction in this species.

Sublethal effects of the chitin synthesis inhibitor, hexaflumuron, in the cotton mirid bug, Apolygus lucorum (Meyer-Dür)

Hexaflumuron is a type of benzoylphenylurea insecticide which is highly toxic for many insects. Sublethal doses of hexaflumuron have been shown to significantly affect insect growth and development. However, the action mechanism of hexaflumuron is not well understood. In the present study, first instar Apolygus lucorum nymphs were exposed to sublethal doses of hexaflumuron based on the estimated 120h acute LC50 valve of 20.53mg/ml. We found that exposure to sublethal hexaflumuron doses resulted in a significant increase in development time and reduced the weights of fifth instar A. lucorum nymphs. We also measured trehalose, which is a primary blood sugar in insects, and the enzyme trehalase that is involved in energy metabolism. Trehalose content in first instar nymphs significantly increased following hexaflumuron treatment while the glucose content, soluble trehalase activity and expression levels of ALTre-1 mRNA decreased significantly. However, no significant changes in membrane-bound trehalase activity and ALTre-2 mRNA expression were observed. In addition, these decreases or increases could be correlated to increases in treatment time or concentration of hexaflumuron, respectively. The present findings indicated that sublethal doses of hexaflumuron could interfere the normal carbohydrate metabolism by depressing the expression of ALTre-1 in A. lucorum, which provide valuable information on the physiology and molecular mechanisms for the toxicity of hexaflumuron.

Catalytic inactivation of alkaline phosphatase by cantharidin, an inhibitor of protein phosphatase

Previous investigations have shown high toxicity of cantharidin to many insects especially lepidopteran.

Lethal and sublethal effects of cantharidin on the life history traits and population parameters of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

BACKGROUND

The cotton bollworm, Helicoverpa armigera (Hübner), is a serious and cosmopolitan pest of many economic crops. Its control has not been adequate owing to its resistance to many groups of insecticides. Toxicity of cantharidin on armyworm and diamondback moth has already been reported. However, its toxicity on H. armigera has not been investigated previously. In this study, lethal and sublethal effects of cantharidin on H. armigera under laboratory conditions are reported.

RESULTS

Results showed gross abnormalities in the population parameters of H. armigera, ranging from larvae to adults. Reduction in larval weight and wing malformation were observed in the cantharidin-treated population cohort, and higher mortality at the larval, pupal and adult stages was observed in cantharidin-treated H. armigera compared with the control. Moreover, almost 5 times less fecundity was recorded in the treated population cohort. Fertility was also severely affected, and reduction in all population parameters was observed.

CONCLUSION

Cantharidin caused larval mortality and other serious abnormalities in H. armigera population parameters, and therefore may have positive implications for pest management decision-making process. More interestingly, the experiment revealed that cantharidin in sublethal dose mimicked insect growth regulator insecticides. Furthermore, cantharidin could be used as a precursor compound for the synthesis of new analogues and compounds to replace ineffective older compounds.

Downregulation of the dopamine D2-like receptor in corpus allatum affects juvenile hormone synthesis in Drosophila melanogaster females

In Drosophila, juvenile hormone (JH) is synthesized de novo in the specialized endocrine gland, corpusallatum (CA). Dopamine (DA) controls JH levels by either stimulating or inhibiting its synthesis and degradation depending on the developmental stage. The present study focuses on the role of D2-like receptors in the regulation of JH synthesis by dopamine. We show that D2-like receptors (DD2R) are expressed in CA cells of Drosophila melanogaster females. In addition, the level of JH production was analyzed in D. melanogaster females with decreased DD2R expression in CA (vs. corresponding control flies) by assessing multiple indices of JH synthesis (JH-hydrolyzing activity and stress reactivity of the system of JH metabolism, activity and stress reactivity of the alkaline phosphatase, activity and stress reactivity of the tyrosine decarboxylase). The differential value obtained for each index suggests increased JH production in female flies that downregulate DD2R. Based on these findings, we postulate that the DA inhibiting effect on the JH synthesis in D. melanogaster is mediated at least in part via D2-like receptors.

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.

Characterization of soluble and membrane-bound alkaline phosphatase in Nilaparvata lugens and their potential relation to development and insecticide resistance

Two forms (soluble and membrane-bound) of alkaline phosphatases (ALPs) were found in the brown planthopper, Nilaparvata lugens. In order to further study ALPs in N. lugens, two putative ALP genes (Nl-ALP1 and Nl-ALP2) were identified in this pest. Both Nl-ALP1 and Nl-ALP2 show approximately the same degree of sequence identity (40-50%) to other insect soluble and membrane-bound forms of ALP. Correlation of ALP activity and mRNA levels at different developmental stages, or following application of 20-hydroxyecdysone (20E) and insecticide fenvalerate, suggests that Nl-ALP1 and Nl-ALP2 might encode a soluble (sALP) and a membrane-bound ALP (mALP), respectively. Nl-ALP1-specific antibody Nl1-I detected only a specific band in soluble protein preparations and Nl-ALP2 specific antibody Nl2-I only detected a specific band in insoluble protein preparations, which provided conclusive linkages between Nl-ALP1 and a sALP and between Nl-ALP2 and a m ALP. Then, Nl-ALP1 was denoted as Nl-sALP for a sALP and Nl-ALP2 was denoted as Nl-mALP for a mALP. Only sALP activity and Nl-sALP mRNA level were induced by 20E and fenvalerate, which was confirmed by the density of specific band detected by Nl1-I in Sus strain with or without fenvalerate treatment. Additionally, the sALP activity, as well as Nl-sALP mRNA level, was significantly higher in a fenvalerate resistant population, compared with Sus strain. These results indicate that the sALP is more responsive to chemical stimulus, such as hormone and insecticide, and might play dual roles in development and insecticide tolerance.

The effects of triazophos on the trehalose content, trehalase activity and their gene expression in the brown planthopper Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

A previous study demonstrated that the flight capacity of Nilaparvata lugens adults treated with triazophos was enhanced significantly. However, the physiological and regulative mechanisms of the flight enhancement are not well understood. Trehalose is a primary blood sugar in insects, and the enzyme trehalase is involved in energy metabolism. The present study investigated the effects of triazophos on the trehalose content, trehalase activity (soluble trehalase and membrane-bound trehalase) and the mRNA transcript levels of their corresponding genes (NlTre-1 and NlTre-2) in fifth instar nymphs, as well as in the brachypterous and macropterous N. lugens adult females. Our findings showed that the trehalose content in fifth instar nymphs as well as in the brachypterous and the macropterous adults significantly decreased following triazophos treatment. However, the glucose content, soluble trehalase activity and expression level of NlTre-1 mRNA increased significantly compared to the controls. No significant enhancement of NlTre-2 expression was found, indicating that regulation of energy metabolism of triazophos-induced flight capacity in N. lugens was not associated with NlTre-2 expression. In addition, soluble trehalase activity and the expression level of NlTre-1 mRNA in the macropterous females was significantly higher than that in the brachypterous females. The present findings provide valuable information on the molecular and regulative mechanisms of the increased flight capacity found in adult N. lugens after treatment with triazophos.

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.

Characterization of putative soluble and membrane-bound trehalases in a hemipteran insect, Nilaparvata lugens

Trehalose is the main blood sugar of insects, and the enzyme trehalase is involved in energy metabolism and controlling trehalose levels in cells. Two forms (soluble and membrane-bound) of trehalase and the corresponding genes (NlTre-1 and NlTre-2) were identified from the brown planthopper, Nilaparvata lugens. Both NlTre-1 and NlTre-2 contain trehalase signature motifs, and NlTre-2 contains a putative transmembrane domain. Comparison of trehalase activity and gene mRNA level at different developmental stages, or following application of 20-hydroxyecdysone (20E), suggests that NlTre-1 and NlTre-2 encode a soluble trehalase and a membrane-bound trehalase respectively. Soluble trehalase activity accounted for the majority of total trehalase activity in N. lugens. Only soluble trehalase activity and NlTre-1 mRNA level could be induced by 20E. Additionally, only soluble trehalase activity was significantly higher in macropterous individuals than in brachypterous morphs. These results indicate that only soluble trehalase is differentially expressed between macropterous and brachypterous individuals and is more responsive to hormone stimulus.