ABSTRACT
The ecdysone receptor, naturally activated by steroidal hormones, is a key protein for molting and reproduction processes of insects. Artificial activation of such receptor by specific pesticides induces an anomalous process of ecdysis, causing death of insects by desiccation and starvation. In this paper, we established a protocol for screening agonistic molecules towards ecdysone receptor of insect cells line S2 (Diptera) and Sf9 (Lepidoptera), transfected with the reporter plasmid ere.b.act.luc. Therefore, we set dose-response curves with the ecdysteroid 20-hydroxyecdysone, the phytoecdysteroid ponasterone-A, and tebufenozide, a pesticide belonging to the class of diacylhydrazines. In both cell lines, the median effective concentration values on reporter gene induction (EC50) of ponasterone-A was the smallest, meaning the most active agonist molecule. In Sf9 cells, tebufenozide had as smaller EC50 than 20-hydroxyecdysone, indicating the high agonistic capability and lepidopteran specificity. The protocol established in this study can be useful for a quick screening and rational research of site-specific pesticides.(AU)
O receptor de ecdisona, naturalmente ativado por hormônios esteroidais, é uma proteína-chave nos processos de muda e reprodução de insetos. A ativação artificial desse receptor por meio de pesticidas específicos induz um processo de ecdise anômala, levando o inseto à morte por dessecação e inanição. Neste trabalho, foi estabelecido um protocolo para a triagem de moléculas agonistas em relação ao receptor de ecdisona nas linhagens celulares responsivas S2 (Diptera) e Sf9 (Lepidoptera), transfectadas com o plasmídeo repórter ere.b.act.luc. Para tanto, curvas de dose-resposta foram estabelecidas com o ecdisteroide 20-hidroxiecdisona, o fitoecdisteroide ponasterona-A e tebufenozida, um pesticida pertencente à classe das diacilhidrazinas. Em ambas linhagens celulares, os valores médios de concentração efetiva para indução gênica (EC50) ponasterona-A foram menores, significando que este é o agonista mais potente. Em células Sf9, a tebufenozida apresentou EC50 menor que a 20-hidroxiecdisona, indicando uma alta atividade agonista e especificidade deste inseticida a lepidópteros. O protocolo estabelecido neste trabalho pode ser utilizado para uma rápida triagem e busca racional de pesticidas de alvo bioquímico específico.(AU)
Subject(s)
Plasmids , Molting , Insecta , Pesticides , EcdysteroneABSTRACT
The cytotoxicological responses to insect growth regulator (IGR), using tebufenozide as ecdysteroid mimic, were investigated in Drosophila Kc cells. Treatment of Kc cells with tebufenozide showed significant growth inhibition and striking morphological changes including aggregation and elongation of the cells. In order to understand the cellular mechanism underlying the response of Drosophila cells to tebufenozide, immunofluorescence microscopy was performed. We found that treatment of Kc cells with tebufenozide enhanced the reorganization of f-actin and stimulated the expression of hsp27. These data suggest a possible association of filamentous actin (f-actin) and hsp27 in the cytotoxicological mechanisms of growth regulators in Drosophila cells.
Subject(s)
Actins , Drosophila , Ecdysteroids , Insecta , Microscopy, Fluorescence , Strikes, EmployeeABSTRACT
Objective To reconstitute a transactivation system in yeast (yeast model) for screening the pesticides acting on ecdysone metabolism route and eventually influencing the process of ecdysis. Methods The fragment of 5 times repeated EcRE from Drosophila melanogaster was synthesized and the HSP27 promoter from D. melanogaster genome was amplified with PCR. The two sequences were connected and followed by a reporting gene——green fluorescence protein(GFP) gene. The EcRE-HSP27 promoter-GFP fragment was inserted into the expression plasmid pPIC3.5 and integrated into the yeast chromosome to construct yeast A. EcR and USP coding sequences of Aedes albopictus were synthesized, and these two fragments were inserted into Pichia pastoris expression plasmid pGAPZ as two respective reading frames. The two reading frames were integrated into Pichia pastoris chromosome in another recombinant site(pGAPZ and pPIC3.5k share different recombinant sites while being integrated into Pichia pastoris yeast chromosome). EcR and USP were constituted and expressed in the yeast. This recombinant yeast was called yeast B. The model yeast was thus constructed. A known ecdysone agonist-tebufenozide was used to test the yeast model. The effect of tebufenozide on the model yeast was observed under fluorescent microscope. Semi-quantitative RT-PCR was used to test the transcrip-tion level of GFP in the tebufenozide affected yeast and the control. Results In the model yeast, the intracellular expressed EcR and USP constituted EcR/USP heterodimer interacting with EcRE, the expression of GFP was activated, and green fluorescence was observed in model yeast under fluorescent microscope. Tebufenozide affected model yeast showed less fluorescence in comparison to the control model yeast, indicating that the transcription of GFP was suppressed by tubufenozide. Yeast housekeeping gene Actin-1 was used as inner control, semi-quantitative RT-PCR was operated and the result was scanned. The ratio of the brightness of GFP to Actin-1 was calculated automatically, and that of tubufenozide added yeast and the control yeast was 0.614 and 1.134 respectively. This result showed a low transcription level of GFP in tebufenozide affected model yeast, comparing to that of the control. Conclusion The ecdysone-related transacting system in yeast has been constructed, and the model yeast can be used to screen the ecdysone agonists which can act on the ecdysone metabolic route.