Search

To prepare a large amount of pure alive Schistosoma japonicum eggs, rabbit was infected with 2000 cercariae and its liver was taken aseptically 38-45 days after infection and homogenized. The homogenate was screened through different sieves(60, 120, 200, 300, 360 meshes per inch respectively), and washed with 1.2% NaCl. The eggs and leftover were then digested with 0.25% trypsin for 2 hours, sieved over 360 meshes per inch and washed with RPMI 1640 medium. The collected eggs reached to (95.1 +/- 6.4)% of live eggs, with a high efficiency.

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 transcription 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 tebufenozide. 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 tebufenozide 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.