Objective Apoptosis or programmed cell death(PCD) has been studied extensively in multicellular organisms,however,very little is known about the molecular mechanisms by which apoptosis occurs in unicellular protozoan parasites.The aim of this study is to characterize the apoptosis or PCD of Trichomonas vaginalis induced by metronidazole (MTZ).Methods T. Vaginalis strain cultures were treated with various concentrations of MTZ and the number of viable cells were determined at different time intervals.The genomic DNA of MTZ treated T. Vaginalis was extracted and DNA fragmentation was analyzed.TUNEL assay was carried out to detect the endonuclease activity in T. Vaginalis after MTZ treatment.Flow cytometric analysis was used to analyse the phosphatidylserine (PS) exposure of T. Vaginalis.Results Metronidazole (MTZ) induced an apoptotic-like cell death in T. Vaginalis.This apoptotic-like cell death was demonstrated by cell shrinkage,phosphatidylserine exposure,and nuclear chromatin condensation.However, no oligonucleosmal DNA laddering was detected.Conclusion The regulatory pathway of apoptotic cell death in T. Vaginalis may be different from multicellular organisms.The determination of protozoan apoptotic pathways leading to cell death might ultimately allow the identification of new therapeutic targets.

Objective To screen cell growth and senescence-related genes of the parasitic pmtist Trichomonas vaginalis,we launched an EST program and isolated two cDNA clones from a T.vaginalis cDNA library,which showed high homology in deduced amino acid sequences to yeast Sir2 and designated as TvSir2 and TvSir2-like.Method The cDNA sequence of TvSIR2 had a length of 1034 base pairs (bp) with an open reading frame of 915 bp,and TvSIR2-like,1214 bp with an open reading frame of 1116 bp.Result The two deduced amino acid sequences shared all the three conserved cole domains with yeast Sir2 and its homologues,suggesting that the two clones were Sir2 homologues. A cDNA fragment from each cDNA clone was subvloned into the expression vector pET-41a.The expression of the fusion proteins in E.coli BL21 stains was induced by isopropylthio-β-D-galactoside (IPTG).Two anti-sera were prepared by immunizing two guinea pigs with the purified fusion proteins, Western-blot analysis demonstrated that each anti-serum reacted with the corresponding recombinant protein and detected a clear band (TvSir2,34 000 Mr;TvSir2-like,42 000 Mr)in protein extracts of the protist.Immunofluolescence techniques showed that TvSir2 and TvSir2-like proteins were both localized in the legions of perinuelear (ER) and Golgi complex.Conclusion Our data suggest that TvSir2 and TvSir2-like were two members of Sir2 family.Their biological functions in the protist would be further studied.