Isolation and characterization of a subtractive library enriched for developmentally regulated transcripts expressed during encystation of Toxoplasmagondii

To survive within infected hosts, Toxoplasma gondii undergoes profound meta bolic and morphological changes by differentiating into a cyst characterize d by its resistance to the immune system and chemotherapy. The stimulus tha t triggers Toxoplasma encystation and the molecular mechanisms regulating t he bradyzoite phenotype are still unknown. Here, we developed a differentia tion method in conjunction with a selective and subtracted cDNA strategy de vised to identify developmentally regulated transcripts. We isolated and an alyzed 65 cDNA clones. In addition to bradyzoite specific cDNAs previously reported, we demonstrate that twelve genes are exclusively or preferentiall y transcribed in the encysted bradyzoite forms of T. gondii using semi-quan titative RT-PCR. Among cDNAs identified, are those encoding predicted homol ogues of chaperones (mitochondrial heat shock protein 60, T-complex protein 1), DNA-damage repair protein, phosphatidylinositol synthase, glucose-6-ph osphate isomerase and enolase. The identification of these genes opens the way for further study of molecular mechanisms controlling gene expression d uring T. gondii encystation. (C) 1999 Elsevier Science B.V. All rights rese rved.