Constitutive upregulation of transcription factors underlies permissive bradyzoite differentiation in a natural isolate ofToxoplasma gondii

Abstract

AbstractToxoplasma gondiibradyzoites play a critical role in pathology due to their long-term persistence in intermediate hosts and their potential to reactivate, resulting in severe diseases in immunocompromised individuals. Currently there is no effective treatment for eliminating bradyzoites. Hence, betterin vitromodels ofT. gondiicyst development would facilitate identification of therapeutic targets for bradyzoites. Herein we characterized a natural isolate ofT. gondii, called Tg68, which showed slowerin vitroreplication of tachyzoites, and permissive bradyzoite development under stress conditionsin vitro. Transcriptional analysis revealed constitutive expression in Tg68 tachyzoites of the key regulators of bradyzoite development includingBFD1,BFD2, and several AP2 factors. Consistent with this finding, Tg68 tachyzoites expressed high levels of bradyzoite-specific genes includingBAG1,ENO1, andLDH2. Moreover, after stress induced differentiation, Tg68 bradyzoites exhibited gene expression profiles of mature bradyzoites, even at early time points. These data suggest that Tg68 tachyzoites exist in a pre-bradyzoite stage primed to readily develop into mature bradyzoites under stress conditionsin vitro. Tg68 presents a novel model for differentiationin vitrothat will serve as a useful tool for investigation of bradyzoite biology and development of therapeutics.SignificanceToxoplasma gondiiis a widespread protozoan that chronically infects ∼30% of the world’s population.T. gondiican differentiate between the fast-growing life stage that causes acute infection and the slow-growing stage that persists in the host for extended periods of time. The slow-growing stage cannot be eliminated by the host immune response or currently known antiparasitic drugs. Studies on the slow-growing stage have been limited due to the limitations ofin vivoexperiments and the challenges ofin vitromanipulation. Here, we characterize a natural isolate ofT. gondii, which constitutively expresses factors that drive development and that is permissive to convert to the slow-growing stage under stress conditionsin vitro. The strain presents a novelin vitromodel for studying the chronic phase of toxoplasmosis and identifying new therapeutic treatments for chronic infections.