A positive feedback loop controls Toxoplasma chronic differentiation

Abstract

Successful infection strategies must balance pathogen ampli cation and persistence. In Toxoplasma gondii, this is accomplished through differentiation into dedicated cyst-forming chronic stages that avoid clearance by the host immune system. The transcription factor BFD1 is both necessary and su cient for stage conversion; however, its regulation is not understood. We examine ve factors transcriptionally activated by BFD1. One of these is a cytosolic RNA-binding protein of the CCCH-type zinc nger family, which we name BFD2. Parasites lacking BFD2 fail to induce BFD1 and are consequently unable to fully differentiate in culture or in mice. BFD2 interacts with the BFD1 transcript in a stress-dependent manner. Deletion of BFD2 reduces BFD1 protein levels, but not mRNA abundance. The reciprocal effects on BFD2 transcription and BFD1 translation outline a positive feedback loop that enforces commitment to differentiation. BFD2 helps explain how parasites commit to the chronic gene-expression program and elucidates how the balance between proliferation and persistence is achieved over the course of infection.

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

“…Consistent with the observed upregulation of AP2 activators and downregulation of AP2 repressors in Tg68 tachyzoites, the master transcription regulator of bradyzoite development called Bradyzoite Deficient 1 (BFD1)(38) and its translation regulator Bradyzoite Deficient 2 (BFD2)(39)/Regulator of Cystogenesis 1 (ROCY1)(40) showed increased expression in Tg68 tachyzoites when compared to ME49 tachyzoites (Fig. 4A).…”

“…First-strand cDNA was synthesized using ProtoScript II first strand cDNA synthesis kit (NEB), and quantitative real-time PCR was performed on QuantStudio 3 real-time PCR system (Applied Biosystems) using PowerUp SYBR green master mix (Applied Biosystems). Relative quantitation was determined by ΔΔCt with data normalized to GCN5B , which is consistently expressed regardless of alkaline treatment(39). Fold changes compared to ME49 tachyzoites were derived from three independent experiments.…”

Iron Stress Affects the Growth and Differentiation of Toxoplasma gondii

“…PP2A holoenzyme contributes to protein dephosphorylation and dephosphorylates eight phosphorylation sites of the bradyzoite formation deficient 2 (BFD2, TGME49_311100) [ 56 ]. BFD2 interacts with the BFD1 transcript under stress, and deletion of BFD2 decreases BFD1 protein levels [ 57 ]. BFD1 accumulates during stress and its synthetic expression is sufficient to drive differentiation [ 58 ].…”

Keeping FIT: Iron-mediated post-transcriptional regulation inToxoplasma gondii

“…Iron deprivation now joins an extensive list of cellular stresses able to trigger stage conversion in Toxoplasma . Recent work is now uncovering the upstream molecular pathways involved in mediating stage conversion (Licon et al ., 2023), however the pathway of how loss of iron directly triggers the stage conversion remains unknown.…”