Translation initiation factor eIF1.2 is a crucial early regulator of Toxoplasma bradyzoite cyst formation

The bradyzoite form of Toxoplasma gondii poses a therapeutic challenge since there is no available effective drug or vaccine for humans. Although differentiation of T. gondii tachyzoites to bradyzoites is a pivotal event during infection, our understanding of this process remains limited to a few differentiation factors that are sparsely linked. Using a chemical mutagenesis screen, we identified the translation initiation factor eIF1.2 as a critical player in T. gondii differentiation. A F97L mutation in eIF1.2 or complete knockout of eIF1.2 (∆eIF1.2) markedly impaired bradyzoite cyst formation in vitro and in vivo. Utilizing single-molecule scanning technology, we demonstrated that the T. gondii eIF1.2 F97L mutation alters the scanning process of the yeast ribosome preinitiation complex on a model yeast mRNA. RNA sequencing and ribosome profiling experiments unveiled that ∆eIF1.2 parasites exhibit defects in upregulating differentiation markers, such as BAG1, LDH2, and regulators, including BFD1 and BFD2/ROCY1, during stress-induced differentiation. Forced expression of BFD1 or BFD2 effectively restored differentiation in ∆eIF1.2 parasites. Our findings indicate that eIF1.2 regulates the translation of key differentiation factors that are essential for establishing chronic infection. Notably, non-tissue cyst-forming apicomplexan parasites only possess one eIF1, whereas most tissue cyst-forming apicomplexans like T. gondii have two eIF1 paralogs, eIF1.1 and eIF1.2. This work sets the stage for further elucidating the specific regulatory role of eIF1.2 in the expression of differentiation-related genes.