Abstract
Toxoplasma gondii, a protozoan parasite, undergoes a complex and poorly understood developmental process that is critical for establishing a chronic infection in its intermediate hosts. Here, we applied single-cell RNA-sequencing (scRNA-seq) on >5,400 Toxoplasma in both tachyzoite and bradyzoite stages using three widely studied strains to construct a comprehensive atlas of cell-cycle and asexual development, revealing hidden states and transcriptional factors associated with each developmental stage. Analysis of SAG1-related sequence (SRS) antigenic repertoire reveals a highly heterogeneous, sporadic expression pattern unexplained by measurement noise, cell cycle, or asexual development. Furthermore, we identified AP2IX-1 as a transcription factor that controls the switching from the ubiquitous SAG1 to rare surface antigens not previously observed in tachyzoites. In addition, comparative analysis between Toxoplasma and Plasmodium scRNA-seq results reveals concerted expression of gene sets, despite fundamental differences in cell division. Lastly, we built an interactive data-browser for visualization of our atlas resource.
Footnotes
We have revised the preprint title and abstract to take into account of additional experiment and analysis that we have performed. In figure 5, we include analysis of a single parasite variant with the unusual co-expression pattern of surface antigens. Based on this analysis, we inferred the role of a previously unknown transcriptional factor and provide experimental evidence to show that its transient expression is sufficent to induce switching of surface antigen to one that is typically found in parasites isolated from cats. In figure 6, we included comparative analysis between single-cell atlases of Toxoplasma gondii and Plasmodium falciparum (of Malaria cell atlas), discovering concerted genetic programs that control life-cycles across these two distantly related apicomplexan parasites.
