AP2X-8 Is Important for Tachyzoite Growth and Bradyzoite Differentiation of Toxoplasma gondii

<i>Toxoplasma gondii</i> is a protozoan parasite capable of establishing chronic infections, with potential reactivation in immunocompromised individuals. However, the molecular mechanisms governing tachyzoite-to-bradyzoite differentiation remain incompletely understood. Previous studies have identified AP2 transcription factors as key regulators of this developmental switch. In this study, we investigated the role of the AP2 factor AP2X-8. Immunofluorescence analysis revealed that AP2X-8 is constitutively expressed in the nucleus of both tachyzoite and bradyzoite stages. Using CRISPR-Cas9-mediated homologous recombination, we successfully generated an <i>ap2X-8</i> knockout strain. Phenotypic assays including plaque formation, invasion, replication, and egress, and bradyzoite differentiation assays, were then performed to assess the impact of <i>ap2X-8</i> deletion. Our analyses showed that the loss of <i>ap2X-8</i> significantly impaired plaque formation and intracellular replication, while invasion and egress were unaffected. Furthermore, <i>ap2X-8</i> knockout enhanced bradyzoite differentiation in vitro. Despite these changes, deletion of <i>ap2X-8</i> did not alter parasite virulence in a mouse infection model. These findings demonstrate that AP2X-8 is an important regulator of <i>T. gondii</i> tachyzoite growth and bradyzoite differentiation, offering new insights into the parasite's developmental regulation.