Dr. Bingjian Ren (Genève / CH), Romuald Haase (Genève / CH), Dr. Bohumil Maco (Genève / CH), Nicolas Dos Santos Pacheco (Genève / CH), Professor Dr. Dominique Soldati-Favre (Genève / CH)
In Toxoplasma gondii, the conoid comprises a cone with spiraling tubulin fibers, preconoidal rings (PCRs), and intraconoidal microtubules (ICMTs). This dynamic organelle undergoes extension and retraction through the apical polar ring (APR) during egress, gliding, and invasion processes. The forces involved in conoid extrusion start to be better understood and its role in directing the F-actin flux to the pellicular space, therefore controlling parasite motility, has been proposed1. However, the contribution of the APR and its interactions with the conoid remain unclear. To advance our comprehension of the APR's architecture, Ultrastructure Expansion Microscopy (U-ExM) was applied to pinpoint known and newly identified APR proteins (APR2-APR7). Our results indicate that the APR forms a fixed multilayered structure. Intriguingly, the conditional depletion of APR7 resulted in significant impairments in both motility and invasion. Electron microscopy revealed a disrupted upper layer of the APR in the absence of APR7, and the use of F-actin binding chromobodies uncovered abnormal flux of F-actin. In summary, this study provides valuable insights into APR assembly and help elucidating how its structure regulates parasite motility.
1. Haase, R et al. Nanoscale imaging of the conoid and functional dissection of its dynamics in Apicomplexa. Curr Opin Microbiol. 2022 Dec:70:102226.