Authors

AT Puig¹; R Haase1¹; N Dos Santos Pacheco¹; B Ren¹; B Maco¹; A Guérin¹; M Martinez²; YW Chang²; D Soldati-Favre¹;  ¹ Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Switzerland;  ² Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, United States

Discussion

Members of the phylum of Apicomplexa are unified by an apical complex consisting of cytoskeletal structures and secretory organelles, tailored for motility, invasion and egress. Gliding is powered by actomyosin-dependent rearward translocation of apically secreted transmembrane adhesins. In the coccidian subgroup of Apicomplexa, the conoid is composed of a cone of spiraling tubulin fibers, preconoidal rings and two intraconoidal microtubules. The conoid is a dynamic organelle that extrudes in motile parasite. Ultrastructure-expansion microscopy applied to known and novel conoid proteins has uncovered the preconoidal rings as hubs for actin polymerization and led to a plausible role of conoid dynamics as gatekeeper for the engagement of F-actin in the glideosome. Rhoptry discharge is vital for invasion and involves docking one or two rhoptries to a macromolecular secretory apparatus within an apical vesicle (AV). T. gondii is armed with 10-12 rhoptries and 5-6 microtubule-associated vesicles (MVs) presumably facilitating iterative rhoptry discharge. Cryo-electron tomography combined with functional analysis of intraconoidal microtubule (ICMT)-associated proteins highlights the pivotal role of ICMTs in scaffolding the discharge of multiple rhoptries.