Fig. 2: An apical vesicle (AV) and rhoptry secretory apparatus (RSA) together mediate docking of the rhoptry to plasma membrane.
From: In situ ultrastructures of two evolutionarily distant apicomplexan rhoptry secretion systems
Arrangement of rhoptry secretion system in C. parvum (a–e) and in T. gondii (f–j). a, f An apical vesicle (AV; pink) and rhoptry secretory apparatus (RSA; dark blue) connect rhoptries (R, R1, R2; orange) to the parasite plasma membrane (PPM; light blue) at the apical end. M: micronemes, IMT: intraconoidal microtubule (purple), and MVs: microtubule-associated vesicles (red). Rhoptry constrictions are denoted by a dark pink colored dashed line. a One rhoptry is fused with the AV in C. parvum while f two rhoptries are in close contact with the AV in T. gondii (s1 and s2 indicate two different sections of the same tomogram). b, g RSA mediates connection of the AV to the PPM. c, h AV-rhoptry junction in C. parvum and T. gondii—c rhoptry connects with the AV, forming a neck with a continuous membrane, which is decorated on the outside by collar-like densities (cyan) in C. parvum while h T. gondii shows docking (no fusion) of rhoptry with the AV, mediated by a tip density (cyan). d, i Top views of RSAs (from orthogonal sectioning planes labeled with green dashed lines in b and g, respectively) that show an 8-fold rotational symmetry. e, j Shape, size and anchoring parameters of AVs in C. parvum (e) and T. gondii (j); the latter also shows AV’s arrangement with respect to IMTs (purple) and MV (red) parameters. AVdist: shortest distance between the AV membrane and the plasma membrane; AVmaj: length of the AV major axis; AVmin: length of the AV minor axis; Ecc: eccentricity; Ψ: anchoring angle of the AV to the plasma membrane; θ: orientation of the AV neck with respect to the minor axis of AV. Measurements are presented as mean ± standard deviation or, in the case of Ψ, simply median. Source data for this figure are provided as a Source Data file. Scale bars in all panels are 50 nm.
