Cellular electron tomography of the apical complex in the apicomplexan parasite Eimeria tenella shows a highly organised gateway for regulated secretion

Journal article

The apical complex of apicomplexan parasites is essential for host cell invasion and intracellular survival and as the site of regulated exocytosis from specialised secretory organelles called rhoptries and micronemes. Despite its importance, there is little data on the three dimensional organisation and quantification of these organelles within the apical complex or how they are trafficked to this specialised region of plasma membrane for exocytosis. In coccidian apicomplexans there is an additional tubulin-containing hollow barrel structure, the conoid, which provides a structural gateway for this specialised secretion. Using a combination of cellular electron tomography and serial block face-scanning electron microscopy (SBF-SEM) we have reconstructed the entire apical end of Eimeria tenella sporozoites. We discovered that conoid fibre number varied, but there was a fixed spacing between fibres, leading to conoids of different sizes. Associated apical structures varied in size to accommodate a larger or smaller conoid diameter. However, the number of subpellicular microtubules on the apical polar ring surrounding the conoid did not vary, suggesting a control of apical complex size. We quantified the number and location of rhoptries and micronemes with in cells and sh ow a h igh ly organised gateway for trafficking and docking of rhoptries, micronemes and vesicles within the conoid around a set of intra-conoidal microtubules. Finally, we provide ultrastructural evidence for fusion of rhoptries directly through the parasite plasma membrane early in infection and the presence of a pore in the parasitophorous vacuole membrane, providing a structural explanation for how rhoptry proteins (ROPs) may be trafficked between the parasite and the host cytoplas

Authors: Burrell, A; Marugan-Hernandez, V; Wheeler, R; Moreira-Leite, F; Ferguson, DJP

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Public Library of Science
• Journal: PLoS Pathogens
• Volume: 18
• Issue: 7
• Pages: e1010666-e1010666
• Publication date: 2022-07-11
• DOI: 10.1371/journal.ppat.1010666
• EISSN: 1553-7374
• ISSN: 1553-7366
• Language: English
• Keywords: Cell biology; Immunology; Secretion; Immunoelectron microscopy; Exocytosis; Anatomy; Plasmodium falciparum; Cryo-electron tomography; Biology; Conoid; Microneme; Apicomplexa; Rhoptry