Fig 1.
Components of the apical complex in sporozoites of E. tenella.
A: cartoon overview of Eimeria tenella ultrastructure. The apical complex is divided into outer conoid (B) and inner conoid (C) components. B and C: Segmentation from a serial section dual axis tomogram. Outer conoid components; conoid fibres (white); 2 pre-conoidal rings (PCR 1 and 2) (light blue and red), apical polar ring (gold) in association with sub-pellicular microtubules (green); B: Inner conoid components, rhoptry (dark blue), microneme (light green), microtubule-associated vesicles (MVs) (yellow), intra-conoidal microtubule pair (pink); Scale bars—200nm; D: Illustrations of measurements carried out of conoid features (n = 14 complete conoid tomograms). Conoid height, apex, and base diameter, fibre length, fibre curvature, fibre angle and fibre spacing. S1 Table contains the measurement data and statistics. Materials and methods describe how the measurements were carried out.
Fig 2.
Secretory organelles and their association with the intra-conoidal microtubules and overlying the plasma membrane.
A: Series of rotational views of a segmentation created from one serial section dual axis tomogram illustrating the spatial grouping and alignment of microneme (light green), rhoptries (dark blue) and MVs (yellow) with the intra-conoidal microtubule pair (pink); B: Segmentation of a serial section dual axis tomogram illustrating the relative positioning of a microneme (light green), rhoptry (dark blue) and MVs (yellow) within the conoid area of the parasite; C and D: slices taken from different tomograms (C) longitudinal view and (D) cross section view illustrating how measurements were taken showing the distances from a microneme (M), rhoptry (R) and microtubule-associated vesicle (MV) to either the intra-conoidal microtubules or conoid. Double-headed red arrows in (D) show where the measurements were taken, single arrow in C for the identification of the conoid in longitudinal sections. Single arrow in D is the location of intra-conoidal microtubules; E-G: Micronemes, MVs and rhoptries were significantly closer to the intra-conoidal microtubules (IM) than to the conoid (C) (t-test, p < 0.0001) (N = 17); H—I: Longitudinal slice views from 8 serial section tomograms illustrating a MV (red arrows), microneme (blue arrows and black arrowheads) in close association with the plasma membrane overlying the conoid in each tomogram. Yellow arrowheads show the outer edge of the conoid in each example. Scale bars– 100nm.
Fig 3.
Characterisation of an electron lucent rhoptry in an intracellular or invading sporozoite.
A: Slice from a Transmission electron microscopy image illustrating an invading or intracellular sporozoite with an electron lucent rhoptry (ELR) (box and A: inset) close to a host cell nucleus (30 min post-infection sample) scale bar 1μm; A: inset: Higher magnification of A illustrating the ELR within the conoid (white arrowheads). Scale bar 500nm; B and B: inset: Slice from a tomogram showing the electron lucent ‘empty’ rhoptry (ELR) which appeared to be continuous with the parasite plasma membrane and associated at its apex with a pore in the parasitophorous membrane creating a channel passing through both the parasite plasma membrane and the PVM connecting the ‘empty rhoptry’ directly with host cell cytoplasm. B–scale bar 100nm; B inset scale bar 50nm; C and D: Segmentation of a serial tomogram outlined in A and B to illustrate the three dimensional organisation and relative positioning of the electron lucent rhoptry (ELR–dark blue), electron dense rhoptry (R–dark blue), conoid fibres (white), MVs (yellow), parasite plasma membrane (purple), parasitophorous vacuole membrane (green), PCR-1 and 2 (light blue and red), subpellicular microtubules (yellow), intra-conoidal microtubules (pink).
Fig 4.
SBF-SEM quantification of micronemes, rhoptries and other major organelles in freshly excysted sporozoites.
A: Longitudinal section slice from an SBF-SEM dataset illustrating the major organelles. B and C: Thin section TEM images to illustrate identification of major organelles. D and E: Quantification and location of microneme and rhoptry organelles in SBF-SEM whole cell reconstructions. F. Combined segmentation illustrating the positioning of all the major organelles: micronemes–yellow, refractile bodies–green, amylopectin granules–red, acidocalcisomes–black, rhoptries–purple, nucleus–blue—Scale bars– 1μm; G. Relative volumes of major organelles in freshly excysted sporozoites.