Figure 1.
Apicomplexa Are Intracellular Parasites
(A) Highly simplified apicomplexan life cycle. Apicomplexans are haplonts, and meiosis (sporogony) immediately follows fertilization. Fertilization might occur within a host cell or extracellularly, giving rise to an oocyst or, less frequently, an invasive stage zygote (ookinete).
(B) Schematic representation of a zoite (not all structures are present in all apicomplexans). AP, apicoplast; AR, apical rings; CC, centrocone; CE, centrosome; CO, conoid; DG, dense granule; ER, endoplasmic reticulum; G, Golgi; IMC, inner membrane complex; MI, mitochondrion; MN, microneme; MT, subpellicular microtubule; NU, nucleus; RH, rhoptry.
(C) Zoites actively invade the cells of their hosts, establishing a specialized parasitophorous vacuole (PV) (in some species the parasite lyses the vacuole and develops freely in the cytoplasm).
Figure 2.
The Diversity of Intracellular Development in Apicomplexans
(A) In T. gondii, two daughters are formed during budding. IMC1, red; MORN1, green (reproduced with permission from [32]).
(B) T. gondii. Histone H2, red; IMC3, green (reproduced from [71]).
(C) In Plasmodium falciparum liver schizont, budding results in massive numbers of zoites. Image courtesy of Volker Heussler.
(D) T. gondii, phase contrast image of parasitophorous vacuole harboring multiple tachyzoites.
(E and F) P. falciparum late erythrocyte schizont. Acyl carrier protein (plastid), green. RBC, red blood cell.
(G–I) Sarcocystis neurona. Two intracellular stages with polyploid nuclei, one in interphase and one during mitosis. Tubulin, red.
(J) S. neurona budding. IMC3, green.
(K) A Theileria schizont divides in association with its host cell. Polymorphic immunodominant molecule (parasite surface), green; γ-tubulin (host centrosomes), red. HN, host nucleus. Image courtesy of Dirk Dobbelaere. The DNA dye DAPI is shown in blue throughout. Not to scale.
Figure 3.
The Flexibility of Apicomplexan Cell Division
Schematic outline of cell division by Toxoplasma (endodyogeny), Plasmodium (schizogony), and Sarcocystis (endopolygeny). The Theileria schizont is divided in association with host cell division (HN, host nucleus). DNA, grey; IMC, purple; centrosome, red. Note that a centriole as center of the spindle plaque body has not been clearly demonstrated in P. falciparum. Both Sarcocystis and Theileria develop directly in the host cell cytoplasm, while Toxoplasma and Plasmodium are contained within a parasitophorous vacuole (light blue).
Figure 4.
The Mechanics of Apicomplexan Mitosis and Budding
(A–C) Schematic representation of the nucleus during interphase (A), mitosis (B), and mid-stage budding (C). Smaller type abbreviations refer to organelle-specific marker proteins in T. gondii (most are available as fluorescent protein in vivo tags, see text for further details and references). AP, apicoplast; AR, apical rings; CC, centrocone; CH, chromosome; CO, conoid; CT, centromere; EX, ER exit site; MT, subpellicular microtubule; NE, nuclear envelope; PR, posterior ring; SP, spindle.
(D–K) Time lapse series of nuclear division in T. gondii reproduced from [32]. The nucleus is labeled in red (Histone H2b-RFP) and MORN1 in green (MORN1-YFP).
Table 1.
Apicomplexan Parasites