3D electron tomography of Plasmodium – Exit WS

Abstract text

The life cycle of Plasmodium includes a short phase of sexual reproduction in the mosquito. Immediately after uptake of the blood meal gametocytes are activated and start to differentiate. Male gametocytes produce eight male flagellated microgametes that egress from the erythrocyte with the help of axonemal movement. Axonemes are microtubule-based cytoskeletal structures essential for ciliary beating and flagellar motility. Canonical axonemes consist of nine doublet microtubules which are linked with dynein motors and nexin linkers and surround two central microtubules. Axonemal microtubules can polymerize from basal bodies, these are extracellular parts of the bipartite microtubule organizing center (MTOC) that connect the axoneme through a nuclear pore with the spindle. Here, we investigate gamete formation in wild-type and mutant parasites. The mutants lack the merozoite thrombospondin-related anonymous protein (MTRAP) and do not egress from the infected cell. Cells were fixated at different time points and serial sections were imaged by transmission electron microscopy to generate several 3D volumes. 3D datasets were segmented by surface rendering to generate 3D models. The generated 3D models reveal that Plasmodium axonemes are formed by a zipping process, cause nuclear fractioning and can feature several aberrations. We imaged both the connection and apparent rupture of the bipartite MTOC into basal bodies and the spindle pole, suggesting a model of axoneme formation. Overall, our data reveal that an astonishing level of inaccuracy stills allows rapid axoneme assembly and efficient gamete motility and fertilization.