Fig 1.
Progression of nuclear cycle stages in mononucleated parasites.
Nuclear division is organized around the centriolar plaque, which spans the nuclear envelope and consists of an extranuclear compartment and an intranuclear compartment acting as the microtubule organizing center. Prior to S–phase initiation and the formation of a mitotic spindle, large, dynamic hemispindles can be observed in the nucleus. Centrins are recruited to the extranuclear compartment of the centriolar plaque during the later hemispindle stages before S–phase occurs. Nuclear division is closed, with the duplicated centriolar plaques eventually moving to opposite sides of the dividing nucleus during chromosome segregation, before nuclei are separated.
Fig 2.
Nuclei cycle asynchronously in multinucleated parasites.
After nuclear division, hemispindle structures remain briefly within the separated nuclei. In parasites with two nuclei, one may enter S–phase earlier than the other; S–phase entry is marked by the rapid accumulation of the replication marker PCNA1 within a nucleus. Asynchrony is visible in both S–phase and nuclear division, as nuclei may show nuclear accumulation of PCNA1 as well as different microtubule structures at different times.
Table 1.
Selected marker for live–cell imaging of P. falciparum schizogony in blood stages.
Fig 3.
The end of nuclear multiplication and formation of daughter cells.
(A) Structures and organelles involved in cytokinesis start forming during early nuclear cycles. Proteins of the IMC and the rhoptries start organizing around the centriolar plaque in cells with nuclei numbers as low as four and develop into larger structures as nuclear multiplication progresses. (B) Daughter cells are formed during segmentation. Concomitant to daughter cell formation, the nuclei are divided in a final, semisynchronous round of nuclear division. One pair of rhoptries associates with the apical end of the developing daughter cells. Segmentation commences when the plasma membrane (PM) starts invaginating. During segmentation, the IMC, which sits below the PM and originates from the apical end, starts enveloping the emerging daughter cell alongside the PM, with the basal complex localizing to the leading edge of the IMC. Concurrently to the expansion of the IMC, subpellicular microtubules start developing from the apical end of the emerging daughter cells. At the end of segmentation, the daughter cells now containing all necessary organelles are pinched off a remnant body containing the food vacuole.