Fig. 9.

a The different steps that occur during closed mitosis and IMC formation in wild-type T. gondii parasites. 1—the centrioles duplicate at the posterior pole of the nucleus and initiate the formation of the spindle; the newly formed spindle and the duplicated centrioles migrate back towards the anterior pole of the nucleus; centromeres and kinetochores cluster together facing centrioles; no centrocone is formed at this stage; 2—the nuclear envelope funnel develops between daughter pairs of centrioles; the spindle microtubules forms in the funnel; centromeres duplicate and associate to the nuclear envelope through kinetochores; 3—opening of the middle part of the funnel; kinetochores are connected to mitotic microtubules; the metaphase plate is organized and daughter cells assembly is initiated; 4—formation of the centrocones by closure of the nuclear envelope against kinetochores that reattach to the nuclear envelope; disappearance of mitotic microtubules; transient persistence of spindle microtubules running through pores at the centrocone basis making half spindles in nucleoplasm; 5—centrocones budding off the nuclear envelope attracted into daughter buds; 6—buds elongation and daughter zoite biogenesis towards accomplishment of karyokinesis and cytokinesis. b ark1D/A-Δku80 dominant negative mutants and TgINCENP2 knock-down parasites are stuck at step number 3. 3′—funnel persistence; kinetochores and centromeres remain associated on external face of the nuclear envelope; centrocone markers are spread into the spindle; daughter cells budding is initiated; 4′—(when wild-type parasites have reached the end of the first endodyogeny) centrioles and probably centromeres continue to duplicate; the mother centriole pair leaves the spindle pole while keeping developing the first bud; daughter centriole pair starts initiating a second bud inside the first one; 5′—(when wild-type parasites have reached the second endodyogeny, i.e. 4 parasites) the two centriole pairs duplicate and probably also centromeres. These later lose association with kinetochores that remain associated to the funnel membrane. The new centrioles start initiating buds, producing the Russian dolls figures. Black: centrioles, blue: kinetochores, green: centromeres, yellow: microtubules, red: CEP250L1 (outer face of the nuclear envelope)