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Fig. 19.4 a Cartoon of the Toxoplasma replication process within a parasitophorous vacuole
inside the host cell (Curtesy of Dr. Marc-Jan Gubbels). b Schematic drawing of Toxoplasma
endodyogeny, where two daughter cells are formed within a mother cell (Modified from Martins-
Duarte et al. 2008; with permissions of the John Wiley and Sons). c Schematic representation of
centrosome and spindle microtubules during the different phases of parasite division process
(Modified after Brooks et al.
2011
; with permissions of the Proceedings of the National Academy
of Sciences). d Electron micrograph of a thin section of a Toxoplasma parasite undergoing
endodyogeny
division of the centrosome at the posterior of the nucleus and the fission of the
Golgi. Two new rudimentary apical complexes appear that are formed by a new
conoid and apical rings from where new subpellicular microtubules and the inner
membrane complex (IMC) will originate. This IMC formed below the parasite
plasma membrane delineates for some time the daughter cells within the mother
cell cytoplasm. As the daughter cells extend, the single nucleus finalizes DNA
replication and assumes a lobular shape, resembling a horseshoe. The chromatin is
then distributed to both poles by an intranuclear spindle.
MORN repeats are believed to act as protein-protein or protein-phospholipid-
binding domains, being important for the organization of membranous and cyto-
skeletal structures (Ju and Huang
2004
; Kunita et al.
2004
; Satouh et al.
2005
). In
Toxoplasma, a protein with MORN repeats named TgMORN1 is a key player in
nuclear division, daughter cell formation, organelle partitioning and basal complex
assembly, and cytokinesis (Fig.
19.5
) (Gubbels et al.
2006
; Lorestani et al.
2010
),
associating with the nuclear centrocone and probably also with a component of the
membrane skeleton that is linking to the IMC. Actin-myosin rings are important
elements for constriction in cytokinesis (Glotzer
2005
). TgMORN1 associates with
IMC components forming a ring during mitosis and cell division, which moves
during mitosis, constricting perpendicular to the parasite longitudinal axis,
resulting in nuclear division and cytokinesis (Gubbels et al.
2006
). This con-
striction may also require myosin C and actin. Myosin C co-localizes with actin at
the posterior end of the parasite, the same position where TgMORN1 was observed
(Delbac et al.
2001
; Gubbels et al.
2006
). In this way, TgMORN1 could be acting
as a connector between the posterior end of the IMC and an internal constrictive
ring formed by myosin C (Gubbels et al.
2006
; Lorestani et al.
2010
). Curiously,
