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Toxoplasma gondii myosins B/C: one gene, two tails, two localizations, and a role in parasite division.

Delbac F, Sänger A, Neuhaus EM, Stratmann R, Ajioka JW, Toursel C, Herm-Götz A, Tomavo S, Soldati T, Soldati D - J. Cell Biol. (2001)

Bottom Line: MyoC is the first marker selectively concentrated at the anterior and posterior polar rings of the inner membrane complex, structures that play a key role in cell shape integrity during daughter cell biogenesis.When transiently expressed, MyoB, MyoC, as well as the common motor domain lacking the tail did not distribute evenly between daughter cells, suggesting some impairment in proper segregation.Altogether, these observations suggest that MyoB/C products play a role in proper daughter cell budding and separation.

View Article: PubMed Central - PubMed

Affiliation: Zentrum für Molekulare Biologie, Universität Heidelberg, D-69120 Heidelberg, Germany.

ABSTRACT
In apicomplexan parasites, actin-disrupting drugs and the inhibitor of myosin heavy chain ATPase, 2,3-butanedione monoxime, have been shown to interfere with host cell invasion by inhibiting parasite gliding motility. We report here that the actomyosin system of Toxoplasma gondii also contributes to the process of cell division by ensuring accurate budding of daughter cells. T. gondii myosins B and C are encoded by alternatively spliced mRNAs and differ only in their COOH-terminal tails. MyoB and MyoC showed distinct subcellular localizations and dissimilar solubilities, which were conferred by their tails. MyoC is the first marker selectively concentrated at the anterior and posterior polar rings of the inner membrane complex, structures that play a key role in cell shape integrity during daughter cell biogenesis. When transiently expressed, MyoB, MyoC, as well as the common motor domain lacking the tail did not distribute evenly between daughter cells, suggesting some impairment in proper segregation. Stable overexpression of MyoB caused a significant defect in parasite cell division, leading to the formation of extensive residual bodies, a substantial delay in replication, and loss of acute virulence in mice. Altogether, these observations suggest that MyoB/C products play a role in proper daughter cell budding and separation.

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Ultrastructural analysis of the residual bodies induced by MyoB overexpression. Thin section electron micrographs of wild-type parasites (A and B) and parasites overexpressing myc–MyoB (C–F). Wild-type parasites divide and form regular rosettes (A and B), whereas the vacuoles of transgenic parasites are highly disorganized (C–E). The boxed region in E is presented at higher magnification in F. Residual bodies are clearly distinguished from parasites, as they lack the IMC and are surrounded only by the plasma membrane (C–F). In wild-type parasites, residual bodies such as the one seen in B were rare. C, conoid; N, nucleus; PM, plasma membrane; PPR, posterior polar ring; RB, residual body. Bars, 1 μm.
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fig9: Ultrastructural analysis of the residual bodies induced by MyoB overexpression. Thin section electron micrographs of wild-type parasites (A and B) and parasites overexpressing myc–MyoB (C–F). Wild-type parasites divide and form regular rosettes (A and B), whereas the vacuoles of transgenic parasites are highly disorganized (C–E). The boxed region in E is presented at higher magnification in F. Residual bodies are clearly distinguished from parasites, as they lack the IMC and are surrounded only by the plasma membrane (C–F). In wild-type parasites, residual bodies such as the one seen in B were rare. C, conoid; N, nucleus; PM, plasma membrane; PPR, posterior polar ring; RB, residual body. Bars, 1 μm.

Mentions: Thin section transmission EM of clones overexpressing MyoB revealed severe morphological defects. The MyoB overexpressers showed a significantly disorganized arrangement within the parasitophorous vacuole (Fig. 9, D and E) compared with the regular rosettes formed by wild-type parasites (Fig. 9, A and B). Presence of residual bodies, as observed by light microscopy, was also visible at the EM level. Most of these large cytoplasmic extensions were directly connected to the parasites, and were not only seen at the posterior (Fig. 9 C) but also toward the anterior pole (Fig. 9 E). Higher magnification clearly revealed that the bleb-like bulges were only surrounded by the plasma membrane and the IMC was absent (Fig. 9 F), confirming the data obtained by confocal microscopy (Fig. 8). The quasi absence of organelles in these residual bodies distinguished them from the structures created by treatment with cytochalasin D (Shaw et al., 2000).


Toxoplasma gondii myosins B/C: one gene, two tails, two localizations, and a role in parasite division.

Delbac F, Sänger A, Neuhaus EM, Stratmann R, Ajioka JW, Toursel C, Herm-Götz A, Tomavo S, Soldati T, Soldati D - J. Cell Biol. (2001)

Ultrastructural analysis of the residual bodies induced by MyoB overexpression. Thin section electron micrographs of wild-type parasites (A and B) and parasites overexpressing myc–MyoB (C–F). Wild-type parasites divide and form regular rosettes (A and B), whereas the vacuoles of transgenic parasites are highly disorganized (C–E). The boxed region in E is presented at higher magnification in F. Residual bodies are clearly distinguished from parasites, as they lack the IMC and are surrounded only by the plasma membrane (C–F). In wild-type parasites, residual bodies such as the one seen in B were rare. C, conoid; N, nucleus; PM, plasma membrane; PPR, posterior polar ring; RB, residual body. Bars, 1 μm.
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Related In: Results  -  Collection

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fig9: Ultrastructural analysis of the residual bodies induced by MyoB overexpression. Thin section electron micrographs of wild-type parasites (A and B) and parasites overexpressing myc–MyoB (C–F). Wild-type parasites divide and form regular rosettes (A and B), whereas the vacuoles of transgenic parasites are highly disorganized (C–E). The boxed region in E is presented at higher magnification in F. Residual bodies are clearly distinguished from parasites, as they lack the IMC and are surrounded only by the plasma membrane (C–F). In wild-type parasites, residual bodies such as the one seen in B were rare. C, conoid; N, nucleus; PM, plasma membrane; PPR, posterior polar ring; RB, residual body. Bars, 1 μm.
Mentions: Thin section transmission EM of clones overexpressing MyoB revealed severe morphological defects. The MyoB overexpressers showed a significantly disorganized arrangement within the parasitophorous vacuole (Fig. 9, D and E) compared with the regular rosettes formed by wild-type parasites (Fig. 9, A and B). Presence of residual bodies, as observed by light microscopy, was also visible at the EM level. Most of these large cytoplasmic extensions were directly connected to the parasites, and were not only seen at the posterior (Fig. 9 C) but also toward the anterior pole (Fig. 9 E). Higher magnification clearly revealed that the bleb-like bulges were only surrounded by the plasma membrane and the IMC was absent (Fig. 9 F), confirming the data obtained by confocal microscopy (Fig. 8). The quasi absence of organelles in these residual bodies distinguished them from the structures created by treatment with cytochalasin D (Shaw et al., 2000).

Bottom Line: MyoC is the first marker selectively concentrated at the anterior and posterior polar rings of the inner membrane complex, structures that play a key role in cell shape integrity during daughter cell biogenesis.When transiently expressed, MyoB, MyoC, as well as the common motor domain lacking the tail did not distribute evenly between daughter cells, suggesting some impairment in proper segregation.Altogether, these observations suggest that MyoB/C products play a role in proper daughter cell budding and separation.

View Article: PubMed Central - PubMed

Affiliation: Zentrum für Molekulare Biologie, Universität Heidelberg, D-69120 Heidelberg, Germany.

ABSTRACT
In apicomplexan parasites, actin-disrupting drugs and the inhibitor of myosin heavy chain ATPase, 2,3-butanedione monoxime, have been shown to interfere with host cell invasion by inhibiting parasite gliding motility. We report here that the actomyosin system of Toxoplasma gondii also contributes to the process of cell division by ensuring accurate budding of daughter cells. T. gondii myosins B and C are encoded by alternatively spliced mRNAs and differ only in their COOH-terminal tails. MyoB and MyoC showed distinct subcellular localizations and dissimilar solubilities, which were conferred by their tails. MyoC is the first marker selectively concentrated at the anterior and posterior polar rings of the inner membrane complex, structures that play a key role in cell shape integrity during daughter cell biogenesis. When transiently expressed, MyoB, MyoC, as well as the common motor domain lacking the tail did not distribute evenly between daughter cells, suggesting some impairment in proper segregation. Stable overexpression of MyoB caused a significant defect in parasite cell division, leading to the formation of extensive residual bodies, a substantial delay in replication, and loss of acute virulence in mice. Altogether, these observations suggest that MyoB/C products play a role in proper daughter cell budding and separation.

Show MeSH
Related in: MedlinePlus