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Organizational changes of the daughter basal complex during the parasite replication of Toxoplasma gondii.

Hu K - PLoS Pathog. (2008)

Bottom Line: This study focuses on key events during the biogenesis of the basal complex using high resolution light microscopy, and reveals that daughter basal complexes are established around the duplicated centrioles independently of the structural integrity of the daughter cortical cytoskeleton, and that they are dynamic "caps" at the growing ends of the daughters.This correlates with the constriction of the basal complex, a process that can be artificially induced by increasing cellular calcium concentration.The basal complex is therefore likely to be a new kind of centrin-based contractile apparatus.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Indiana University, Bloomington, Indiana, United States of America. kehu@indiana.edu

ABSTRACT
The apicomplexans are a large group of parasitic protozoa, many of which are important human and animal pathogens, including Plasmodium falciparum and Toxoplasma gondii. These parasites cause disease only when they replicate, and their replication is critically dependent on the proper assembly of the parasite cytoskeletons during cell division. In addition to their importance in pathogenesis, the apicomplexan parasite cytoskeletons are spectacular structures. Therefore, understanding the cytoskeletal biogenesis of these parasites is important not only for parasitology but also of general interest to broader cell biology. Previously, we found that the basal end of T. gondii contains a novel cytoskeletal assembly, the basal complex, a cytoskeletal compartment constructed in concert with the daughter cortical cytoskeleton during cell division. This study focuses on key events during the biogenesis of the basal complex using high resolution light microscopy, and reveals that daughter basal complexes are established around the duplicated centrioles independently of the structural integrity of the daughter cortical cytoskeleton, and that they are dynamic "caps" at the growing ends of the daughters. Compartmentation and polarization of the basal complex is first revealed at a late stage of cell division upon the recruitment of an EF-hand containing calcium binding protein, TgCentrin2. This correlates with the constriction of the basal complex, a process that can be artificially induced by increasing cellular calcium concentration. The basal complex is therefore likely to be a new kind of centrin-based contractile apparatus.

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The Initial Construction of the TgMORN1 Ring Is Likely to Be Independent of the Structural Integrity of the Daughter Cortical Cytoskeleton (cf. Video S2)A parasitophorous vacuole containing eight dividing parasites expressing EGFP-TgMORN1 (green) and mCherryFP-TgTubA1 (red) was treated with 2.5 μM oryzalin at time 0. No daughter cortical microtubules can be detected in these parasites, but the initiation (cf. Video S2, 33–48 min) and the construction (cf. Video S2, 60–120 min) of the basal complex are not affected. As previously reported [9,17], the spindle pole (arrowheads) fails to replicate in the presence of 2.5 μM oryzalin.Insets: 2.5× magnification of regions indicated by the dotted frames.All images are maximum intensity projections of deconvolved 3D stacks.
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ppat-0040010-g007: The Initial Construction of the TgMORN1 Ring Is Likely to Be Independent of the Structural Integrity of the Daughter Cortical Cytoskeleton (cf. Video S2)A parasitophorous vacuole containing eight dividing parasites expressing EGFP-TgMORN1 (green) and mCherryFP-TgTubA1 (red) was treated with 2.5 μM oryzalin at time 0. No daughter cortical microtubules can be detected in these parasites, but the initiation (cf. Video S2, 33–48 min) and the construction (cf. Video S2, 60–120 min) of the basal complex are not affected. As previously reported [9,17], the spindle pole (arrowheads) fails to replicate in the presence of 2.5 μM oryzalin.Insets: 2.5× magnification of regions indicated by the dotted frames.All images are maximum intensity projections of deconvolved 3D stacks.

Mentions: The daughter cortical cytoskeleton and the basal complex appear to grow in concert during cell division. Is the construction and growth of the basal complex, a seemingly “downstream” structure, dependent on the structural integrity of the daughter cortical cytoskeleton? To address this question, the construction of the basal complex was tracked in living parasites whose cortical microtubule extension and the daughter cortical cytoskeleton formation were severely disrupted by treating with oryzalin, a plant herbicide that binds to T. gondii α-tubulin and inhibits the construction of the spindle and the cortical microtubules, but not the centriole replication, during daughter formation (Figure 7; Video S2) [9,10,21]. As expected, the mother's conoid, cortical microtubules, and basal complex are not affected by the oryzalin treatment, and the overall morphology of the mother cell remains normal until the distorted daughters attempt to bud. Daughter cortical microtubules, however, completely fail to appear. Despite the inhibition of the formation of functional daughter cortical cytoskeleton, the initiation of TgMORN1 ring formation proceeds normally (Video S2, 33 and 48 min). Furthermore, complete TgMORN1 rings are formed ∼30 min after the initiation (Video S2; Figure 7, t = 60 min), enlarge to ∼1.2 μm (similar to the diameter of the basal complex in untreated daughters with extending cortical cytoskeletons [cf. Figure 5, t = 70 min]), and retain their ring morphology till “budding”, at which point the organization of the basal complex becomes unclear due to the distorted parasite morphology. The initiation, construction and maintenance of the daughter basal ring complex are therefore independent of the structural integrity of the daughter cortical cytoskeleton.


Organizational changes of the daughter basal complex during the parasite replication of Toxoplasma gondii.

Hu K - PLoS Pathog. (2008)

The Initial Construction of the TgMORN1 Ring Is Likely to Be Independent of the Structural Integrity of the Daughter Cortical Cytoskeleton (cf. Video S2)A parasitophorous vacuole containing eight dividing parasites expressing EGFP-TgMORN1 (green) and mCherryFP-TgTubA1 (red) was treated with 2.5 μM oryzalin at time 0. No daughter cortical microtubules can be detected in these parasites, but the initiation (cf. Video S2, 33–48 min) and the construction (cf. Video S2, 60–120 min) of the basal complex are not affected. As previously reported [9,17], the spindle pole (arrowheads) fails to replicate in the presence of 2.5 μM oryzalin.Insets: 2.5× magnification of regions indicated by the dotted frames.All images are maximum intensity projections of deconvolved 3D stacks.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2211554&req=5

ppat-0040010-g007: The Initial Construction of the TgMORN1 Ring Is Likely to Be Independent of the Structural Integrity of the Daughter Cortical Cytoskeleton (cf. Video S2)A parasitophorous vacuole containing eight dividing parasites expressing EGFP-TgMORN1 (green) and mCherryFP-TgTubA1 (red) was treated with 2.5 μM oryzalin at time 0. No daughter cortical microtubules can be detected in these parasites, but the initiation (cf. Video S2, 33–48 min) and the construction (cf. Video S2, 60–120 min) of the basal complex are not affected. As previously reported [9,17], the spindle pole (arrowheads) fails to replicate in the presence of 2.5 μM oryzalin.Insets: 2.5× magnification of regions indicated by the dotted frames.All images are maximum intensity projections of deconvolved 3D stacks.
Mentions: The daughter cortical cytoskeleton and the basal complex appear to grow in concert during cell division. Is the construction and growth of the basal complex, a seemingly “downstream” structure, dependent on the structural integrity of the daughter cortical cytoskeleton? To address this question, the construction of the basal complex was tracked in living parasites whose cortical microtubule extension and the daughter cortical cytoskeleton formation were severely disrupted by treating with oryzalin, a plant herbicide that binds to T. gondii α-tubulin and inhibits the construction of the spindle and the cortical microtubules, but not the centriole replication, during daughter formation (Figure 7; Video S2) [9,10,21]. As expected, the mother's conoid, cortical microtubules, and basal complex are not affected by the oryzalin treatment, and the overall morphology of the mother cell remains normal until the distorted daughters attempt to bud. Daughter cortical microtubules, however, completely fail to appear. Despite the inhibition of the formation of functional daughter cortical cytoskeleton, the initiation of TgMORN1 ring formation proceeds normally (Video S2, 33 and 48 min). Furthermore, complete TgMORN1 rings are formed ∼30 min after the initiation (Video S2; Figure 7, t = 60 min), enlarge to ∼1.2 μm (similar to the diameter of the basal complex in untreated daughters with extending cortical cytoskeletons [cf. Figure 5, t = 70 min]), and retain their ring morphology till “budding”, at which point the organization of the basal complex becomes unclear due to the distorted parasite morphology. The initiation, construction and maintenance of the daughter basal ring complex are therefore independent of the structural integrity of the daughter cortical cytoskeleton.

Bottom Line: This study focuses on key events during the biogenesis of the basal complex using high resolution light microscopy, and reveals that daughter basal complexes are established around the duplicated centrioles independently of the structural integrity of the daughter cortical cytoskeleton, and that they are dynamic "caps" at the growing ends of the daughters.This correlates with the constriction of the basal complex, a process that can be artificially induced by increasing cellular calcium concentration.The basal complex is therefore likely to be a new kind of centrin-based contractile apparatus.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Indiana University, Bloomington, Indiana, United States of America. kehu@indiana.edu

ABSTRACT
The apicomplexans are a large group of parasitic protozoa, many of which are important human and animal pathogens, including Plasmodium falciparum and Toxoplasma gondii. These parasites cause disease only when they replicate, and their replication is critically dependent on the proper assembly of the parasite cytoskeletons during cell division. In addition to their importance in pathogenesis, the apicomplexan parasite cytoskeletons are spectacular structures. Therefore, understanding the cytoskeletal biogenesis of these parasites is important not only for parasitology but also of general interest to broader cell biology. Previously, we found that the basal end of T. gondii contains a novel cytoskeletal assembly, the basal complex, a cytoskeletal compartment constructed in concert with the daughter cortical cytoskeleton during cell division. This study focuses on key events during the biogenesis of the basal complex using high resolution light microscopy, and reveals that daughter basal complexes are established around the duplicated centrioles independently of the structural integrity of the daughter cortical cytoskeleton, and that they are dynamic "caps" at the growing ends of the daughters. Compartmentation and polarization of the basal complex is first revealed at a late stage of cell division upon the recruitment of an EF-hand containing calcium binding protein, TgCentrin2. This correlates with the constriction of the basal complex, a process that can be artificially induced by increasing cellular calcium concentration. The basal complex is therefore likely to be a new kind of centrin-based contractile apparatus.

Show MeSH
Related in: MedlinePlus