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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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TgCentrin2 Is Recruited to the Daughter Basal Complex at the Time of Basal Complex Constriction, Which Reveals the Compartmentation and Polarity of the Basal Complex before the Closure of Its Posterior End(A) TgCentrin2 is clearly localized to a ring structure (indicated by dotted frames) in daughter parasites with a partially constricted basal complex.(B) TgCentrin2 basal labeling (indicated by dotted frames) in the daughter is pronounced during cytokinesis, when the daughters start to take over mother's plasma membrane.(C) A TgCentrin2 ring (indicated by dotted frames) is also present in parasites that have just finished cytokinesis, but whose basal complexes are not yet fully closed.Green, mCherryFP-TgMORN1 (pseudo-color); red, EGFP-TgCentrin2 (pseudo-color); blue, anti-IMC1 antibody detected by Alexa350-anti-mouse IgG.Similar exposure time (0.8 s/plane for Figure S3 and [A and B], and 0.6 s/plane for [C]) and the same brightness, and contrast setting were applied to the TgCentrin2 panels in Figure S3 and this figure to enable comparison of the relative level of Tgcentrin2 in the daughter basal complexes at different stages.Insets: 2× magnification of regions indicated by the dotted frames. The insets in the rightmost panels merge only TgCentrin2 and TgMORN1 images, and different brightness/contrast settings from the single channel images are applied to these panels to emphasize the difference in localization between these two proteins.All images are maximum intensity projections of deconvolved 3D stacks.
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ppat-0040010-g008: TgCentrin2 Is Recruited to the Daughter Basal Complex at the Time of Basal Complex Constriction, Which Reveals the Compartmentation and Polarity of the Basal Complex before the Closure of Its Posterior End(A) TgCentrin2 is clearly localized to a ring structure (indicated by dotted frames) in daughter parasites with a partially constricted basal complex.(B) TgCentrin2 basal labeling (indicated by dotted frames) in the daughter is pronounced during cytokinesis, when the daughters start to take over mother's plasma membrane.(C) A TgCentrin2 ring (indicated by dotted frames) is also present in parasites that have just finished cytokinesis, but whose basal complexes are not yet fully closed.Green, mCherryFP-TgMORN1 (pseudo-color); red, EGFP-TgCentrin2 (pseudo-color); blue, anti-IMC1 antibody detected by Alexa350-anti-mouse IgG.Similar exposure time (0.8 s/plane for Figure S3 and [A and B], and 0.6 s/plane for [C]) and the same brightness, and contrast setting were applied to the TgCentrin2 panels in Figure S3 and this figure to enable comparison of the relative level of Tgcentrin2 in the daughter basal complexes at different stages.Insets: 2× magnification of regions indicated by the dotted frames. The insets in the rightmost panels merge only TgCentrin2 and TgMORN1 images, and different brightness/contrast settings from the single channel images are applied to these panels to emphasize the difference in localization between these two proteins.All images are maximum intensity projections of deconvolved 3D stacks.

Mentions: Interestingly, although TgCentrin2 is hardly detectable in the basal ring complex earlier during cell division (cf. Figure 3B and Figure S3), it is clearly localized to the daughter basal complex as a ring at a late stage when the daughter basal complex appears to be constricted (Figure 8A). Its ring-like localization in the basal complex is also pronounced during cytokinesis when the daughters start to take over mother's plasma membrane (Figure 8B), and after cytokinesis when the basal complex is still open at both ends (Figure 8C). In all cases, the TgCentrin2 basal ring is located to the posterior of the TgMORN1 ring (Figures 8 and 9). The compartmentation and polarization of the basal complex are thus revealed upon the recruitment of TgCentrin2 prior to the closure of the basal complex.


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

Hu K - PLoS Pathog. (2008)

TgCentrin2 Is Recruited to the Daughter Basal Complex at the Time of Basal Complex Constriction, Which Reveals the Compartmentation and Polarity of the Basal Complex before the Closure of Its Posterior End(A) TgCentrin2 is clearly localized to a ring structure (indicated by dotted frames) in daughter parasites with a partially constricted basal complex.(B) TgCentrin2 basal labeling (indicated by dotted frames) in the daughter is pronounced during cytokinesis, when the daughters start to take over mother's plasma membrane.(C) A TgCentrin2 ring (indicated by dotted frames) is also present in parasites that have just finished cytokinesis, but whose basal complexes are not yet fully closed.Green, mCherryFP-TgMORN1 (pseudo-color); red, EGFP-TgCentrin2 (pseudo-color); blue, anti-IMC1 antibody detected by Alexa350-anti-mouse IgG.Similar exposure time (0.8 s/plane for Figure S3 and [A and B], and 0.6 s/plane for [C]) and the same brightness, and contrast setting were applied to the TgCentrin2 panels in Figure S3 and this figure to enable comparison of the relative level of Tgcentrin2 in the daughter basal complexes at different stages.Insets: 2× magnification of regions indicated by the dotted frames. The insets in the rightmost panels merge only TgCentrin2 and TgMORN1 images, and different brightness/contrast settings from the single channel images are applied to these panels to emphasize the difference in localization between these two proteins.All images are maximum intensity projections of deconvolved 3D stacks.
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Related In: Results  -  Collection

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ppat-0040010-g008: TgCentrin2 Is Recruited to the Daughter Basal Complex at the Time of Basal Complex Constriction, Which Reveals the Compartmentation and Polarity of the Basal Complex before the Closure of Its Posterior End(A) TgCentrin2 is clearly localized to a ring structure (indicated by dotted frames) in daughter parasites with a partially constricted basal complex.(B) TgCentrin2 basal labeling (indicated by dotted frames) in the daughter is pronounced during cytokinesis, when the daughters start to take over mother's plasma membrane.(C) A TgCentrin2 ring (indicated by dotted frames) is also present in parasites that have just finished cytokinesis, but whose basal complexes are not yet fully closed.Green, mCherryFP-TgMORN1 (pseudo-color); red, EGFP-TgCentrin2 (pseudo-color); blue, anti-IMC1 antibody detected by Alexa350-anti-mouse IgG.Similar exposure time (0.8 s/plane for Figure S3 and [A and B], and 0.6 s/plane for [C]) and the same brightness, and contrast setting were applied to the TgCentrin2 panels in Figure S3 and this figure to enable comparison of the relative level of Tgcentrin2 in the daughter basal complexes at different stages.Insets: 2× magnification of regions indicated by the dotted frames. The insets in the rightmost panels merge only TgCentrin2 and TgMORN1 images, and different brightness/contrast settings from the single channel images are applied to these panels to emphasize the difference in localization between these two proteins.All images are maximum intensity projections of deconvolved 3D stacks.
Mentions: Interestingly, although TgCentrin2 is hardly detectable in the basal ring complex earlier during cell division (cf. Figure 3B and Figure S3), it is clearly localized to the daughter basal complex as a ring at a late stage when the daughter basal complex appears to be constricted (Figure 8A). Its ring-like localization in the basal complex is also pronounced during cytokinesis when the daughters start to take over mother's plasma membrane (Figure 8B), and after cytokinesis when the basal complex is still open at both ends (Figure 8C). In all cases, the TgCentrin2 basal ring is located to the posterior of the TgMORN1 ring (Figures 8 and 9). The compartmentation and polarization of the basal complex are thus revealed upon the recruitment of TgCentrin2 prior to the closure of the basal complex.

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