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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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Related in: MedlinePlus

Time-lapse Images Showing That the TgMORN1 Ring Is Initiated around the Duplicated Centrioles (cf. Video S1)Images are selected time points from a time-lapse experiment tracking the cell division of four parasites expressing EGFP-TgMORN1 (green) and mCherryFP-TgTubA1 (red) (cf. Video S1). See text for detailed description of the time sequence. Top and bottom panels are 2× magnification of regions indicated by the dotted frames. Yellow arrows (t = 0–40 min), the initiation sites of the basal complex around the centrioles; green arrows (t = 50–110 min), daughter basal ring complex; green arrowheads (t = 60–70 min), TgMORN1 labeling of the daughter apical complex; red arrowheads (t = 70 min), the centriole labeling that is just separated from the conoid labeling of mCherryFP-TgTubA1.All images are maximum intensity projections of deconvolved 3D stacks.
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ppat-0040010-g005: Time-lapse Images Showing That the TgMORN1 Ring Is Initiated around the Duplicated Centrioles (cf. Video S1)Images are selected time points from a time-lapse experiment tracking the cell division of four parasites expressing EGFP-TgMORN1 (green) and mCherryFP-TgTubA1 (red) (cf. Video S1). See text for detailed description of the time sequence. Top and bottom panels are 2× magnification of regions indicated by the dotted frames. Yellow arrows (t = 0–40 min), the initiation sites of the basal complex around the centrioles; green arrows (t = 50–110 min), daughter basal ring complex; green arrowheads (t = 60–70 min), TgMORN1 labeling of the daughter apical complex; red arrowheads (t = 70 min), the centriole labeling that is just separated from the conoid labeling of mCherryFP-TgTubA1.All images are maximum intensity projections of deconvolved 3D stacks.

Mentions: (C) In interphase parasites, the basal labeling of TgMORN1 (green arrows) is clearly separated from the cortical microtubules (red, mCherryFP-TgTubA1, small gray arrows). The inset shows a magnified view of the centriole/spindle pole assembly, showing red TgTubA1 in the centriole and green TgMORN1 in the spindle pole. At this point in the cell cycle, tubulin labeling of the spindle pole is weak, but will become stronger in early cell division (cf. Figure 5). White arrow, conoid labeling by mCherryFP-TgTubA1.


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

Hu K - PLoS Pathog. (2008)

Time-lapse Images Showing That the TgMORN1 Ring Is Initiated around the Duplicated Centrioles (cf. Video S1)Images are selected time points from a time-lapse experiment tracking the cell division of four parasites expressing EGFP-TgMORN1 (green) and mCherryFP-TgTubA1 (red) (cf. Video S1). See text for detailed description of the time sequence. Top and bottom panels are 2× magnification of regions indicated by the dotted frames. Yellow arrows (t = 0–40 min), the initiation sites of the basal complex around the centrioles; green arrows (t = 50–110 min), daughter basal ring complex; green arrowheads (t = 60–70 min), TgMORN1 labeling of the daughter apical complex; red arrowheads (t = 70 min), the centriole labeling that is just separated from the conoid labeling of mCherryFP-TgTubA1.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-g005: Time-lapse Images Showing That the TgMORN1 Ring Is Initiated around the Duplicated Centrioles (cf. Video S1)Images are selected time points from a time-lapse experiment tracking the cell division of four parasites expressing EGFP-TgMORN1 (green) and mCherryFP-TgTubA1 (red) (cf. Video S1). See text for detailed description of the time sequence. Top and bottom panels are 2× magnification of regions indicated by the dotted frames. Yellow arrows (t = 0–40 min), the initiation sites of the basal complex around the centrioles; green arrows (t = 50–110 min), daughter basal ring complex; green arrowheads (t = 60–70 min), TgMORN1 labeling of the daughter apical complex; red arrowheads (t = 70 min), the centriole labeling that is just separated from the conoid labeling of mCherryFP-TgTubA1.All images are maximum intensity projections of deconvolved 3D stacks.
Mentions: (C) In interphase parasites, the basal labeling of TgMORN1 (green arrows) is clearly separated from the cortical microtubules (red, mCherryFP-TgTubA1, small gray arrows). The inset shows a magnified view of the centriole/spindle pole assembly, showing red TgTubA1 in the centriole and green TgMORN1 in the spindle pole. At this point in the cell cycle, tubulin labeling of the spindle pole is weak, but will become stronger in early cell division (cf. Figure 5). White arrow, conoid labeling by mCherryFP-TgTubA1.

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