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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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TgMORN1 Containing Ring Structures Are Found around the Centrioles after Centriole Duplication(A) Ring like structures containing TgMORN1 (green, EGFP-TgMORN1, green arrows) are constructed around the duplicated centrioles (red, mCherryFP-TgCentrin1, red arrows) after the duplicated centrioles return to the apical end of the nucleus.(B) TgCentrin2 (pseudo-colored red, EGFP-TgCentrin2) is undetectable in these TgMORN1 rings (pseudo-colored green, mCherryFP-TgMORN1). Arrows, centriole labeling by TgCentrin2; arrowheads, the mother and the future daughter's apical polar ring labeling by TgCentrin2. Note that a weak concentration of TgCentrin2 fluorescence can be seen at the upper-right portion of the inset in the TgCentrin2 panel. The identity of this concentration is not clear at the present.Blue, anti-IMC1 antibody detected by Alexa350-anti-mouse IgG. Lack of IMC1 antibody labeling in nascent daughters at this stage might be caused by poor epitope accessibility (cf. Figure 4 and Figure S3).Insets: 2× magnification of regions indicated by the dotted frames.All images are maximum intensity projections of deconvolved 3D stacks.
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ppat-0040010-g003: TgMORN1 Containing Ring Structures Are Found around the Centrioles after Centriole Duplication(A) Ring like structures containing TgMORN1 (green, EGFP-TgMORN1, green arrows) are constructed around the duplicated centrioles (red, mCherryFP-TgCentrin1, red arrows) after the duplicated centrioles return to the apical end of the nucleus.(B) TgCentrin2 (pseudo-colored red, EGFP-TgCentrin2) is undetectable in these TgMORN1 rings (pseudo-colored green, mCherryFP-TgMORN1). Arrows, centriole labeling by TgCentrin2; arrowheads, the mother and the future daughter's apical polar ring labeling by TgCentrin2. Note that a weak concentration of TgCentrin2 fluorescence can be seen at the upper-right portion of the inset in the TgCentrin2 panel. The identity of this concentration is not clear at the present.Blue, anti-IMC1 antibody detected by Alexa350-anti-mouse IgG. Lack of IMC1 antibody labeling in nascent daughters at this stage might be caused by poor epitope accessibility (cf. Figure 4 and Figure S3).Insets: 2× magnification of regions indicated by the dotted frames.All images are maximum intensity projections of deconvolved 3D stacks.

Mentions: The first sign of cell division is the migration of the centriole to the basal pole of the nucleus, where it replicates (Nishi M, Hu K, Murray J, Roos D, manuscript submitted). The replicated centrioles sandwich the spindle pole (Figure 2), which at this point still appears as one spot. Surprisingly, ring structures containing TgMORN1 are observed forming around the duplicated centrioles even before the separation of the future apical and basal regions of the daughter parasites (Figure 3). These rings are at the outer edges of the initially planar aggregations of daughter cytoskeletal elements that will later become the daughter cortical cytoskeletons (Figure 4). The TgMORN1 rings are therefore likely to be the precursor of the future daughter basal ring complex. Two other components of the mature basal complex in adult parasites, TgCentrin2 (Figure 3B) and TgDLC (data not shown), however, are not found in these early ring structures.


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

Hu K - PLoS Pathog. (2008)

TgMORN1 Containing Ring Structures Are Found around the Centrioles after Centriole Duplication(A) Ring like structures containing TgMORN1 (green, EGFP-TgMORN1, green arrows) are constructed around the duplicated centrioles (red, mCherryFP-TgCentrin1, red arrows) after the duplicated centrioles return to the apical end of the nucleus.(B) TgCentrin2 (pseudo-colored red, EGFP-TgCentrin2) is undetectable in these TgMORN1 rings (pseudo-colored green, mCherryFP-TgMORN1). Arrows, centriole labeling by TgCentrin2; arrowheads, the mother and the future daughter's apical polar ring labeling by TgCentrin2. Note that a weak concentration of TgCentrin2 fluorescence can be seen at the upper-right portion of the inset in the TgCentrin2 panel. The identity of this concentration is not clear at the present.Blue, anti-IMC1 antibody detected by Alexa350-anti-mouse IgG. Lack of IMC1 antibody labeling in nascent daughters at this stage might be caused by poor epitope accessibility (cf. Figure 4 and Figure S3).Insets: 2× 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-g003: TgMORN1 Containing Ring Structures Are Found around the Centrioles after Centriole Duplication(A) Ring like structures containing TgMORN1 (green, EGFP-TgMORN1, green arrows) are constructed around the duplicated centrioles (red, mCherryFP-TgCentrin1, red arrows) after the duplicated centrioles return to the apical end of the nucleus.(B) TgCentrin2 (pseudo-colored red, EGFP-TgCentrin2) is undetectable in these TgMORN1 rings (pseudo-colored green, mCherryFP-TgMORN1). Arrows, centriole labeling by TgCentrin2; arrowheads, the mother and the future daughter's apical polar ring labeling by TgCentrin2. Note that a weak concentration of TgCentrin2 fluorescence can be seen at the upper-right portion of the inset in the TgCentrin2 panel. The identity of this concentration is not clear at the present.Blue, anti-IMC1 antibody detected by Alexa350-anti-mouse IgG. Lack of IMC1 antibody labeling in nascent daughters at this stage might be caused by poor epitope accessibility (cf. Figure 4 and Figure S3).Insets: 2× magnification of regions indicated by the dotted frames.All images are maximum intensity projections of deconvolved 3D stacks.
Mentions: The first sign of cell division is the migration of the centriole to the basal pole of the nucleus, where it replicates (Nishi M, Hu K, Murray J, Roos D, manuscript submitted). The replicated centrioles sandwich the spindle pole (Figure 2), which at this point still appears as one spot. Surprisingly, ring structures containing TgMORN1 are observed forming around the duplicated centrioles even before the separation of the future apical and basal regions of the daughter parasites (Figure 3). These rings are at the outer edges of the initially planar aggregations of daughter cytoskeletal elements that will later become the daughter cortical cytoskeletons (Figure 4). The TgMORN1 rings are therefore likely to be the precursor of the future daughter basal ring complex. Two other components of the mature basal complex in adult parasites, TgCentrin2 (Figure 3B) and TgDLC (data not shown), however, are not found in these early ring structures.

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