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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 Constriction of the Daughter TgCentrin2 Basal Ring at a Late Stage of the Cell Cycle Can Be Induced by Treatment with Calcium Ionophore A23187 (cf. Video S3)A parasite expressing EGFP-TgCentrin2 that has started its cytokinesis. EGFP-TgCentrin2 has already been recruited to the basal complex of the daughters (one of which is indicated by the arrows) at this point. Upon A23187 treatment, the EGFP-TgCentrin2 labeling clearly constricts from ∼0.9 μm (time 0) to ∼0.5 μm (time 0:09:13) in less than 10 min. The morphology of the basal complex in control parasites at a similar stage does not change when treated with 0.1% DMSO alone (unpublished data).Arrowheads, TgCentrin2 basal complex labeling in the mother cell.Insets: 2× magnification of the daughter basal complex indicated by the arrows.All images except for the DIC image are maximum intensity projections of deconvolved 3D stacks.
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ppat-0040010-g010: The Constriction of the Daughter TgCentrin2 Basal Ring at a Late Stage of the Cell Cycle Can Be Induced by Treatment with Calcium Ionophore A23187 (cf. Video S3)A parasite expressing EGFP-TgCentrin2 that has started its cytokinesis. EGFP-TgCentrin2 has already been recruited to the basal complex of the daughters (one of which is indicated by the arrows) at this point. Upon A23187 treatment, the EGFP-TgCentrin2 labeling clearly constricts from ∼0.9 μm (time 0) to ∼0.5 μm (time 0:09:13) in less than 10 min. The morphology of the basal complex in control parasites at a similar stage does not change when treated with 0.1% DMSO alone (unpublished data).Arrowheads, TgCentrin2 basal complex labeling in the mother cell.Insets: 2× magnification of the daughter basal complex indicated by the arrows.All images except for the DIC image are maximum intensity projections of deconvolved 3D stacks.

Mentions: Like the TgMORN1 compartment, the TgCentrin2 basal compartment also undergoes significant constriction, from a ∼1.0 μm ring to a diffraction limited spot (Figures 8 and 9). Consistent with the involvement of centrin homologs in calcium sensitive contractile apparatus in other systems [22–24], the constriction of the TgCentrin2 basal compartment can be artificially induced in daughter parasites at a late stage of cell division when the intracellular calcium concentration is elevated by treatment with calcium ionophore, A23187 (Figure 10; Video S3).


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

Hu K - PLoS Pathog. (2008)

The Constriction of the Daughter TgCentrin2 Basal Ring at a Late Stage of the Cell Cycle Can Be Induced by Treatment with Calcium Ionophore A23187 (cf. Video S3)A parasite expressing EGFP-TgCentrin2 that has started its cytokinesis. EGFP-TgCentrin2 has already been recruited to the basal complex of the daughters (one of which is indicated by the arrows) at this point. Upon A23187 treatment, the EGFP-TgCentrin2 labeling clearly constricts from ∼0.9 μm (time 0) to ∼0.5 μm (time 0:09:13) in less than 10 min. The morphology of the basal complex in control parasites at a similar stage does not change when treated with 0.1% DMSO alone (unpublished data).Arrowheads, TgCentrin2 basal complex labeling in the mother cell.Insets: 2× magnification of the daughter basal complex indicated by the arrows.All images except for the DIC image 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-g010: The Constriction of the Daughter TgCentrin2 Basal Ring at a Late Stage of the Cell Cycle Can Be Induced by Treatment with Calcium Ionophore A23187 (cf. Video S3)A parasite expressing EGFP-TgCentrin2 that has started its cytokinesis. EGFP-TgCentrin2 has already been recruited to the basal complex of the daughters (one of which is indicated by the arrows) at this point. Upon A23187 treatment, the EGFP-TgCentrin2 labeling clearly constricts from ∼0.9 μm (time 0) to ∼0.5 μm (time 0:09:13) in less than 10 min. The morphology of the basal complex in control parasites at a similar stage does not change when treated with 0.1% DMSO alone (unpublished data).Arrowheads, TgCentrin2 basal complex labeling in the mother cell.Insets: 2× magnification of the daughter basal complex indicated by the arrows.All images except for the DIC image are maximum intensity projections of deconvolved 3D stacks.
Mentions: Like the TgMORN1 compartment, the TgCentrin2 basal compartment also undergoes significant constriction, from a ∼1.0 μm ring to a diffraction limited spot (Figures 8 and 9). Consistent with the involvement of centrin homologs in calcium sensitive contractile apparatus in other systems [22–24], the constriction of the TgCentrin2 basal compartment can be artificially induced in daughter parasites at a late stage of cell division when the intracellular calcium concentration is elevated by treatment with calcium ionophore, A23187 (Figure 10; Video S3).

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