Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 99, Issue 4, Pages 2014-2019Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.022554999
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Funding
- NIA NIH HHS [R21 AG060216] Funding Source: Medline
- NIGMS NIH HHS [R21 GM60216] Funding Source: Medline
- NIMH NIH HHS [R21 MH060216] Funding Source: Medline
- Wellcome Trust Funding Source: Medline
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Toxoplasma gondii is an intracellular parasite that proliferates within most nucleated cells, an important human pathogen, and a model for the study of human and veterinary parasitic infections. We used a stable yellow fluorescent protein-alpha-tubulin transgenic line to determine the structure of the microtubule cytoskeleton in T. gondii. Imaging of living yellow fluorescent protein-a-tubulin parasites by laser-scanning confocal microscopy (LSCM) failed to resolve the 22 subpellicular microtubules characteristic of the parasite cytoskeleton. To understand this result, we analyzed sources of noise in the LSCM and identified illumination fluctuations on time scales from microseconds to hours that introduce significant amounts of noise. We confirmed that weakly fluorescent structures could not be imaged in LSCM by using fluorescent bead standards. By contrast, wide-field microscopy (WFM) did visualize weak fluorescent standards and e individual microtubules of the parasite cytoskeleton. We therefore measured the fluorescence per unit length of microtubule by using WFM and used this information to estimate the tubulin content of the conoid (a structure important for T. gondii infection) and in the mitotic spindle pole. The conoid contains sufficient tubulin for approximate to10 microtubule segments of 0.5-mum length, indicating that tubulin forms the structural core of the organelle. We also show that the T. gondii mitotic spindle contains approximate to1 microtubule per chromosome. This analysis expands the understanding of structures used for invasion and intracellular proliferation by an important human pathogen and shows the advantage of WFM combined with image deconvolution over LSCM for quantitative studies of weakly fluorescent structures in moderately thin living cells.
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