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Determination of Ploidy Levels and Nuclear DNA Content in Cryptococcus neoformans by Flow Cytometry: Drawbacks with
Yun C Chang1, Michael J Davis1, Kyung J Kwon-Chung1
1Molecular Microbiology Section, Laboratory of Clinical Immunology and Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Journal of Fungi (Basel, Switzerland)
|April 26, 2024
Summary
Propidium iodide (PI) staining is the most reliable method for Cryptococcus cell cycle and ploidy analysis, despite cell size variations. Alternative dyes showed nonspecific staining, limiting their use in Cryptococcus DNA content analysis.
Area of Science:
- Mycology
- Cell Biology
- Biotechnology
Background:
- Flow cytometry is a standard technique for analyzing cell populations, including DNA content for ploidy and cell cycle studies.
- Accurate DNA content analysis in Cryptococcus is crucial for understanding fungal biology and pathogenesis.
- Traditional DNA-binding dyes like propidium iodide (PI) are commonly used but can be affected by cell size variations.
Purpose of the Study:
- To evaluate the reliability of propidium iodide (PI) staining for Cryptococcus ploidy and cell cycle analysis.
- To assess alternative DNA-binding dyes (SYTOX Green, SYBR Green I) for improved accuracy in Cryptococcus DNA analysis.
- To investigate the impact of cell size variability on flow cytometry-based ploidy determination in Cryptococcus.
Main Methods:
- Flow cytometry was used for cell cycle and ploidy determination in Cryptococcus.
- Cells were fixed and stained with DNA-binding fluorescent dyes, primarily propidium iodide (PI).
- The ImageStream system was employed to analyze fluorescence intensity shifts related to cell size.
Main Results:
- Propidium iodide (PI) staining showed variability in fluorescence intensity due to significant changes in Cryptococcus cell size, confounding accurate ploidy analysis.
- The ImageStream system successfully interpreted fluorescence intensity shifts unrelated to ploidy changes caused by increased cell size.
- SYTOX Green and SYBR Green I demonstrated nonspecific nuclear DNA staining in Cryptococcus, unlike their performance in Saccharomyces cerevisiae.
Conclusions:
- Despite limitations with cell size variability, propidium iodide (PI) remains the most reliable method for Cryptococcus cell cycle and ploidy analysis currently.
- Further development of DNA-binding dyes or methods is needed to mitigate variability caused by drastic cell size and shape changes in Cryptococcus.
- Alternative dyes like SYTOX Green and SYBR Green I are not suitable for nuclear DNA staining in Cryptococcus.
