Problem of size dependence in fluorescence DNA cytometry

Area of Science:

• Cell biology
• Biophysics
• Cytometry

Background:

• Accurate DNA content measurement is crucial for cell analysis and disease diagnosis.
• The relationship between cell size, DNA concentration, and fluorescence intensity is complex.
• Previous studies have not fully addressed the size-dependent effect in DNA measurements.

Purpose of the Study:

• To investigate the relationship between fluorescence intensity, area, thickness, and DNA concentration in DNA-bearing polyacrylamide films.
• To understand and quantify the size-dependent effect on human cell nuclei.
• To identify methods for minimizing the size-dependent effect in DNA content analysis.

Main Methods:

• Utilized an epi-illumination cytofluorometer for measurements.
• Employed DAPI staining at 50 ng/ml for DNA-bearing polyacrylamide films.
• Performed theoretical analysis alongside experimental measurements.

Main Results:

• Confirmed the inevitability of a size-dependent effect on human cell nuclei (DNA concentration ~10 mg/ml).
• Demonstrated that flattening nuclei to <0.33 microns thickness virtually negates this effect.
• Identified reduced dye concentration and thin, uniform smears (e.g., via hypotonic treatment) as practical minimization strategies.

Conclusions:

• The size-dependent effect is a significant factor in DNA content determination, particularly for different cell types and tumor aneuploidy.
• Awareness and mitigation of this effect are essential for accurate cytometric DNA analysis.
• Optimizing sample preparation techniques is key to overcoming measurement biases.