Flow cytometric correlation between BrdU/Hoechst quench effect and base pair composition in mammalian cell nuclei

Area of Science:

• Cell Biology
• Genetics
• Biophysics

Background:

• Cell cycle analysis often uses bromodeoxyuridine (BrdU) incorporation to label DNA.
• Hoechst dye fluorescence is quenched by BrdU substitution in chromatin.
• Mammalian cell cultures exhibit distinct fluorescence peaks after BrdU labeling, indicating cell maturity classes.

Purpose of the Study:

• To investigate species-specific differences in Hoechst fluorescence quenching by BrdU-substituted DNA.
• To correlate fluorescence quenching patterns with DNA base composition and organization.

Main Methods:

• Culturing mammalian cells (human, bovine, Micromys minutus) in BrdU-supplemented media.
• Analyzing Hoechst fluorescence histograms using flow cytometry.
• Estimating AT-content using base-pair specific dyes.

Main Results:

• Differential Hoechst fluorescence quenching observed, varying among species.
• Human and bovine cells showed more quenching with unifilary BrdU substitution compared to bifilary.
• Micromys minutus cells exhibited the reverse pattern, with higher quenching at bifilary substitution.
• Flow cytometry confirmed AT-content differences (Micromys: 62.0%, human: 60.6%, bovine: 53.2%).
• AT-content alone did not fully explain the observed quenching discrepancies.

Conclusions:

• Species-specific DNA sequence organization, beyond overall AT-content, influences Hoechst fluorescence quenching by BrdU.
• Factors like base-pair interspersion patterns and lateral asymmetry are critical for understanding these differences.
• This has implications for accurate cell cycle analysis and DNA content estimation across species.