Measuring S-Phase Duration from Asynchronous Cells Using Dual EdU-BrdU Pulse-Chase Labeling Flow Cytometry

Area of Science:

• Cell Biology
• Genetics
• Molecular Biology

Background:

• Eukaryotic DNA replication occurs during S phase, utilizing numerous initiation sites and complex replication programs.
• S phase duration is crucial for genome stability, with defects linked to cancer and aging.
• Existing methods for measuring S phase duration are indirect, often requiring cell synchronization or mathematical modeling, which can introduce artifacts.

Purpose of the Study:

• To develop a simple, robust, and direct method for measuring S phase duration in unperturbed eukaryotic cells.
• To assess the impact of drugs or mutations on S phase duration without artifacts.
• To compare S phase duration across different cell types, including cancer cell lines and primary cells.

Main Methods:

• A dual EdU-BrdU pulse-labeling strategy with incremental thymidine chases was employed.
• Flow cytometry was used to quantify cells entering and exiting S phase.
• The method was validated in human, mouse, and Drosophila cells, including both adherent and suspension cultures.

Main Results:

• The novel method accurately measures S phase duration without requiring cell synchronization or genome engineering.
• The technique successfully characterized S phase dynamics in various cell types, including primary cells and cell lines.
• A significant finding was that several common cancer cell lines exhibit a longer S phase duration compared to untransformed cells.

Conclusions:

• This new method provides a direct and artifact-free measurement of S phase duration in diverse eukaryotic systems.
• The findings highlight potential differences in replication dynamics between cancerous and normal cells, with implications for understanding cancer biology.
• The technique's versatility makes it valuable for studying cell cycle regulation and the effects of genetic or chemical perturbations.