S-phase detailed analysis in KB cells by bromdeoxyuridine labelling

A method based on the sequential BrdU incorporation followed by differential spiralization of the chromosomes was used for analysis of S-phase in KB cells when Brdu was added to the cultures for 19, 24 and 26 hours before fixation. The S-phase was subdivided into three subphases, each recognisable by a specific incorporation pattern at metaphase: late-S (LS), middle-S (MS) and early -S (ES). Two other intermediary subphases, mid-early S (mES) and mid-late S (mLS) have also been distinguished but their accurate identification is generally difficult. A high degree of asynchrony in KB cells population was observed as well as a wide variability concerning the duration of S-phase (BrdU = bromdeoxyuridine).