An improved immunocytochemical procedure for high-sensitivity detection of incorporated bromodeoxyuridine

This report describes an improved immunochemical procedure to stain cells in suspension for incorporated bromodeoxyuridine (BrdUrd) and total DNA content. The procedure consists of five steps: chromatin proteins are extracted by treating with 0.1 M HCl and 0.7% Triton X-100 to facilitate DNA denaturation and to minimize nonspecific staining; cellular DNA is denatured by heating to 100 degrees C in distilled water; BrdUrd in single-stranded DNA (ssDNA) is stained using an immunochemical procedure; autofluorescence is reduced using sodium borohydride (NaBH4); and DNA is stained with the fluorescent dye propidium iodide. With this procedure, the BrdUrd incorporated by CHO cells during periods as short as a few seconds can be detected using flow cytometry. In addition, the stoichiometry of the immunofluorescent staining procedure is high.