Sister Chromatid Exchange as a Genotoxic Stress Marker.

Sister chromatid exchange (SCE) is the phenomenon of partial DNA exchange during DNA replication. SCE detection has been developed through eliciting DNA's semiconservative replicative nature. Thymidine analogues such as 5'-bromodeoxyuridine (BrdU) and ethynyldeoxyuridine (EdU) are incorporated into the newly synthesized DNA for two cell cycles. The addition of Colcemid to the culture blocks and synchronizes cells at mitosis, and conventional cytogenetic preparations are made. Differential staining methods with Hoechst dye and Giemsa (Fluorescence Plus Giemsa staining), antibody detection against BrdU, or highly specific Click reaction to EdU, allow the newly synthesized DNA within a chromatid to be recognized. SCEs represent a point of DNA template exchange during DNA synthesis, visualized by differential chromatid staining or harlequin chromosomes. We will introduce three basic protocols in this chapter including non-fluorescence and fluorescence methods for SCE microscopic analysis. SCE is a very sensitive marker of genotoxic stress during replication.