Figure 8.

A representation of the two markers used to assess proliferating cells in comparison with the stages of the cell cycle. Ki-67, an endogenous marker of proliferation is expressed during all active phases of the cell cycle (M, G₂, S, and G₁; Scholzen and Gerdes, 2000). BrdU, an exogenous marker, is incorporated into cells when the DNA is single stranded, which occurs during the S-phase of the cell cycle. Although cells arrested in G₁ or G₂ phases are considered mitotically active and express Ki67, they would not incorporate BrdU. The outer arrow depicts the cell cycle in ethanol-exposed cells arrested in G1 phase, where cells would express Ki-67 but not incorporate BrdU.