Figure 1.

Mps1 is imported into the nucleus at the G₂/M boundary. (A) Subcellular localization of YFP-Mps1 in asynchronized SW480 cells. Distribution of YFP-Mps1 was classified into three categories. Representative images are shown. The percentage of cells in each category was determined from inspecting images of at least 200 cells. (B) Localization of endogenous Mps1 after Leptomycin B (LMB) treatment for 2 h. (C) Live cell imaging of SW480-YFPMps1 cell at the G₂/M boundary or in G₁/S phase. Cells were incubated in an environmental chamber. Images from YFP channel or bright field were taken every 15 min. (D and E) Treatment of RO-3306 blocks SW480YFP-Mps1 cells at G₂/M, with increased Cyclin B expression without phosphorylation of MPM-2, a typical mitotic marker. SW480YFP-Mps1 cells treated with DMSO or RO-3306 for 0 or 19 h were harvested and stained with propidium iodine (PI) prior to FACS analysis using FACScan. RO-3306-treated but not DMOS-treated cells show 4X DNA content, with G₂/M arrest. (F) YFP-Mps1 is translocated into the nucleus in cells arrested at G₂/M following RO-3306 treatment. Nuclei are identified by DAPI staining.