Protein phosphatase 1 (PP1) is a ubiquitous serine/threonine phosphatase that regulates many cellular processes, including cell division. When transiently expressed as fluorescent protein (FP) fusions, the three PP1 isoforms, α, β/δ, and γ1, are active phosphatases with distinct localization patterns. We report here the establishment and characterization of HeLa cell lines stably expressing either FP-PP1γ or FP alone. Time-lapse imaging reveals dynamic targeting of FP-PP1γ to specific sites throughout the cell cycle, contrasting with the diffuse pattern observed for FP alone. FP-PP1γ shows a nucleolar accumulation during interphase. On entry into mitosis, it localizes initially at kinetochores, where it exchanges rapidly with the diffuse cytoplasmic pool. A dramatic relocalization of PP1 to the chromosome-containing regions occurs at the transition from early to late anaphase, and by telophase FP-PP1γ also accumulates at the cleavage furrow and midbody. The changing spatio-temporal distribution of PP1γ revealed using the stable PP1 cell lines implicates it in multiple processes, including nucleolar function, the regulation of chromosome segregation and cytokinesis.
Automated Tracking of Root for Confocal Time-lapse Imaging of Cellular Processes