Figure 2

Time-lapsed image analysis of stem cell populations show heterogeneity in proliferative activity.

(a) Cell division occurring in a human muscle stem cell population. Total time lapsed is 4.5 hours, scale bar represents 50 microns. (b) Individual cell tracking (Cytotracker,) through 4 generations. The paths for parent and daughter cells are shown as an overlay on phase contrast images. Division times are used to construct cell lineage trees. The vertical distance on the corresponding lineage trees represents the cell division time or the amount of time the cell was on screen. lpar; c) Heterogeneity in cell division times can be detected by cell lineage analysis (human muscle stem cells are shown here). Individual cells were examined using time-lapsed imaging over 3 days. Lineage history trees show the presence of both dividing and nondividing cells in the population. Variation in cell division times is also detected. Most current growth models assume homogeneity with a constant division time and exponential growth. (d) Identification of dividing and nondividing cells in time-lapsed images after addition of BrdU to media for 48 hours and immunostaining for BrdU. Muscle stem cell populations contain both dividing (BrdU + cells and nondividing (BrdU-) cells. Desmin staining illustrates that molecular heterogeneity for the myogenic cytoplasmic protein does not correspond with proliferative heterogeneity.