Functional analysis of Msx2-overexpressing breast cell lines. (a) Measurement of cell proliferation rates by MTT assay. Significance was determined by comparing the slopes of the lines of best fit. (b) Measurement of colony forming ability of cellsby clonogenic assays. (c) Measurement of caspase-3 and -7 activation as an indicator of apoptosis. Values are relative to control levels. (d) Cell cycle analysis by propidium iodide staining. Values represent the percentage of cells within sub-G1 gate. For all assays, values denote the mean readings of three independent replicates (n = 3 within each experiment), and error bars represent SD within replicate experiments. Unpaired, two-tailed Student's t-tests were used to determine the significance of difference between samples.