Measurements of broad sense heritability of generation time and motility in cancer cell lines

Experiments were conducted over 7 months to record the motility and generation time of four cancer cell lines - HeLa, HT1080, MCF7 and MDA-MB-231 - in cell culture. Cell lines were cultured in vitro on a well plate for 24 hours before being placed into the environmental chamber of a Nikon TiE Timelapse Microscope. Multiple points within every well were chosen and videoed over a period of 72 hours. These videos were then analysed and cell motility and division tracked using MtrackJ and ImageJ. Records were kept of which cells divided and the track number assigned to each daughter cell. This allowed comparison between and within cell families so the heritability of the cell traits, motility and generation time, could be estimated. Broad sense heritability was estimated as the slope parameter of an ordinary least squares regression between related cells. Three cell-cell relationships were tested, mother-daughter, sister-sister and cousin-cousin. Our results showed that cell motility has high and significant heritability for all cell lines tested whereas generation time showed little or no significant heritability for the cell lines tested. This is consistent with expectations that traits closely linked to fitness will in general have lower heritability. These results are important for cancer evolution as heritability (a prerequisite for natural selection to be able to act) has never before been measured for any traits in cancer cells.