Separation and maintenance of normal cells from human embryonic stem cells with trisomy 12 mosaicism

Human embryonic stem cells (hESCs) are pluripotent and hold great promise as useful tools in basic scientific research and in the field of regenerative medicine. However, several studies have recently reported chromosomal abnormalities such as gains of chromosomes 12, 17 and X in hESCs. This genetic instability presents an obstacle in the application of hESCs as sources of cell therapies. We found that trisomy 12 was correlated with changes in hESC colony morphology during hESC maintenance. In this study, we investigated whether normal and trisomy 12 cells could be separated in hESC cultures displaying trisomy 12 mosaicism with two types of colony morphology using a mechanical transfer technique. Eight sublines were cultured from eight hESC colonies displaying normal or abnormal morphology. Four sublines with normal morphology had normal chromosome 12 numbers, whereas the four sublines with abnormal morphology displayed trisomy 12. These results indicate that a hESC colony with a minor degree of chromosomal mosaicism and normal morphology could proceed to a colony with normal chromosomes after prolonged cultures with mechanical transfer. Therefore, analysis of cultures for chromosomal abnormalities when changes in colony morphology are observed during culture is essential for maintaining normal hESC lines.