| Summary: | Summary: Human pluripotent stem cells (hPSCs) are susceptible to numerical and structural chromosomal alterations during long-term culture. We show that mitotic errors occur frequently in hPSCs and that prometaphase arrest leads to very rapid apoptosis in undifferentiated but not in differentiated cells. hPSCs express high levels of proapoptotic protein NOXA in undifferentiated state. Knocking out NOXA by CRISPR or upregulation of the anti-apoptosis gene BCL-XL significantly reduced mitotic cell death, allowing the survival of aneuploid cells and the formation of teratomas significantly larger than their wild-type parental hPSCs. These results indicate that the normally low threshold of apoptosis in hPSCs can safeguard their genome integrity by clearing cells undergoing abnormal division. The amplification of BCL2L1 on chromosome 20q11.21, a frequent mutation in hPSCs, although not directly oncogenic, reduces the sensitivity of hPSCs to damage caused by erroneous mitosis and increases the risk of gaining aneuploidy. : In this article, Na, Barbaric and colleagues showed that aberrant mitosis is common in hPSCs. A high level of NOXA, a proapoptotic protein, makes hPSCs highly sensitive to mitotic stress, thus cells with chromosomal abnormality are eliminated. Anti-apoptotic mutations, such as BCL2L1 CNV, significantly enhanced the survival ability of hPSCs and increased the chance of aneuploid cell retention. Key words: human pluripotent stem cells, chromosome instability, apoptosis, BCL-XL, NOXA
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