Too much to differentiate: aneuploidy promotes proliferation and teratoma formation in embryonic stem cells.

Aneuploidy, or an uneven number of chromosomes, has mostly detrimental consequences in eukaryotic cells, which include impaired proliferation as well as compromised DNA replication and protein folding. Unexpectedly, a new study published in this issue of The EMBO Journal shows that in murine embryonic stem cells aneuploidy does not interfere with proliferation, but rather hinders their differentiation capacity, thus propelling the formation of poorly differentiated teratomas.