It is vital that vertebrates maintain cells in an undifferentiated state before gastrulation - but how do they do this? In mammals, the maintenance of embryonic stem (ES) cells and the inner cell mass (ICM) requires Oct4, a class V POU domain (PouV) protein. Now, on p. 2011, Gillian Morrison and Joshua Brickman show that the role of Oct4 in mammals is related to the ability of PouV to regulate multipotency in other vertebrates. They show that PouV depletion in Xenopus downregulates Bmp4, which is needed to maintain cells in a non-committed state. The authors transfected mouse ES cells lacking Oct4 with PouV proteins from several vertebrates and found that those from Xenopus and axolotl (but not zebrafish) were able to support long-term self-renewal. Furthermore, PouV proteins regulate similar genes in ES cells and Xenopus embryos. The authors conclude that the ability of mammalian Oct4 to maintain self-renewing ES...

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