Tetraploid chimeras indicate that Oct4 is not required extraembryonically ∼E7.5, while diploid chimeras indicate that Oct4^+/+ can compensate for Oct4^−/− cells embryonically.

<p>All embryos transferred to a surrogate and depicted or described in panels A–E were induced with tamoxifen ∼E6.0 and ∼E6.5 to compensate for the variability in developmental timing associated with transfer (<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003957#pgen.1003957.s012" target="_blank">Table S1Q</a>,AB). Scale bars in panels A–D are 200 um. <b>A</b> A representative embryo from aggregation of Oct4^+/+ RFP ES cells with a tetraploid Oct4^f/f embryo. Oct4^f/f extraembryonic tissue yielded E9.5 chimeric embryos with no phenotype. <b>B</b> An Oct4^f/f;CreER^T2+/− E9.5 embryo with the Oct4^{COND MUT} phenotype. <b>C</b> Oct4 depletion in extraembryonic tissue is compatible with WT development. A representative chimera consisting of RFP+ Oct4^+/+ ES cell derived embryo and tetraploid Oct4^f/f;CreER^T2+/− extraembryonic tissue. The embryo has turned (compare panel ‘B’ where the tail is behind to panel ‘C’ where it is in front), undergone NTC and posterior extension (compare the lack of somites and short tail in panel ‘B’ to the somites and full-length tail in ‘C’). <b>D</b> The most severe embryonic defect observed in a diploid chimeras consisting of Oct4^+/+ and Oct4^f/f;CreER^T2+/− cells. The neural tube is open between closure points 1 and 2, indicated here with a black bracket. All Oct4^{COND MUT} features aside from cranial NTC defect, which is still present in 5/16 mosaic embryos, are rescued by Oct4^+/+ cells in these diploid chimeras (16/16). For example, this embryo has ‘turned’ such that it faces its tail and the posterior has extended normally. <b>E</b> Quantification of the genotypes and phenotypes of recovered chimeric embryos.