Nature 525, E6–E9 (2015); doi:10.1038/nature15513

During extensive revisions of this BCA, we inadvertently omitted a citation by Takaho A. Endo that used variant calls from RNA-seq data to conclude that the purported Fgf4-induced stem cells (FI-SCs) described in Obokata et al.1 constituted a mixture of trophoblastic and embryonic stem cells2. Our analysis, performed independently, reached similar conclusions. We regret this oversight.