OCT4 is expressed in extraembryonic endoderm stem (XEN) cell progenitors during somatic cell reprogramming

During development, progenitors of embryonic stem (ES) and extraembryonic endoderm stem (XEN) cells are concomitantly specified within the inner cell mass (ICM) of the mouse blastocyst. Similarly, XEN cells are induced (iXEN cells) alongside induced pluripotent stem (iPS) cells following overexpression ofOct4,Sox2,Klf4andMyc(OSKM) during somatic cell reprogramming. It is unclear how or why this cocktail produces both stem cell types, but OCT4 has been associated with non-pluripotent outcomes. In this report, we show that, during OSKM reprogramming, many individualOct4-GFP-expressing cells are fated to become iXEN cells. Interestingly, SKM alone was also sufficient to induce iXEN cell formation, likely via activation of endogenousOct4.These observations indicate that iXEN cell formation is not strictly an artifact ofOct4overexpression. Moreover, our results suggest that a pathway to XEN may be an integral feature of establishing pluripotency during reprogramming, as in early embryo development. We performed RNAseq on iXEN cell lines that had been clonally derived from Oct4-EGFP-positive single cells following retroviral reprogramming of mouse embryonic fibroblasts (MEFs) using Oct4, Sox2, Klf4, and Myc overexpression. Each sample (IXEN79-IXEN83) represents a distinct, clonally derived iXEN cell line. We compared transcriptomes of iXEN cells derived from lentiviral reprogramming of mouse embryonic fibroblasts (MEFs) using either Oct4, Sox2, Klf4, Myc overexpression (IXOSKM01-IXOSKM05) or Sox2, Klf4, Myc overexpression (IX_SKM06-IX_SKM10). Each sample represents a stable iXEN cell line, of passage >11, derived from reprogramming distinct MEF preps.