Nanog induces hyperplasia without initiating tumors

Though expression of the homeobox transcription factor Nanog is generally restricted to pluripotent cells and early germ cells, many contradictory reports about Nanog's involvement in tumorigenesis exist. To address this, a modified Tet-On system was utilized to generate Nanog-inducible mice. Following prolonged Nanog expression, phenotypic alterations were found to be restricted to the intestinal tract, leaving other major organs unaffected. Intestinal and colonic epithelium hyperplasia was observed-intestinal villi had doubled in length and hyperplastic epithelium outgrowths were seen after 7days. Increased proliferation of crypt cells and downregulation of the tumor suppressors Cdx2 and Klf4 was detected. ChIP analysis showed physical interaction of Nanog with the Cdx2 and Klf4 promoters, indicating a regulatory conservation from embryonic development. Despite downregulation of tumor suppressors and increased proliferation, ectopic Nanog expression did not lead to tumor formation. We conclude that unlike other pluripotency-related transcription factors, Nanog cannot be considered an oncogene.

Establishment of totipotency does not depend on Oct4A

Oct4A is a core component of the regulatory network of pluripotent cells, and by itself can reprogram neural stem cells into pluripotent cells in mouse and humans. However, its role in defining totipotency and inducing pluripotency during embryonic development is still unclear. We genetically eliminated maternal Oct4A using a Cre-lox approach in mouse and found that the establishment of totipotency was not affected, as shown by the generation of live pups. After complete inactivation of both maternal and zygotic Oct4A expression, the embryos still formed Oct4-GFP– and Nanog–expressing inner cell masses, albeit non-pluripotent, indicating that Oct4A is not a determinant for the pluripotent cell lineage separation. Interestingly, Oct4A-deficient oocytes were able to reprogram fibroblasts into pluripotent cells. Our results clearly demonstrate that, in contrast to its role in the maintenance of pluripotency, maternal Oct4A is crucial for neither the establishment of totipotency in embryos, nor the induction of pluripotency in somatic cells using oocytes.

Zfp296 is a novel, pluripotent-specific reprogramming factor

Expression of the four transcription factors Oct4, Sox2, Klf4, and c-Myc (OSKM) is sufficient to reprogram somatic cells into induced pluripotent stem (iPSCs). However, this process is slow and inefficient compared with the fusion of somatic cells with embryonic stem cells (ESCs), indicating that ESCs express additional factors that can enhance the efficiency of reprogramming. We had previously developed a method to detect and isolate early neural induction intermediates during the differentiation of mouse ESCs. Using the gene expression profiles of these intermediates, we identified 23 ESC-specific transcripts and tested each for the ability to enhance iPSC formation. Of the tested factors, zinc finger protein 296 (Zfp296) led to the largest increase in mouse iPSC formation. We confirmed that Zfp296 was specifically expressed in pluripotent stem cells and germ cells. Zfp296 in combination with OSKM induced iPSC formation earlier and more efficiently than OSKM alone. Through mouse chimera and teratoma formation, we demonstrated that the resultant iPSCs were pluripotent. We showed that Zfp296 activates transcription of the Oct4 gene via the germ cell–specific conserved region 4 (CR4), and when overexpressed in mouse ESCs leads to upregulation of Nanog expression and downregulation of the expression of differentiation markers, including Sox17, Eomes, and T, which is consistent with the observation that Zfp296 enhances the efficiency of reprogramming. In contrast, knockdown of Zfp296 in ESCs leads to the expression of differentiation markers. Finally, we demonstrated that expression of Zfp296 in ESCs inhibits, but does not block, differentiation into neural cells.