Expression and roles of blastocyst lineage-determining genes during somatic cell reprogramming

In order to properly use stem cells, it is important that we first understand how these cells are establish and maintained. One of the most widely used stem cells are induced pluripotent stem cells (iPSCs) which provide great therapeutic promise and a novel source of ethical stem cells for research models. iPSCs are created by overexpression Oct4, Sox2, Klf4 and c-Myc (OSKM) in a somatic cell. As studies have sought to improve reprogramming efficiency and develop the most embryonically identical stem cells, our lab has uncovered that OSKM is not a specific cocktail for pluripotency formation. Instead OSKM induces additional cell fates including the formation of a multipotent stem cell termed induced extraembryonic endoderm stem (iXEN) cells. This raises the question as to how two distinct stem cell types arise in parallel. Interestingly, in embryo development we observe the same pluripotent and multipotent extraembryonic endoderm lineages form in parallel. Using our knowledge of normal embryo development, I set out to identify what blastocyst lineage markers can help us identify early iPSC and iXEN colonies as they start to form and mature. Of these markers, we observed that endogenous OCT4 is expressed in both iXEN and iPSC colonies. Based on the expression pattern of the key embryonic transcription factor, OCT4, we further focused on how this transcription factor may have a dual role in establishing iPSC and iXEN fates. Lastly, we altered the reprogramming cocktail using additional embryonic transcription factors to determine how these factors affect the propensity for pluripotency or extraembryonic endoderm fate.