Dissecting the role of TGF-beta pathway in human Pluripotent Stem Cells

Human Embryonic Stem Cells (hESCs) and induced Pluripotent Stem cells (hiPSCs) are characterized by the ability to give rise all cell types found in the adult and to be expanded indefinitely in vitro. Understanding the molecular mechanisms controlling pluripotency is fundamental to differentiate human pluripotent cells into cells types useful for clinical applications. The signaling pathway of TGF-beta and FGF are known to maintain pluripotency in human cells. Only a handful of factors controlling pluripotency have previously been identified, such as the transcription factors OCT4, SOX2 and NANOG. Therefore, I used a systematic approach to identify novel components of the pluripotency network. Here I focused on the role of TGF-beta pathway, in order to find direct functional targets downstream of this pathway. Through comparative transcriptome analysis intersected with genome location data, I obtained a list of 21 putative transcription factors, out of which 8 were confirmed. Further functional assays led to the identification of four transcription factors that are able to maintain hESCs and hiPSCs undifferentiated in the absence of TGF-beta. Particularly, one of these four transcription factors has never been studied, so I focused on it. I then characterized the transcriptional program under the control of this factor in order to understand how it maintains the human pluripotency network. Interestingly, I found that this factor regulates both pluripotency and cell morphology. Finally, knockdown of this factor during the reprogramming strongly reduces the number of iPSCs obtained.