OCT4 Facilitated Alteration of Human Cell Fate

Abstract

OCT4 is one of four transcription factors known to induce pluripotency when expressed together in somatic cells. However, brief expression of these pluripotency inducing factors in somatic skin fibroblasts followed by treatment with lineage specific culture conditions results in direct conversion towards alternative lineage specific cell types. Our group has previously shown that expression of OCT4 alone in adult human fibroblasts followed by treatment with hematopoietic supportive conditions resulted in the generation of multi-potent blood progenitors without transitioning through a pluripotent intermediate. Despite never having been associated with transcriptional regulation within the hematopoietic compartment, expression of OCT4 induced expression of hematopoietic factors in skin fibroblasts. As such, I hypothesized that ectopic expression of OCT4 in human somatic cells can induce changes in transcription that bestow the potential to make cell fate choices in response to external stimuli. In direct support of this notion, we revealed that expression of OCT4 in adult human fibroblasts, followed by culturing in neural supportive conditions resulted in the generation of tri-potent neural progenitors, suggesting the effects of OCT4 were not specific or limited to activation of hematopoietic programs. In an effort to understand how OCT4 bestows the potential to make cell fate choices, we assessed the individual vs combined impact of OCT4 and the extracellular environment on transcription during direct conversion of fibroblasts to both blood and neural progenitors. In doing so, we have started to define an induced state of transcriptional activity that is distinct from cells transitioning to pluripotency, and instead characterized by expression related to lineage iii PhD Thesis – RR Mitchell McMaster University - Biochemistry development that is responsive to changes in the extracellular environment that we have termed OCT4 induced plasticity (OiP). Moreover, we revealed that OCT4 mediated direct conversion can facilitate the reprogramming of hematopoietic progenitor cells towards neural progenitor cells, suggesting that this cellular reprogramming approach is not limited to the use of differentiated fibroblasts. In summary, this thesis expands our current knowledge on both the use and understanding of OCT4 as a facilitator of cellular reprogramming in human somatic cells.