Investigating the Role of the Extracellular Environment in Oct4-Mediated Cellular Reprogramming

Abstract

The overexpression of one transcription factor alone – Oct4 – can alter cell fate. In conjunction with lineage-specifying culture conditions, Oct4 can generate multi-lineage blood and neural progenitors without traversing pluripotency. During this conversion, cells achieve a unique cellular status, distinct from that of the somatic or pluripotent states, termed Oct4-induced plasticity, or OiP. This plastic state is characterized by a morphological shift from spindle-elongated to compact-cuboidal cells, which manifests only with culturing in Reprogramming media, suggesting that the extracellular environment plays an key role in this process. However, the precise component(s) of the growth media that inhibit or permit sustained Oct4-expression remains unknown. In direct support of this notion, we revealed that the serum component of Fibroblast media is a crucial factor in preventing OiP, as only serum-free formulations are able to sustain Oct4 expression and induce the plastic state. These results uncover the importance of the extracellular environment, which works collectively with Oct4 to induce OiP, a synergism previously overlooked in the reprogramming field. Identification of these factor(s) may allow for optimization of media formulations as well as the identification of small-molecules that may improve OiP generation or even substitute for the role of ectopic Oct4. As well, the identification of N-cad as a marker of plastic cells as well as the generation of a screening platform to identify chemical activators of endogenous Oct4 will aid in further understanding the nature of OiP as well as the generation of transgene-free cell products. Taken together, elucidation of the larger role of Oct4 in OiP and pluripotency will enable greater control of cell fate conversion, which is essential for this field to evolve.