Unleashing the Developmental Potential of induced Pluripotent Stem Cells
  • Hans R. Scholer Ph.D
  • SLS Colloquia / Oct 4th 04:00pm / BLDG 110 ROOM N104

The pluripotent and multipotent states of mammalian stem cells are governed by the formation of a highly interconnected regulatory network comprising specifically expressed transcription factors organized together with widely expressed transcription factors. The transcriptional network exhibits a hierarchical structure, with a small number of transcription factors playing an essential role in maintaining cellular potency and regulating the expression and/or function of numerous auxiliary transcription factors. The ultimate goal of cell and developmental biology is to program cells at will. One powerful way to convert any given cell type into another is to achieve a pluripotent stem cell state that resembles that of embryonic stem cells. However, to achieve pluripotency, somatic cells need a supply of exogenous transcription factors.

Reprogramming of mouse and human somatic cells into pluripotent stem cells, termed induced pluripotent stem cells (iPSC), was first described by Yamanaka using fibroblasts in a procedure that required the virally expressed transcription factor quartet of Oct4, Sox2, c-Myc, and Klf4 (OSKM). Later, we reported that the POU transcription factor Oct4 alone is sufficient for directly reprogramming adult mouse and human fetal neural stem cells into iPS cells, indicating that Oct4 plays a crucial role in the reprogramming process. In my presentation I will show that the SKM combination is sufficient for reprogramming mouse somatic cells into iPSCs. Retroviral silencing requires the simultaneous expression of Sox2 and c-Myc, perhaps accounting for the discrepancy with previous studies that used retroviral vectors to generate iPSCs without Oct4. Surprisingly, SKM activates the pluripotency network even in Oct4-knockout fibroblasts. Reprogramming in the absence of exogenous Oct4 results in iPSCs characterized by more faithful gene expression and greatly improved developmental potential. Our data suggests that expression of exogenous Oct4 during reprogramming leads to off-target gene activation, worsening the quality of the generated iPSCs, and thereby bearing major implications for further development and application of iPSC technology.