Abstract
The discovery of induced pluripotent stem (iPS) cells provides not only new approaches for cell replacement therapy, but also new ways for drug screening. However, the undefined mechanism and relatively low efficiency of reprogramming have limited the application of iPS cells. In an attempt to further optimize the reprogramming condition, we unexpectedly observed that removing c-Myc from the Oct-4, Sox-2, Klf-4, and c-Myc (OSKM) combination greatly enhanced the generation of iPS cells. The iPS cells generated without c-Myc attained salient pluripotent characteristics and were capable of producing full-term mice through tetraploid complementation. We observed that forced expression of c-Myc induced the expression of many genes involved in cell cycle control and a hyperproliferation state of the mouse embryonic fibroblasts during the early stage of reprogramming. This enhanced proliferation of mouse embryonic fibroblasts correlated negatively to the overall reprogramming efficiency. By applying small molecule inhibitors of cell proliferation at the early stage of reprogramming, we were able to improve the efficiency of iPS cell generation mediated by OSKM. Our data demonstrated that the proliferation rate of the somatic cell plays critical roles in reprogramming. Slowing down the proliferation of the original cells might be beneficial to the induction of iPS cells.
Highlights
The relationship between somatic cell proliferation and reprogramming efficiency remains elusive
We observed that forced expression of c-Myc induced the expression of many genes involved in cell cycle control and a hyperproliferation state of the mouse embryonic fibroblasts during the early stage of reprogramming
The overall reprogramming efficiency decreased when using late-passage MEFs, which was consistent with the notion that cellular senescence is a roadblock of reprogramming [20], omission of c-Myc continued to enhance the generation of induced pluripotent stem (iPS) colonies (Fig. 1, F and G)
Summary
The relationship between somatic cell proliferation and reprogramming efficiency remains elusive. Results: Reducing somatic cell proliferation by removing c-Myc or adding anti-proliferative compounds dramatically improves induced pluripotent stem cell generation. We observed that forced expression of c-Myc induced the expression of many genes involved in cell cycle control and a hyperproliferation state of the mouse embryonic fibroblasts during the early stage of reprogramming. This enhanced proliferation of mouse embryonic fibroblasts correlated negatively to the overall reprogramming efficiency. By applying small molecule inhibitors of cell proliferation at the early stage of reprogramming, we were able to improve the efficiency of iPS cell generation mediated by OSKM. Slowing down the proliferation of the original cells might be beneficial to the induction of iPS cells
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