| Embryonic stem cells play an important role in regeneration medicine due to its differentiation ability to all three germ layers. The ethical concerns and immunecompatibility issues limits the potential clinical application of embryonic stem cells. The groundbreaking work in 2006 demonstrated that ectopic expression of defined transcription factors by virus infection could reprogram somatic cells to induced pluripotent stem cells(iPSC). However, genetic manipulation and low efficiency hindered its clinical application. Small molecule compounds have been found extremely useful to improve the generation of iPSC or compensate the requirement of certain oncogenic factors. They also contribute to dissecting the underlying mechanisms of reprogramming.In our research we find that the commonly used biological reagent, bromodeoxyuridine(BrdU), is able to enhance Yamanaka factor-mediated reprogramming. More interestingly, BrdU can replace Oct4, the most critical factor in iPS generation. Further studies demonstrate that BrdU enables full-chemical induction of mouse iPSs(CiPS) with several chemical cocktails, and the minimal combination being BrdU, CHIR99021, Repsox, and Forskolin. The CiPSC resemble embryonic stem cells in terms of their gene expression, epigenetic status, in vivo differentiation and chimera generation. We also find that BrdU may promote reprogramming by reducing the global DNA methylation level.Since BrdU has already been used in patients, the BrdU-cocktail may lay a foundation for full-chemical induction of human i PS and may provide a safer strategy to generate clinically applicable iPS. |
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