Reprogramming of mouse somatic cells into pluripotent stem cells using a combination of small molecules

Somatic cells can be reprogrammed to generate induced pluripotent stem cells (iPSCs) by overexpression of four transcription factors, Oct4, Klf4, Sox2, and c-Myc. Bmi1 is responsible for conversion of adult mouse astrocytes and fibroblasts into neural stem cell-like cells and conversion of fibroblasts into iPSCs under enforced expression of Oct4. Here, in the first step of generating iPSCs, stable intermediate cells were generated from mouse astrocytes by Bmi1 in the absence of other transcription factors. These cells [called induced epiblast stem cell (EpiSC)-like cells (iEpiSCLCs)] are similar to EpiSCs in terms of expression of specific markers, epigenetic state, and ability to differentiate into three germ layers. Treatment with MEK/ERK and GSK3 pathway inhibitors in the presence of leukemia inhibitory factor resulted in conversion of iEpiSCLCs into iPSCs that were similar to mouse embryonic stem cells (mESCs), suggesting that Bmi1 is sufficient to reprogram astrocytes to pluripotency. Next, Bmi1 function was replaced with Shh activators (oxysterol and purmorphamine), which demonstrated that specific combinations of small molecules alone can reprogram mouse fibroblasts into iPSCs. These iPSCs resembled mESCs in terms of global gene expression profile, epigenetic status, and developmental potential, demonstrating that combinations of small molecules can compensate for reprogramming factors and are sufficient to directly reprogram mouse somatic cells into iPSCs. 4 Affymetrix and 4 Agilent samples