Abstract
Ectopic expression of Oct4, Sox2, cMyc, and Klf4 confers a pluripotent state upon several differentiated cell types, generating induced pluripotent stem cells (iPSCs) [1-8]. iPSC derivation is highly inefficient, and the underlying mechanisms are largely unknown. This low efficiency suggests the existence of additional cooperative factors whose identification is critical for understanding reprogramming. In addition, the therapeutic use of iPSCs relies on the development of efficient nongenetic means of factor delivery, and although a handful of replacement molecules have been identified, their use yields a further reduction to the already low reprogramming efficiency [9-11]. Thus, the identification of compounds that enhance rather than solely replace the function of the reprogramming factors will be of great use. Here, we demonstrate that inhibition of Tgfbbeta signaling cooperates in the reprogramming of murine fibroblasts by enabling faster, more efficient induction of iPSCs, whereas activation of Tgfbeta signaling blocks reprogramming. In addition to exhibiting a strong cooperative effect, the Tgfbeta receptor inhibitor bypasses the requirement for exogenous cMyc or Sox2, highlighting its dual role as a cooperative and replacement factor. The identification of a highly characterized pathway operating in iPSC induction will open new avenues for mechanistic dissection of the reprogramming process.