MicroRNAs are ~22 nt long small noncoding RNA molecules that silence post-transcription gene expression. It has proven that microRNAs are widely expressed in eukaryotes and play an important role in the regulation of cell differentiation and development, growth metabolism, and many other cell activities. Induced pluripotent stem cells (iPS) are a type of pluripotent stem cells reprogrammed from somatic cells and exhibit the essential characteristics of embryonic stem cells. iPS technology has been widely applied in the biological and medical fields, and the key of it is reprogramming of somatic epigenetic state. Therefore, it is of important theoretical and practical significance to study the mechanisms of somatic reprogramming for establishment of an improved iPS technology. The methods of transfection of defined exogenetic stem factors, such as Oct4, Sox2, Klf4, and c-Myc into somatic cells through viral vectors have been continuously improving, but the genome integration and reactivation of the oncogenic gene increase the tumorigenicity of induced cells. The integration-free ways, such as adenovirus, plasmid, recombinant proteins, and L-myc replacement used in iPS technology significantly reduce the risk of cancer. However, the inducing mechanisms are still unclear. Recent studies showed that microRNA affect the process of somatic cell reprogramming, especially embryonic stem cell regulating (ESCC) family of microRNAs (miR302/367, miR200, miR-34, and miR290/295) enhances the reprogramming of embryonic fibro-blasts to iPS. This article reviews the recent progresses of roles of microRNA in iPS.
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