Micro-managing and restraining pluripotent stem cells by MYC

The MYC proto-oncogene, which encodes a master transcriptional regulator c-Myc (herein termed Myc), has a key role in stem cell (SC) pluripotency and tumourigenesis. Its deregulated expression contributes to cancer development and enhances the efficiency of reprogramming differentiated cells back to a pluripotent state in induced pluripotent SCs (iPSCs) that resemble embryonic SCs (ESCs). In addition to Myc's ability to directly regulate mRNA transcription, it also directly regulates microRNAs (miRNAs), thus providing an additional level of complexity to gene regulation. However, it had not been well understood how the complex network of Myc target genes contributes to pluripotency in ESCs and to tumourigenesis, two phenomena that are likely inter-related. In this issue of The EMBO Journal, Lin et al (2009) document a role of Myc in the maintenance of murine ESC (mESC) pluripotency through the regulation of a set of miRNAs that suppress differentiation, in addition to those that have been previously implicated in self-renewal capacity.