In the December 7th online edition of PNAS, Z. Ouyang et al. from Stanford University reported their study results using high power statistical analysis of a data base containing transcript abundance and regulators of gene expression. The data were generated from experiments using RNA sequencing and ChIP sequencing experiments in determining the presence of transcription factors in mouse embryonic stem cells. The investigators found that 65% of the variation in gene expression is result of binding 12 transcription factors (TFs). These TFs, based upon their activity, were segregated into 2 groups. One group such as E2f1, Myc, Mycn, and Zfx act as activators. The second group such as Oct4, Nanog, Sox2, Smad1, Stat3, Esrrb, and Tcfcp2l1 can either activate or repress their target genes. The two groups in concert activate genes which are differentially upregulated in ESCs. The authors further noted that "in the absence of binding by the first group, the binding of the second group is associated with genes that are repressed in ESCs and de-repressed upon early differentiation."