FIGURE 21-6 Transcriptional network regulating pluripotency of ES cells. Each of three master transcription factors, Oct4, Sox2, and Nanog, binds to its own promoter as well as to the promoters of the other two (black lines), forming a positive autoregulatory loop that activates transcription of each of these genes. These transcription factors also bind to the transcription-control regions of many active genes encoding proteins and micro-RNAs important for the proliferation and self-renewal of ES cells as well as to those of many genes that are silenced in undifferentiated ES cells and that encode proteins and micro-RNAs essential for the formation of many differentiated cell types (magenta lines). See L. A. Boyer et al., 2006, Curr. Opin. Genet. Devel. 16:455–462.