Myc family members are critical to maintain embryonic stem cells (ESC) in the 
undifferentiated state. However, the mechanism by which they perform this task 
has not yet been elucidated. Here we show that Myc directly upregulates the 
transcription of all core components of the Polycomb repressive complex 2 (PRC2) 
as well as the ESC-specific PRC2-associated factors. By expressing Myc protein 
fused with the estrogen receptor (Myc-ER) in fibroblasts, we observed that Myc, 
binding to the regulatory elements of Suz12, Ezh2, and Eed, induces the 
acetylation of histones H3 and H4 and the recruitment of elongating RNA 
polymerase II at their promoters. The silencing of both c-Myc and N-Myc in ESC 
results in reduced expression of PRC2 and H3K27me3 at Polycomb target 
developmental regulators and upregulation of genes involved in primitive 
endoderm differentiation. The ectopic expression of PRC2 in ESC, either silenced 
for c-Myc and N-Myc or induced to differentiate by leukemia inhibitory factor 
(LIF) withdrawal, is sufficient to maintain the H3K27me3 mark at genes with 
bivalent histone modifications and keep repressed the genes involved in ESC 
differentiation. Thus, Myc proteins control the expression of developmental 
regulators via the upregulation of the Polycomb PRC2 complex.