Argonaute-2- null embryonic stem cells are retarded in self-renewal and differentiation

RNA interference (RNAi) pathways regulate self-renewal and differentiation of embryonic stem (ES) cells. Argonaute 2 ( Ago2 ) is a vital component of RNA-induced silencing complex (RISC) and the only Ago protein with slicer activity. We generated Ago2 -deficient ES cells by conditional gene targeting. Ago2- deficient ES cells are defective in the small-RNA-mediated gene silencing and are significantly compromised in biogenesis of mature microRNA. The self-renewal rate of Ago2 -deficient ES cells is affected due to failure of silencing of Cdkn1a by ES-cell-specific microRNAs (miRNA) in the absence of Ago2 . Interestingly, unlike Dicer- and Dgcr8 -deficient ES cells, they differentiate to all three germ layers both in vivo and in vitro . However, early differentiation of Ago2 -deficient ES cells is delayed by 2–4 days as indicated by persistence of higher levels of self-renewal/ pluripotency markers during differentiation. Further, appearance of morphological and differentiation markers is also delayed during the differentiation. In this study we show that Ago2 is essential for normal self-renewal and differentiation. Also, our data suggest that self-renewal and differentiation of ES cells are regulated by both siRNA and miRNA pathways.