English: The “core” regulators of pluripotency Oct4, Sox2 and Nanog, act in concert with other transcription and chromatin modifying factors to establish and maintain the transcriptional program of pluripotency. The accessible chromatin of ES cells may allow for increased global transcription resulting in expression of many genes, their splicing isoforms, intergenic spliced mRNAs, non-coding intergenic transcripts and antisense transcripts. The function of these novel transcripts in ES cells is not yet understood. Antisense transcripts are thought to regulate the expression of their sense counterparts, possibly by sense-anti-sense pairing and production of siRNAs. Endogenous siRNAs have been recently detected in oocytes (Tam et al., 2008; Watanabe et al., 2008), but so far they have not been described in ES cells. miRNAs however, have been shown to be expressed in ES cells and are required for their proliferation and differentiation (reviewed in (Bibikova et al., 2008)).