BAF155 and not BAF 170 have not been found in other cell types. In addition to its role in transcriptional regulation during early embryogenesis, a homologue of BRG1 was also identified in a screen for genes that are essential for nuclear reprogramming in the cytoplasm of frog (Xenopus laevis) oocytes33. It is not clear whether the oocyte contains a specialized complex that is responsible for the nuclear-reprogramming activity. However, given that mouse ESCs are also capable of nuclear reprogramming, the complex present in oocytes might be akin to the esBAF complex. Additional evidence that the esBAF complex is essential for pluripotency comes from the observation that deletion of BAF47 or BAF155 is lethal to the embryo before it has implanted34,35. To differentiate into cells of different lineages, pluripotent ESCs need to exit from the state of self-renewal by silencing genes that potentiate the ESC state. BAF complexes are also crucial for this exit from the ESC state: this is evident from a study showing that RNAi-mediated depletion of BAF57 or BAF155 (components of esBAF) prevents silencing of Nanog, which encodes a master regulatory transcription factor, and also hinders chromatin compaction and hetero-chromatin formation during differentiation36.
