Chromatin analysis of adult pluripotent stem cells reveals their unique maintenance strategy

Many highly regenerative organisms maintain adult pluripotent stem cells throughout their life, but how the long-term maintenance of pluripotency is accomplished is unclear. To decipher the regulatory logic of adult pluripotent stem cells we analyzed the chromatin organization of stem cell genes in the planarian Schmidtea mediterranea. We identify a special chromatin state of stem cell genes, that is distinct from that of tissue-specific genes and rather resembles that of ubiquitous genes. Where tissue-specific promoters have detectable transcription factor binding sites, the promoters of stem cell-specific genes instead have sequence features that broadly decrease nucleosome binding affinity. This genic organization makes pluripotency gene expression the default state, that is abandoned only when significant levels of tissue-specific transcription factors have accumulated