Heterochromatin lossening by Oct4 in somatic cell reprogramming

The success of Yamanaka factor reprogramming mouse embryonic fibroblasts (MEFs) into induced pluripotent stem cells (iPSCs) suggests that some factor(s) must remodel the nuclei from a condensed state to a relaxed state to facilitate factor binding to target genes. We asked how the Yamanaka factor-dependent chromatin opening occurs. We found Oct4, but neither Sox2 nor Klf4, is responsible for the loosening of the condensed state. Oct4 acts as a pioneer factor that facilitates the binding of Klf4 and the expression of epithelial genes in the early stage of reprogramming. Overall design: Examination of chromatin status in 9 samples and a Flag control