Project description:A dramatic difference in global DNA methylation between male and female cells characterizes mouse embryonic stem cells (ESCs), unlike somatic cells. We analyzed DNA methylation changes during reprogramming of male and female somatic cells and in resulting induced pluripotent stem cells (iPSCs). At an intermediate reprogramming stage, somatic and pluripotency enhancers are targeted for partial methylation and demethylation. Demethylation within pluripotency enhancers often occurs at ESC binding sites of pluripotency transcription factors. Late in reprogramming, global hypomethylation is induced in a female-specific manner. Genome-wide hypomethylation in female cells affects many genomic landmarks, including enhancers and imprint control regions, and accompanies the reactivation of the inactive X-chromosome. The loss of one of the two X-chromosomes in propagating female iPSCs is associated with genome-wide methylation gain. Collectively, our findings highlight the dynamic regulation of DNA methylation at enhancers during reprogramming and reveal that X-chromosome dosage dictates global DNA methylation levels in iPSCs.
Project description:The generation of induced pluripotent stem cells (iPSCs) involves activation of the endogenous pluripotency circuitry and global DNA demethylation late in reprogramming, but temporal resolution of these events are insufficient using existing stage markers. Here, we generated murine transgenic lines harboring dual fluorescent reporters reflecting cell-state specific expression of the master pluripotency factor Oct4 and the 5-methylcytosine dioxygenase Tet1. By assessing reprogramming intermediates based on dual reporter patterns, we identified a sequential order of Tet1 and Oct4 gene activation at proximal and distal regulatory elements following pluripotency entry. A transient phase of global gene repression accompanies full activation of Tet1, precedes activation of meiotic and gametogenesis genes, and distinguishes phases of global DNA demethylation reminiscent of germ-line reprogramming. Loss of Tet1 is compatible with reprogramming towards full Oct4 gene activation, but generates iPSCs with epigenetic defects. Therefore, the transcriptional logic of Tet1 expression signals an epigenetic roadmap towards efficient reprogramming.
Project description:The generation of induced pluripotent stem cells (iPSCs) involves activation of the endogenous pluripotency circuitry and global DNA demethylation late in reprogramming, but temporal resolution of these events are insufficient using existing stage markers. Here, we generated murine transgenic lines harboring dual fluorescent reporters reflecting cell-state specific expression of the master pluripotency factor Oct4 and the 5-methylcytosine dioxygenase Tet1. By assessing reprogramming intermediates based on dual reporter patterns, we identified a sequential order of Tet1 and Oct4 gene activation at proximal and distal regulatory elements following pluripotency entry. A transient phase of global gene repression accompanies full activation of Tet1, precedes activation of meiotic and gametogenesis genes, and distinguishes phases of global DNA demethylation reminiscent of germ-line reprogramming. Loss of Tet1 is compatible with reprogramming towards full Oct4 gene activation, but generates iPSCs with epigenetic defects. Therefore, the transcriptional logic of Tet1 expression signals an epigenetic roadmap towards efficient reprogramming.
Project description:The generation of induced pluripotent stem cells (iPSCs) involves activation of the endogenous pluripotency circuitry and global DNA demethylation late in reprogramming, but temporal resolution of these events are insufficient using existing stage markers. Here, we generated murine transgenic lines harboring dual fluorescent reporters reflecting cell-state specific expression of the master pluripotency factor Oct4 and the 5-methylcytosine dioxygenase Tet1. By assessing reprogramming intermediates based on dual reporter patterns, we identified a sequential order of Tet1 and Oct4 gene activation at proximal and distal regulatory elements following pluripotency entry. A transient phase of global gene repression accompanies full activation of Tet1, precedes activation of meiotic and gametogenesis genes, and distinguishes phases of global DNA demethylation reminiscent of germ-line reprogramming. Loss of Tet1 is compatible with reprogramming towards full Oct4 gene activation, but generates iPSCs with epigenetic defects. Therefore, the transcriptional logic of Tet1 expression signals an epigenetic roadmap towards efficient reprogramming.
