Year 5

When this grant was awarded in 2008, reprogramming to the induced pluripotent state was just achieved by Shinya Yamanaka through the ectopic expression of Oct4, Sox2, Klf4 and cMyc in mouse fibroblasts. The overall goal of this proposal was to understand the molecular mechanisms underlying in vitro reprogramming of somatic cells of the mouse to iPSCs and to apply this knowledge to the reprogramming of human somatic cells. During the last funding period, our work particularly aimed at mechanistic questions: (i) determining the molecular origin of the spatio-temporal demarcation of the DNA binding sites of the reprogramming factors, and how the reprogramming factors induce chromatin changes, employing systematic and comprehensive mapping approaches; (ii) defining how the reprogramming factors induce a specific transcriptional output on target genes; (iii) identifying the steps of the reprogramming process to mouse iPSCs, which revealed an unprecedented detail of the reprogramming process and established that transition through a multitude of hierarchical stages is a fundamental feature of the reprogramming process; (iv) determining the dynamics of DNA methylation in reprogramming; (v) gaining a better understanding of how repressive Polycomb proteins control the reprogramming process; (vi) assessing the three-dimensional organization of the genome during reprogramming; and (vii) using the human iPSC approach for disease studies. Together, our findings provide novel mechanistic insights into the reprogramming process.