Statement of Benefit to California:
Year 1The discovery of induced pluripotent stem (iPS) cells by Shinya Yamanaka in 2006 marks a major landmark in the fields of stem cell biology and regenerative medicine. iPS cells can be obtained by co‐expression of four transcription factors in differentiated cells. The reprogramming process takes 2‐3 weeks and is very inefficient with about 1 in a 1000 somatic cells giving rise to an iPS cell. In previous work, we and others had demonstrated that mouse iPS cells are highly similar to ES cells in their molecular and functional characteristics as they for example can support adult chimerism with germline
contribution. The goal of the New Faculty Award proposal is to understand the molecular mechanisms underlying transcription factor‐ induced reprogramming of differentiated cells and to define the iPS cell state.
During this funding period, our efforts have focused on all three Aims. Within Aim 1, we have addressed a range of technical strategies to improve the reprogramming process. In Aim 2, we have analyzed human and mouse iPS cells in comparison to ES cells and attempted a better definition of the iPS cell state. In Aims 3, we are currently attempting to define barriers of the reprogramming process and begin to understand the transcriptional network that leads to reprogrammed cells.
Year 2The discovery of induced pluripotent stem (iPS) cells, which are derived from differentiated cells by simply overexpression a few transcription factors, by Shinya Yamanaka in 2006 marks a major landmark in the fields of stem cell biology and regenerative medicine. To unfold the full potential of reprogramming for disease studies and regenerative medicine, we believe that it is important to understand the molecular mechanisms underlying transcription factor‐ induced reprogramming and to carefully characterize the iPS cell state. To this end, during the third year of funding, we have devised a novel screen to identify factors important for the reprogramming process and allow replacement of the original reprogramming factors. We also studied the role of candidate transcriptional and chromatin regulators in the reprogramming process, which led us to identify novel barriers of the reprogramming process and to a better understanding of how chromatin interferes with the reprogramming process. We have also made progress in understanding the function of the reprogramming factors. Regarding human iPS cell lines, we have derived iPS cells from patients carrying X-linked diseases, and are beginning to characterize them molecularly. Together, we hope that our work will contribute to a better understanding of the reprogramming process.
Year 3Cellular reprogramming and the generation of induced pluripotent stem cells (iPSCs) from differentiated cells has enabled the creation of patient-specific stem cells for use in disease modeling. Reprogramming to the induced pluripotent state can be achieved through the ectopic expression of Oct4, Sox2, Klf4 and cMyc. Insight into the role that the reprogramming factors, various signaling pathways and epigenetic mechanisms play during the different stages of reprogramming remains limited, partly due to the low efficiency with which somatic cells convert to pluripotency. During the past year we have made great progress in (i) defining the molecular requirement for the reprogramming factors; (ii) gaining a better understanding of how repressive chromatin states control the reprogramming process; (iii) determining the differential regulation of chromatin states during reprogramming; (iv) identifying novel reprogramming stages; (v) assessing the three-dimensional organization of the genome during reprogramming; and (vi) determining the influence of a specific signaling pathway and its downstream effectors on different stages of the reprogramming process. Together, our findings provide novel mechanistic insights into the reprogramming process, which will form the basis of approaches to approve the efficiency of the process.
Year 4When 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.