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Histone H3.3 epigenetic regulation of cellular plasticity

Funding Type: 
Basic Biology V
Grant Number: 
Funds requested: 
$592 800
Funding Recommendations: 
Not recommended
Grant approved: 
Public Abstract: 
The ability of cells to adopt new fates—termed ‘plasticity’—is at the heart of the most powerful applications of stem cell-based regenerative medicine including induced human pluripotent and embryonic stem cells (IPSCs; ESCs). However, surprisingly the mechanisms regulating plasticity are mostly unknown. Our goal is to produce transformative knowledge about plasticity to bridge this important gap. The assumption in the field is that transcription factors such as Oct4 are the key plasticity regulators. We challenge that dogma with our hypothesis that plasticity is regulated by an exciting new mechanism involving histone proteins that control gene function. We hypothesize more specifically that a very unusual type of histone called H3.3 controls plasticity. H3.3 is the only histone in its family that exhibits flexibility in terms of how it binds to and regulates DNA function such as gene expression. We predict that the unique flexibility of H3.3 is integral to cellular plasticity. Using innovative tools including powerful mouse and human iPSCs and ESCs that lack H3.3, we will determine the role of H3.3 in plasticity. The proposed studies will catalyze cutting-edge new technological advances that will have great clinical significance for the stem cell and regenerative medicine fields. This work also has important implications for childhood brain tumors, where H3.3 is mutated. Overall, in these ways the potential for rapid transformative impact from this research is exceptional.
Statement of Benefit to California: 
The proposed research will greatly benefit the State of California in a number of ways. The studies will be transformative for stem cell research leading to new medical therapies based on stem cells and regenerative medicine that will aid the people of California. The research also directly bears on cancer and knowledge gained may provide a foundation for new cancer therapies that benefit the State. New technologies may also be developed based on the data produced by the proposed work enabling economic development and increased employment in the State.
Review Summary: 
The proposal is focused on the role of H3.3 histone in stem cell plasticity. The investigators proposed to knock out H3.3 in pluripotent stem cells and to determine the role of H3.3 in stem cell plasticity. It is predicted that H3.3 will promote several forms of plasticity and the aims are presented to address these predictions. In aim1 they proposed to analyze regulation of pluripotent-associated plasticity in Embryonic Stem Cells (ESCs) by histone H3.3 and in aim2 examine the role of H3.3 in inherent and inducible plasticity that enable cellular re-programming to generate Induced Pluripotent Stem Cells (iPSCs). If successful, these studies will introduce a new dogma for stem cell plasticity. Novelty and Transformative Potential - There is some circumstantial evidence suggesting that H3.3 histones promote euchromatin formation and are deposited on chromatin independently of DNA replication, however, the preliminary data are not supporting this hypothesis and therefore, the proposed hypothesis is not based on solid reasoning. - It was concluded that many components were lacking in the application regarding a role of H3.3 histones in promoting “plasticity”. Thus, a successful outcome would not likely be transformative by challenging dogma or making a breakthrough in basic stem cell biology. Feasibility and Experimental Potential - The proposed experimental approach is not adequately to test the hypothesis nor does it set out to determine the role of plasticity factors. - It is unclear what the outcome measures are to define success. Thus it is difficult to assess feasibility. A clearer description of outcomes regarding the epigenetic state, the ability to change transcription or modify plasticity is recommended. - Appropriate facilities are available to complete the proposed research studies. Overall, the scientific environment is adequate for project success. Principal Investigator (PI) and Research Team - The PI is a well established investigator, with a proven publication track record and a strong background in molecular biology focusing on the mechanisms of action of specific transcription factors. The level of commitment by the PI is adequate for successful completion of the proposed studies. - The PI has involved prominent scientists as consultants in this project. This will improve the likelihood of success for the project. Responsiveness to the RFA - The proposal is highly responsive to the RFA. Histone variants might play some role in promoting and maintaining the pluripotent state, but at this point is difficult to anticipate the impact in the field of these studies. - The proposed research will utilize human iPSCs and ESCs that lack H3.3 to determine the role of H3.3 in plasticity.
  • Alexander Meissner

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