Epigenetic pre-programming of human ES cells that leads to differentiation bias
Human embryonic stem cells (hESCs) carry great potential for cell replacement therapies, since they can differentiate into number of different cell types. Therefore, it is crucial to understand the differentiation and proliferation of hESCs. We previously demonstrated that not all hESCs were created equal by documenting that two NIH hESC lines (i.e., HSF1 and HSF6) generated human neurons with different characteristics when they were differentiated into neural lineages under the same differentiation procedure. Specifically, HSF1 generates cells of forebrain origin while HSF6 gives rise to more posterior and non-forebrain neurons. These findings clearly indicate a differentiation bias between hESCs. Our knowledge on the control of cell-fate specification has been based on studies using animal models. However, not only the human genome is different from those of animals, but also the epigenetic blueprints differ significantly between human and animal stem cells. The epigenetic blueprints determine the specificity, timing, or quantity of expression of particular genes or cohorts of genes. In this proposal, we will reveal the unique epigenetic blueprints of several hESC lines that define their differentiation bias when they are allowed to differentiate along the neural lineage. Our results will reveal the link between the epigenetic blueprint and the differentiation bias of hESCs or induced pluripotent stem (iPS) cells. The approach of this proposal will enable us to predict the differentiation bias of a particular hESC or iPS cell line in the future based on its epigenetic blueprint without laboriously going through differentiation procedures for each lineage to empirically determine whether a particular line can be differentiated into a particular cell lineage. This approach will save tremendous amount of time and resources when the cells are planned to be used for therapeutic applications. Furthermore, our proposed study will reveal whether we can rewrite the epigenetic blueprint in hESCs or iPS cells using number of different factors. Taken together, understanding the genetic and epigenetic mechanisms underlying hESC differentiation bias may shed light on the nature of the developmental program and suggest strategies for controlling hESC and iPS cell differentiation.
Human embryonic stem cells (hESCs) hold great potential for cell replacement therapy where cells are lost due to disease or injury. For the diseases of the central nervous system, hESC-derived neurons could be used for repair. This approach requires careful characterization of hESCs prior to utilizing their therapeutic potentials. Our preliminary findings demonstrated that certain hESC lines show differentiation bias when they are allowed to differentiate along the neural lineage in culture. In our application, we propose to reveal the unique epigenetic blueprints of several hESC lines that define the differentiation decision of hESCs. The unique epigenetic blueprints may arise from embryo-specific genetic variations or stochastic events accumulated during in vitro culturing. Such a problem, though initially surfaced when dealing with different hESC lines, might also apply to pluripotent stem cells that are derived using the induced pluripotent stem (iPS) cell technology. Our proposed studies will help us understand the genetic and epigenetic mechanisms underlying hESC differentiation bias and it may shed light on the nature of the developmental program controlling hESC and iPS cell differentiation. Numerous residents of California suffer from diseases that could potentially be cured by using stem cell based therapies. In order to be able to use hESCs and/or iPS cells for therapy, better understanding of their differentiation is absolutely needed. There is no question that the information obtained from the experiments of this proposal will benefit the residents of California with respect to stem cell therapy.