Human embryonic stem cells (hESCs) are able to divide indefinitely and under the proper conditions, can essentially become any cell in the human body. They are derived from the developing human embryo and carry great promise for regenerative medicine. However, these cells demonstrate an instability surrounding the state of the X chromosome. Male (XY) cells and female (XX) cells use a mechanism called X chromosome inactivation (XCI) to achieve equal expression of genes on the X chromosomes. XCI happens specifically in female cells and shuts down one of the two X chromosomes. The silencing of the X chromosome is a life-or-death decision that is made early in development, but when exactly remains unclear. Female cells from humans always possess one inactive and one active X chromosome. hESCs with the same X inactivation pattern as adult cells and those that have not undergone XCI have been derived, yet the cause for this heterogeneity is unknown. Given that lines can change their XCI state over time, and this volatility may have far-reaching impact, we propose to study why this happens. In addition, we will test whether the different X chromosome states affect the utility of hESCs.
The proposed project will benefit the state of California and its citizens as follows:
1. Human embryonic stem cells could revolutionize modern medicine if used in cell-based therapies. However, the translational use of hESCs will not be realized unless we can ensure reproducible derivation of high quality stem cells. Our proposal works towards identifying markers that can be used as benchmarks to assess the quality of female hESCs. Therefore, our work will have practical implications for stem cell therapy and the use of hESCs in disease studies and basic biology.
2. Our team is composed of two research groups with expertise in stem cell biology. In addition to creating highly skilled jobs, the proposed research activities will create an interdisciplinary education environment for training the next generation of California citizens at all levels, including high school, undergraduate, graduate students, as well as postdoctoral fellows.
3. All scientific findings produced from these studies will be publicly available to non-profit and academic organizations in California, and any intellectual property developed by this project will be developed under the guidelines of CIRM to benefit the State of California.
X chromosome inactivation (XCI) is a process by which one of the two X chromosomes in female cells is silenced through epigenetic mechanisms, resulting in no expression of most of the genes residing on the inactive X chromosome. This silencing ensures equal expression of X-linked genes in male and female cells, which is critical for normal cell function. Human embryonic stem cells (hESCs) display various X chromosome states, including a state in which both X chromosomes are active and another state in which one X chromosome is active and the other is inactive. In some cases, the inactive X chromosome displays epigenetic abnormalities. The applicant proposes to interrogate how these different states are established and how they affect the behavior of hESC. The goal is to clarify the XCI process in human cells and to determine whether certain X chromosome states compromise the utility of hESCs for basic and clinical applications.
Significance and Innovation
- The application addresses a significant issue in human pluripotent stem cell biology with implications for all studies utilizing female hESCs and also for human induced pluripotent stem cell (hiPSC) models of X-linked disease.
- The proposed model for the progression of X chromosome states in hESC is innovative and compelling.
Feasibility and Experimental Design
- Overall, the preliminary data were considered strong, although evidence of the applicant’s ability to perform the proposed gene knock down and gene targeting experiments in hESCs is lacking.
- Some of the proposed staining procedures are likely to be very challenging, and their feasibility is not entirely supported by preliminary data.
- Some of the preliminary data do not agree with recently published hiPSC data; this deserves careful attention, as the proposed experiments are critical for resolving these discrepancies.
- Reviewers viewed the proposed approaches as generally well conceived and much of the study as feasible.
Principal Investigator (PI) and Research Team
- The PI has impeccable credentials within this field and is well funded.
- The research team is outstanding, and a collaborator provides important complementary expertise.
Responsiveness to the RFA
- The proposed work is responsive to the RFA.