Cellular and Molecular Determinants of Pluripotency and Stability

Funding Type: 
Basic Biology I
Grant Number: 
ICOC Funds Committed: 
Stem Cell Use: 
Embryonic Stem Cell
iPS Cell
Cell Line Generation: 
iPS Cell
Public Abstract: 
hESCs are pluripotent cells that can be maintained indefinitely in culture. These characteristics have led to much enthusiasm for their potential use in cell-replacement therapies. One obstacle to realizing this potential is the incomplete knowledge of mechanisms involved regulating pluripotent fate decisions including survival, self-renewal and stability. While hESCs can be maintained in vitro, cells grown in continuous culture have been shown to develop aberrations associated with cancer in vivo. Therefore it is the goal of this work to determine the mechansims that regulate pluripotent stem cell growth without giving rise to abnormal stem cells with the potential for tumor formation.
Statement of Benefit to California: 
Pluripotent stem cells (PSCs) have the potential to revolutinize medicine for use in cell-based therapies. However, the translational use of hESCs will not be realized unless we understand how pluripotency is regulated in these cells. Defining how pluripotency is controlled could improve our ability to derive new cell lines in a more controlled conditions. This could enhance California as a recognized world leader in PSC research through the generation of a centralized and comprehensive resource of PSC lines with potential clinical use. This work will also create jobs to support this effort, and validate the decision of California voters who ensured the passage of Proposition 71. Our proposal to improve our understanding of PSC pluripotency and stability will make treatment strategies from hESCs one-step closer.
Progress Report: 
  • Pluripotent human stem cell lines can develop into any cell type in the body. In order to exploit the power of these cells for use in research or therapy, we need to be able to grow them in the laboratory in pure form and efficiently turn them into specific types of mature cell. Current methods for growing pluripotent stem cells yield mixed populations of cells, some of which have limited capacity for growth and development, others that represent true pluripotent stem cells. Thus, the stem cell cultures are like an ecosystem, with many components. We are studying the culture microenvironment of the stem cell to learn how it regulates cell growth. In order to do this we have to understand the heterogeneity in stem cell cultures. To this end, we have developed techniques to analyze the molecular makeup of single stem cells, and to track their fates. These techniques enable us to identify the most primitive cells in the culture with the greatest potential for growth and differentiation. These cells tend to be spatially segregated from other more mature cells, in a specialized microenvironment that helps them to maintain their ability to grow and turn into specialized cells. We have identified some key components of the microenvironment that keep stem cells in the primitive pluripotent state. We will use these techniques to develop means to produce pure populations of specialized cells from stem cell cultures.
  • Our aim is to gain a detailed understanding of how human embryonic stem cells are regulated- how do embryonic stem cells decide whether to multiply to produce more stem cells, or to begin forming specialized cell types. We have found that human embryonic stem cultures are not homogeneous but are composed of different cellular subpopulations whose identities can be clearly defined at the molecular level. Only a minority of cells in the population has the capacity for self renewal, the ability to form new stem cells. This ability to divide to produce new stem cells depends on factors made by the stem cells themselves. Other cells in the culture have begun the process of specialization, with many on the way to becoming precursors of the central nervous system. Again, the choice to become a nerve cell depends on signals from surrounding cells in the culture. Understanding the conversations between subsets of stem cells is crucial to efforts to grow pure populations of stem cells or specialized cell types.
  • Human pluripotent stem cells are defined by their abilities to multiply indefinitely in the laboratory and to turn into any type of body cell. However, stem cell cultures are not composed of one cell type, but are heterogeneous. In this study, we took a close up look at human embryonic stem cell cultures by examining the properties of individual single cells, rather than studying the population as a whole. The result show that the population of cells in the culture dish comprises a complex hierarchy, from primitive cells with great capacity for multiplication through to cells just on the verge of becoming specialized cell types. Specific signals govern how cells at different stages of this hierarchy behave: whether they divide to form more stem cells, or begin to specialize into different cell types such as nerve cells. The cells themselves produce signals that govern how they move through this hierarchy. By understanding these internal dialogues between different populations in stem cell culture, we can learn how to control stem cell behaviour, and to understand why some stem cell lines respond differently to others under specific culture conditions. In turn, this knowledge will enhance our ability to propagate stem cells and to turn them into particular cell types useful in research or regenerative medicine.

© 2013 California Institute for Regenerative Medicine