The ability to reprogram myriad differentiated cells back into a pluripotent stem cell state highlights the remarkable plasticity of somatic cells. Effort is needed to better understand the inherent plasticity of tissue stem cells as well as the underlying regulatory mechanisms, so that we can learn about how to control cell fates in tissue engineering and regenerative medicine. Epithelial cells are long known to possess inherent plasticity, best manifested by their ability to become mesenchymal cells as well as to revert back to an epithelial state, under appropriate stimuli. This plasticity is important for generating mesenchymal cell types during embryogenesis, and is thought to be required for malignant cancer cells to form distant metastases. Recent studies have inspired the hypothesis that the mechanisms that regulate this plasticity are used in committed tissue epithelial cells to control stem cell fates. The mammary epithelia serve an outstanding model system to test this hypothesis, owing to the well-established methods to prospectively isolate and functionally characterize their residential stem cells. The basal layer of the mammary epithelia harbors multipotent stem cells and cells that can turn into such stem cells under conditions such as transplantation and pregnancy. We will organically combine cutting-edge single-cell analysis with state-or-art technology such as tissue-specific gene knockout and inducible overexpression, in vivo and ex vivo stem cell assays, as well as molecular studies to address the following fundamentally important questions: 1) How many cell type subsets or cellular states exist in the mammary basal cell population and do these states correspond to distinct positions in the spectrum of epithelial/EMT plasticity? 2) Are multipotent stem cells or cells with the capacity to become such stem cells defined in part by their high plasticity, namely the potential to adopt both mesenchymal-like and terminal epithelial fates? 3) What is the key molecular circuitry that regulates such plasticity, and whether/how this circuitry dictates the stay of a basal cell in a stem cell state?

Public Health Relevance

Proper control of the self-renewal, proliferation and differentiation of a stem/progenitor cell is important for building or regenerating a functional tissue. Too much self-renewal and proliferation may cause cancer, whereas failure to maintain stem/progenitor cells or terminal differentiation will result in inability to generate or sustain the desired tissue leading to diseases. The proposed studies will help us understand how plastic the epithelial cell fates are and how stem cell states are regulated. They may implicate novel molecular targets for treating diseases such as breast cancer, and will provide fundamental knowledge necessary to design successful stem cell therapy.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
Project #
Application #
Study Section
Development - 1 Study Section (DEV1)
Program Officer
Gibbs, Kenneth D
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of California Irvine
Schools of Medicine
United States
Zip Code
MacLean, Adam L; Hong, Tian; Nie, Qing (2018) Exploring intermediate cell states through the lens of single cells. Curr Opin Syst Biol 9:32-41