Program Director/Principal Investigator (Last, First, Middle): Nystul, Todd Gregory Abstract This proposal outlines a strategy for identifying the mechanisms that allow for precise specification of the stem cell fate within a dynamic tissue environment and for elucidating the mechanism of competition for stem cell niche occupancy. Accomplishing the aims in this proposal will be an important milestone toward the long-term goal of building a detailed model of epithelial stem cell regulation in order to develop regenerative medicine- based therapies and understand how the process fails in disease states such as cancer. The follicle stem cells (FSCs) have many features in common with mammalian epithelial progenitors and will likely be an excellent model for epithelial stem cell biology. Like several other types of epithelial stem cells in Drosophila and mammals, FSCs are stably maintained by a non-dedicated population of niche cells and depend on Wnt/wg and EGFR signals for self-renewal. In addition, FSCs produce daughter cells that differentiate over the course of several divisions but also retain the capacity to compete with resident stem cells for niche occupancy, much like transit amplifying cells in mammalian epithelial stem cell lineages. However, the precise mechanisms that govern these fundamental features of epithelial stem cell biology remain poorly understood. Based on published studies and significant preliminary data, the central hypothesis of the proposal is that FSC self-renewal is established by localized autocrine and juxtacrine signaling within the niche, and that a cellular memory of these niche signals preserves the ability of newly produced daughter cells to participate in niche competition. A corollary to this hypothesis is the idea that the genetic basis for niche competition is dependent on the relative capacity of a stem cell and a potential replacement cell for self-renewal or differentiation.
The specific aims, which will provide complementary approaches to addressing these hypotheses, are: (1) determine how essential niche signals interact to precisely specify FSCs within a dynamic tissue; (2) identify the molecular switch that regulates the segregation of FSC and daughter cell fates; and (3) elucidate the mechanism of FSC niche competition. Newly developed tools and the finding that wg and EGFR are specific FSC niche signals make it possible to achieve the first aim.
The second aim will be use biochemistry and cell biology techniques, and will build from the thorough understanding of Six-family transcription factors and groucho-mediated repression provided by the literature.
The third aim will combine the detailed knowledge of FSC niche function provided by previous work and the first two aims with a new collection of hypercompetition mutants to obtain a comprehensive understanding of how niche competition is regulated. This project is significant because it will provide detailed mechanistic insight into the function of epithelial stem cell niches. It is an innovative departure from previous studies that focuses on building a comprehensive model of the FSC niche and on understanding novel concepts, the dynamic niche and niche competition. Ultimately, it will provide a detailed understanding of the conserved mechanisms that regulate epithelial stem cells. PHS 398/2590 (Rev. 11/07) Page 1 Continuation Format Page

Public Health Relevance

The proposed research is relevant to public health because it will provide a foundation for understanding a novel type of regulation of epithelial stem cells. Epithelial stem cells are central to both normal homeostasis and the progression of diseases such as cancer, so understanding how they are regulated their native, in vivo contexts is important for the development of cancer treatments and regenerative medicine-based therapies and will contribute to the NIH mission to improve health. The proposed project will also contribute significantly to the NIH mission to foster fundamental creative discoveries by providing a model for the study of epithelial stem cell niches and the opportunity to investigate novel mechanisms for stem cell regulation including a dynamic niche composition and competition for niche occupancy. PHS 398/2590 (Rev. 11/07) Page 1 Continuation Format Page

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM097158-07
Application #
9330863
Study Section
Development - 1 Study Section (DEV1)
Program Officer
Salazar, Desiree Lynn
Project Start
2011-07-01
Project End
2020-06-30
Budget Start
2017-07-01
Budget End
2018-06-30
Support Year
7
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of California San Francisco
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
094878337
City
San Francisco
State
CA
Country
United States
Zip Code
94118
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Ulmschneider, Bryne; Grillo-Hill, Bree K; Benitez, Marimar et al. (2016) Increased intracellular pH is necessary for adult epithelial and embryonic stem cell differentiation. J Cell Biol 215:345-355
Johnston, Michael J; Bar-Cohen, Shaked; Paroush, Ze'ev et al. (2016) Phosphorylated Groucho delays differentiation in the follicle stem cell lineage by providing a molecular memory of EGFR signaling in the niche. Development 143:4631-4642
Vlachos, Stephanie; Jangam, Sharayu; Conder, Ryan et al. (2015) A Pak-regulated cell intercalation event leading to a novel radial cell polarity is involved in positioning of the follicle stem cell niche in the Drosophila ovary. Development 142:82-91
Castanieto, Angela; Johnston, Michael J; Nystul, Todd G (2014) EGFR signaling promotes self-renewal through the establishment of cell polarity in Drosophila follicle stem cells. Elife 3:
Kronen, Maria R; Schoenfelder, Kevin P; Klein, Allon M et al. (2014) Basolateral junction proteins regulate competition for the follicle stem cell niche in the Drosophila ovary. PLoS One 9:e101085
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Sahai-Hernandez, Pankaj; Castanieto, Angela; Nystul, Todd G (2012) Drosophila models of epithelial stem cells and their niches. Wiley Interdiscip Rev Dev Biol 1:447-57