Stem Cell Multipotency During Quiescence

Karp, Xantha

Abstract

There is a fundamental gap in the understanding of how stem cells retain the capacity to produce multiple cell types during lengthy periods of cellular quiescence, or non-division. Because the maintenance of multipotency during quiescence is an essential aspect of stem cell function, this gap presents a barrier to the understanding of stem cell biology. C. elegans is a powerful model for studying the regulation of cell fate. Quiescence can be modeled in C. elegans using the dauer larva stage, adopted midway through development in response to adverse environmental conditions. All progenitor cells remain quiescent during dauer, and this quiescence is regulated by the same pathways that regulate quiescence in mammalian stem cells. The long term goal of this lab is to use C. elegans to decipher the mechanisms that promote multipotency during dauer. FOXO transcription factors are key regulators of stem cell maintenance across species, and are candidates for coordinating quiescence and multipotency. FOXO controls quiescence by known mechanisms, but little is known about how FOXO regulates developmental pathways to control multipotency. The objective of this application is to unravel the mechanisms by which the FOXO ortholog, DAF-16 impacts developmental pathways during dauer. Preliminary data establish that FOXO/DAF-16 regulates three different developmental pathways in two progenitor cell types in order to preserve multipotency during dauer. Building on these data, three specific aims are proposed. 1) Analyze the role of FOXO/daf-16 in modulating a temporal cell fate pathway. Genetic and molecular experiments will provide the first mechanistic insight into how FOXO/daf-16 regulates this temporal fate pathway. 2) Characterize the role of the putative FOXO/DAF-16 target gene unk-1 in promoting multipotency. Genetic experiments will establish the relationship between unk-1, encoding a conserved zinc finger protein, and genes within three developmental pathways. Completion of this aim will result in the characterization of the first mediator of FOXO/DAF-16 in controlling multipotency during quiescence. 3) Identify genes downstream of FOXO/DAF-16 that promote multipotency. Genes whose expression changes in FOXO/daf-16 mutant dauer larvae are unknown. In this aim, such genes will be identified by next generation sequencing, and tested functionally for a role in the regulation of cell fate. This work will lead o a genome scale knowledge of genes that regulate multipotency downstream of FOXO/DAF-16. Work proposed here is innovative because modeling stem cells using C. elegans dauer larvae will enable the study of quiescent, multipotent cells in vivo, at single cell resolution, complementing mammalian studies. The proposed work is significant because it is expected to result in the elucidation of mechanisms by which FOXO/DAF-16 coordinates developmental pathways to achieve the emergent property of multipotency, advancing our understanding of the links between quiescence and stem cell fate.

Public Health Relevance

The proposed research is relevant to public health and to the missions of the NIH and NIGMS because the discovery of evolutionarily conserved mechanisms regulating cell fate in quiescent progenitor cells is expected to advance the fundamental understanding of human stem cell biology. Ultimately, the proposed work is expected lay the foundation for the development of new therapies involving stem cells.