Quantitative, temporal, and spatial features of exogenous signaling direct embryonic stem cell fate

In vivo, stem cells reside in specialized microenvironments that regulate cell fate by controlling the types, levels, timing, and spatial organization of extrinsic signals. It is not clear how stem cell fate information is encoded within these microenvironments, nor is it clear how fate is regulated during embryogenesis when cell microenvironment is in flux. Using leukemia inhibitory factor (LIF) - induced self-renewal of mouse embryonic stem cells (ESCs) as a model system for extrinsic control of stem cell fate, we investigated the contribution of quantitative, temporal, and spatial features of exogenous signaling to stem cell fate control. Combining quantitative single-cell immunocytochemistry, mathematical modeling of gp130 - Janus kinase - signal transducer and activator of transcription (gp130-Jak-STAT) signaling, and a computational analysis of spatial organization, we have produced a comprehensive analysis of the role of gp130-Jak-STAT signaling dynamics in the control of early ESC self-renewal and differentiation decisions.; Our results demonstrate that ESC fate is directed by the quantitative, temporal and spatial features of the gp130 ligand (such as LIF) signals cells receive from their micro environment. Furthermore, ESCs employ control mechanisms including autocrine expression of gp130 ligands and dynamic regulation of gp130 ligand responsiveness via positive-feedback control of gp130-Jak-STAT pathway expression, to both alter their gp130 ligand microenvironment and adapt to it. These novel ESC control mechanisms actively regulate the ligand threshold, as well as the timing and spatial organization of self-renewal and differentiation. A consequence of the signaling interrelationship between ESCs and their environment is the formation of a fixed-location-independent autoregulatory niche controlling cell fate. These results suggest that stem cell fate can be determined and temporally/spatially regulated at the level of cell signaling dynamics rather than exclusively in downstream cell fate processes, a consequence which has implications on the process and hierarchy of stem cell fate control. This work provides mechanistic insight into extrinsic regulation of stem cell fate and thereby suggests tools and approaches for precise manipulation of stem cell fate---a necessary milestone in the development of stem cell therapeutics.