Abstract
A stem cell's decision to self-renew or differentiate is thought to critically depend on signaling cues provided by its environment. It is unclear whether stem cells have the intrinsic capacity to control their responsiveness to environmental signals that can be fluctuating and noisy. Using a novel single-cell microRNA activity reporter, we show that miR-142 is bimodally expressed in embryonic stem cells, creating two states indistinguishable by pluripotency markers. A combination of modeling and quantitative experimental data revealed that mESCs switch stochastically between the two miR-142 states. We find that cells with high miR-142 expression are irresponsive to differentiation signals while cells with low miR-142 expression can respond to differentiation cues. We elucidate the molecular mechanism underpinning the bimodal regulation of miR-142 as a double-negative feedback loop between miR-142 and KRAS/ERK signaling and derive a quantitative description of this bistable system. miR-142 switches the activation status of key intracellular signaling pathways thereby locking cells in an undifferentiated state. This reveals a novel mechanism to maintain a stem cell reservoir buffered against fluctuating signaling environments.
Highlights
Mouse embryonic stem cells constitute a powerful system to study the molecular mechanism of fate decisions in controlled in vitro environment (Rue & Martinez Arias, 2015). mESCs are continuous cell lines derived from the inner cell mass of the blastocyst (Evans & Kaufman, 1981; Martin, 1981)
Whereas the role of transcription factor heterogeneity in defining different pluripotent substates is well established (Chambers et al, 2007; Singh et al, 2007; Toyooka et al, 2008), it is largely unknown whether such dynamic heterogeneity exists at the level of miRNA expression. To address this gap in our knowledge, we used a single-cell miRNA activity reporter to identify miR-142 that is bimodally expressed in mESCs under pluripotency-maintaining conditions. miR-142 expression levels stratify mESCs with indistinguishable expression of pluripotency markers into two distinct subpopulations: mESCs with low miR-142 levels are amenable to signalinduced differentiation, while cells with high miR-142 levels are irresponsive to differentiation cues
Our results support a model in which a double-negative feedback loop between Kras/ERK signaling and miR-142 produces a bistable system trapping mESCs in either a “low” miR-142 state that has a high level of ERK/AKT activity and is competent to differentiate or on the other hand a “high” miR-142 state that has a low level of ERK/AKT activity and is blocked from differentiation
Summary
Mouse embryonic stem cells (mESCs) constitute a powerful system to study the molecular mechanism of fate decisions in controlled in vitro environment (Rue & Martinez Arias, 2015). mESCs are continuous cell lines derived from the inner cell mass of the blastocyst (Evans & Kaufman, 1981; Martin, 1981). Whereas the role of transcription factor heterogeneity in defining different pluripotent substates is well established (Chambers et al, 2007; Singh et al, 2007; Toyooka et al, 2008), it is largely unknown whether such dynamic heterogeneity exists at the level of miRNA expression. To address this gap in our knowledge, we used a single-cell miRNA activity reporter to identify miR-142 that is bimodally expressed in mESCs under pluripotency-maintaining conditions. We propose that the self-generated miR-142 twostate system functions to maintain a stem cell reservoir that is protected from differentiation signals from the environment
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Published Version
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