TGF-β-Superfamily Signaling Regulates Embryonic Stem Cell Heterogeneity: Self-Renewal as a Dynamic and Regulated Equilibrium

Abstract

Embryonic stem cells dynamically fluctuate between phenotypic states, as defined by expression levels of genes such as Nanog, while remaining pluripotent. The dynamic phenotype of stem cells is in part determined by gene expression control and dictated by various signaling pathways and transcriptional regulators. We sought to define the activities of two TGF-beta-related signaling pathways, Bone morphogenetic protein (BMP) and Nodal signaling, in modulating mouse embryonic stem cell heterogeneity in undifferentiated culture conditions. Both BMP and Nodal signaling pathways were seen to be active in distinct Nanog subpopulations, with subtle quantitative differences in activity. Pharmacological and genetic modulation of BMP or Nodal signaling strongly influenced the heterogeneous state of undifferentiated ES cells, as assessed by dynamic expression of Nanog reporters. Inhibition of Nodal signaling enhanced BMP activity, which through the downstream target Id factors, enhanced the capacity of ES cells to remain in the Nanog-high epigenetic state. The combined inhibition of Nodal and BMP signaling resulted the accumulation of Nanog-negative cells, even in the presence of LIF, uncovering a shared role for BMP and Nodal signaling in maintaining Nanog expression and repression of differentiation. These results demonstrate a complex requirement for both arms of TGF-beta-related signaling to influence the dynamic cellular phenotype of undifferentiated ES cells in serum-based media, and that differing subpopulations of ES cells in heterogeneous culture have distinct responses to these signaling pathways. Several pathways, including BMP, Nodal, and FGF signaling, have important regulatory function in defining the steady-state distribution of heterogeneity of stem cells.

Pluripotency factors and Polycomb Group proteins repress aryl hydrocarbon receptor expression in murine embryonic stem cells

“…Two of the most prominent endogenous AHR functions are the inhibition of TGFβ signaling pathways (Fan et al, 2010; Chang et al, 2007) and the cooperation with the retinoblastoma protein RB1 to promote cell cycle arrest (Puga et al, 2005). Given the requirement for TGFβ-related signaling to maintain a uniform population of proliferating undifferentiated ES cells (Galvin-Burgess et al, 2013) and the impairment of pluripotency when all three members of the retinoblastoma family, are ablated (Dannenberg et al, 2000), it is attractive to speculate that TGFβ and RB might be the targets of these functions and that expression of a functional AHR in ES cells might be detrimental to their survival but beneficial to their differentiation.…”

The pituitary TGFβ1 system as a novel target for the treatment of resistant prolactinomas

“…TGFβs are multifunctional cytokines known to play crucial regulatory roles in cellular proliferation and differentiation, angiogenesis, extracellular matrix modification and immunomodulation (Yoshinaga et al 2008), and have powerful effects on embryogenesis, development and tissue homeostasis (Heldin et al 2009; Galvin-Burgess et al 2013; Itoh et al 2014). The TGFβ family comprises more than 30 highly pleiotropic molecules including activins, inhibins, nodal, bone morphogenetic proteins (BMPs), the anti-muellerian hormone (AMH), and several growth and differentiation factors (GDFs) among others (Derynck & Akhurst 2007).…”

Concise Review: Pursuing Self-Renewal and Pluripotency with the Stem Cell Factor Nanog

“…Interestingly, STAT3 can also directly activate Nanog transcription by binding to an enhancer region upstream of the Nanog promoter, together with Brachyury[68]. Likewise, other signaling cascades, including FGF/MEK[69], GSK3β[70], and TGFβ[71, 72], as well as local changes in chromatin structures by chromatin remodeling complexes such as PBAF[73], are also important for maintaining Nanog levels in undifferentiated cells and for down-regulating Nanog in order to execute differentiation programs.…”