Wnt Signaling Mediates Self-Organization and Axis Formation in Embryoid Bodies

Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA.
Cell stem cell (Impact Factor: 22.27). 12/2008; 3(5):508-18. DOI: 10.1016/j.stem.2008.09.013
Source: PubMed


Embryonic stem cells (ESCs) form descendants of all three germ layers when differentiated as aggregates, termed embryoid bodies. In vivo, differentiation of cells depends on signals and morphogen gradients that provide instructive and positional cues, but do such gradients exist in embryoid bodies? We report here the establishment of anteroposterior polarity and the formation of a primitive streak-like region in the embryoid body, dependent on local activation of the Wnt pathway. In this region, cells undergo an epithelial-to-mesenchymal transition and differentiate into mesendodermal progenitors. Exogenous Wnt3a protein posteriorizes the embryoid body, resulting in predominantly mesendodermal differentiation. Conversely, inhibiting Wnt signaling promotes anterior character and results in neurectodermal differentiation. The activation of Wnt signaling and primitive streak formation requires external signals but is self-reinforcing after initiation. Our findings show that the Wnt pathway mediates the local execution of a gastrulation-like process in the embryoid body, which displays an unexpected degree of self-organization.

  • Source
    • "Next, we addressed whether the differentiation-inducing effect of WNT on EpiSCs explains the conflicting reports on the role of WNT in ESCs. While we previously demonstrated that endogenous WNT signals support ESC selfrenewal by inhibiting their differentiation into EpiSCs (ten Berge et al., 2011), we and others also demonstrated that WNT signals induce differentiation of ESCs in EBs (Nostro et al., 2008; ten Berge et al., 2008). However, a transient EpiSC signature has been detected in differentiating EBs (Zhang et al., 2010). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Therapeutic application of human embryonic stem cells (hESCs) requires precise control over their differentiation. However, spontaneous differentiation is prevalent, and growth factors induce multiple cell types; e.g., the mesoderm inducer BMP4 generates both mesoderm and trophoblast. Here we identify endogenous WNT signals as BMP targets that are required and sufficient for mesoderm induction, while trophoblast induction is WNT independent, enabling the exclusive differentiation toward either lineage. Furthermore, endogenous WNT signals induce loss of pluripotency in hESCs and their murine counterparts, epiblast stem cells (EpiSCs). WNT inhibition obviates the need to manually remove differentiated cells to maintain cultures and improves the efficiency of directed differentiation. In EpiSCs, WNT inhibition stabilizes a pregastrula epiblast state with novel characteristics, including the ability to contribute to blastocyst chimeras. Our findings show that endogenous WNT signals function as hidden mediators of growth factor-induced differentiation and play critical roles in the self-renewal of hESCs and EpiSCs. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
    Full-text · Article · Jan 2015 · Stem Cell Reports
  • Source
    • "Interestingly, some of the authors pointed out that they were astonished to find that the autonomously formed (entirely self-organized) EBs showed close similarities with regard to gastrulation-related gene activation cascades as compared to real mouse embryos [ten Berge et al., 2008]. Symmetry breaking is a crucial initial process required for axis development during basic body pattern formation. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The rapid progress in the stem cell field, in particular in cell reprogramming, combined with certain recent observations from experimental embryology, has ignited a new discussion on stem cell terminology. The current use of terms describing stem cell potentiality is inconsistent and can be confusing, in particular the widely used term pluripotency and its distiction from totipotency. For cells possessing a complete differentiation potential (but lacking an autonomous embryo-structuring capacity) the term omnipotency (or, as recently proposed, plenipotency) has been coined. The present commentary takes up this discussion and confronts it with recent reports on 'engineering' viable fish embryos or gastrulating human germ disc models using 'pluripotent'/omnipotent cells, as well as on symmetry breaking in aggregates of mouse embryonic stem cells. It is concluded that we should start contemplating not only the terminology but also, even more urgently, the ethical implications of the perspective of constructing embryonic anlagen in humans. © 2014 S. Karger AG, Basel.
    Full-text · Article · Dec 2014 · Cells Tissues Organs
  • Source
    • "Cardiomyocyte-specific staining of TaP4 EBsections with antibodies against sarcomeric a-actinin revealed efficient commitment to the cardiac line (Fig. 1A, B). CMs were found in the inner compartment of the EBs and tended to undergo spatial polarization as described for the mesodermal germ layer during murine EB development [20]. Similar results were found for differentiated aPIG44 EBs (Fig. 1C, D). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Cardiomyocytes (CMs) from induced pluripotent stem (iPS) cells mark an important achievement in the development of in vitro pharmacological, toxicological and developmental assays and in the establishment of protocols for cardiac cell replacement therapy. Using CMs generated from murine embryonic stem cells and iPS cells we found increased cell–matrix interaction and more matured embryoid body (EB) structures in iPS cell-derived EBs. However, neither suspension-culture in form of purified cardiac clusters nor adherence-culture on traditional cell culture plastic allowed for extended culture of CMs. CMs grown for five weeks on polystyrene exhibit signs of massive mechanical stress as indicated by α-smooth muscle actin expression and loss of sarcomere integrity. Hydrogels from polyacrylamide allow adapting of the matrix stiffness to that of cardiac tissue. We were able to eliminate the bottleneck of low cell adhesion using 2,5-Dioxopyrrolidin-1-yl-6-acrylamidohexanoate as a crosslinker to immobilize matrix proteins on the gels surface. Finally we present an easy method to generate polyacrylamide gels with a physiological Young's modulus of 55 kPa and defined surface ligand, facilitating the culture of murine and human iPS-CMs, removing excess mechanical stresses and reducing the risk of tissue culture artifacts exerted by stiff substrates.
    Full-text · Article · Aug 2014 · Biomaterials
Show more