Distinct Wnt-driven primitive streak-like populations reflect in vivo lineage precursors

Abstract

During gastrulation, epiblast cells are pluripotent and their fate is thought to be constrained principally by their position. Cell fate is progressively restricted by localised signalling cues from areas including the primitive streak. However, it is unknown whether this restriction accompanies, at the individual cell level, a reduction in potency. Investigation of these early transition events in vitro is possible via the use of epiblast stem cells (EpiSCs), self-renewing pluripotent cell lines equivalent to the postimplantation epiblast. Strikingly, mouse EpiSCs express gastrulation stage regional markers in self-renewing conditions. Here, we examined the differentiation potential of cells expressing such lineage markers. We show that undifferentiated EpiSC cultures contain a major subfraction of cells with reversible early primitive streak characteristics, which is mutually exclusive to a neural-like fraction. Using in vitro differentiation assays and embryo grafting we demonstrate that primitive streak-like EpiSCs are biased towards mesoderm and endoderm fates while retaining pluripotency. The acquisition of primitive streak characteristics by self-renewing EpiSCs is mediated by endogenous Wnt signalling. Elevation of Wnt activity promotes restriction towards primitive streak-associated lineages with mesendodermal and neuromesodermal characteristics. Collectively, our data suggest that EpiSC pluripotency encompasses a range of reversible lineage-biased states reflecting the birth of pioneer lineage precursors from a pool of uncommitted EpiSCs similar to the earliest cell fate restriction events taking place in the gastrula stage epiblast.

The zebrafish tailbud contains two independent populations of midline progenitor cells that maintain long-term germ layer plasticity and differentiate based on local signaling cues

“…Combined with results from PWPCs in zebrafish, mouse and cell culture (Bouldin et al, 2015;Garriock et al, 2015;Gouti et al, 2014;Henrique et al, 2015;Jurberg et al, 2014;Martin and Kimelman, 2012;Tsakiridis et al, 2014), our data indicate that Wnt signaling has a conserved role in the induction of all tailbud mesoderm from discrete bipotential neuromesodermal progenitors. As in PWPCs, Wnt induces mesodermal fate through repression of sox2 expression.…”

“…In the posterior wall of the tailbud and in cell culture, Wnt signaling induces new mesoderm from PWPCs (Bouldin et al, 2015;Garriock et al, 2015;Gouti et al, 2014;Henrique et al, 2015;Jurberg et al, 2014;Martin and Kimelman, 2012;Tsakiridis et al, 2014). To determine whether Wnt signaling also induces new mesoderm formation within the tailbud MPCs, we used heat shockinducible transgenic lines to temporally inhibit (hsp70l:TCFΔC-GFP) or activate (hsp70l:β-Catenin-TFP) Wnt signaling (Martin and Kimelman, 2012;Veldman et al, 2013).…”

Cdx2Efficiently Induces Trophoblast Stem-Like Cells in Naïve, but Not Primed, Pluripotent Stem Cells

“…Thus, unlike 129-derived ESC/iPSCs, 129-derived EpiSCs are not competent to respond to overexpressed Cdx2 by activating TSC gene expression, pointing to differences in developmental potential. Consistent with this proposal, EpiSCs are thought to be primed to differentiate into germ layer derivatives and express markers of the late epiblast, including Sox17, Gata6, Foxa2, and T [5,6,13,44,45]. We therefore hypothesized that the degree of lineage priming could differ between ESC/iPSCs that do not efficiently produce TSC-like cells and ESC/iPSCs that do efficiently produce TSC-like cells.…”

Independent regulation of vertebral number and vertebral identity by microRNA-196 paralogs

“…The repression of Wnt by trunk Hox genes is less intuitive because, at least on a Cdx2/4 mutant background, ectopic Hoxb8 has been shown to maintain Wnt expression in the tailbud (29). However, the importance of precise Wnt levels in the early steps of axis formation, and of cellular context, are beginning to be appreciated (59,70) and may underlie such discrepancies. Exactly how miR-196 activity integrates within the genetic networks controlling PM progenitor maintenance and differentiation remains to be fully elucidated.…”