Formative pluripotent stem cells show features of epiblast cells poised for gastrulation

Abstract

The pluripotency of mammalian early and late epiblast could be recapitulated by naïve embryonic stem cells (ESCs) and primed epiblast stem cells (EpiSCs), respectively. However, these two states of pluripotency may not be sufficient to reflect the full complexity and developmental potency of the epiblast during mammalian early development. Here we report the establishment of self-renewing formative pluripotent stem cells (fPSCs) which manifest features of epiblast cells poised for gastrulation. fPSCs can be established from different mouse ESCs, pre-/early-gastrula epiblasts and induced PSCs. Similar to pre-/early-gastrula epiblasts, fPSCs show the transcriptomic features of formative pluripotency, which are distinct from naïve ESCs and primed EpiSCs. fPSCs show the unique epigenetic states of E6.5 epiblast, including the super-bivalency of a large set of developmental genes. Just like epiblast cells immediately before gastrulation, fPSCs can efficiently differentiate into three germ layers and primordial germ cells (PGCs) in vitro. Thus, fPSCs highlight the feasibility of using PSCs to explore the development of mammalian epiblast.

Developments in pluripotency: a new formative state

“…3,8,9 All these states show cell polarity, a transcriptome indicative of formative pluripotency and, as far as assayed, 8 glycolytic metabolism. Surprisingly, comparative analysis of the transcriptomic and epigenomic data generated by these groups 3,8,9 and in the current study 6 show that the intermediate pluripotent ESCs in each of the culture conditions resemble different time points in the naïve-to-primed transition, over a timespan ranging from approximately E5.0 to E6.5 6 (Fig. 1).…”

“…General trends within this timespan include a gradual increase in DNA methylation levels and a gradual switch from naïve transcription factor (TF) expression towards formative TF expression, seemingly followed by a more immediate switch towards lineage-biased TF expression in primed EpiSCs. 3,6,8,9 Interestingly, based on discriminative features, the pluripotent states as reported in these studies could be categorized into a more naïve-like intermediate state and a more primed-like intermediate state, the latter including the fPSCs (Fig. 1).…”

“…On the other hand, formative pluripotent cells were supposed to be able to differentiate towards primordial germ cells (PGCs; the early precursors of gametes), a potential that is lost in primed EpiSCs. 1 In a recent paper published in Cell Research, Wang et al 6 now report the establishment of in vitro mouse formative pluripotent stem cells (fPSCs), generated from either E5.5-6.5 epiblasts, ESCs (Fig. 1) or induced pluripotent stem cells (iPSCs).…”

“…To enable capturing the formative pluripotent state, Wang et al 6 use the growth factors Activin A and Fgf2, similar to what is used for mouse EpiSCs. 5 However, the powerful use of Matrigelbased three-dimensional (3D) culture conditions, combined with inhibition of the Wnt/β-catenin pathway, allows to stably maintain formative epiblast-like embryoids, referred to as fPSCs, which show polarization and lumen formation.…”

“…The fPSCs are functionally pluripotent in that they contribute to chimeras, are able to form teratomas and are capable of in vitro differentiation towards either of the three germ layers. Importantly, the fPSCs as established by Wang et al 6 can efficiently differentiate into PGCs, a unique feature as compared to ESCs and EpiSCs. Epigenetic characterization showed that the fPSCs are close to primed EpiSCs: the fPSCs contain high levels of DNA methylation and elevated levels of H3K27me3 at bivalent promoters of genes that are poised for activity, 7 while female fPSCs contain an inactivated X chromosome.…”