Combinatorial Smad2/3 Activities Downstream of Nodal Signaling Maintain Embryonic/Extra-Embryonic Cell Identities during Lineage Priming

Summary

Epiblast cells in the early post-implantation stage mammalian embryo undergo a transition described as lineage priming before cell fate allocation, but signaling pathways acting upstream remain ill defined. Genetic studies demonstrate that Smad2/3 double-mutant mouse embryos die shortly after implantation. To learn more about the molecular disturbances underlying this abrupt failure, here we characterized Smad2/3-deficient embryonic stem cells (ESCs). We found that Smad2/3 double-knockout ESCs induced to form epiblast-like cells (EpiLCs) display changes in naive and primed pluripotency marker gene expression, associated with the disruption of Oct4-bound distal regulatory elements. In the absence of Smad2/3, we observed enhanced Bmp target gene expression and de-repression of extra-embryonic gene expression. Cell fate allocation into all three embryonic germ layers is disrupted. Collectively, these experiments demonstrate that combinatorial Smad2/3 functional activities are required to maintain distinct embryonic and/or extra-embryonic cell identity during lineage priming in the epiblast before gastrulation.

Graphical Abstract

Highlights

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  Smad2/3 alters the transcriptome and activity of distal regulatory elements in EpiLCs

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  Smad2 prevents expression of extra-embryonic genes during priming and differentiation

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  Smad2/3 is essential for mesoderm and definitive endoderm cell fate allocation

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  Smad2/3 signaling balances Bmp signaling during neural precursor differentiation

Abstract

Using genetic ablation of Smad2/3 effectors downstream of Nodal signaling in mouse embryonic stem cells, Senft et al. show a requirement for Smad2/3 signaling to maintain embryonic/extra-embryonic cell identities during lineage priming before mesoderm and endoderm cell fate allocation and to balance Nodal/Bmp signaling during ectoderm differentiation.