E2a Is Necessary for Smad2/3-Dependent Transcription and the Direct Repression of lefty during Gastrulation

Abstract

Summary Transcription factor complexes have varied effects on cell fate and behavior, but how this diversification of function occurs is largely unknown. The Nodal signaling pathway has many biological functions that all converge on the transcription factors Smad2/3. Smad2/3 has many cofactors, and alternative usage of these may provide a mechanism for modulating Smad2/3 function. Here we investigated how perturbation of the cofactor E2a affects global patterns of Smad2/3 binding and gene expression during gastrulation. We find that E2a regulates early development in two ways. E2a changes the position of Smad2/3 binding at the Nodal inhibitor lefty, resulting in direct repression of lefty that is critical for mesendoderm specification. Separately, E2a is necessary to drive transcription of Smad2/3 target genes, including critical regulators of dorsal cell fate and morphogenesis. Overall, we find that E2a functions as both a transcriptional repressor and activator to precisely regulate Nodal signaling.

Id genes are essential for early heart formation

“…Consistent with our hypothesis, siRNA-mediated knockdown of two transcription factors, Tcf3 and Foxa2, is sufficient to up-regulate Mesp1 expression and promote Kdr + mesoderm formation. Mechanistically, Tcf3 is a wellcharacterized target of Id proteins (for review, see Yang et al 2014) and is also known to interact with the Smad/ Foxh1 complex to regulate Smad2/3-dependent transcription in mesendoderm progenitors (Yoon et al 2011;Wills and Baker 2015). In turn, the potent endoderm determinant Foxa2 (Stainier 2002;Viotti et al 2014), is expressed in mesendoderm progenitors in a Smad2-dependent manner in mouse embryos (Vincent et al 2003), suggesting that Tcf3 might cooperate with Smad2 to regulate Foxa2.…”

The transcription factor E2A drives neural differentiation in pluripotent cells

“…We also reported that components of the Nodal signalling pathway were downregulated upon overexpression of E2A homodimers, and conversely upregulated during differentiation of E-protein knockout cells. Interestingly, E2A has also been shown to repress transcription of lefty in Xenopus, with knockout of E2A causing upregulation of lefty and a subsequent failure in mesendodermal fate specification (Wills and Baker, 2015). We propose that E2A could be playing a similar role to repress Nodal signalling in ES cells, but during neural fate commitment -a process in which inhibition of Nodal signalling is already known to be important (Vallier et al, 2004;Watanabe et al, 2005).…”

“…In Xenopus embryos, loss of E2A has been associated with inhibition of gastrulation (Yoon et al, 2011). Additionally, E2A and HEB have been shown to be cofactors of the Nodal signalling pathway, both in human ES cells and in Xenopus (Yoon et al, 2011), with E2A playing a dual role to directly repress the Nodal target gene, lefty, during 3 mesendoderm specification in Xenopus, whilst also driving the expression of dorsal cell fate genes (Wills and Baker, 2015).…”

A Nodal/Eph signalling relay drives the transition from apical constriction to apico-basal shortening in ascidian endoderm invagination

“…Interestingly, in Xenopus, Nodal signalling is necessary for normal EphA4 expression (Wills and Baker, 2015) in the mesoderm and both signalling pathways are required for the internalization of the mesendoderm (Evren et al, 2014). The presence of this association in both taxa could reflect either convergence or an ancestral state.…”