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

• Published in: Developmental cell 2015-02, Vol.32 (3), p.345-357
• Main Authors: Wills, Andrea E., Baker, Julie C.
• Format: Article
• Language: English
• Subjects: Animals; Cell Differentiation - physiology; Endoderm - metabolism; Gastrulation - physiology; Gene Expression Regulation, Developmental - physiology; Mesoderm - metabolism; Signal Transduction - genetics; Signal Transduction - physiology; Smad2 Protein - metabolism; Smad3 Protein - metabolism; Transcription Factors - metabolism; Transforming Growth Factor beta - metabolism; Xenopus - embryology; Xenopus - metabolism; Xenopus Proteins - metabolism
• ISSN: 1534-5807; 1878-1551
• DOI: 10.1016/j.devcel.2014.11.034

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 investigate 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. •Nodal target genes require E2a to couple Smad2/3 occupancy to gene expression•E2a directly inhibits expression of the Nodal inhibitor lefty•E2a inhibition of lefty is critical for mesendoderm specification•E2a also functions as an activator of dorsal morphogenesis genes Using genome-wide profiling in X. tropicalis, Wills and Baker show that the cofactor E2a determines the transcriptional outcome of Smad2/3 binding. E2a promotes repression at the lefty promoter by shifting Smad2/3 binding to a less active region, while at other Smad2/3 targets, it couples Smad2/3 binding to transcriptional activation.