Eomesodermin Requires Transforming Growth Factor-β/Activin Signaling and Binds Smad2 to Activate Mesodermal Genes

Abstract

The T-box gene Eomesodermin (Eomes) is required for early embryonic mesoderm differentiation in mouse, frog (Xenopus laevis), and zebrafish, is important in late cardiac development in Xenopus, and for CD8؉ T effector cell function in mouse. Eomes can ectopically activate many mesodermal genes. However, the mechanism by which Eomes activates transcription of these genes is poorly understood. We report that Eomes protein interacts with Smad2 and is capable of working in a non-cell autonomous manner via transfer of Eomes protein between adjacent embryonic cells. Blocking of Eomes protein transfer using a farnesylated red fluorescent protein (CherryF) also prevents Eomes nuclear accumulation. Transfer of Eomes protein between cells is mediated by the Eomes carboxyl terminus (456 -692). A carbohydrate binding domain within the Eomes carboxyl-terminal region is sufficient for transfer and important for gene activation. We propose a novel mechanism by which Eomes helps effect a cellular response to a morphogen gradient.

Pluripotency factors regulate definitive endoderm specification through eomesodermin

“…Of interest, recent studies demonstrate that EOMES interacts with SMAD2/3 to control the expression of mesoderm markers in Xenopus (Picozzi et al 2009). This implies that EOMES function in germ layer specification has been redirected during evolution to replace VegT, while its direct interaction with Activin/Nodal signaling has been conserved.…”

“…Studies in the mouse and frog have shown that EOMES cooperates with Activin/Nodal signaling during endoderm differentiation (Arnold et al 2008;Picozzi et al 2009). To explore this relationship more thoroughly, we first validated the importance of Activin/Nodal signaling in our in vitro system using the potent Activin type I receptor inhibitor SB431542 (Inman et al 2002).…”

Genome-wide view of TGFβ/Foxh1 regulation of the early mesendoderm program

“…S11). Eomes, a T-box protein, binds Smad2 and has been implicated in Nodal-mediated mesendoderm induction in Xenopus, zebrafish and mammalian epiblast stem cells (Arnold et al, 2008;Picozzi et al, 2009;Slagle et al, 2011;Teo et al, 2011). Recently, ChIP-seq analysis of Eomes has been reported in Xenopus (Gentsch et al, 2013), allowing for a direct test of whether both Smad2/3 and Eomes are bound to the aforementioned 15 genes.…”

Taking the Middle Road

“…As an example, heterotaxy and, less frequently, HPE are associated with mutations in the Foxh1 gene whose protein product is a co-factor of the Smad2/Smad4 transcriptional complex that transmits the Nodal signal from receptor to nucleus. Animal studies indicate that the task of transmitting the totality of the Nodal signal across all cell types is shared by other TFs, namely Mixer and Eomesodermin, suggesting Foxh1 mutations should be more viable than Nodal mutations (Germain et al, 2000;Kunwar et al, 2003;Picozzi et al, 2009;Slagle et al, 2011). A general complication in assessing whether Nodal pathway mutations cause heterotaxy or HPE is the dual role of Nodal signaling in establishing the PCP, other midline tissue and the SMO on the one hand, and on the other hand in establishing laterality downstream of these events (Nakamura et al, 2006).…”