In mesendoderm progenitors differentiated from embryonic stem cells in vitro, FOXH1 and SMAD3 are pre-bound to the GSC gene (inferred from mouse homologs). The same situation is inferred to occur in cells of the primitive streak. NODAL signaling causes phosphorylation of SMAD2 and SMAD3, which transit to the nucleus with SMAD4. SMAD2 interacts with SMAD3 at the promoter of the GSC gene (Martin-Malpartida et al. 2017, Funa et al. 2015, and inferred from mouse homologs). After activation by NODAL, phosphorylated SMAD2 and SMAD3 are also complexed with TRIM33 in the nucleus and the p-2S-SMAD2,3:TRIM33 complex binds methylated histone H3 lysine-9 and acetylated histone H3 lysine-18 at the promoter of GSC, which may open chromatin at the promoter (inferred from mouse homologs). Beta-catenin (CTNNB1) activated by Wnt signaling also binds the GSC gene and interacts directly with SMADs to yield full activation of GSC (Funa et al. 2015). EOMES also binds regulatory regions of the GSC gene and is crucial for its activation (Teo et al. 2011, and inferred from mouse homologs). The basal transcription factor TBPL2 (TRF3) also binds the promoter of the GSC gene (Liang et al. 2020).