Transcription factor required for both mesoderm and endoderm formation in the embryo; signaling determinants and concentration levels may determine which germ layer is formed. Acts together with beta-catenin to activate genes that are responsible for mesoderm induction including wnt-8, eomes t/bra, siamois, mix1 and sox17. Directly binds to promoter DNA. Patterns the mesoderm along the dorsoventral and posterior axis. Activates siamois gene transcription when alone or in combination with beta-catenin, but inhibits siamois transcription in combination with pou5f1.1/oct-25. Forms a repression complex on the promoters of the nodal/nr1 and siamois genes with the maternal factors tcf7l1/tcf3 and pouf5.1/oct-25. Interacts (via C-terminus) with tcf7l1/tcf3 (via N-terminus). Also interacts with the other POU-domain transcription factors pou5f1.2/oct-91 and pou5f1.3/oct-60 (By similarity). Maternally localized to the vegetal hemisphere of oocytes. Zygotic expression parallels blastopore formation and shifts from dorsal expression in the marginal zone of late blastula and early gastrula stages to a ventral/lateral expression at later stages. During neurula and tailbud stages, expressed in the posterior and anterior ends of the embryo. During tailbud stages, expressed in a subset of interneurons in the neural tube. Expressed both maternally and zygotically. Expression declines considerably at the end of gastrulation but continues at a low level until the tadpole stage (stage 38). By mesoderm-inducers including t/bra, and both FGF and TGF-beta family members. FGF signaling is not required for initial expression in the dorsal marginal zone, but is required for its continued expression during mid to late gastrula stages.