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 (By similarity). 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). Vegetally localized in oocytes and expressed in the presumptive endoderm and mesoderm at early gastrula stage. Expression is down-regulated in the endoderm by the end of gastrulation but maintained in the lateral and ventral mesoderm of the blastopore lip. Expressed both maternally and zygotically.