Transcription factor that play a central role in proper axial mesendoderm morphogenesis and endoderm formation. Required for efficient differentiation of cells from the primitive streak stage to blood (By similarity). Expressed early in embryogenis in a sickle-shaped area in the posterior zone of the blastoderm. With the beginning of gastrulation, it is found in the primitive streak primordium, then in the young and medium-sized streak, however not in the mesoderm after its emergence. In the fully-extended streak, it is restricted to its middle, i.e. the prospective ventral mesoderm. It is then undetectable by in later stages. Belongs to the paired homeobox family.