Sequence-specific transcription factor which is part of a developmental regulatory system that provides cells with specific positional identities on the anterior-posterior axis. Acts on the anterior body structures. Expressed along the entire length of the primitive streak. In early neurogenesis it is expressed in lateral and paraxial mesoderm, endoderm and superficial ectoderm or in the neural tube. From late neurogenesis to mid-embryogenesis, it presents similar spatial domains in the lateral mesoderm, endoderm and superficial ectoderm but is not detectable in the posterior hindbrain and has increased dramatically in rhombomere 4. Belongs to the Antp homeobox family. Labial subfamily.