Sequence-specific transcription factor which is part of a developmental regulatory system that provides cells with specific positional identities on the anterior-posterior axis. Expressed both maternally and zygotically, from ova through to 48 hours post-fertilization. At the 10-somite stage, expressed in the paraxial mesoderm with an anterior expression limit at somite 5. At the 20-somite stage, expressed in the developing CNS with an anterior expression adjacent to the somite 3/4 boundary. Belongs to the Antp homeobox family.