Sequence-specific transcription factor which is part of a developmental regulatory system that provides cells with specific positional identities on the anterior-posterior axis. First expressed at the 1-2 somite stage. By the 3-4 somite stage, the anterior expression limit in the developing hindbrain is at the rhombomere 5/6 boundary, and this is maintained until the 20 somite stage. By 30 hours post-fertilization, there is also limited expression within rhombomere 5. Belongs to the Antp homeobox family.