Sequence-specific transcription factor. Part of a developmental regulatory system that provides cells with specific positional identities on the anterior-posterior axis. Acts on the anterior body structures. Seems to act in the maintenance and/or generation of hindbrain segments. First expressed at 50% epiboly in the shield region. During somitogenesis, present in the spinal cord and endoderm with an anterior expression limit at around rhombomere 4. By retinoic acid. Belongs to the Antp homeobox family. Labial subfamily.