Sequence-specific transcription factor which is part of a developmental regulatory system that provides cells with specific positional identities on the anterior-posterior axis. Required for proper head development. During embryogenesis, expressed in mandibular lobe, hypopharyngeal organ, neural and epidermal cells of procephalic lobe, sensory cells of clypeolabrum, posterior midgut, thoracic and abdominal segments. Expressed both maternally and zygotically. High expression in embryos and third instar larvae, lower expression in pupae. Belongs to the Antp homeobox family. Labial subfamily. It is uncertain whether Met-1, Met-2 or Met-7 is the initiator.