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 12 hours post-fertilization (hpf) in the dorsal pre-somitic mesoderm and neural keel at posterior levels, extending into the ventral somitic mesoderm during budding. At 22-26 hpf, expression decreases in the lateral and ventral mesoderm, but is maintained in the neural rod. Expression decreases from posterior to anterior with an anterior expression limit at somite 11. At 24-26 hpf, posterior expression begin to weaken and is undetectable by 40-56 hpf. Belongs to the Abd-B homeobox family. Extended C-terminus.