May play a role in very early embryogenesis, gastrulation, and the development and subdivision of the diencephalon and the midbrain. Appears at 9 hours of development, and at 12 hours of development significant levels are found in the developing brain posterior to ocular vesicles. Distributed mainly in the midbrain, part of the diencephalon beneath the epiphysis and in the epiphysis at 18 hours of development. Found in the ventral part of the midbrain and in the dorsal part of the diencephalon at 24 hours of development. Belongs to the paired homeobox family. Bicoid subfamily.