May play a role in very early embryogenesis, gastrulation, and the development and subdivision of the diencephalon and the midbrain. Embryonic expression is highly dynamic. In early gastrula embryos, expressed in the involuting presumptive anterior mesoderm. Found in the head rudiment at 9 hours of development, and at 12 hours of development expression increases at the caudal side but decreases at the rostral side. With the extension of the body axis, expression extends to neuroectodermal regions fated to become fore- and mid-brain; detected in the presumptive border between the midbrain and the hindbrain at 18 hours of development, and found in the diencephalon and the midbrain at 24 hours of development. Found in embryos at 0-2 hours of development, levels decrease drastically at 6 hours of development but increase again at 12 hours of development. Belongs to the paired homeobox family. Bicoid subfamily.