Transcriptional regulator which may play a role in the differentiation and maintenance of meso-diencephalic dopaminergic (mdDA) neurons (By similarity). Required for lens and retinal development and for pituitary pre-placode formation and cell specification. In the adult, high levels detected in the eye and much lower levels in internal organs such as liver, gastrointestinal system, heart, genitourinary system and pancreas. Expressed throughout development with low levels detected from 3-8 hpf and highest levels in developing brain and lens at 24 hpf. In the embryo, expressed in anterior neural plate and later in lens and pituitary cells. Detected in the forebrain, lens and pectoral fin buds at 24 hpf. Becomes restricted to the lens equatorial region by 48 hpf. Strongest expression detected in the diencephalon and pituitary at 48 hpf. Evident in the cartilage surrounding the mouth at 72 hpf, appearing in the iris of the eye, developing lower jaw and the branchial arches at 96 hpf and extending to developing musculature along the trunk. During lens development, exhibits widespread expression during the primary differentiation phase of lens formation and then restricted to the region of secondary fiber cell differentiation during the phase of lens growth. Expressed in both proliferating and early differentiating progenitor cells of the posterior tuberculum. Belongs to the paired homeobox family. Bicoid subfamily.