Required for eye and tectum development. May act as a transcriptional repressor. In embryos, expressed in mesencephalon with strongest expression dorsally, diencephalon, and rhombencephalon. During somitogenesis, anterior expression which partly overlaps the future eye field, gradually decreases while midbrain expression intensifies and becomes restricted to the presumptive tectum. In adult, strong expression in forebrain, midbrain and cerebellum. Not expressed maternally. First detected at 9 hours post-fertilization (hpf), with high levels until 24 hpf. Also expressed in adult. Belongs to the paired homeobox family.