Transcriptional repressor. Dimerization is required for DNA-binding. First expressed in the anterior neural field of stage 15 embryos. At stage 18, localized in three domains of the brain (rostral forebrain, midbrain and hindbrain) and in the eye anlage. Cerebral and retinal expression persists at later stages with additional expression in the branchial arches, at the base of the hatching gland, and in the pancreas. Expressed both maternally and zygotically. Maternal expression is weak but still detectable at the blastula stage. Zygotic expression starts during gastrulation and progresses to strong expression at stages 30 and 45. The leucine-zipper is required for dimerization and transcriptional repression.