Transcriptional repressor. Shows complex and dynamic expression during early embryonic development. Prominent in many regions of the developing central nervous system, particularly in midbrain-hindbrain boundary, hindbrain and spinal cord. Strongly expressed in the retina, ear, branchial arches, hatching gland, heart, pronephric duct, gut, proctodeum, pectoral fin and swim bladder. Expressed both maternally and zygotically with continuous expression from the zygote to the early larva. Expression dramatically decreases at 30 and 50% epiboly stages, then increases from midgastrulaion onwards, being maintained at a high level until the protruding-mouth stage. The leucine-zipper is required for dimerization and transcriptional repression.