Transcriptional activator. Expressed zygotically. First detected at the mid-blastula transition. Confined to the future ectoderm by the shield stage, and to the presumptive neuroectoderm by the 75-80% epiboly stage. From the tail bud to the 3-somite stage, expressed throughout the neural plate, except in the anterior margin; strongest expression in the presumptive ventral diencephalon. At the 12- to 25-somite stage, expressed broadly in the central nervous system. From 24-30 hours post-fertilization, restricted to the ventral diencephalon, midbrain and hindbrain/anterior spinal cord region, and to the retina and lens.