Transcriptional repressor. At the onset of gastrulation, expressed in the superficial layer of cells in the dorsal blastopore lip (Spemann organizer). In the open neural plate, expressed in a row of cells destined to become the floor plate of the neural tube. After neural tube closure, only detected in the tailtip and a small area located at the midbrain/hindbrain boundary. Expressed both maternally and zygotically. Maternal expression levels are low and become further reduced after fertilization. Zygotic expression begins at the mid-blastula transition and peaks during the gastrula/neurula stages. A lower level of expression is then maintained during tailbud and later stages.