Transcriptional repressor. Plays a fundamental role in notochord formation, acting within the mesodermal region. Expressed throughout the embryo during pre-gastrula stages. Localized to the dorsal lip of the blastopore (Spemann organizer) during early gastrulation, after which expression continues in tissues derived from the organizer. Expressed in the notochord during mid-gastrulation. During neurulation, expressed in the notochord, archenteron roof and the prospective floor plate. Also expressed in the region that will become the epiphysis, the pineal body precursor. By the early tailbud stages, expression is limited to posterior notochord and floor plate before becoming restricted to the tip of the tail in the tadpole. Expressed both maternally and zygotically. Expression increases markedly at the mid-blastula transition (MBT) and peaks at the onset of gastrulation before declining rapidly during the gastrula stages. Another decrease in expression levels occurs towards the end of the neurula stages, although expression is retained into the late tailbud stages. By activin, derriere, fgf2/bFGF and wnt8. Repressed by bmp4/dvr-4.