Probable orphan nuclear receptor. Binds to a response element containing repeats of the motif 5'-AGGTCA-3'. Required for anterior-posterior patterning during organogenesis. Acts with chordin to play a role in patterning the midbrain-hindbrain. Isoform Em is required for integrin-mediated cell matrix interaction during neurulation and for the morphogenetic movements leading to formation of the neural tube. Also mediates the effect of retinoic acid on primary neurogenesis. Homodimer. Transiently expressed in differentiating cells of all embryonic germ layers. Expressed in an anterior to posterior concentration gradient from late gastrula to midneurula stages. Shows a complicated spatio-temporal pattern of expression during neurulation, being predominant in the neural plate and neural crest in midneurula embryos. At late tailbud (stage 30), mainly expressed in the head mesenchyme, gill arches and tail tip. Expression persists in the epidermis, somites and endoderm, and in the central nervous system, expression is restricted to the midbrain, hindbrain and part of the spinal cord. Isoforms Oo and Em are both expressed in the brain and isoform Oo is expressed in the germ cells of both the adult testis and ovary. Isoform Oo is expressed both maternally and zygotically, being predominantly expressed in oocytes and embryos before the midblastula transition but present at later stages at very low levels. Isoform Em is expressed zygotically between late gastrula stage and late tailbud stage 30, being predominant during tailbud stages. By retinoic acid. Embryonic form. Oocyte form. Belongs to the nuclear hormone receptor family. NR6 subfamily.