Nuclear orphan receptors are DNA binding proteins that share the domai
n structure of the nuclear hormone receptor superfamily, although liga
nds are unknown. We have identified an orphan receptor in Xenopus laev
is and named it xGCNF based on its high degree of sequence homology to
the previously described murine germ cell nuclear factor (mGCNF). In
gel-electrophoresis mobility shift analysis experiments in vitro trans
lated xGCNF and mGCNF proteins both bind specifically as homodimers to
the same response element, a direct repeat of the half-site consensus
AGGTCA with zero spacing (DR0). Transcripts of xGCNF are found in ooc
ytes and in much smaller amounts in the testes. In developmental North
ern blots and RNase protection using RNA from different embryonic. sta
ges, zygotic expression of xGCNF peaks at midneurula. From late gastru
la to midneurula stages, an anterior to posterior concentration gradie
nt of the RNA was observed in whole mount in situ analysis. This anter
o-posterior gradient of expression was also observed in exogastrulae,
both in the ectoderm and mesoderm. In the midneurula embryo, the mRNA
was predominantly found in the neural plate and neural crest. Transcri
ption of xGCNF in animal cap explants occurred independent of mesoderm
induction.