We report here the identification of a unique vertebrate nuclear recep
tor, Tlx, which is expressed exclusively in the neuroepithelium of the
embryonic brain. Sequence comparison reveals striking similarity to t
he product of the Drosophila terminal/gap gene tailless (tll)(1), whic
h is expressed in the embryonic brain and is required for brain develo
pment in flies. In vitro DNA-binding assays demonstrated that Tlx and
Tll proteins share a target gene specificity that, is unique among the
nuclear receptor superfamily. Ectopic expression of Tlx in fly embryo
s caused a repression of segmentation comparable to that elicited by T
ll. The similarities in structure, expression pattern, target gene spe
cificity and phenotypes in transgenic flies suggest conservation of ge
netic programs upstream and downstream of this Tlx/Tll class of nuclea
r receptors during embryogenesis.