RELATIONSHIP BETWEEN DROSOPHILA GAP GENE TAILLESS AND A VERTEBRATE NUCLEAR RECEPTOR TLX

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.