THE XENOPUS HOMOLOG OF THE DROSOPHILA GENE TAILLESS HAS A FUNCTION INEARLY EYE DEVELOPMENT

Genetic circuits responsible for the development of photoreceptive org ans appear to be evolutionarily conserved. Here, the Xenopus homologue Xtll of the Drosophila gene tailless (tll), which we find to be expre ssed during early eye development, is characterized with respect to it s relationship to vertebrate regulators of eye morphogenesis, such as Pax6 and Rx, Expression of all three genes is first detected in the ar ea corresponding to the eye anlagen within the open neural plate in pa rtially overlapping, but not identical, patterns. During the evaginati on of the optic vesicle, Xtll expression is most prominent in the opti c stalk, as well as in the distal tip of the forming vesicle. In tadpo le-stage embryos, Xtll gene transcription is most prominent in the cil iary margin of the optic cup, Inhibition of Xtll function in Xenopus e mbryos interferes specifically with the evagination of the eye vesicle and, in consequence, Xpax6 gene expression is severely reduced in suc h manipulated embryos. These findings suggest that Xtll serves an impo rtant regulatory function in the earliest phases of vertebrate eye dev elopment.