BETA-3-TUBULIN IS DIRECTLY REPRESSED BY THE ENGRAILED PROTEIN IN DROSOPHILA

In Drosophila, Engrailed is a nuclear regulatory protein with essentia l roles during embryonic development, Although Engrailed is a transcri ption factor, little progress has been achieved in identifying its tar get genes. We report here the identification of an effector gene, the beta 3-tubulin gene, as a direct target of Engrailed. The cytological location of beta 3-tubulin, 60C, is a strong site of Engrailed binding on polytene chromosomes. Immunostaining analysis of a transgenic line containing a P[beta 3-tubulin-lacZ] construct shows an additional sit e of Engrailed binding at the location of the transgene. Molecular ana lysis allowed identification of several Engrailed binding sites, both in vitro and in vivo, within the first intron of the beta 3-tubulin lo cus. Engrailed binding sites identified in vitro are active in larvae. Furthermore, expression of beta 3-tubulin is derepressed in the ectod erm of engrailed mutant embryos. Repression of beta 3-tubulin by Engra iled is also obtained when Engrailed is ectopically expressed in embry onic mesoderm. Finally, two different sets of Engrailed binding sites are shown to be involved in the early and late regulation of beta 3-tu bulin by Engrailed during embryogenesis.